ElGamal Cryptosystem

Proposed by Taher Elgamal in 1985
• Can be viewed as an extension of the DHKE protocol
• Security is also based on the hardness of the discrete logarithm
problem and the Diffie–Hellman problem
• Based on modular exponentiation and factorization of large numbers
• In RSA block cipher, plaintext (and ciphertext) are integers between 0 and n-1 for some n
• Typically |n| = 1024 bits
• Means, 𝑛 ≤ 2
1024 or 309 decimal digits