xref: /openssl/crypto/ffc/ffc_key_generate.c (revision ddb13b28)
1 /*
2  * Copyright 2019-2021 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