org.cryptimeleon.craco.enc.asym.elgamal

Class ElgamalEncryption

java.lang.Object

org.cryptimeleon.craco.enc.asym.elgamal.ElgamalEncryption

All Implemented Interfaces:

AsymmetricEncryptionScheme, EncryptionScheme, org.cryptimeleon.math.serialization.annotations.RepresentationRestorer, org.cryptimeleon.math.serialization.Representable, org.cryptimeleon.math.serialization.StandaloneRepresentable

public class ElgamalEncryption
extends java.lang.Object
implements AsymmetricEncryptionScheme

Encryption scheme originally presented by Elgamal in [1]. The key generation, encryption and decryption algorithm can be described as follows:

Let G be a cyclic group of order $q$.

Key generation: - Choose a \in Z_q = {0,1, ..., q-1} uniformly at random. - Choose generator g of G uniformly at random. - The private key is (G, g, a, h = g^a) and the public key is (G, g, h)

Encryption of message m \in G under public key pk = (G, g, h): - Choose r \in Z_q uniformly at random. - The ciphertext is c = (c_1, c_2) = (g^r, m * h^r)

Decryption of c = (c_1, c_2) under private key sk = (G, g, a, h): - The message is m = c_2 * c_1^{-a}

[1] T. Elgamal, "A public key cryptosystem and a signature scheme based on discrete logarithms," in IEEE Transactions on Information Theory, vol. 31, no. 4, pp. 469-472, July 1985.

Constructor Summary

Constructors

Constructor and Description
ElgamalEncryption(org.cryptimeleon.math.structures.groups.Group groupG)
ElgamalEncryption(org.cryptimeleon.math.serialization.Representation repr)

Method Summary

Modifier and Type	Method and Description
PlainText	decrypt(CipherText cipherText, DecryptionKey privateKey) Decrypts the given cipher text using the given decryption key.
CipherText	encrypt(PlainText plainText, EncryptionKey publicKey) Encrypts the given plain text using the given encryption key.
CipherText	encrypt(PlainText plainText, EncryptionKey publicKey, java.math.BigInteger random) Encrypt message under public key and use given randomness.
boolean	equals(java.lang.Object o)
EncryptionKeyPair	generateKeyPair() Generates a public/private-key pair for the specified group.
org.cryptimeleon.math.structures.groups.Group	getGroup()
org.cryptimeleon.math.serialization.Representation	getRepresentation()
int	hashCode()
ElgamalCipherText	restoreCipherText(org.cryptimeleon.math.serialization.Representation repr) Restores the ciphertext corresponding to the given representation.
ElgamalPrivateKey	restoreDecryptionKey(org.cryptimeleon.math.serialization.Representation repr) Restores the decryption key corresponding to the given representation.
ElgamalPublicKey	restoreEncryptionKey(org.cryptimeleon.math.serialization.Representation repr) Restores the encryption key corresponding to the given representation.
PlainText	restorePlainText(org.cryptimeleon.math.serialization.Representation repr) Restores the plaintext corresponding to the given representation.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.cryptimeleon.craco.enc.EncryptionScheme

decrypt, encrypt, restoreFromRepresentation

Constructor Detail

ElgamalEncryption

public ElgamalEncryption(org.cryptimeleon.math.structures.groups.Group groupG)

ElgamalEncryption

public ElgamalEncryption(org.cryptimeleon.math.serialization.Representation repr)

Method Detail

getGroup

public org.cryptimeleon.math.structures.groups.Group getGroup()

encrypt

public CipherText encrypt(PlainText plainText,
                          EncryptionKey publicKey)

Description copied from interface: EncryptionScheme

Encrypts the given plain text using the given encryption key.

Specified by:

encrypt in interface EncryptionScheme

Parameters:

plainText - the plaintext to encrypt

publicKey - the key to use for encryption

Returns:

the resulting ciphertext

encrypt

public CipherText encrypt(PlainText plainText,
                          EncryptionKey publicKey,
                          java.math.BigInteger random)

Encrypt message under public key and use given randomness.

This function is used internally. Randomness is either uniform at random to obtain the standard Elgamal Encryption. But, e.g. for Fujisaki-Okamoto transform, the randomness is the result of mangling the message with additional randomness.

Parameters:

plainText - the message to encrypt

publicKey - the key to use for encryption

random - the randomness to use for encryption

Returns:

the encrypted message as a cipher text

decrypt

public PlainText decrypt(CipherText cipherText,
                         DecryptionKey privateKey)

Description copied from interface: EncryptionScheme

Decrypts the given cipher text using the given decryption key.

Specified by:

decrypt in interface EncryptionScheme

Parameters:

cipherText - the ciphertext to decrypt

privateKey - the key to use for decryption

Returns:

the resulting plaintext

generateKeyPair

public EncryptionKeyPair generateKeyPair()

Generates a public/private-key pair for the specified group.

Specified by:

generateKeyPair in interface AsymmetricEncryptionScheme

Returns:

A pair of a private key and the corresponding public key.

restorePlainText

public PlainText restorePlainText(org.cryptimeleon.math.serialization.Representation repr)

Description copied from interface: EncryptionScheme

Restores the plaintext corresponding to the given representation.

Specified by:

restorePlainText in interface EncryptionScheme

Parameters:

repr - the representation to restore the plaintext from

Returns:

the plaintext corresponding to the given representation

restoreCipherText

public ElgamalCipherText restoreCipherText(org.cryptimeleon.math.serialization.Representation repr)

Description copied from interface: EncryptionScheme

Restores the ciphertext corresponding to the given representation.

Specified by:

restoreCipherText in interface EncryptionScheme

Parameters:

repr - the representation to restore the ciphertext from

Returns:

the ciphertext corresponding to the given representation

restoreEncryptionKey

public ElgamalPublicKey restoreEncryptionKey(org.cryptimeleon.math.serialization.Representation repr)

Description copied from interface: EncryptionScheme

Restores the encryption key corresponding to the given representation.

Specified by:

restoreEncryptionKey in interface EncryptionScheme

Parameters:

repr - the representation to restore the encryption key from

Returns:

the encryption corresponding to the given representation

restoreDecryptionKey

public ElgamalPrivateKey restoreDecryptionKey(org.cryptimeleon.math.serialization.Representation repr)

Description copied from interface: EncryptionScheme

Restores the decryption key corresponding to the given representation.

Specified by:

restoreDecryptionKey in interface EncryptionScheme

Parameters:

repr - the representation to restore the decryption key from

Returns:

the decryption key corresponding to the given representation

getRepresentation

public org.cryptimeleon.math.serialization.Representation getRepresentation()

Specified by:

getRepresentation in interface org.cryptimeleon.math.serialization.Representable

equals

public boolean equals(java.lang.Object o)

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object