The Damgard-Jurik scheme is a scheme which provides homomorphic addition, and limited multiplication on encrypted data. More...

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

Include dependency graph for djcs.h:

Go to the source code of this file.

Data Structures
struct	djcs_public_key
	Public key for use in the Paillier system. More...

struct	djcs_private_key
	Private key for use in the Paillier system. More...

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

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

int	djcs_generate_key_pair (djcs_public_key pk, djcs_private_key vk, hcs_random *hr, unsigned long s, unsigned long bits)
	Initialise a key pair with modulus size `bits`. More...

void	djcs_encrypt (djcs_public_key pk, hcs_random hr, mpz_t rop, mpz_t plain1)
	Encrypt a value `plain1`, and set `rop` to the encrypted result. More...

void	djcs_reencrypt (djcs_public_key pk, hcs_random hr, mpz_t rop, mpz_t op)
	Reencrypt an encrypted value `op`. More...

void	djcs_ep_add (djcs_public_key *pk, mpz_t rop, mpz_t cipher1, mpz_t plain1)
	Add a plaintext value `plain1` to an encrypted value `cipher1`, storing the result in `rop`. More...

void	djcs_ee_add (djcs_public_key *pk, mpz_t rop, mpz_t cipher1, mpz_t cipher2)
	Add an encrypted value `cipher2` to an encrypted value `cipher1`, storing the result in `rop`. More...

void	djcs_ep_mul (djcs_public_key *pk, mpz_t rop, mpz_t cipher1, mpz_t plain1)
	Multiply a plaintext value `plain1` with an encrypted value `cipher1`, storing the result in `rop`. More...

void	djcs_decrypt (djcs_private_key *vk, mpz_t rop, mpz_t cipher1)
	Decrypt a value `cipher1`, and set `rop` to the decrypted result. More...

void	djcs_clear_public_key (djcs_public_key *pk)
	Clears all data in a djcs_public_key. More...

void	djcs_clear_private_key (djcs_private_key *vk)
	Clears all data in a djcs_private_key. More...

void	djcs_free_public_key (djcs_public_key *pk)
	Frees a djcs_public_key and all associated memory. More...

void	djcs_free_private_key (djcs_private_key *vk)
	Frees a djcs_private_key and all associated memory. More...

int	djcs_verify_key_pair (djcs_public_key pk, djcs_private_key vk)
	Check certain values shared between public and private keys to ensure they indeed are pairs. More...

char *	djcs_export_public_key (djcs_public_key *pk)
	Export a public key as a string. More...

char *	djcs_export_private_key (djcs_private_key *vk)
	Export a private key as a string. More...

int	djcs_import_public_key (djcs_public_key pk, const char json)
	Import a public key from a string. More...

int	djcs_import_private_key (djcs_private_key vk, const char json)
	Import a private key from a string. More...

Detailed Description

The Damgard-Jurik scheme is a scheme which provides homomorphic addition, and limited multiplication on encrypted data.

It is a generalisation of the Paillier cryptoscheme, where the modulus n^2 is extended to n^(s+1) for s > 0.

Function Documentation

djcs_public_key* djcs_init_public_key ( void )

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

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

djcs_private_key* djcs_init_private_key ( void )

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

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

int djcs_generate_key_pair	(	djcs_public_key *	pk,
		djcs_private_key *	vk,
		hcs_random *	hr,
		unsigned long	s,
		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.

Whilst s is variable and and can be any value upto a minimum of 32 bits, beware when calling the function with large values. The modulus grows exponentially given s, so even small values greater than 7 will incur massive performance penalties, and increase the risk of overflow (~40 million digits for the modulus for this to occur).

Warning: This function attempts to allocate memory, so calling this twice in sucession with the same keys will cause your program to lose a pointer to this allocated memory, resulting in a memory leak. If you wish to call this function in this manner, ensure djcs_clear_public_key and/or djcs_clear_private_key are called prior.

Parameters

pk	A pointer to an initialised djcs_public_key
vk	A pointer to an initialised djcs_private_key
hr	A pointer to an initialised hcs_random type
s	The size exponent for the ciphertext space we wish to work in
bits	The number of bits for the modulus of the key

void djcs_encrypt	(	djcs_public_key *	pk,
		hcs_random *	hr,
		mpz_t	rop,
		mpz_t	plain1
	)

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

Parameters

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

void djcs_reencrypt	(	djcs_public_key *	pk,
		hcs_random *	hr,
		mpz_t	rop,
		mpz_t	op
	)

Reencrypt an encrypted value op.

Upon decryption, this newly encrypted value, rop, will retain the same value as op.

Parameters

pk	A pointer to an initialised djcs_public_key
hr	A pointer to an initialised hcs_random type
rop	mpz_t where the newly encrypted value is stored
op	mpz_t to be reencrypted

void djcs_ep_add	(	djcs_public_key *	pk,
		mpz_t	rop,
		mpz_t	cipher1,
		mpz_t	plain1
	)

Add a plaintext value plain1 to an encrypted value cipher1, storing the result in rop.

Parameters

pk	A pointer to an initialised djcs_public_key
rop	mpz_t where the newly encrypted value is stored
cipher1	mpz_t to be added together
plain1	mpz_t to be added together

void djcs_ee_add	(	djcs_public_key *	pk,
		mpz_t	rop,
		mpz_t	cipher1,
		mpz_t	cipher2
	)

Add an encrypted value cipher2 to an encrypted value cipher1, storing the result in rop.

Parameters

pk	A pointer to an initialised djcs_public_key.
rop	mpz_t where the newly encrypted value is stored
cipher1	mpz_t to be added together
cipher2	mpz_t to be added together

void djcs_ep_mul	(	djcs_public_key *	pk,
		mpz_t	rop,
		mpz_t	cipher1,
		mpz_t	plain1
	)

Multiply a plaintext value plain1 with an encrypted value cipher1, storing the result in rop.

Parameters

pk	A pointer to an initialised djcs_public_key
rop	Where the new encrypted result is stored
cipher1	The encrypted value which is to be multipled to
plain1	The plaintext value which is to be multipled

void djcs_decrypt	(	djcs_private_key *	vk,
		mpz_t	rop,
		mpz_t	cipher1
	)

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

rop and cipher1 can aliases for the same mpz_t.

Parameters

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

void djcs_clear_public_key ( djcs_public_key * pk )

Clears all data in a djcs_public_key.

This does not free memory in the keys, only putting it into a state whereby they can be safely used to generate new key values.

Parameters

pk	A pointer to an initialised djcs_public_key

void djcs_clear_private_key ( djcs_private_key * vk )

Clears all data in a djcs_private_key.

This does not free memory in the keys, only putting it into a state whereby they can be safely used to generate new key values.

Parameters

vk	A pointer to an initialised djcs_private_key

void djcs_free_public_key ( djcs_public_key * pk )

Frees a djcs_public_key and all associated memory.

The key memory is not zeroed, so one must call djcs_clear_public_key if it is required. one does not need to call djcs_clear_public_key before using this function.

Parameters

pk	A pointer to an initialised djcs_public_key

void djcs_free_private_key ( djcs_private_key * vk )

Frees a djcs_private_key and all associated memory.

The key memory is not zeroed, so one must call djcs_clear_private_key if it is required. one does not need to call djcs_clear_private_key before using this function.

Parameters

vk	v pointer to an initialised djcs_private_key

int djcs_verify_key_pair	(	djcs_public_key *	pk,
		djcs_private_key *	vk
	)

Check certain values shared between public and private keys to ensure they indeed are pairs.

This checks only the n and s values, and assumes that the caller has not altered other internal values. If the caller has only interacted with the keys through the usual functions, then this should guarantee the keys are pairs.

Parameters

pk	A pointer to an initialised djcs_public_key
vk	A pointer to an initialised djcs_private_key

Returns: non-zero if keys are valid, else zero

char* djcs_export_public_key ( djcs_public_key * pk )

Export a public key as a string.

We only store the minimum required values to restore the key. In this case, these are the s and n values.

The format these strings export as is as a JSON object.

Parameters

pk	A pointer to an initialised djcs_public_key

Returns: A string representing the given key, else NULL on error

char* djcs_export_private_key ( djcs_private_key * vk )

Export a private key as a string.

We only store the minimum required values to restore the key. In this case, these are the s, n and d values. The remaining values are then computed from these on import.

Parameters

vk	A pointer to an initialised djcs_private_key

Returns: A string representing the given key, else NULL on error

int djcs_import_public_key	(	djcs_public_key *	pk,
		const char *	json
	)

Import a public key from a string.

The input string is expected to match the format given by the export functions.

Parameters

pk	A pointer to an initialised djcs_public_key
json	A string storing the contents of a public key

Returns: non-zero if success, else zero on format error

int djcs_import_private_key	(	djcs_private_key *	vk,
		const char *	json
	)

Import a private key from a string.

The input string is expected to match the format given by the export functions.

Parameters

vk	A pointer to an initialised djcs_private_key
json	A string storing the contents of a private key

Returns: non-zero if success, else zero on format error

Data Structures

Functions

Detailed Description

Function Documentation