Elgamal encryption

The Elgamal algorithm is an asymmetric key encryption algorithm for public key cryptography which is based on Diffie-Hellman key agreement. It was described by Taher Elgamal in 1984. The Elgamal algorithm is used in the free GNU Privacy Guard software, recent versions of PGP, and other cryptosystems. The Digital Signature Algorithm is a signature scheme is a variant of the ElGamal signature scheme, which should not be confused with the Elgamal algorithm.

Miscellaneous

Elgamal is malleable in an extreme way: for example, given an encryption (c_1, c_2) of some (possibly unknown) message m, one can easily construct an encryption (c_1, 2 cdot c_2) of the message 2m. Therefore Elgamal is not secure under chosen ciphertext attack. On the other hand, the Cramer-Shoup system (which is based on Elgamal) is secure under chosen ciphertext attack.

Related Topics:
Malleable - Chosen ciphertext attack - Cramer-Shoup system

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