Module elgamal

The twisted ElGamal encryption implementation.

The message space consists of any number that is representable as a scalar (a.k.a. “exponent”) for Curve25519.

A twisted ElGamal ciphertext consists of two components:

• A Pedersen commitment that encodes a message to be encrypted
• A “decryption handle” that binds the Pedersen opening to a specific public key

In contrast to the traditional ElGamal encryption scheme, the twisted ElGamal encodes messages directly as a Pedersen commitment. Therefore, proof systems that are designed specifically for Pedersen commitments can be used on the twisted ElGamal ciphertexts.

As the messages are encrypted as scalar elements (a.k.a. in the “exponent”), one must solve the discrete log to recover the originally encrypted value.

Structs

• DecryptHandle
  Decryption handle for Pedersen commitment.
• ElGamal
  Algorithm handle for the twisted ElGamal encryption scheme
• ElGamalCiphertext
  Ciphertext for the ElGamal encryption scheme.
• ElGamalKeypair
  A (twisted) ElGamal encryption keypair.
• ElGamalPubkey
  Public key for the ElGamal encryption scheme.
• ElGamalSecretKey
  Secret key for the ElGamal encryption scheme.

Constants

• ELGAMAL_KEYPAIR_LEN
  Byte length of an ElGamal keypair