1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3
4 #include "tomcrypt_private.h"
5
6 #ifdef LTC_MDH
7
s_dh_groupsize_to_keysize(int groupsize)8 static int s_dh_groupsize_to_keysize(int groupsize)
9 {
10 /* The strength estimates from https://tools.ietf.org/html/rfc3526#section-8
11 * We use "Estimate 2" to get an appropriate private key (exponent) size.
12 */
13 if (groupsize <= 0) {
14 return 0;
15 }
16 if (groupsize <= 192) {
17 return 30; /* 1536-bit => key size 240-bit */
18 }
19 if (groupsize <= 256) {
20 return 40; /* 2048-bit => key size 320-bit */
21 }
22 if (groupsize <= 384) {
23 return 52; /* 3072-bit => key size 416-bit */
24 }
25 if (groupsize <= 512) {
26 return 60; /* 4096-bit => key size 480-bit */
27 }
28 if (groupsize <= 768) {
29 return 67; /* 6144-bit => key size 536-bit */
30 }
31 if (groupsize <= 1024) {
32 return 77; /* 8192-bit => key size 616-bit */
33 }
34 return 0;
35 }
36
dh_generate_key(prng_state * prng,int wprng,dh_key * key)37 int dh_generate_key(prng_state *prng, int wprng, dh_key *key)
38 {
39 unsigned char *buf;
40 unsigned long keysize;
41 int err, max_iterations = LTC_PK_MAX_RETRIES;
42
43 LTC_ARGCHK(key != NULL);
44 LTC_ARGCHK(ltc_mp.name != NULL);
45
46 /* good prng? */
47 if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
48 return err;
49 }
50
51 keysize = s_dh_groupsize_to_keysize(mp_unsigned_bin_size(key->prime));
52 if (keysize == 0) {
53 err = CRYPT_INVALID_KEYSIZE;
54 goto freemp;
55 }
56
57 /* allocate buffer */
58 buf = XMALLOC(keysize);
59 if (buf == NULL) {
60 err = CRYPT_MEM;
61 goto freemp;
62 }
63
64 key->type = PK_PRIVATE;
65 do {
66 /* make up random buf */
67 if (prng_descriptor[wprng]->read(buf, keysize, prng) != keysize) {
68 err = CRYPT_ERROR_READPRNG;
69 goto freebuf;
70 }
71 /* load the x value - private key */
72 if ((err = mp_read_unsigned_bin(key->x, buf, keysize)) != CRYPT_OK) {
73 goto freebuf;
74 }
75 /* compute the y value - public key */
76 if ((err = mp_exptmod(key->base, key->x, key->prime, key->y)) != CRYPT_OK) {
77 goto freebuf;
78 }
79 err = dh_check_pubkey(key);
80 } while (err != CRYPT_OK && max_iterations-- > 0);
81
82 freebuf:
83 zeromem(buf, keysize);
84 XFREE(buf);
85 freemp:
86 if (err != CRYPT_OK) dh_free(key);
87 return err;
88 }
89
90 #endif /* LTC_MDH */
91