The ElGamal scheme is a scheme which provides homormophic multiplication. More...

#include <gmp.h>
#include "hcs_random.h"

Include dependency graph for egcs.h:

Data Structures
struct	egcs_cipher
	Ciphertext type for use in the ElGamal scheme. More...

struct	egcs_public_key
	Public key for use in the ElGamal scheme. More...

struct	egcs_private_key
	Private key for use in the ElGamal scheme. More...

Functions
egcs_public_key *	egcs_init_public_key (void)
	Initialise a egcs_public_key and return a pointer to the newly created structure. More...

egcs_private_key *	egcs_init_private_key (void)
	Initialise a egcs_private_key and return a pointer to the newly created structure. More...

void	egcs_generate_key_pair (egcs_public_key pk, egcs_private_key vk, hcs_random *hr, const unsigned long bits)
	Initialise a key pair with modulus size `bits`. More...

egcs_cipher *	egcs_init_cipher (void)
	Initialise a egcs_cipher and return a pointer to the newly created structure. More...

void	egcs_set (egcs_cipher rop, egcs_cipher op)
	Copy value of op to rop. More...

void	egcs_encrypt (egcs_public_key pk, hcs_random hr, egcs_cipher *rop, mpz_t plain1)
	Encrypt a value `plain1`, and set `rop` to the encrypted result. More...

void	egcs_ee_mul (egcs_public_key pk, egcs_cipher rop, egcs_cipher ct1, egcs_cipher ct2)
	Multiply an encrypted value `ct1` with an encrypted value `ct2`, storing the result in `rop`. More...

void	egcs_decrypt (egcs_private_key vk, mpz_t rop, egcs_cipher cipher1)
	Decrypt a value `cipher1`, and set `rop` to the decrypted result. More...

void	egcs_clear_cipher (egcs_cipher *ct)
	Zero all data related to the given egcs_cipher. More...

void	egcs_free_cipher (egcs_cipher *ct)
	Free all associated memory with a given egcs_cipher. More...

void	egcs_clear_public_key (egcs_public_key *pk)
	Zero all memory associated with a egcs_public_key. More...

void	egcs_clear_private_key (egcs_private_key *vk)
	Zero all memory associated with a egcs_private_key. More...

void	egcs_free_public_key (egcs_public_key *pk)
	Frees a egcs_public_key and all associated memory. More...

void	egcs_free_private_key (egcs_private_key *vk)
	Frees a egcs_private_key and all associated memory. More...

Detailed Description

The ElGamal scheme is a scheme which provides homormophic multiplication.

It is usually used with some padding scheme similar to RSA. This implementation only provides unpadded values to exploit this property.

Due to the nature of the ciphertext, this implementation provides a unique type for the ciphertext, rather than just using gmp mpz_t types. These can be used with the provided initialisation functions, and should be freed on program termination.

All mpz_t values can be alises unless otherwise stated.

Function Documentation

egcs_public_key* egcs_init_public_key ( void )

Initialise a egcs_public_key and return a pointer to the newly created structure.

Returns: A pointer to an initialised egcs_public_key, NULL on allocation failure

egcs_private_key* egcs_init_private_key ( void )

Initialise a egcs_private_key and return a pointer to the newly created structure.

Returns: A pointer to an initialised egcs_private_key, NULL on allocation failure

void egcs_generate_key_pair	(	egcs_public_key *	pk,
		egcs_private_key *	vk,
		hcs_random *	hr,
		const unsigned long	bits
	)

Initialise a key pair with modulus size bits.

It is required that pk and vk are initialised before calling this function. pk and vk are expected to not be NULL.

In practice the bits value should usually be greater than 2048 to ensure sufficient security.

Parameters

pk	A pointer to an initialised egcs_public_key
vk	A pointer to an initialised egcs_private_key
hr	A pointer to an initialised hcs_random type
bits	The number of bits for the modulus of the key

egcs_cipher* egcs_init_cipher ( void )

Initialise a egcs_cipher and return a pointer to the newly created structure.

Returns: A pointer to an initialised egcs_cipher, NULL on allocation failure

void egcs_set	(	egcs_cipher *	rop,
		egcs_cipher *	op
	)

Copy value of op to rop.

Parameters

rop	A pointer to an initialised egcs_cipher
op	A pointer to an initialised egcs_cipher

void egcs_encrypt	(	egcs_public_key *	pk,
		hcs_random *	hr,
		egcs_cipher *	rop,
		mpz_t	plain1
	)

Encrypt a value plain1, and set rop to the encrypted result.

Parameters

pk	A pointer to an initialised egcs_public_key
hr	A pointer to an initialised hcs_random type
rop	egcs_cipher where the result is to be stored
plain1	mpz_t to be encrypted

void egcs_ee_mul	(	egcs_public_key *	pk,
		egcs_cipher *	rop,
		egcs_cipher *	ct1,
		egcs_cipher *	ct2
	)

Multiply an encrypted value ct1 with an encrypted value ct2, storing the result in rop.

Parameters

pk	A pointer to an initialised egcs_public_key
rop	egcs_cipher where the result is to be stored
ct1	egcs_cipher to be multiplied together
ct2	egcs_cipher to be multiplied together

void egcs_decrypt	(	egcs_private_key *	vk,
		mpz_t	rop,
		egcs_cipher *	cipher1
	)

Decrypt a value cipher1, and set rop to the decrypted result.

Parameters

vk	A pointer to an initialised egcs_private_key
rop	mpz_t where the decrypted result is stored
cipher1	egcs_cipher to be decrypted

void egcs_clear_cipher ( egcs_cipher * ct )

Zero all data related to the given egcs_cipher.

Parameters

ct	A pointer to an initialised egcs_cipher

void egcs_free_cipher ( egcs_cipher * ct )

Free all associated memory with a given egcs_cipher.

Parameters

ct	A pointer to an initialised egcs_cipher

void egcs_clear_public_key ( egcs_public_key * pk )

Zero all memory associated with a egcs_public_key.

This does not free the memory, so the key is safe to use immediately after calling this.

Parameters

pk	A pointer to an initialised egcs_public_key

void egcs_clear_private_key ( egcs_private_key * vk )

Zero all memory associated with a egcs_private_key.

This does not free the memory, so the key is safe to use immediately after calling this.

Parameters

vk	A pointer to an initialised egcs_private_key

void egcs_free_public_key ( egcs_public_key * pk )

Frees a egcs_public_key and all associated memory.

Parameters

pk	A pointer to an initialised egcs_public_key

void egcs_free_private_key ( egcs_private_key * vk )

Frees a egcs_private_key and all associated memory.

Parameters

vk	A pointer to an initialised egcs_private_key

Data Structures

Functions

Detailed Description

Function Documentation