1 /*
2 * Copyright 2019-2022 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10 #include "internal/ffc.h"
11
12 /*
13 * SP800-56Ar3 5.6.1.1.4 Key pair generation by testing candidates.
14 * Generates a private key in the interval [1, min(2 ^ N - 1, q - 1)].
15 *
16 * ctx must be set up with a libctx (for fips mode).
17 * params contains the FFC domain parameters p, q and g (for DH or DSA).
18 * N is the maximum bit length of the generated private key,
19 * s is the security strength.
20 * priv_key is the returned private key,
21 */
ossl_ffc_generate_private_key(BN_CTX * ctx,const FFC_PARAMS * params,int N,int s,BIGNUM * priv)22 int ossl_ffc_generate_private_key(BN_CTX *ctx, const FFC_PARAMS *params,
23 int N, int s, BIGNUM *priv)
24 {
25 int ret = 0, qbits = BN_num_bits(params->q);
26 BIGNUM *m, *two_powN = NULL;
27
28 /* Deal with the edge cases where the value of N and/or s is not set */
29 if (s == 0)
30 goto err;
31 if (N == 0)
32 N = params->keylength ? params->keylength : 2 * s;
33
34 /* Step (2) : check range of N */
35 if (N < 2 * s || N > qbits)
36 return 0;
37
38 two_powN = BN_new();
39 /* 2^N */
40 if (two_powN == NULL || !BN_lshift(two_powN, BN_value_one(), N))
41 goto err;
42
43 /* Step (5) : M = min(2 ^ N, q) */
44 m = (BN_cmp(two_powN, params->q) > 0) ? params->q : two_powN;
45
46 do {
47 /* Steps (3, 4 & 7) : c + 1 = 1 + random[0..2^N - 1] */
48 if (!BN_priv_rand_range_ex(priv, two_powN, 0, ctx)
49 || !BN_add_word(priv, 1))
50 goto err;
51 /* Step (6) : loop if c > M - 2 (i.e. c + 1 >= M) */
52 if (BN_cmp(priv, m) < 0)
53 break;
54 } while (1);
55
56 ret = 1;
57 err:
58 BN_free(two_powN);
59 return ret;
60 }
61