secure communication
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Secure communicationMost popular encryption algorithms overview
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AgendaOne-time padStream ciphers
A5/1Symmetric block ciphers
DES (weak), 3DES (secure), AES (secure)Asymmetric block ciphers
RSA (slow)Elliptic curves (fast)
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One-time padMain features:
Totally secure crypto technicA key has to be the same length as
a plain textA key has to be truly randomXOR operation is often used to
combine a key and a textImpractical in most cases due to the
above key length requirement
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Stream ciphersInspiration from the one-time padTypes:
synchronousself-synchronizing
LFSR (linear feedback shift registers)
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A5/1 stream cipherFeatures:
Used in GSM networks114 bit length keystreamBased on three LSFRsSuccessful attacks exist
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DESDES, Data Encryption Standard, was developed in the 1970s at IBM and based on design of Horst Feistel.
It is a symmetric-key algorithm based on Feistel network.
Key size is 56 bits only and it is considered insecure now.
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3DES3DES - Triple DES
Brute force attack on 2DES can use “meet in the middle” technique.
It is a symmetric-key algorithm based on Feistel network.
Key size is 168 bits only and it is considered insecure now.
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AESAES, Advanced Encryption Standard, established in 2001 by the NIST and based on design of Joan Daemen and Vincent Rijmen.
It is a symmetric-key algorithm based on Galois field.
Supported key sizes are 128, 192 or 256 bits.
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Block cipher modesA mode of operation is used to encrypt more than one block of plain data. The following is the list of some popular modes:
ECB - Electronic Codebook - the simplest modeCBC - Cipher Block ChainingOFB - Output Feedback - makes a synchronous stream cipherCFB - Cipher Feedback - makes a self-synchronizing stream cipherCTR - Counter - makes a synchronous stream cipher
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RSARSA, described in 1977, was called after its inventors Ron Rivest, Adi Shamir, and Leonard Adleman.
It is a public key algorithm.
Key size could be in range of 1024 to 4096 bits
It is a relatively slow algorithm and usually used to share keys for symmetric algorithms.
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Elliptic curve cryptographyIt is based on the algebraic structure of elliptic curves.
This is the fastest public key algorithm as of now.
256 bit ECC public key provides security compared to 3072 bit RSA public key.
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ReferencesIntroduction to Cryptography by Christof PaarCryptography and Computer Privacy