códigos y criptografía francisco rodríguez henríquez security attacks: active and passive active...

Códigos y Criptografía Francisco Rodríguez Henríquez

Security Attacks: Active and Passive• Active

• Masquerade (impersonation)• Replay

• Modification of message

• Denial of service

• Passive• Traffic analysis

• Release of message contents


Classes of Security Attacks

• Interruption

• Interception

• Modification

• FabricationAnita Betito


Classes of Security Attacks: Interruption

• Interruption

• Interception

• Modification


• Availability


Classes of Security Attacks: Interception

• Interruption

• Interception

• Modification

• Fabrication Anita Betito

• Confidentiality


Classes of Security Attacks: modification

• Interruption

• Interception

• Modification

• Fabrication Anita Betito• Integrity


Classes of Security Attacks: fabrication

• Interruption

• Interception

• Modification


• Authenticity


Security Services

• Confidentiality - protect info value • Authentication - protect info origin (sender)

• Identification - ensure identity of users

• Integrity - protect info accuracy • Non-repudiation - protect from deniability • Access control - access to info/resources • Availability - ensure info delivery


Some Practical Applications "Any sufficiently advanced technology is indistinguishable from

magic.” Arthur C. Clarke.

• secure mail• secure communications• network authentication• electronic voting• electronic notary• digital money (digital wallet)• data distribution


Secure Mail: PGP (Pretty Good Privacy)• Pretty Good Privacy was created by Philip R. Zimmermann. For that,

he was the target of a three-year criminal investigation, because the US government held that US export restrictions for cryptographic software were violated when PGP spread all around the world following its 1991 publication as freeware. Despite of this government persecution, PGP nonetheless became the most widely used email encryption software in the world.

• PGP is a freeware. A copy of the software can be obtain at,

PGP download site: http://web.mit.edu/network/pgp.html


Secure Communications• Scenarios

– Security for real-time electronic links– local area networks– link encryption– cellular (and ordinary) phones and faxes

• Goals– message privacy– sender and recipient authentication– non-repudiation

• Tools– key-agreement protocols– secret-key cryptosystems– public-key cryptosystems– digital signatures– certicates


Data Distribution• Scenarios

– conditional access TV – software distribution via CD ROM – information bulletin boards

• Goals– broadcast operation (TV, CD ROM) – message privacy – selective reception

• Tools– secret key cryptography – public key cryptography – secure hardware


Electronic Voting

• Scenarios– general elections– shareholders meetings– secure distributed computation

• Goals– anonymity– fairness– accountability

• Tools– RSA-based mathematics– blind signatures– sender untraceability protocols


Digital Money (Digital Wallet)• Scenarios

– replacement for paper money – more flexible than credit cards

• Goals– anonymity – untraceability – fairness – dividability – transferability – off line (from bank) operations – universality

• Tools– more RSA based mathematics – zero knowledge protocols – secure hardware tokens


Some Research Interests in Cryptography

• Design of cryptographic algorithms • Analysis of cryptographic algorithms • Design of cryptographic protocols • Hardware and software implementations

• Applications of cryptography


Cryptography Schemes

SenderSender ReceiverReceiver

AdversaryAdversary

Message

Problem: How to have secure communication over an insecure channel?


Solution A: Trusted Third Party

using this model requires us to: • design an algorithm for the security transformation

• generate the secret information used by the algorithm

• develop methods to distribute the secret information

• specify a protocol enabling the principals to use the

transformation & secret info for a security service


Solution B: Secret-key cryptography

SenderSender ReceiverReceiver

AdversaryAdversary

Ciphertext

•Exchange the key over a secure channel•Functions f(e; -) and g(d; -) are inverses of one another•Encryption and decryption processes are symmetric

key: e or d

C := f(e; M) M := g(d; C)


Problems with secret-key cryptography:

• requires establishment of a secure channel for key exchange

• two parties cannot start communication if they never met


Alternative: Public-Key Cryptography

• requires establishment of a public-key directory in which everyone publishes their encryption keys

• two parties can start communication even they never met

• provides ability to sign digital data

códigos y criptografía francisco rodríguez henríquez security attacks: active and passive active...

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