15.2.3 ElGamal

Bigloo supports ElGamal encryption (but not signing). Bigloo’s implementation is minimal.

For consistency with RSA ElGamal keys are similarly named as their RSA counterparts.

Bigloo Cryptography class: ElGamal-Key

Bigloo Cryptography class: Complete-ElGamal-Key

(class ElGamal-Key
  p::bignum
  g::bignum
  y::bignum)
(final-class Complete-ElGamal-Key::ElGamal-Key
  x::bignum)) ;; the private key

Bigloo Cryptography procedure: extract-public-elgamal-key complete-key

Returns a copy of the public part (as ElGamal Key).

Bigloo Cryptography procedure: elgamal-encrypt key m

Encrypts the bignum m using the given public key. The result are two values c1 and c2.

Note that ElGamal encryption needs random bytes for every encryption. This means that this function may return different results with the same parameters. It furthermore implies that the result is insecure if the operating system provides bad random numbers, or if Bigloo’s random-number generation is buggy. For critical applications be sure to verify both requirements.

Bigloo Cryptography procedure: elgamal-decrypt complete-key c1 c2

Decrypts an ElGamal encrypted message (consisting of the two bignums c1 and c2) with the given private key.

Bigloo Cryptography procedure: elgamal-key-length key

Returns the key length in bytes.

ElGamal works very similar to RSA. Have a look at RSA’s example section.

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