129 lines
3.8 KiB
C
129 lines
3.8 KiB
C
/*
|
|
* Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
|
|
*
|
|
* Licensed under the OpenSSL license (the "License"). You may not use
|
|
* this file except in compliance with the License. You can obtain a copy
|
|
* in the file LICENSE in the source distribution or at
|
|
* https://www.openssl.org/source/license.html
|
|
*/
|
|
|
|
/*
|
|
* NB: These functions have been upgraded - the previous prototypes are in
|
|
* dh_depr.c as wrappers to these ones. - Geoff
|
|
*/
|
|
|
|
#include <stdio.h>
|
|
#include "internal/cryptlib.h"
|
|
#include <openssl/bn.h>
|
|
#include "dh_local.h"
|
|
|
|
static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
|
|
BN_GENCB *cb);
|
|
|
|
int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
|
|
BN_GENCB *cb)
|
|
{
|
|
if (ret->meth->generate_params)
|
|
return ret->meth->generate_params(ret, prime_len, generator, cb);
|
|
return dh_builtin_genparams(ret, prime_len, generator, cb);
|
|
}
|
|
|
|
/*-
|
|
* We generate DH parameters as follows
|
|
* find a prime p which is prime_len bits long,
|
|
* where q=(p-1)/2 is also prime.
|
|
* In the following we assume that g is not 0, 1 or p-1, since it
|
|
* would generate only trivial subgroups.
|
|
* For this case, g is a generator of the order-q subgroup if
|
|
* g^q mod p == 1.
|
|
* Or in terms of the Legendre symbol: (g/p) == 1.
|
|
*
|
|
* Having said all that,
|
|
* there is another special case method for the generators 2, 3 and 5.
|
|
* Using the quadratic reciprocity law it is possible to solve
|
|
* (g/p) == 1 for the special values 2, 3, 5:
|
|
* (2/p) == 1 if p mod 8 == 1 or 7.
|
|
* (3/p) == 1 if p mod 12 == 1 or 11.
|
|
* (5/p) == 1 if p mod 5 == 1 or 4.
|
|
* See for instance: https://en.wikipedia.org/wiki/Legendre_symbol
|
|
*
|
|
* Since all safe primes > 7 must satisfy p mod 12 == 11
|
|
* and all safe primes > 11 must satisfy p mod 5 != 1
|
|
* we can further improve the condition for g = 2, 3 and 5:
|
|
* for 2, p mod 24 == 23
|
|
* for 3, p mod 12 == 11
|
|
* for 5, p mod 60 == 59
|
|
*
|
|
* However for compatibility with previous versions we use:
|
|
* for 2, p mod 24 == 11
|
|
* for 5, p mod 60 == 23
|
|
*/
|
|
static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
|
|
BN_GENCB *cb)
|
|
{
|
|
BIGNUM *t1, *t2;
|
|
int g, ok = -1;
|
|
BN_CTX *ctx = NULL;
|
|
|
|
ctx = BN_CTX_new();
|
|
if (ctx == NULL)
|
|
goto err;
|
|
BN_CTX_start(ctx);
|
|
t1 = BN_CTX_get(ctx);
|
|
t2 = BN_CTX_get(ctx);
|
|
if (t2 == NULL)
|
|
goto err;
|
|
|
|
/* Make sure 'ret' has the necessary elements */
|
|
if (!ret->p && ((ret->p = BN_new()) == NULL))
|
|
goto err;
|
|
if (!ret->g && ((ret->g = BN_new()) == NULL))
|
|
goto err;
|
|
|
|
if (generator <= 1) {
|
|
DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
|
|
goto err;
|
|
}
|
|
if (generator == DH_GENERATOR_2) {
|
|
if (!BN_set_word(t1, 24))
|
|
goto err;
|
|
if (!BN_set_word(t2, 11))
|
|
goto err;
|
|
g = 2;
|
|
} else if (generator == DH_GENERATOR_5) {
|
|
if (!BN_set_word(t1, 60))
|
|
goto err;
|
|
if (!BN_set_word(t2, 23))
|
|
goto err;
|
|
g = 5;
|
|
} else {
|
|
/*
|
|
* in the general case, don't worry if 'generator' is a generator or
|
|
* not: since we are using safe primes, it will generate either an
|
|
* order-q or an order-2q group, which both is OK
|
|
*/
|
|
if (!BN_set_word(t1, 12))
|
|
goto err;
|
|
if (!BN_set_word(t2, 11))
|
|
goto err;
|
|
g = generator;
|
|
}
|
|
|
|
if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
|
|
goto err;
|
|
if (!BN_GENCB_call(cb, 3, 0))
|
|
goto err;
|
|
if (!BN_set_word(ret->g, g))
|
|
goto err;
|
|
ok = 1;
|
|
err:
|
|
if (ok == -1) {
|
|
DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
|
|
ok = 0;
|
|
}
|
|
|
|
BN_CTX_end(ctx);
|
|
BN_CTX_free(ctx);
|
|
return ok;
|
|
}
|