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/*
* Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (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
*/
/*
* DH low level APIs are deprecated for public use, but still ok for
* internal use.
*
* NOTE: When generating keys for key-agreement schemes - FIPS 140-2 IG 9.9
* states that no additional pairwise tests are required (apart from the tests
* specified in SP800-56A) when generating keys. Hence DH pairwise tests are
* omitted here.
*/
#include "internal/deprecated.h"
#include <stdio.h>
#include "internal/cryptlib.h"
#include <openssl/bn.h>
#include <openssl/sha.h>
#include "crypto/dh.h"
#include "crypto/security_bits.h"
#include "dh_local.h"
#ifndef FIPS_MODULE
static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
BN_GENCB *cb);
#endif /* FIPS_MODULE */
int ossl_dh_generate_ffc_parameters(DH *dh, int type, int pbits, int qbits,
BN_GENCB *cb)
{
int ret, res;
#ifndef FIPS_MODULE
if (type == DH_PARAMGEN_TYPE_FIPS_186_2)
ret = ossl_ffc_params_FIPS186_2_generate(dh->libctx, &dh->params,
FFC_PARAM_TYPE_DH,
pbits, qbits, &res, cb);
else
#endif
ret = ossl_ffc_params_FIPS186_4_generate(dh->libctx, &dh->params,
FFC_PARAM_TYPE_DH,
pbits, qbits, &res, cb);
if (ret > 0)
dh->dirty_cnt++;
return ret;
}
int ossl_dh_get_named_group_uid_from_size(int pbits)
{
/*
* Just choose an approved safe prime group.
* The alternative to this is to generate FIPS186-4 domain parameters i.e.
* return dh_generate_ffc_parameters(ret, prime_len, 0, NULL, cb);
* As the FIPS186-4 generated params are for backwards compatibility,
* the safe prime group should be used as the default.
*/
int nid;
switch (pbits) {
case 2048:
nid = NID_ffdhe2048;
break;
case 3072:
nid = NID_ffdhe3072;
break;
case 4096:
nid = NID_ffdhe4096;
break;
case 6144:
nid = NID_ffdhe6144;
break;
case 8192:
nid = NID_ffdhe8192;
break;
/* unsupported prime_len */
default:
return NID_undef;
}
return nid;
}
#ifdef FIPS_MODULE
static int dh_gen_named_group(OSSL_LIB_CTX *libctx, DH *ret, int prime_len)
{
DH *dh;
int ok = 0;
int nid = ossl_dh_get_named_group_uid_from_size(prime_len);
if (nid == NID_undef)
return 0;
dh = ossl_dh_new_by_nid_ex(libctx, nid);
if (dh != NULL
&& ossl_ffc_params_copy(&ret->params, &dh->params)) {
ok = 1;
ret->dirty_cnt++;
}
DH_free(dh);
return ok;
}
#endif /* FIPS_MODULE */
int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
BN_GENCB *cb)
{
#ifdef FIPS_MODULE
if (generator != 2)
return 0;
return dh_gen_named_group(ret->libctx, ret, prime_len);
#else
if (ret->meth->generate_params)
return ret->meth->generate_params(ret, prime_len, generator, cb);
return dh_builtin_genparams(ret, prime_len, generator, cb);
#endif /* FIPS_MODULE */
}
#ifndef FIPS_MODULE
/*-
* 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
*/
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;
if (prime_len > OPENSSL_DH_MAX_MODULUS_BITS) {
ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE);
return 0;
}
if (prime_len < DH_MIN_MODULUS_BITS) {
ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL);
return 0;
}
ctx = BN_CTX_new_ex(ret->libctx);
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->params.p == NULL && ((ret->params.p = BN_new()) == NULL))
goto err;
if (ret->params.g == NULL && ((ret->params.g = BN_new()) == NULL))
goto err;
if (generator <= 1) {
ERR_raise(ERR_LIB_DH, DH_R_BAD_GENERATOR);
goto err;
}
if (generator == DH_GENERATOR_2) {
if (!BN_set_word(t1, 24))
goto err;
if (!BN_set_word(t2, 23))
goto err;
g = 2;
} else if (generator == DH_GENERATOR_5) {
if (!BN_set_word(t1, 60))
goto err;
if (!BN_set_word(t2, 59))
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_ex2(ret->params.p, prime_len, 1, t1, t2, cb, ctx))
goto err;
if (!BN_GENCB_call(cb, 3, 0))
goto err;
if (!BN_set_word(ret->params.g, g))
goto err;
/* We are using safe prime p, set key length equivalent to RFC 7919 */
ret->length = (2 * ossl_ifc_ffc_compute_security_bits(prime_len)
+ 24) / 25 * 25;
ret->dirty_cnt++;
ok = 1;
err:
if (ok == -1) {
ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB);
ok = 0;
}
BN_CTX_end(ctx);
BN_CTX_free(ctx);
return ok;
}
#endif /* FIPS_MODULE */
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