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csrp-gmp/srp.c
Tom Cocagne 7ec0c6c2ae initial commit
2010-10-01 14:32:10 -04:00

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/*
* Secure Remote Password 6a implementation
* Copyright (c) 2010 Tom Cocagne. All rights reserved.
* http://csrp.googlecode.com/p/csrp/
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of the Google Code nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL TOM COCAGNE BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#ifdef WIN32
#include <Wincrypt.h>
#else
#include <sys/time.h>
#endif
#include <alloca.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <openssl/bn.h>
#include <openssl/sha.h>
#include <openssl/crypto.h>
#include <openssl/rand.h>
#include "srp.h"
/* 2048-bit prime & generator pair from RFC 5054 */
#define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
#define G_HEX "2"
static const BIGNUM * N = 0;
static const BIGNUM * g = 0;
static const BIGNUM * k = 0;
static int g_initialized = 0;
struct SRPVerifier
{
const char * username;
const unsigned char * bytes_B;
int authenticated;
unsigned char M [SRP_SHA256_DIGEST_LENGTH];
unsigned char H_AMK [SRP_SHA256_DIGEST_LENGTH];
unsigned char session_key [SRP_SHA256_DIGEST_LENGTH];
};
struct SRPUser
{
BIGNUM *a;
BIGNUM *A;
BIGNUM *S;
const unsigned char * bytes_A;
int authenticated;
const char * username;
const unsigned char * password;
int password_len;
unsigned char M [SRP_SHA256_DIGEST_LENGTH];
unsigned char H_AMK [SRP_SHA256_DIGEST_LENGTH];
unsigned char session_key [SRP_SHA256_DIGEST_LENGTH];
};
static BIGNUM * H_nn( const BIGNUM * n1, const BIGNUM * n2 )
{
unsigned char buff[ SHA256_DIGEST_LENGTH ];
int len_n1 = BN_num_bytes(n1);
int len_n2 = BN_num_bytes(n2);
int nbytes = len_n1 + len_n2;
unsigned char * bin = (unsigned char *) alloca( nbytes );
BN_bn2bin(n1, bin);
BN_bn2bin(n2, bin + len_n1);
SHA256( bin, nbytes, buff );
return BN_bin2bn(buff, SHA256_DIGEST_LENGTH, NULL);
}
static BIGNUM * H_ns( const BIGNUM * n, const unsigned char * bytes, int len_bytes )
{
unsigned char buff[ SHA256_DIGEST_LENGTH ];
int len_n = BN_num_bytes(n);
int nbytes = len_n + len_bytes;
unsigned char * bin = (unsigned char *) alloca( nbytes );
BN_bn2bin(n, bin);
memcpy( bin + len_n, bytes, len_bytes );
SHA256( bin, nbytes, buff );
return BN_bin2bn(buff, SHA256_DIGEST_LENGTH, NULL);
}
static BIGNUM * calculate_x( const BIGNUM * salt, const char * username, const unsigned char * password, int password_len )
{
unsigned char ucp_hash[SHA256_DIGEST_LENGTH];
SHA256_CTX ctx;
SHA256_Init( &ctx );
SHA256_Update( &ctx, username, strlen(username) );
SHA256_Update( &ctx, ":", 1 );
SHA256_Update( &ctx, password, password_len );
SHA256_Final( ucp_hash, &ctx );
return H_ns( salt, ucp_hash, sizeof(ucp_hash) );
}
static void update_hash( SHA256_CTX *ctx, const BIGNUM * n )
{
unsigned long len = BN_num_bytes(n);
unsigned char * n_bytes = (unsigned char *) alloca( len );
BN_bn2bin(n, n_bytes);
SHA256_Update(ctx, n_bytes, len);
}
static void hash_num( const BIGNUM * n, unsigned char * dest )
{
int nbytes = BN_num_bytes(n);
unsigned char * bin = (unsigned char *) alloca( nbytes );
BN_bn2bin(n, bin);
SHA256( bin, nbytes, dest );
}
static void calculate_M( unsigned char * dest, const char * I, const BIGNUM * s,
const BIGNUM * A, const BIGNUM * B, const unsigned char * K )
{
unsigned char H_N[ SHA256_DIGEST_LENGTH ];
unsigned char H_g[ SHA256_DIGEST_LENGTH ];
unsigned char H_I[ SHA256_DIGEST_LENGTH ];
unsigned char H_xor[ SHA256_DIGEST_LENGTH ];
SHA256_CTX ctx;
int i = 0;
hash_num( N, H_N );
hash_num( g, H_g );
SHA256((const unsigned char *)I, strlen(I), H_I);
for (i=0; i < SHA256_DIGEST_LENGTH; i++ )
H_xor[i] = H_N[i] ^ H_g[i];
SHA256_Init( &ctx );
SHA256_Update( &ctx, H_xor, sizeof(H_xor) );
SHA256_Update( &ctx, H_I, sizeof(H_I) );
update_hash( &ctx, s );
update_hash( &ctx, A );
update_hash( &ctx, B );
SHA256_Update( &ctx, K, SHA256_DIGEST_LENGTH );
SHA256_Final( dest, &ctx );
}
static void calculate_H_AMK( unsigned char *dest, const BIGNUM * A, const unsigned char * M, const unsigned char * K )
{
SHA256_CTX ctx;
SHA256_Init( &ctx );
update_hash( &ctx, A );
SHA256_Update( &ctx, M, SHA256_DIGEST_LENGTH);
SHA256_Update( &ctx, K, SHA256_DIGEST_LENGTH);
SHA256_Final( dest, &ctx );
}
/***********************************************************************************************************
*
* Exported Functions
*
***********************************************************************************************************/
void srp_init()
{
#ifdef WIN32
HCRYPTPROV wctx;
#else
FILE *fp = 0;
#endif
unsigned char buff[32];
BIGNUM *tN = BN_new();
BIGNUM *tg = BN_new();
BN_hex2bn( &tN, N_HEX );
BN_hex2bn( &tg, G_HEX );
N = tN;
g = tg;
k = H_nn(N,g);
#ifdef WIN32
CryptAcquireContext(&wctx, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
CryptGenRandom(wctx, sizeof(buff), (BYTE*) buff);
CryptReleaseContext(wctx, 0);
#else
fp = fopen("/dev/urandom", "r");
if (fp)
{
fread(buff, sizeof(buff), 1, fp);
fclose(fp);
}
else
{
/* Dirty... but better than nothing. */
gettimeofday( (struct timeval *)buff, 0);
}
#endif
RAND_seed( buff, sizeof(buff) );
g_initialized = 1;
}
void srp_fini()
{
g_initialized = 0;
BN_free((BIGNUM *)N);
BN_free((BIGNUM *)g);
BN_free((BIGNUM *)k);
N = 0;
g = 0;
}
int srp_is_initialized()
{
return g_initialized;
}
void srp_gen_sv( const char * username,
const unsigned char * password, int len_password,
const unsigned char ** bytes_s, int * len_s,
const unsigned char ** bytes_v, int * len_v )
{
BIGNUM * s = BN_new();
BIGNUM * v = BN_new();
BIGNUM * x = 0;
BN_CTX *ctx = BN_CTX_new();
BN_rand(s, 32, -1, 0);
x = calculate_x( s, username, password, len_password );
BN_mod_exp(v, g, x, N, ctx);
*len_s = BN_num_bytes(s);
*len_v = BN_num_bytes(v);
*bytes_s = (const unsigned char *) malloc( *len_s );
*bytes_v = (const unsigned char *) malloc( *len_v );
BN_bn2bin(s, (unsigned char *) *bytes_s);
BN_bn2bin(v, (unsigned char *) *bytes_v);
BN_free(s);
BN_free(v);
BN_free(x);
BN_CTX_free(ctx);
}
/* Out: bytes_B, len_B.
*
* On failure, bytes_B will be set to NULL and len_B will be set to 0
*/
struct SRPVerifier * srp_verifier_new( const char * username,
const unsigned char * bytes_s, int len_s,
const unsigned char * bytes_v, int len_v,
const unsigned char * bytes_A, int len_A,
const unsigned char ** bytes_B, int * len_B)
{
BIGNUM *s = BN_bin2bn(bytes_s, len_s, NULL);
BIGNUM *v = BN_bin2bn(bytes_v, len_v, NULL);
BIGNUM *A = BN_bin2bn(bytes_A, len_A, NULL);
BIGNUM *u = 0;
BIGNUM *B = BN_new();
BIGNUM *S = BN_new();
BIGNUM *b = BN_new();
BIGNUM *tmp1 = BN_new();
BIGNUM *tmp2 = BN_new();
BN_CTX *ctx = BN_CTX_new();
int ulen = strlen(username) + 1;
struct SRPVerifier * ver = (struct SRPVerifier *) malloc( sizeof(struct SRPVerifier) );
ver->username = (char *) malloc( ulen );
memcpy( (char*)ver->username, username, ulen );
ver->authenticated = 0;
/* SRP-6a safety check */
BN_mod(tmp1, A, N, ctx);
if ( !BN_is_zero(tmp1) )
{
BN_rand(b, 256, -1, 0);
/* B = kv + g^b */
BN_mul(tmp1, k, v, ctx);
BN_mod_exp(tmp2, g, b, N, ctx);
BN_add(B, tmp1, tmp2);
u = H_nn(A,B);
/* S = (A *(v^u)) ^ b */
BN_mod_exp(tmp1, v, u, N, ctx);
BN_mul(tmp2, A, tmp1, ctx);
BN_mod_exp(S, tmp2, b, N, ctx);
hash_num(S, ver->session_key);
calculate_M( ver->M, username, s, A, B, ver->session_key );
calculate_H_AMK( ver->H_AMK, A, ver->M, ver->session_key );
*len_B = BN_num_bytes(B);
*bytes_B = malloc( *len_B );
BN_bn2bin( B, (unsigned char *) *bytes_B );
ver->bytes_B = *bytes_B;
}
else
{
*len_B = 0;
*bytes_B = NULL;
}
BN_free(s);
BN_free(v);
BN_free(A);
if (u) BN_free(u);
BN_free(B);
BN_free(S);
BN_free(b);
BN_free(tmp1);
BN_free(tmp2);
BN_CTX_free(ctx);
return ver;
}
void srp_verifier_delete( struct SRPVerifier * ver )
{
free( (char *) ver->username );
free( (unsigned char *) ver->bytes_B );
free( ver );
}
int srp_verifier_is_authenticated( struct SRPVerifier * ver )
{
return ver->authenticated;
}
const char * srp_verifier_get_username( struct SRPVerifier * ver )
{
return ver->username;
}
/* Key length is SRP_SHA256_DIGEST_LENGTH */
const unsigned char * srp_verifier_get_session_key( struct SRPVerifier * ver )
{
return ver->session_key;
}
/* user_M must be exactly SRP_SHA256_DIGEST_LENGTH bytes in size */
void srp_verifier_verify_session( struct SRPVerifier * ver, const unsigned char * user_M, const unsigned char ** bytes_HAMK )
{
if ( memcmp( ver->M, user_M, SRP_SHA256_DIGEST_LENGTH ) == 0 )
{
ver->authenticated = 1;
*bytes_HAMK = ver->H_AMK;
}
else
*bytes_HAMK = NULL;
}
/*******************************************************************************/
struct SRPUser * srp_user_new( const char * username,
const unsigned char * bytes_password, int len_password )
{
struct SRPUser *usr = (struct SRPUser *) malloc( sizeof(struct SRPUser) );
int ulen = strlen(username) + 1;
usr->a = BN_new();
usr->A = BN_new();
usr->S = BN_new();
usr->username = (const char *) malloc(ulen);
usr->password = (const unsigned char *) malloc(len_password);
usr->password_len = len_password;
memcpy((char *)usr->username, username, ulen);
memcpy((char *)usr->password, bytes_password, len_password);
usr->bytes_A = 0;
return usr;
}
void srp_user_delete( struct SRPUser * usr )
{
BN_free( usr->a );
BN_free( usr->A );
BN_free( usr->S );
free((char *)usr->username);
free((char *)usr->password);
if (usr->bytes_A)
free( (char *)usr->bytes_A );
free( usr );
}
int srp_user_is_authenticated( struct SRPUser * usr)
{
return usr->authenticated;
}
const char * srp_user_get_username( struct SRPUser * usr )
{
return usr->username;
}
/* Key length is SRP_SHA256_DIGEST_LENGTH */
const unsigned char * srp_user_get_session_key( struct SRPUser * usr )
{
return usr->session_key;
}
/* Output: username, bytes_A, len_A */
void srp_user_start_authentication( struct SRPUser * usr, const char ** username,
const unsigned char ** bytes_A, int * len_A )
{
BN_CTX *ctx = BN_CTX_new();
BN_rand(usr->a, 256, -1, 0);
BN_mod_exp(usr->A, g, usr->a, N, ctx);
BN_CTX_free(ctx);
*len_A = BN_num_bytes(usr->A);
*bytes_A = malloc( *len_A );
BN_bn2bin( usr->A, (unsigned char *) *bytes_A );
usr->bytes_A = *bytes_A;
*username = usr->username;
}
/* Output: bytes_M. Buffer length is SRP_SHA256_DIGEST_LENGTH */
void srp_user_process_challenge( struct SRPUser * usr,
const unsigned char * bytes_s, int len_s,
const unsigned char * bytes_B, int len_B,
const unsigned char ** bytes_M )
{
BIGNUM *s = BN_bin2bn(bytes_s, len_s, NULL);
BIGNUM *B = BN_bin2bn(bytes_B, len_B, NULL);
BIGNUM *u = 0;
BIGNUM *x = 0;
BIGNUM *v = BN_new();
BIGNUM *tmp1 = BN_new();
BIGNUM *tmp2 = BN_new();
BIGNUM *tmp3 = BN_new();
BN_CTX *ctx = BN_CTX_new();
u = H_nn(usr->A,B);
x = calculate_x( s, usr->username, usr->password, usr->password_len );
/* SRP-6a safety check */
if ( !BN_is_zero(B) && !BN_is_zero(u) )
{
BN_mod_exp(v, g, x, N, ctx);
/* S = (B - k*(g^x)) ^ (a + ux) */
BN_mul(tmp1, u, x, ctx);
BN_add(tmp2, usr->a, tmp1); /* tmp2 = (a + ux) */
BN_mod_exp(tmp1, g, x, N, ctx);
BN_mul(tmp3, k, tmp1, ctx); /* tmp3 = k*(g^x) */
BN_sub(tmp1, B, tmp3); /* tmp1 = (B - K*(g^x)) */
BN_mod_exp(usr->S, tmp1, tmp2, N, ctx);
hash_num(usr->S, usr->session_key);
calculate_M( usr->M, usr->username, s, usr->A, B, usr->session_key );
calculate_H_AMK( usr->H_AMK, usr->A, usr->M, usr->session_key );
*bytes_M = usr->M;
}
else
{
*bytes_M = NULL;
}
BN_free(s);
BN_free(B);
BN_free(u);
BN_free(x);
BN_free(v);
BN_free(tmp1);
BN_free(tmp2);
BN_free(tmp3);
BN_CTX_free(ctx);
}
/* bytes_HAMK must be exactly SRP_SHA256_DIGEST_LENGTH bytes in size */
void srp_user_verify_session( struct SRPUser * usr, const unsigned char * bytes_HAMK )
{
if ( memcmp( usr->H_AMK, bytes_HAMK, SRP_SHA256_DIGEST_LENGTH ) == 0 )
usr->authenticated = 1;
}
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