public-key cryptography theory and practiceabhij/book/pkc/pkcslides...alice wants to send a...
TRANSCRIPT
![Page 1: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/1.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Public-key CryptographyTheory and Practice
Abhijit Das
Department of Computer Science and EngineeringIndian Institute of Technology Kharagpur
Chapter 1: Overview
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 2: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/2.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
What is Cryptography?
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 3: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/3.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
What is Cryptography?
Cryptography is the study of techniques for preventingaccess to sensitive data by parties who are not authorizedto access the data.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 4: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/4.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
What is Cryptography?
Cryptography is the study of techniques for preventingaccess to sensitive data by parties who are not authorizedto access the data.
Cryptanalysis is the study of techniques for breakingcryptographic systems.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 5: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/5.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
What is Cryptography?
Cryptography is the study of techniques for preventingaccess to sensitive data by parties who are not authorizedto access the data.
Cryptanalysis is the study of techniques for breakingcryptographic systems.
Cryptology = Cryptography + Cryptanalysis
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 6: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/6.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
What is Cryptography?
Cryptography is the study of techniques for preventingaccess to sensitive data by parties who are not authorizedto access the data.
Cryptanalysis is the study of techniques for breakingcryptographic systems.
Cryptology = Cryptography + Cryptanalysis
Cryptanalysis is useful for strengthening cryptographicprimitives.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 7: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/7.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
What is Cryptography?
Cryptography is the study of techniques for preventingaccess to sensitive data by parties who are not authorizedto access the data.
Cryptanalysis is the study of techniques for breakingcryptographic systems.
Cryptology = Cryptography + Cryptanalysis
Cryptanalysis is useful for strengthening cryptographicprimitives.
Maintaining security and privacy is an ancient and primitiveneed.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 8: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/8.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
What is Cryptography?
Cryptography is the study of techniques for preventingaccess to sensitive data by parties who are not authorizedto access the data.
Cryptanalysis is the study of techniques for breakingcryptographic systems.
Cryptology = Cryptography + Cryptanalysis
Cryptanalysis is useful for strengthening cryptographicprimitives.
Maintaining security and privacy is an ancient and primitiveneed.
Particularly relevant for military and diplomatic applications.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 9: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/9.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
What is Cryptography?
Cryptography is the study of techniques for preventingaccess to sensitive data by parties who are not authorizedto access the data.
Cryptanalysis is the study of techniques for breakingcryptographic systems.
Cryptology = Cryptography + Cryptanalysis
Cryptanalysis is useful for strengthening cryptographicprimitives.
Maintaining security and privacy is an ancient and primitiveneed.
Particularly relevant for military and diplomatic applications.
Wide deployment of the Internet makes everybody a userof cryptographic tools.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 10: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/10.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 11: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/11.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 12: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/12.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.Alice wants to send a plaintext message M to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 13: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/13.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.Alice wants to send a plaintext message M to Bob.
Alice encrypts M to generate the ciphertext messageC = fe(M, Ke).
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 14: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/14.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.Alice wants to send a plaintext message M to Bob.
Alice encrypts M to generate the ciphertext messageC = fe(M, Ke).Ke is the encryption key .
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 15: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/15.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.Alice wants to send a plaintext message M to Bob.
Alice encrypts M to generate the ciphertext messageC = fe(M, Ke).Ke is the encryption key .
C is sent to Bob over the public channel.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 16: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/16.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.Alice wants to send a plaintext message M to Bob.
Alice encrypts M to generate the ciphertext messageC = fe(M, Ke).Ke is the encryption key .
C is sent to Bob over the public channel.Bob decrypts C to recover the plaintext messageM = fd (C, Kd ).
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 17: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/17.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.Alice wants to send a plaintext message M to Bob.
Alice encrypts M to generate the ciphertext messageC = fe(M, Ke).Ke is the encryption key .
C is sent to Bob over the public channel.Bob decrypts C to recover the plaintext messageM = fd (C, Kd ).Kd is the decryption key .
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 18: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/18.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.Alice wants to send a plaintext message M to Bob.
Alice encrypts M to generate the ciphertext messageC = fe(M, Ke).Ke is the encryption key .
C is sent to Bob over the public channel.Bob decrypts C to recover the plaintext messageM = fd (C, Kd ).Kd is the decryption key .
Knowledge of Kd is required to retrieve M from C.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 19: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/19.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Message Encryption
Required for secure transmission of messages over apublic channel.Alice wants to send a plaintext message M to Bob.
Alice encrypts M to generate the ciphertext messageC = fe(M, Ke).Ke is the encryption key .
C is sent to Bob over the public channel.Bob decrypts C to recover the plaintext messageM = fd (C, Kd ).Kd is the decryption key .
Knowledge of Kd is required to retrieve M from C.An eavesdropper (intruder, attacker, adversary, opponent,enemy) cannot decrypt C.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 20: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/20.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Secret-key or Symmetric Encryption
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 21: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/21.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Secret-key or Symmetric Encryption
Ke = Kd .
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 22: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/22.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Secret-key or Symmetric Encryption
Ke = Kd .
Algorithms are fast and suitable for software and hardwareimplementations.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 23: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/23.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Secret-key or Symmetric Encryption
Ke = Kd .
Algorithms are fast and suitable for software and hardwareimplementations.
The common key has to be agreed upon by Alice and Bobbefore the actual communication.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 24: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/24.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Secret-key or Symmetric Encryption
Ke = Kd .
Algorithms are fast and suitable for software and hardwareimplementations.
The common key has to be agreed upon by Alice and Bobbefore the actual communication.
Each pair of communicating parties needs a secret key.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 25: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/25.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Secret-key or Symmetric Encryption
Ke = Kd .
Algorithms are fast and suitable for software and hardwareimplementations.
The common key has to be agreed upon by Alice and Bobbefore the actual communication.
Each pair of communicating parties needs a secret key.
If there are many communicating pairs, the key storagerequirement is high.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 26: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/26.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 27: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/27.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 28: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/28.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Introduced by Rivest, Shamir and Adleman (1978).
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 29: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/29.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Introduced by Rivest, Shamir and Adleman (1978).
Ke is the public key known to everybody (even toenemies).
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 30: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/30.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Introduced by Rivest, Shamir and Adleman (1978).
Ke is the public key known to everybody (even toenemies).
Kd is the private key to be kept secret.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 31: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/31.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Introduced by Rivest, Shamir and Adleman (1978).
Ke is the public key known to everybody (even toenemies).
Kd is the private key to be kept secret.
It is difficult to compute Kd from Ke.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 32: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/32.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Introduced by Rivest, Shamir and Adleman (1978).
Ke is the public key known to everybody (even toenemies).
Kd is the private key to be kept secret.
It is difficult to compute Kd from Ke.
Anybody can send messages to anybody. Only the properrecipient can decrypt.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 33: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/33.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Introduced by Rivest, Shamir and Adleman (1978).
Ke is the public key known to everybody (even toenemies).
Kd is the private key to be kept secret.
It is difficult to compute Kd from Ke.
Anybody can send messages to anybody. Only the properrecipient can decrypt.
No need to establish keys a priori.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 34: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/34.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Introduced by Rivest, Shamir and Adleman (1978).
Ke is the public key known to everybody (even toenemies).
Kd is the private key to be kept secret.
It is difficult to compute Kd from Ke.
Anybody can send messages to anybody. Only the properrecipient can decrypt.
No need to establish keys a priori.
Each party requires only one key-pair for communicatingwith everybody.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 35: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/35.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Public-key or Asymmetric Encryption
Ke 6= Kd .
Introduced by Rivest, Shamir and Adleman (1978).
Ke is the public key known to everybody (even toenemies).
Kd is the private key to be kept secret.
It is difficult to compute Kd from Ke.
Anybody can send messages to anybody. Only the properrecipient can decrypt.
No need to establish keys a priori.
Each party requires only one key-pair for communicatingwith everybody.
Algorithms are slow, in general.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 36: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/36.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Real-life Analogy
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 37: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/37.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Real-life Analogy
Symmetric encryption
Alice locks the message in a box by a key.
Bob uses a copy of the same key to unlock.
Public-key Cryptography: Theory and Practice Abhijit Das
![Page 38: Public-key Cryptography Theory and Practiceabhij/book/PKC/PKCslides...Alice wants to send a plaintext message M to Bob. Public-key Cryptography: Theory and Practice Abhijit Das Common](https://reader035.vdocuments.us/reader035/viewer/2022063010/5fc41d5a2c8940573d693321/html5/thumbnails/38.jpg)
Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Real-life Analogy
Symmetric encryption
Alice locks the message in a box by a key.
Bob uses a copy of the same key to unlock.
Asymmetric encryption
Alice presses a self-locking padlock in order to lock thebox. The locking process does not require a real key.
Bob has the key to open the padlock.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Symmetric and Asymmetric Encryption Together
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Symmetric and Asymmetric Encryption Together
Alice reads Bob’s public key Ke.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Symmetric and Asymmetric Encryption Together
Alice reads Bob’s public key Ke.
Alice generates a random secret key K .
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Symmetric and Asymmetric Encryption Together
Alice reads Bob’s public key Ke.
Alice generates a random secret key K .
Alice encrypts M by K to generate C = fe(M, K ).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Symmetric and Asymmetric Encryption Together
Alice reads Bob’s public key Ke.
Alice generates a random secret key K .
Alice encrypts M by K to generate C = fe(M, K ).
Alice encrypts K by Ke to generate L = fE (K , Ke).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Symmetric and Asymmetric Encryption Together
Alice reads Bob’s public key Ke.
Alice generates a random secret key K .
Alice encrypts M by K to generate C = fe(M, K ).
Alice encrypts K by Ke to generate L = fE (K , Ke).
Alice sends (C, L) to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Symmetric and Asymmetric Encryption Together
Alice reads Bob’s public key Ke.
Alice generates a random secret key K .
Alice encrypts M by K to generate C = fe(M, K ).
Alice encrypts K by Ke to generate L = fE (K , Ke).
Alice sends (C, L) to Bob.
Bob recovers K as K = fD(L, Kd).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Symmetric and Asymmetric Encryption Together
Alice reads Bob’s public key Ke.
Alice generates a random secret key K .
Alice encrypts M by K to generate C = fe(M, K ).
Alice encrypts K by Ke to generate L = fE (K , Ke).
Alice sends (C, L) to Bob.
Bob recovers K as K = fD(L, Kd).
Bob decrypts C as M = fd(C, K ).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Alice procures a lock L with key K . Alice wants to send Kto Bob for a future secret communication.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Alice procures a lock L with key K . Alice wants to send Kto Bob for a future secret communication.
Alice procures another lock LA with key KA.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Alice procures a lock L with key K . Alice wants to send Kto Bob for a future secret communication.
Alice procures another lock LA with key KA.
Bob procures a lock LB with key KB.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Alice procures a lock L with key K . Alice wants to send Kto Bob for a future secret communication.
Alice procures another lock LA with key KA.
Bob procures a lock LB with key KB.
Alice puts K in a box, locks the box by LA using KA, andsends the box to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Alice procures a lock L with key K . Alice wants to send Kto Bob for a future secret communication.
Alice procures another lock LA with key KA.
Bob procures a lock LB with key KB.
Alice puts K in a box, locks the box by LA using KA, andsends the box to Bob.
Bob locks the box by LB using KB, and sends thedoubly-locked box back to Alice.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Alice procures a lock L with key K . Alice wants to send Kto Bob for a future secret communication.
Alice procures another lock LA with key KA.
Bob procures a lock LB with key KB.
Alice puts K in a box, locks the box by LA using KA, andsends the box to Bob.
Bob locks the box by LB using KB, and sends thedoubly-locked box back to Alice.
Alice unlocks LA by KA and sends the box again to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Alice procures a lock L with key K . Alice wants to send Kto Bob for a future secret communication.
Alice procures another lock LA with key KA.
Bob procures a lock LB with key KB.
Alice puts K in a box, locks the box by LA using KA, andsends the box to Bob.
Bob locks the box by LB using KB, and sends thedoubly-locked box back to Alice.
Alice unlocks LA by KA and sends the box again to Bob.
Bob unlocks LB by KB and obtains K .
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange
Real-life analogy
Alice procures a lock L with key K . Alice wants to send Kto Bob for a future secret communication.
Alice procures another lock LA with key KA.
Bob procures a lock LB with key KB.
Alice puts K in a box, locks the box by LA using KA, andsends the box to Bob.
Bob locks the box by LB using KB, and sends thedoubly-locked box back to Alice.
Alice unlocks LA by KA and sends the box again to Bob.
Bob unlocks LB by KB and obtains K .
A third party always finds the box locked either by LA or LB
or both.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Alice generates a key pair (Ae, Ad ).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Alice generates a key pair (Ae, Ad ).
Bob generates a key pair (Be, Bd).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Alice generates a key pair (Ae, Ad ).
Bob generates a key pair (Be, Bd).
Alice sends her public-key Ae to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Alice generates a key pair (Ae, Ad ).
Bob generates a key pair (Be, Bd).
Alice sends her public-key Ae to Bob.
Bob sends his public-key Be to Alice.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Alice generates a key pair (Ae, Ad ).
Bob generates a key pair (Be, Bd).
Alice sends her public-key Ae to Bob.
Bob sends his public-key Be to Alice.
Alice computes KAB = f (Ae, Ad , Be).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Alice generates a key pair (Ae, Ad ).
Bob generates a key pair (Be, Bd).
Alice sends her public-key Ae to Bob.
Bob sends his public-key Be to Alice.
Alice computes KAB = f (Ae, Ad , Be).
Bob computes KBA = f (Be, Bd , Ae).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Alice generates a key pair (Ae, Ad ).
Bob generates a key pair (Be, Bd).
Alice sends her public-key Ae to Bob.
Bob sends his public-key Be to Alice.
Alice computes KAB = f (Ae, Ad , Be).
Bob computes KBA = f (Be, Bd , Ae).
The protocol insures KAB = KBA to be used by Alice andBob as a shared secret.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Key Agreement or Key Exchange (contd.)
Alice generates a key pair (Ae, Ad ).
Bob generates a key pair (Be, Bd).
Alice sends her public-key Ae to Bob.
Bob sends his public-key Be to Alice.
Alice computes KAB = f (Ae, Ad , Be).
Bob computes KBA = f (Be, Bd , Ae).
The protocol insures KAB = KBA to be used by Alice andBob as a shared secret.
An intruder cannot compute this secret using Ae and Be
only.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Digital Signatures
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Digital Signatures
Alice establishes her binding to a message M by digitallysigning it.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Digital Signatures
Alice establishes her binding to a message M by digitallysigning it.
Signing: Only Alice has the capability to sign M.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Digital Signatures
Alice establishes her binding to a message M by digitallysigning it.
Signing: Only Alice has the capability to sign M.
Verification: Anybody can verify whether Alice’s signatureon M is valid.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Digital Signatures
Alice establishes her binding to a message M by digitallysigning it.
Signing: Only Alice has the capability to sign M.
Verification: Anybody can verify whether Alice’s signatureon M is valid.
Forging: Nobody can forge signatures on behalf of Alice.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Digital Signatures
Alice establishes her binding to a message M by digitallysigning it.
Signing: Only Alice has the capability to sign M.
Verification: Anybody can verify whether Alice’s signatureon M is valid.
Forging: Nobody can forge signatures on behalf of Alice.
Digital signatures are based on public-key techniques.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Digital Signatures
Alice establishes her binding to a message M by digitallysigning it.
Signing: Only Alice has the capability to sign M.
Verification: Anybody can verify whether Alice’s signatureon M is valid.
Forging: Nobody can forge signatures on behalf of Alice.
Digital signatures are based on public-key techniques.
Signature generation ≡ Decryption (uses private key), andSignature verification ≡ Encryption (uses public key).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Digital Signatures
Alice establishes her binding to a message M by digitallysigning it.
Signing: Only Alice has the capability to sign M.
Verification: Anybody can verify whether Alice’s signatureon M is valid.
Forging: Nobody can forge signatures on behalf of Alice.
Digital signatures are based on public-key techniques.
Signature generation ≡ Decryption (uses private key), andSignature verification ≡ Encryption (uses public key).
Non-repudiation: An entity should not be allowed to denyvalid signatures made by him.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Message Recovery
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Message Recovery
Generation
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Message Recovery
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Message Recovery
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice signs M by her private key to obtain the signedmessage S = fs(M, Kd ).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Message Recovery
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice signs M by her private key to obtain the signedmessage S = fs(M, Kd ).
VerificationRecover M from S by using Alice’s public key:M = fv (S, Ke).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Message Recovery
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice signs M by her private key to obtain the signedmessage S = fs(M, Kd ).
VerificationRecover M from S by using Alice’s public key:M = fv (S, Ke).
ForgingK ′
d 6= Kd generates forged signature S′ = fs(M, K ′
d ).Verification yields M ′ = fv (S′
, Ke) 6= M.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Message Recovery
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice signs M by her private key to obtain the signedmessage S = fs(M, Kd ).
VerificationRecover M from S by using Alice’s public key:M = fv (S, Ke).
ForgingK ′
d 6= Kd generates forged signature S′ = fs(M, K ′
d ).Verification yields M ′ = fv (S′
, Ke) 6= M.
DrawbackAlgorithms are slow, not suitable for long messages.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
Generation
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice generates a short representative m = H(M) of M.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice generates a short representative m = H(M) of M.Alice uses her private-key: s = fs(m, Kd).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice generates a short representative m = H(M) of M.Alice uses her private-key: s = fs(m, Kd).Alice publishes (M, s) as the signed message.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice generates a short representative m = H(M) of M.Alice uses her private-key: s = fs(m, Kd).Alice publishes (M, s) as the signed message.
Verification
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice generates a short representative m = H(M) of M.Alice uses her private-key: s = fs(m, Kd).Alice publishes (M, s) as the signed message.
VerificationCompute the representative m = H(M).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice generates a short representative m = H(M) of M.Alice uses her private-key: s = fs(m, Kd).Alice publishes (M, s) as the signed message.
VerificationCompute the representative m = H(M).Use Alice’s public-key to generate m′ = fv (s, Ke).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice generates a short representative m = H(M) of M.Alice uses her private-key: s = fs(m, Kd).Alice publishes (M, s) as the signed message.
VerificationCompute the representative m = H(M).Use Alice’s public-key to generate m′ = fv (s, Ke).Accept the signature if and only if m = m′.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Signature With Appendix
GenerationAlice generates a key-pair (Ke, Kd ), publishes Ke, andkeeps Kd secret.Alice generates a short representative m = H(M) of M.Alice uses her private-key: s = fs(m, Kd).Alice publishes (M, s) as the signed message.
VerificationCompute the representative m = H(M).Use Alice’s public-key to generate m′ = fv (s, Ke).Accept the signature if and only if m = m′.
ForgingVerification is expected to fail if a key K ′
d 6= Kd is used togenerate s.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Alice proves her identity to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Alice proves her identity to Bob.
Alice demonstrates to Bob her knowledge of a secret pieceof information.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Alice proves her identity to Bob.
Alice demonstrates to Bob her knowledge of a secret pieceof information.
Alice may or may not reveal the secret itself to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Alice proves her identity to Bob.
Alice demonstrates to Bob her knowledge of a secret pieceof information.
Alice may or may not reveal the secret itself to Bob.
Both symmetric and asymmetric techniques are used forentity authentication.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Alice proves her identity to Bob.
Alice demonstrates to Bob her knowledge of a secret pieceof information.
Alice may or may not reveal the secret itself to Bob.
Both symmetric and asymmetric techniques are used forentity authentication.
Simplest Example: Passwords
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Alice proves her identity to Bob.
Alice demonstrates to Bob her knowledge of a secret pieceof information.
Alice may or may not reveal the secret itself to Bob.
Both symmetric and asymmetric techniques are used forentity authentication.
Simplest Example: PasswordsTime-invariant
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Alice proves her identity to Bob.
Alice demonstrates to Bob her knowledge of a secret pieceof information.
Alice may or may not reveal the secret itself to Bob.
Both symmetric and asymmetric techniques are used forentity authentication.
Simplest Example: PasswordsTime-invariantSecret revealed to the verifier
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Entity Authentication
Alice proves her identity to Bob.
Alice demonstrates to Bob her knowledge of a secret pieceof information.
Alice may or may not reveal the secret itself to Bob.
Both symmetric and asymmetric techniques are used forentity authentication.
Simplest Example: PasswordsTime-invariantSecret revealed to the verifierWeak authentication
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.Bob generates a challenge C and sends C to Alice.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.Bob generates a challenge C and sends C to Alice.Alice responds to C by sending a response R back to Bob.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.Bob generates a challenge C and sends C to Alice.Alice responds to C by sending a response R back to Bob.Bob determines whether the response R is satisfactory.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.Bob generates a challenge C and sends C to Alice.Alice responds to C by sending a response R back to Bob.Bob determines whether the response R is satisfactory.Generating R from C requires the knowledge of the secret.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.Bob generates a challenge C and sends C to Alice.Alice responds to C by sending a response R back to Bob.Bob determines whether the response R is satisfactory.Generating R from C requires the knowledge of the secret.Absence of the knowledge of the secret fails to generate asatisfactory response with a good probability p.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.Bob generates a challenge C and sends C to Alice.Alice responds to C by sending a response R back to Bob.Bob determines whether the response R is satisfactory.Generating R from C requires the knowledge of the secret.Absence of the knowledge of the secret fails to generate asatisfactory response with a good probability p.The above protocol may be repeated more than once.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.Bob generates a challenge C and sends C to Alice.Alice responds to C by sending a response R back to Bob.Bob determines whether the response R is satisfactory.Generating R from C requires the knowledge of the secret.Absence of the knowledge of the secret fails to generate asatisfactory response with a good probability p.The above protocol may be repeated more than once.If Bob receives satisfactory response in every iteration, heaccepts Alice’s identity.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Challenge-response Authentication
Alice does not reveal her secret directly to Bob.Bob generates a challenge C and sends C to Alice.Alice responds to C by sending a response R back to Bob.Bob determines whether the response R is satisfactory.Generating R from C requires the knowledge of the secret.Absence of the knowledge of the secret fails to generate asatisfactory response with a good probability p.The above protocol may be repeated more than once.If Bob receives satisfactory response in every iteration, heaccepts Alice’s identity.
DrawbackC and R may reveal to Bob or an eavesdropper someknowledge about Alice’s secret.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Zero-knowledge Protocol
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Zero-knowledge Protocol
A special class of challenge-response techniques.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Zero-knowledge Protocol
A special class of challenge-response techniques.
No information is leaked to Bob or to any third party.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Message Encryption and Key AgreementDigital SignaturesEntity Authentication
Zero-knowledge Protocol
A special class of challenge-response techniques.
No information is leaked to Bob or to any third party.
A real-life example
Right exit
A
BLeft exit
Door with secret key
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Secret Sharing
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Secret Sharing
A secret is distributed to n parties.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Secret Sharing
A secret is distributed to n parties.
All of these n parties should cooperate to reconstruct thesecret.
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Secret Sharing
A secret is distributed to n parties.
All of these n parties should cooperate to reconstruct thesecret.
Participation of only 6 n − 1 parties should fail toreconstruct the secret.
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Secret Sharing
A secret is distributed to n parties.
All of these n parties should cooperate to reconstruct thesecret.
Participation of only 6 n − 1 parties should fail toreconstruct the secret.
Generalization
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Secret Sharing
A secret is distributed to n parties.
All of these n parties should cooperate to reconstruct thesecret.
Participation of only 6 n − 1 parties should fail toreconstruct the secret.
Generalization
Any m (or more) parties can reconstruct the secret (forsome m 6 n).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Secret Sharing
A secret is distributed to n parties.
All of these n parties should cooperate to reconstruct thesecret.
Participation of only 6 n − 1 parties should fail toreconstruct the secret.
Generalization
Any m (or more) parties can reconstruct the secret (forsome m 6 n).
Participation of only 6 m − 1 parties should fail toreconstruct the secret.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions
Used to convert strings of any length to strings of a fixedlength.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions
Used to convert strings of any length to strings of a fixedlength.Used for the generation of (short) representatives ofmessages.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions
Used to convert strings of any length to strings of a fixedlength.Used for the generation of (short) representatives ofmessages.Symmetric techniques are typically used for designinghash functions.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions
Used to convert strings of any length to strings of a fixedlength.Used for the generation of (short) representatives ofmessages.Symmetric techniques are typically used for designinghash functions.
Modification detection code (MDC)An unkeyed hash function is used to guard againstunauthorized/accidental message alterations. Signatureschemes also use MDC’s.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions
Used to convert strings of any length to strings of a fixedlength.Used for the generation of (short) representatives ofmessages.Symmetric techniques are typically used for designinghash functions.
Modification detection code (MDC)An unkeyed hash function is used to guard againstunauthorized/accidental message alterations. Signatureschemes also use MDC’s.
Message authentication code (MAC)A keyed hash function is used to authenticate the source ofmessages.
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions: Properties
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions: Properties
A collision for a hash function H is a pair of two distinctstrings x , y with H(x) = H(y). Collisions must exist for anyhash function.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions: Properties
A collision for a hash function H is a pair of two distinctstrings x , y with H(x) = H(y). Collisions must exist for anyhash function.
First pre-image resistance
For most hash values y , it should be difficult to find a stringx with H(x) = y .
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions: Properties
A collision for a hash function H is a pair of two distinctstrings x , y with H(x) = H(y). Collisions must exist for anyhash function.
First pre-image resistance
For most hash values y , it should be difficult to find a stringx with H(x) = y .
Second pre-image resistance
Given a string x , it should be difficult to find a differentstring x ′ with H(x ′) = H(x).
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Cryptographic Hash Functions: Properties
A collision for a hash function H is a pair of two distinctstrings x , y with H(x) = H(y). Collisions must exist for anyhash function.
First pre-image resistance
For most hash values y , it should be difficult to find a stringx with H(x) = y .
Second pre-image resistance
Given a string x , it should be difficult to find a differentstring x ′ with H(x ′) = H(x).
Collision resistance
It should be difficult to find two distinct strings x , x ′ withH(x) = H(x ′).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Digital Certificates
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Digital Certificates
A public-key certificate insures that a public key actuallybelongs to an entity.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Digital Certificates
A public-key certificate insures that a public key actuallybelongs to an entity.
Certificates are issued by a trusted CertificationAuthority (CA).
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Digital Certificates
A public-key certificate insures that a public key actuallybelongs to an entity.
Certificates are issued by a trusted CertificationAuthority (CA).
A certificate consists of a public key and other additionalinformation about the owner of the key.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Digital Certificates
A public-key certificate insures that a public key actuallybelongs to an entity.
Certificates are issued by a trusted CertificationAuthority (CA).
A certificate consists of a public key and other additionalinformation about the owner of the key.
The authenticity of a certificate is achieved by the digitalsignature of the CA on the certificate.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Digital Certificates
A public-key certificate insures that a public key actuallybelongs to an entity.
Certificates are issued by a trusted CertificationAuthority (CA).
A certificate consists of a public key and other additionalinformation about the owner of the key.
The authenticity of a certificate is achieved by the digitalsignature of the CA on the certificate.
Compromised certificates are revoked and a certificaterevocation list (CRL) is maintained by the CA.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Secret SharingCryptographic Hash FunctionsDigital Certificates
Digital Certificates
A public-key certificate insures that a public key actuallybelongs to an entity.
Certificates are issued by a trusted CertificationAuthority (CA).
A certificate consists of a public key and other additionalinformation about the owner of the key.
The authenticity of a certificate is achieved by the digitalsignature of the CA on the certificate.
Compromised certificates are revoked and a certificaterevocation list (CRL) is maintained by the CA.
If a certificate is not in the CRL, and the signature of theCA on the certificate is verified, one gains the desiredconfidence of treating the public-key as authentic.
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Cryptosystems
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Cryptosystems
Partial breaking of a cryptosystemThe attacker succeeds in decrypting some ciphertextmessages, but without any guarantee that this capabilitywould help him break new ciphertext messages in future.
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Cryptosystems
Partial breaking of a cryptosystemThe attacker succeeds in decrypting some ciphertextmessages, but without any guarantee that this capabilitywould help him break new ciphertext messages in future.
Complete breaking of a cryptosystemThe attacker possesses the capability of decrypting anyciphertext message. This may be attributed to a knowledgeof the decryption key(s).
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Cryptosystems
Partial breaking of a cryptosystemThe attacker succeeds in decrypting some ciphertextmessages, but without any guarantee that this capabilitywould help him break new ciphertext messages in future.
Complete breaking of a cryptosystemThe attacker possesses the capability of decrypting anyciphertext message. This may be attributed to a knowledgeof the decryption key(s).
Passive attackThe attacker only intercepts messages meant for others.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Cryptosystems
Partial breaking of a cryptosystemThe attacker succeeds in decrypting some ciphertextmessages, but without any guarantee that this capabilitywould help him break new ciphertext messages in future.
Complete breaking of a cryptosystemThe attacker possesses the capability of decrypting anyciphertext message. This may be attributed to a knowledgeof the decryption key(s).
Passive attackThe attacker only intercepts messages meant for others.
Active attackThe attacker alters and/or deletes messages and evencreates unauthorized messages.
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Types of Passive Attack
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Types of Passive Attack
Ciphertext-only attack: The attacker has nocontrol/knowledge of the ciphertexts and the correspondingplaintexts. This is the most difficult (but practical) attack.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Types of Passive Attack
Ciphertext-only attack: The attacker has nocontrol/knowledge of the ciphertexts and the correspondingplaintexts. This is the most difficult (but practical) attack.
Known plaintext attack: The attacker knows someplaintext-ciphertext pairs. Easily mountable in public-keysystems.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Types of Passive Attack
Ciphertext-only attack: The attacker has nocontrol/knowledge of the ciphertexts and the correspondingplaintexts. This is the most difficult (but practical) attack.
Known plaintext attack: The attacker knows someplaintext-ciphertext pairs. Easily mountable in public-keysystems.
Chosen plaintext attack: A known plaintext attack wherethe plaintext messages are chosen by the attacker.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Types of Passive Attack
Ciphertext-only attack: The attacker has nocontrol/knowledge of the ciphertexts and the correspondingplaintexts. This is the most difficult (but practical) attack.
Known plaintext attack: The attacker knows someplaintext-ciphertext pairs. Easily mountable in public-keysystems.
Chosen plaintext attack: A known plaintext attack wherethe plaintext messages are chosen by the attacker.
Adaptive chosen plaintext attack: A chosen plaintextattack where the plaintext messages are chosen adaptivelyby the attacker.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Types of Passive Attack (contd.)
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Types of Passive Attack (contd.)
Chosen ciphertext attack: A known plaintext attackwhere the ciphertext messages are chosen by the attacker.Mountable if the attacker gets hold of the victim’sdecryption device.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Types of Passive Attack (contd.)
Chosen ciphertext attack: A known plaintext attackwhere the ciphertext messages are chosen by the attacker.Mountable if the attacker gets hold of the victim’sdecryption device.
Adaptive chosen ciphertext attack: A chosen ciphertextattack where the ciphertext messages are chosenadaptively by the attacker.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures
Total break: An attacker knows the signing key or has afunction that is equivalent to the signature generationtransformation.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures
Total break: An attacker knows the signing key or has afunction that is equivalent to the signature generationtransformation.
Selective forgery: An attacker can generate signatures(without the participation of the legitimate signer) on a setof messages chosen by the attacker.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures
Total break: An attacker knows the signing key or has afunction that is equivalent to the signature generationtransformation.
Selective forgery: An attacker can generate signatures(without the participation of the legitimate signer) on a setof messages chosen by the attacker.
Existential forgery: The attacker can generate signatureson certain messages over which the attacker has nocontrol.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures (contd.)
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures (contd.)
Key-only attack: The attacker knows only the verification(public) key of the signer. This is the most difficult attack tomount.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures (contd.)
Key-only attack: The attacker knows only the verification(public) key of the signer. This is the most difficult attack tomount.
Known message attack: The attacker knows somemessages and the signatures of the signer on thesemessages.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures (contd.)
Key-only attack: The attacker knows only the verification(public) key of the signer. This is the most difficult attack tomount.
Known message attack: The attacker knows somemessages and the signatures of the signer on thesemessages.
Chosen message attack: This is similar to the knownmessage attack except that the messages for which thesignatures are known are chosen by the attacker.
Public-key Cryptography: Theory and Practice Abhijit Das
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Common Cryptographic PrimitivesOther Cryptographic Primitives
Attacks on Cryptosystems
Classification of AttacksAttacks on Encryption SchemesAttacks on Digital Signatures
Attacks on Digital Signatures (contd.)
Key-only attack: The attacker knows only the verification(public) key of the signer. This is the most difficult attack tomount.
Known message attack: The attacker knows somemessages and the signatures of the signer on thesemessages.
Chosen message attack: This is similar to the knownmessage attack except that the messages for which thesignatures are known are chosen by the attacker.
Adaptive chosen message attack: The messages to besigned are adaptively chosen by the attacker.
Public-key Cryptography: Theory and Practice Abhijit Das