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paillier.c
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paillier.c
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/*
***Modified version***
libpaillier - A library implementing the Paillier cryptosystem.
Copyright (C) 2006 SRI International.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <gmp.h>
#include "paillier.h"
void
init_rand( gmp_randstate_t rand, paillier_get_rand_t get_rand, int bytes )
{
void* buf;
mpz_t s;
buf = malloc(bytes);
get_rand(buf, bytes);
gmp_randinit_default(rand);
mpz_init(s);
mpz_import(s, bytes, 1, 1, 0, 0, buf);
gmp_randseed(rand, s);
mpz_clear(s);
free(buf);
}
void
complete_pubkey( paillier_pubkey_t* pub )
{
mpz_mul(pub->n_squared, pub->n, pub->n);
mpz_add_ui(pub->n_plusone, pub->n, 1);
}
void
complete_prvkey( paillier_prvkey_t* prv, paillier_pubkey_t* pub )
{
mpz_powm(prv->x, pub->n_plusone, prv->lambda, pub->n_squared);
mpz_sub_ui(prv->x, prv->x, 1);
mpz_div(prv->x, prv->x, pub->n);
mpz_invert(prv->x, prv->x, pub->n);
}
void
paillier_keygen( int modulusbits,
paillier_pubkey_t** pub,
paillier_prvkey_t** prv,
paillier_get_rand_t get_rand )
{
mpz_t p;
mpz_t q;
gmp_randstate_t rand;
/* allocate the new key structures */
*pub = (paillier_pubkey_t*) malloc(sizeof(paillier_pubkey_t));
*prv = (paillier_prvkey_t*) malloc(sizeof(paillier_prvkey_t));
/* initialize our integers */
mpz_init((*pub)->n);
mpz_init((*pub)->n_squared);
mpz_init((*pub)->n_plusone);
mpz_init((*prv)->lambda);
mpz_init((*prv)->x);
mpz_init(p);
mpz_init(q);
/* pick random (modulusbits/2)-bit primes p and q */
init_rand(rand, get_rand, modulusbits / 8 + 1);
do
{
do
mpz_urandomb(p, rand, modulusbits / 2);
while( !mpz_probab_prime_p(p, 10) );
do
mpz_urandomb(q, rand, modulusbits / 2);
while( !mpz_probab_prime_p(q, 10) );
/* compute the public modulus n = p q */
mpz_mul((*pub)->n, p, q);
} while( !mpz_tstbit((*pub)->n, modulusbits - 1) );
complete_pubkey(*pub);
(*pub)->bits = modulusbits;
/* compute the private key lambda = lcm(p-1,q-1) */
mpz_sub_ui(p, p, 1);
mpz_sub_ui(q, q, 1);
mpz_lcm((*prv)->lambda, p, q);
complete_prvkey(*prv, *pub);
/* clear temporary integers and randstate */
mpz_clear(p);
mpz_clear(q);
gmp_randclear(rand);
}
paillier_ciphertext_t*
paillier_enc( paillier_ciphertext_t* res,
paillier_pubkey_t* pub,
paillier_plaintext_t* pt,
paillier_get_rand_t get_rand )
{
mpz_t r;
gmp_randstate_t rand;
mpz_t x;
/* pick random blinding factor */
mpz_init(r);
init_rand(rand, get_rand, pub->bits / 8 + 1);
do
mpz_urandomb(r, rand, pub->bits);
while( mpz_cmp(r, pub->n) >= 0 );
/* compute ciphertext */
if( !res )
{
res = (paillier_ciphertext_t*) malloc(sizeof(paillier_ciphertext_t));
mpz_init(res->c);
mpz_init(res->r); // I added this
}
mpz_init(x);
mpz_powm(res->c, pub->n_plusone, pt->m, pub->n_squared);
mpz_powm(x, r, pub->n, pub->n_squared);
mpz_mul(res->c, res->c, x);
mpz_mod(res->c, res->c, pub->n_squared);
mpz_set(res->r, r); // I added this
mpz_clear(x);
mpz_clear(r);
gmp_randclear(rand);
return res;
}
paillier_plaintext_t*
paillier_dec( paillier_plaintext_t* res,
paillier_pubkey_t* pub,
paillier_prvkey_t* prv,
paillier_ciphertext_t* ct )
{
if( !res )
{
res = (paillier_plaintext_t*) malloc(sizeof(paillier_plaintext_t));
mpz_init(res->m);
}
mpz_powm(res->m, ct->c, prv->lambda, pub->n_squared);
mpz_sub_ui(res->m, res->m, 1);
mpz_div(res->m, res->m, pub->n);
mpz_mul(res->m, res->m, prv->x);
mpz_mod(res->m, res->m, pub->n);
return res;
}
void
paillier_mul( paillier_pubkey_t* pub,
paillier_ciphertext_t* res,
paillier_ciphertext_t* ct0,
paillier_ciphertext_t* ct1 )
{
mpz_mul(res->c, ct0->c, ct1->c);
mpz_mod(res->c, res->c, pub->n_squared);
}
void
paillier_exp( paillier_pubkey_t* pub,
paillier_ciphertext_t* res,
paillier_ciphertext_t* ct,
paillier_plaintext_t* pt )
{
mpz_powm(res->c, ct->c, pt->m, pub->n_squared);
}
paillier_plaintext_t*
paillier_plaintext_from_ui( unsigned long int x )
{
paillier_plaintext_t* pt;
pt = (paillier_plaintext_t*) malloc(sizeof(paillier_plaintext_t));
mpz_init_set_ui(pt->m, x);
return pt;
}
paillier_plaintext_t*
paillier_plaintext_from_bytes( void* m, int len )
{
paillier_plaintext_t* pt;
pt = (paillier_plaintext_t*) malloc(sizeof(paillier_plaintext_t));
mpz_init(pt->m);
mpz_import(pt->m, len, 1, 1, 0, 0, m);
return pt;
}
void*
paillier_plaintext_to_bytes( int len,
paillier_plaintext_t* pt )
{
void* buf0;
void* buf1;
size_t written;
buf0 = mpz_export(0, &written, 1, 1, 0, 0, pt->m);
if( written == len )
return buf0;
buf1 = malloc(len);
memset(buf1, 0, len);
if( written == 0 )
/* no need to copy anything, pt->m = 0 and buf0 was not allocated */
return buf1;
else if( written < len )
/* pad with leading zeros */
memcpy(buf1 + (len - written), buf0, written);
else
/* truncate leading garbage */
memcpy(buf1, buf0 + (written - len), len);
free(buf0);
return buf1;
}
paillier_plaintext_t*
paillier_plaintext_from_str( char* str )
{
return paillier_plaintext_from_bytes(str, strlen(str));
}
char*
paillier_plaintext_to_str( paillier_plaintext_t* pt )
{
char* buf;
size_t len;
buf = (char*) mpz_export(0, &len, 1, 1, 0, 0, pt->m);
buf = (char*) realloc(buf, len + 1);
buf[len] = 0;
return buf;
}
paillier_ciphertext_t*
paillier_ciphertext_from_bytes( void* c, int len )
{
paillier_ciphertext_t* ct;
ct = (paillier_ciphertext_t*) malloc(sizeof(paillier_ciphertext_t));
mpz_init(ct->c);
mpz_import(ct->c, len, 1, 1, 0, 0, c);
return ct;
}
void*
paillier_ciphertext_to_bytes( int len,
paillier_ciphertext_t* ct )
{
void* buf;
int cur_len;
cur_len = mpz_sizeinbase(ct->c, 2);
cur_len = PAILLIER_BITS_TO_BYTES(cur_len);
buf = malloc(len);
memset(buf, 0, len);
mpz_export(buf + (len - cur_len), 0, 1, 1, 0, 0, ct->c);
return buf;
}
char*
paillier_pubkey_to_hex( paillier_pubkey_t* pub )
{
return mpz_get_str(0, 16, pub->n);
}
char*
paillier_prvkey_to_hex( paillier_prvkey_t* prv )
{
return mpz_get_str(0, 16, prv->lambda);
}
paillier_pubkey_t*
paillier_pubkey_from_hex( char* str )
{
paillier_pubkey_t* pub;
pub = (paillier_pubkey_t*) malloc(sizeof(paillier_pubkey_t));
mpz_init_set_str(pub->n, str, 16);
pub->bits = mpz_sizeinbase(pub->n, 2);
mpz_init(pub->n_squared);
mpz_init(pub->n_plusone);
complete_pubkey(pub);
return pub;
}
paillier_prvkey_t*
paillier_prvkey_from_hex( char* str, paillier_pubkey_t* pub )
{
paillier_prvkey_t* prv;
prv = (paillier_prvkey_t*) malloc(sizeof(paillier_prvkey_t));
mpz_init_set_str(prv->lambda, str, 16);
mpz_init(prv->x);
complete_prvkey(prv, pub);
return prv;
}
void
paillier_freepubkey( paillier_pubkey_t* pub )
{
mpz_clear(pub->n);
mpz_clear(pub->n_squared);
mpz_clear(pub->n_plusone);
free(pub);
}
void
paillier_freeprvkey( paillier_prvkey_t* prv )
{
mpz_clear(prv->lambda);
mpz_clear(prv->x);
free(prv);
}
void
paillier_freeplaintext( paillier_plaintext_t* pt )
{
mpz_clear(pt->m);
free(pt);
}
void
paillier_freeciphertext( paillier_ciphertext_t* ct )
{
mpz_clear(ct->c);
mpz_clear(ct->r);
free(ct);
}
void
paillier_get_rand_file( void* buf, int len, char* file )
{
FILE* fp;
void* p;
fp = fopen(file, "r");
p = buf;
while( len )
{
size_t s;
s = fread(p, 1, len, fp);
p += s;
len -= s;
}
fclose(fp);
}
void
paillier_get_rand_devrandom( void* buf, int len )
{
paillier_get_rand_file(buf, len, "/dev/random");
}
void
paillier_get_rand_devurandom( void* buf, int len )
{
paillier_get_rand_file(buf, len, "/dev/urandom");
}
paillier_ciphertext_t*
paillier_create_enc_zero()
{
paillier_ciphertext_t* ct;
/* make a NON-RERANDOMIZED encryption of zero for the purposes of
homomorphic computation */
/* note that this is just the number 1 */
ct = (paillier_ciphertext_t*) malloc(sizeof(paillier_ciphertext_t));
mpz_init_set_ui(ct->c, 1);
return ct;
}