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/*
* Copyright 2019-2021 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
*/
#include "internal/ffc.h"
/*
* SP800-56Ar3 5.6.1.1.4 Key pair generation by testing candidates.
* Generates a private key in the interval [1, min(2 ^ N - 1, q - 1)].
*
* ctx must be set up with a libctx (for fips mode).
* params contains the FFC domain parameters p, q and g (for DH or DSA).
* N is the maximum bit length of the generated private key,
* s is the security strength.
* priv_key is the returned private key,
*/
int ossl_ffc_generate_private_key(BN_CTX *ctx, const FFC_PARAMS *params,
int N, int s, BIGNUM *priv)
{
int ret = 0, qbits = BN_num_bits(params->q);
BIGNUM *m, *two_powN = NULL;
/* Deal with the edge cases where the value of N and/or s is not set */
if (s == 0)
goto err;
if (N == 0)
N = params->keylength ? params->keylength : 2 * s;
/* Step (2) : check range of N */
if (N < 2 * s || N > qbits)
return 0;
two_powN = BN_new();
/* 2^N */
if (two_powN == NULL || !BN_lshift(two_powN, BN_value_one(), N))
goto err;
/* Step (5) : M = min(2 ^ N, q) */
m = (BN_cmp(two_powN, params->q) > 0) ? params->q : two_powN;
do {
/* Steps (3, 4 & 7) : c + 1 = 1 + random[0..2^N - 1] */
if (!BN_priv_rand_range_ex(priv, two_powN, 0, ctx)
|| !BN_add_word(priv, 1))
goto err;
/* Step (6) : loop if c > M - 2 (i.e. c + 1 >= M) */
if (BN_cmp(priv, m) < 0)
break;
} while (1);
ret = 1;
err:
BN_free(two_powN);
return ret;
}
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