1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
|
/* Copyright (c) 2019, Google Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#include <CCryptoBoringSSL_ec_key.h>
#include <string.h>
#include <CCryptoBoringSSL_ec.h>
#include <CCryptoBoringSSL_err.h>
#include <CCryptoBoringSSL_digest.h>
#include <CCryptoBoringSSL_hkdf.h>
#include <CCryptoBoringSSL_mem.h>
#include "../fipsmodule/ec/internal.h"
EC_KEY *EC_KEY_derive_from_secret(const EC_GROUP *group, const uint8_t *secret,
size_t secret_len) {
#define EC_KEY_DERIVE_MAX_NAME_LEN 16
const char *name = EC_curve_nid2nist(EC_GROUP_get_curve_name(group));
if (name == NULL || strlen(name) > EC_KEY_DERIVE_MAX_NAME_LEN) {
OPENSSL_PUT_ERROR(EC, EC_R_UNKNOWN_GROUP);
return NULL;
}
// Assemble a label string to provide some key separation in case |secret| is
// misused, but ultimately it's on the caller to ensure |secret| is suitably
// separated.
static const char kLabel[] = "derive EC key ";
char info[sizeof(kLabel) + EC_KEY_DERIVE_MAX_NAME_LEN];
OPENSSL_strlcpy(info, kLabel, sizeof(info));
OPENSSL_strlcat(info, name, sizeof(info));
// Generate 128 bits beyond the group order so the bias is at most 2^-128.
#define EC_KEY_DERIVE_EXTRA_BITS 128
#define EC_KEY_DERIVE_EXTRA_BYTES (EC_KEY_DERIVE_EXTRA_BITS / 8)
if (EC_GROUP_order_bits(group) <= EC_KEY_DERIVE_EXTRA_BITS + 8) {
// The reduction strategy below requires the group order be large enough.
// (The actual bound is a bit tighter, but our curves are much larger than
// 128-bit.)
OPENSSL_PUT_ERROR(EC, ERR_R_INTERNAL_ERROR);
return NULL;
}
uint8_t derived[EC_KEY_DERIVE_EXTRA_BYTES + EC_MAX_BYTES];
size_t derived_len =
BN_num_bytes(EC_GROUP_get0_order(group)) + EC_KEY_DERIVE_EXTRA_BYTES;
assert(derived_len <= sizeof(derived));
if (!HKDF(derived, derived_len, EVP_sha256(), secret, secret_len,
/*salt=*/NULL, /*salt_len=*/0, (const uint8_t *)info,
strlen(info))) {
return NULL;
}
EC_KEY *key = EC_KEY_new();
BN_CTX *ctx = BN_CTX_new();
BIGNUM *priv = BN_bin2bn(derived, derived_len, NULL);
EC_POINT *pub = EC_POINT_new(group);
if (key == NULL || ctx == NULL || priv == NULL || pub == NULL ||
// Reduce |priv| with Montgomery reduction. First, convert "from"
// Montgomery form to compute |priv| * R^-1 mod |order|. This requires
// |priv| be under order * R, which is true if the group order is large
// enough. 2^(num_bytes(order)) < 2^8 * order, so:
//
// priv < 2^8 * order * 2^128 < order * order < order * R
!BN_from_montgomery(priv, priv, &group->order, ctx) ||
// Multiply by R^2 and do another Montgomery reduction to compute
// priv * R^-1 * R^2 * R^-1 = priv mod order.
!BN_to_montgomery(priv, priv, &group->order, ctx) ||
!EC_POINT_mul(group, pub, priv, NULL, NULL, ctx) ||
!EC_KEY_set_group(key, group) || !EC_KEY_set_public_key(key, pub) ||
!EC_KEY_set_private_key(key, priv)) {
EC_KEY_free(key);
key = NULL;
goto err;
}
err:
OPENSSL_cleanse(derived, sizeof(derived));
BN_CTX_free(ctx);
BN_free(priv);
EC_POINT_free(pub);
return key;
}
|
