Secure communicationMost popular encryption algorithms overview

AgendaOne-time padStream ciphers

A5/1Symmetric block ciphers

DES (weak), 3DES (secure), AES (secure)Asymmetric block ciphers

RSA (slow)Elliptic curves (fast)

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

Stream ciphersInspiration from the one-time padTypes:

synchronousself-synchronizing

LFSR (linear feedback shift registers)

A5/1 stream cipherFeatures:

Used in GSM networks114 bit length keystreamBased on three LSFRsSuccessful attacks exist

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.

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.

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.

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

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.

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.

ReferencesIntroduction to Cryptography by Christof PaarCryptography and Computer Privacy

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