Saturday 18 June 2011


Secret key (symmetric encryption)

Use a secret key (or a pair of directly related keys) for both decryption and encryption.
  • Advanced Encryption Standard (AES), also known as Rijndael.
  • Blowfish. Designed by Schneier as a general-purpose algorithm, intended as a replacement for the aging DE.
  • Data Encryption Standard (DES), formerly DE Algorithm.
  • IDEA (International Data Encryption Algorithm). Formerly IPES (Improved PES), another replacement for DES. Is used by PGP (Pretty Good Privacy). Performs transformations on data splitted in blocks, using a key.
  • RC4 or ARC4. Stream cipher widely-used in protocols such as SSL for Internet traffic and WEP for wireless networks.
  • Tiny Encryption Algorithm. Easy to implement block cipher algorithme using some formulas.
  • PES (Proposed Encryption Standard). Older name for IDEA.

Public key (asymmetric encryption)

Use a pair of keys, designated as public key and private key. The public key encrypt the message, only the private key permits to decrypt it.
  • DSA (Digital Signature Algorithm). Generate keys with prime and random numbers. Was used by US agencies, and now public domain.
  • ElGamal. Based on Diffie-Hellman, used by GNU Privacy Guard software, PGP, and other cryptographic systems.
  • RSA (Rivest, Shamir, Adleman). Widely used in electronic commerce protocols. Use prime numbers.
  • Diffie-Hellman (Merkle) key exchange (or exponential key exchange). Method and algorithm to share secret over an unprotected communications channel. Used by RSA.
  • NTRUEncrypt. Make use of rings of polynomials with convolution multiplications.

Message digest functions

A message digest is a code resulting of the encryption of a string or data of any length, processed by a hash function.
  • MD5. Used for checking ISO images of CDs or DVDs.
  • RIPEMD (RACE Integrity Primitives Evaluation Message Digest). Based upon the principles of MD4 and similar to SHA-1.
  • SHA-1 (Secure Hash Algorithm 1). Most commonly used of the SHA set of related cryptographic hash functions. Was designed by the NSA agency.
  • HMAC. keyed-hash message authentication.
  • Tiger (TTH). Usually used in Tiger tree hashes.

Cryptographic using pseudo-random numbers

Techniques in cryptography

Secret sharing, Secret Splitting, Key Splitting, M of N algorithms.
  • Shamir's secret sharing scheme. This is a formula based on polynomial interpolation.
  • Blakley's secret sharing scheme. Is geometric in nature, the secret is a point in an m-dimensional space.

Other techniques and decryption

  • Subset sum. Given a set of integers, does any subset sum equal zero? Used in cryptography.
  • Shor's algorithm. Quantum algorithm able to decrypt a code based on asymetric functions such as RSA.