1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * Elliptic Curve (Russian) Digital Signature Algorithm for Cryptographic API
4 *
5 * Copyright (c) 2019 Vitaly Chikunov <vt@altlinux.org>
6 *
7 * References:
8 * GOST 34.10-2018, GOST R 34.10-2012, RFC 7091, ISO/IEC 14888-3:2018.
9 *
10 * Historical references:
11 * GOST R 34.10-2001, RFC 4357, ISO/IEC 14888-3:2006/Amd 1:2010.
12 *
13 * This program is free software; you can redistribute it and/or modify it
14 * under the terms of the GNU General Public License as published by the Free
15 * Software Foundation; either version 2 of the License, or (at your option)
16 * any later version.
17 */
18
19 #include <linux/module.h>
20 #include <linux/crypto.h>
21 #include <crypto/streebog.h>
22 #include <crypto/internal/akcipher.h>
23 #include <crypto/akcipher.h>
24 #include <linux/oid_registry.h>
25 #include "ecrdsa_params.asn1.h"
26 #include "ecrdsa_pub_key.asn1.h"
27 #include "ecc.h"
28 #include "ecrdsa_defs.h"
29
30 #define ECRDSA_MAX_SIG_SIZE (2 * 512 / 8)
31 #define ECRDSA_MAX_DIGITS (512 / 64)
32
33 struct ecrdsa_ctx {
34 enum OID algo_oid; /* overall public key oid */
35 enum OID curve_oid; /* parameter */
36 enum OID digest_oid; /* parameter */
37 const struct ecc_curve *curve; /* curve from oid */
38 unsigned int digest_len; /* parameter (bytes) */
39 const char *digest; /* digest name from oid */
40 unsigned int key_len; /* @key length (bytes) */
41 const char *key; /* raw public key */
42 struct ecc_point pub_key;
43 u64 _pubp[2][ECRDSA_MAX_DIGITS]; /* point storage for @pub_key */
44 };
45
get_curve_by_oid(enum OID oid)46 static const struct ecc_curve *get_curve_by_oid(enum OID oid)
47 {
48 switch (oid) {
49 case OID_gostCPSignA:
50 case OID_gostTC26Sign256B:
51 return &gost_cp256a;
52 case OID_gostCPSignB:
53 case OID_gostTC26Sign256C:
54 return &gost_cp256b;
55 case OID_gostCPSignC:
56 case OID_gostTC26Sign256D:
57 return &gost_cp256c;
58 case OID_gostTC26Sign512A:
59 return &gost_tc512a;
60 case OID_gostTC26Sign512B:
61 return &gost_tc512b;
62 /* The following two aren't implemented: */
63 case OID_gostTC26Sign256A:
64 case OID_gostTC26Sign512C:
65 default:
66 return NULL;
67 }
68 }
69
ecrdsa_verify(struct akcipher_request * req)70 static int ecrdsa_verify(struct akcipher_request *req)
71 {
72 struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
73 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
74 unsigned char sig[ECRDSA_MAX_SIG_SIZE];
75 unsigned char digest[STREEBOG512_DIGEST_SIZE];
76 unsigned int ndigits = req->dst_len / sizeof(u64);
77 u64 r[ECRDSA_MAX_DIGITS]; /* witness (r) */
78 u64 _r[ECRDSA_MAX_DIGITS]; /* -r */
79 u64 s[ECRDSA_MAX_DIGITS]; /* second part of sig (s) */
80 u64 e[ECRDSA_MAX_DIGITS]; /* h \mod q */
81 u64 *v = e; /* e^{-1} \mod q */
82 u64 z1[ECRDSA_MAX_DIGITS];
83 u64 *z2 = _r;
84 struct ecc_point cc = ECC_POINT_INIT(s, e, ndigits); /* reuse s, e */
85
86 /*
87 * Digest value, digest algorithm, and curve (modulus) should have the
88 * same length (256 or 512 bits), public key and signature should be
89 * twice bigger.
90 */
91 if (!ctx->curve ||
92 !ctx->digest ||
93 !req->src ||
94 !ctx->pub_key.x ||
95 req->dst_len != ctx->digest_len ||
96 req->dst_len != ctx->curve->g.ndigits * sizeof(u64) ||
97 ctx->pub_key.ndigits != ctx->curve->g.ndigits ||
98 req->dst_len * 2 != req->src_len ||
99 WARN_ON(req->src_len > sizeof(sig)) ||
100 WARN_ON(req->dst_len > sizeof(digest)))
101 return -EBADMSG;
102
103 sg_copy_to_buffer(req->src, sg_nents_for_len(req->src, req->src_len),
104 sig, req->src_len);
105 sg_pcopy_to_buffer(req->src,
106 sg_nents_for_len(req->src,
107 req->src_len + req->dst_len),
108 digest, req->dst_len, req->src_len);
109
110 vli_from_be64(s, sig, ndigits);
111 vli_from_be64(r, sig + ndigits * sizeof(u64), ndigits);
112
113 /* Step 1: verify that 0 < r < q, 0 < s < q */
114 if (vli_is_zero(r, ndigits) ||
115 vli_cmp(r, ctx->curve->n, ndigits) == 1 ||
116 vli_is_zero(s, ndigits) ||
117 vli_cmp(s, ctx->curve->n, ndigits) == 1)
118 return -EKEYREJECTED;
119
120 /* Step 2: calculate hash (h) of the message (passed as input) */
121 /* Step 3: calculate e = h \mod q */
122 vli_from_le64(e, digest, ndigits);
123 if (vli_cmp(e, ctx->curve->n, ndigits) == 1)
124 vli_sub(e, e, ctx->curve->n, ndigits);
125 if (vli_is_zero(e, ndigits))
126 e[0] = 1;
127
128 /* Step 4: calculate v = e^{-1} \mod q */
129 vli_mod_inv(v, e, ctx->curve->n, ndigits);
130
131 /* Step 5: calculate z_1 = sv \mod q, z_2 = -rv \mod q */
132 vli_mod_mult_slow(z1, s, v, ctx->curve->n, ndigits);
133 vli_sub(_r, ctx->curve->n, r, ndigits);
134 vli_mod_mult_slow(z2, _r, v, ctx->curve->n, ndigits);
135
136 /* Step 6: calculate point C = z_1P + z_2Q, and R = x_c \mod q */
137 ecc_point_mult_shamir(&cc, z1, &ctx->curve->g, z2, &ctx->pub_key,
138 ctx->curve);
139 if (vli_cmp(cc.x, ctx->curve->n, ndigits) == 1)
140 vli_sub(cc.x, cc.x, ctx->curve->n, ndigits);
141
142 /* Step 7: if R == r signature is valid */
143 if (!vli_cmp(cc.x, r, ndigits))
144 return 0;
145 else
146 return -EKEYREJECTED;
147 }
148
ecrdsa_param_curve(void * context,size_t hdrlen,unsigned char tag,const void * value,size_t vlen)149 int ecrdsa_param_curve(void *context, size_t hdrlen, unsigned char tag,
150 const void *value, size_t vlen)
151 {
152 struct ecrdsa_ctx *ctx = context;
153
154 ctx->curve_oid = look_up_OID(value, vlen);
155 if (!ctx->curve_oid)
156 return -EINVAL;
157 ctx->curve = get_curve_by_oid(ctx->curve_oid);
158 return 0;
159 }
160
161 /* Optional. If present should match expected digest algo OID. */
ecrdsa_param_digest(void * context,size_t hdrlen,unsigned char tag,const void * value,size_t vlen)162 int ecrdsa_param_digest(void *context, size_t hdrlen, unsigned char tag,
163 const void *value, size_t vlen)
164 {
165 struct ecrdsa_ctx *ctx = context;
166 int digest_oid = look_up_OID(value, vlen);
167
168 if (digest_oid != ctx->digest_oid)
169 return -EINVAL;
170 return 0;
171 }
172
ecrdsa_parse_pub_key(void * context,size_t hdrlen,unsigned char tag,const void * value,size_t vlen)173 int ecrdsa_parse_pub_key(void *context, size_t hdrlen, unsigned char tag,
174 const void *value, size_t vlen)
175 {
176 struct ecrdsa_ctx *ctx = context;
177
178 ctx->key = value;
179 ctx->key_len = vlen;
180 return 0;
181 }
182
ecrdsa_unpack_u32(u32 * dst,void * src)183 static u8 *ecrdsa_unpack_u32(u32 *dst, void *src)
184 {
185 memcpy(dst, src, sizeof(u32));
186 return src + sizeof(u32);
187 }
188
189 /* Parse BER encoded subjectPublicKey. */
ecrdsa_set_pub_key(struct crypto_akcipher * tfm,const void * key,unsigned int keylen)190 static int ecrdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
191 unsigned int keylen)
192 {
193 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
194 unsigned int ndigits;
195 u32 algo, paramlen;
196 u8 *params;
197 int err;
198
199 err = asn1_ber_decoder(&ecrdsa_pub_key_decoder, ctx, key, keylen);
200 if (err < 0)
201 return err;
202
203 /* Key parameters is in the key after keylen. */
204 params = ecrdsa_unpack_u32(¶mlen,
205 ecrdsa_unpack_u32(&algo, (u8 *)key + keylen));
206
207 if (algo == OID_gost2012PKey256) {
208 ctx->digest = "streebog256";
209 ctx->digest_oid = OID_gost2012Digest256;
210 ctx->digest_len = 256 / 8;
211 } else if (algo == OID_gost2012PKey512) {
212 ctx->digest = "streebog512";
213 ctx->digest_oid = OID_gost2012Digest512;
214 ctx->digest_len = 512 / 8;
215 } else
216 return -ENOPKG;
217 ctx->algo_oid = algo;
218
219 /* Parse SubjectPublicKeyInfo.AlgorithmIdentifier.parameters. */
220 err = asn1_ber_decoder(&ecrdsa_params_decoder, ctx, params, paramlen);
221 if (err < 0)
222 return err;
223 /*
224 * Sizes of algo (set in digest_len) and curve should match
225 * each other.
226 */
227 if (!ctx->curve ||
228 ctx->curve->g.ndigits * sizeof(u64) != ctx->digest_len)
229 return -ENOPKG;
230 /*
231 * Key is two 256- or 512-bit coordinates which should match
232 * curve size.
233 */
234 if ((ctx->key_len != (2 * 256 / 8) &&
235 ctx->key_len != (2 * 512 / 8)) ||
236 ctx->key_len != ctx->curve->g.ndigits * sizeof(u64) * 2)
237 return -ENOPKG;
238
239 ndigits = ctx->key_len / sizeof(u64) / 2;
240 ctx->pub_key = ECC_POINT_INIT(ctx->_pubp[0], ctx->_pubp[1], ndigits);
241 vli_from_le64(ctx->pub_key.x, ctx->key, ndigits);
242 vli_from_le64(ctx->pub_key.y, ctx->key + ndigits * sizeof(u64),
243 ndigits);
244
245 if (ecc_is_pubkey_valid_partial(ctx->curve, &ctx->pub_key))
246 return -EKEYREJECTED;
247
248 return 0;
249 }
250
ecrdsa_max_size(struct crypto_akcipher * tfm)251 static unsigned int ecrdsa_max_size(struct crypto_akcipher *tfm)
252 {
253 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
254
255 /*
256 * Verify doesn't need any output, so it's just informational
257 * for keyctl to determine the key bit size.
258 */
259 return ctx->pub_key.ndigits * sizeof(u64);
260 }
261
ecrdsa_exit_tfm(struct crypto_akcipher * tfm)262 static void ecrdsa_exit_tfm(struct crypto_akcipher *tfm)
263 {
264 }
265
266 static struct akcipher_alg ecrdsa_alg = {
267 .verify = ecrdsa_verify,
268 .set_pub_key = ecrdsa_set_pub_key,
269 .max_size = ecrdsa_max_size,
270 .exit = ecrdsa_exit_tfm,
271 .base = {
272 .cra_name = "ecrdsa",
273 .cra_driver_name = "ecrdsa-generic",
274 .cra_priority = 100,
275 .cra_module = THIS_MODULE,
276 .cra_ctxsize = sizeof(struct ecrdsa_ctx),
277 },
278 };
279
ecrdsa_mod_init(void)280 static int __init ecrdsa_mod_init(void)
281 {
282 return crypto_register_akcipher(&ecrdsa_alg);
283 }
284
ecrdsa_mod_fini(void)285 static void __exit ecrdsa_mod_fini(void)
286 {
287 crypto_unregister_akcipher(&ecrdsa_alg);
288 }
289
290 module_init(ecrdsa_mod_init);
291 module_exit(ecrdsa_mod_fini);
292
293 MODULE_LICENSE("GPL");
294 MODULE_AUTHOR("Vitaly Chikunov <vt@altlinux.org>");
295 MODULE_DESCRIPTION("EC-RDSA generic algorithm");
296 MODULE_ALIAS_CRYPTO("ecrdsa-generic");
297