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10 * Historical references: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 <linux/scatterlist.h>
26 #include "ecrdsa_params.asn1.h"
27 #include "ecrdsa_pub_key.asn1.h"
28 #include "ecc.h"
29 #include "ecrdsa_defs.h"
30
31 #define ECRDSA_MAX_SIG_SIZE (2 * 512 / 8)
32 #define ECRDSA_MAX_DIGITS (512 / 64)
33
34 struct ecrdsa_ctx {
35 enum OID algo_oid; /* overall public key oid */
36 enum OID curve_oid; /* parameter */
37 enum OID digest_oid; /* parameter */
38 const struct ecc_curve *curve; /* curve from oid */
39 unsigned int digest_len; /* parameter (bytes) */
40 const char *digest; /* digest name from oid */
41 unsigned int key_len; /* @key length (bytes) */
42 const char *key; /* raw public key */
43 struct ecc_point pub_key;
44 u64 _pubp[2][ECRDSA_MAX_DIGITS]; /* point storage for @pub_key */
45 };
46
get_curve_by_oid(enum OID oid)47 static const struct ecc_curve *get_curve_by_oid(enum OID oid)
48 {
49 switch (oid) {
50 case OID_gostCPSignA:
51 case OID_gostTC26Sign256B:
52 return &gost_cp256a;
53 case OID_gostCPSignB:
54 case OID_gostTC26Sign256C:
55 return &gost_cp256b;
56 case OID_gostCPSignC:
57 case OID_gostTC26Sign256D:
58 return &gost_cp256c;
59 case OID_gostTC26Sign512A:
60 return &gost_tc512a;
61 case OID_gostTC26Sign512B:
62 return &gost_tc512b;
63 /* The following two aren't implemented: */
64 case OID_gostTC26Sign256A:
65 case OID_gostTC26Sign512C:
66 default:
67 return NULL;
68 }
69 }
70
ecrdsa_verify(struct akcipher_request * req)71 static int ecrdsa_verify(struct akcipher_request *req)
72 {
73 struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
74 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
75 unsigned char sig[ECRDSA_MAX_SIG_SIZE];
76 unsigned char digest[STREEBOG512_DIGEST_SIZE];
77 unsigned int ndigits = req->dst_len / sizeof(u64);
78 u64 r[ECRDSA_MAX_DIGITS]; /* witness (r) */
79 u64 _r[ECRDSA_MAX_DIGITS]; /* -r */
80 u64 s[ECRDSA_MAX_DIGITS]; /* second part of sig (s) */
81 u64 e[ECRDSA_MAX_DIGITS]; /* h \mod q */
82 u64 *v = e; /* e^{-1} \mod q */
83 u64 z1[ECRDSA_MAX_DIGITS];
84 u64 *z2 = _r;
85 struct ecc_point cc = ECC_POINT_INIT(s, e, ndigits); /* reuse s, e */
86
87 /*
88 * Digest value, digest algorithm, and curve (modulus) should have the
89 * same length (256 or 512 bits), public key and signature should be
90 * twice bigger.
91 */
92 if (!ctx->curve ||
93 !ctx->digest ||
94 !req->src ||
95 !ctx->pub_key.x ||
96 req->dst_len != ctx->digest_len ||
97 req->dst_len != ctx->curve->g.ndigits * sizeof(u64) ||
98 ctx->pub_key.ndigits != ctx->curve->g.ndigits ||
99 req->dst_len * 2 != req->src_len ||
100 WARN_ON(req->src_len > sizeof(sig)) ||
101 WARN_ON(req->dst_len > sizeof(digest)))
102 return -EBADMSG;
103
104 sg_copy_to_buffer(req->src, sg_nents_for_len(req->src, req->src_len),
105 sig, req->src_len);
106 sg_pcopy_to_buffer(req->src,
107 sg_nents_for_len(req->src,
108 req->src_len + req->dst_len),
109 digest, req->dst_len, req->src_len);
110
111 vli_from_be64(s, sig, ndigits);
112 vli_from_be64(r, sig + ndigits * sizeof(u64), ndigits);
113
114 /* Step 1: verify that 0 < r < q, 0 < s < q */
115 if (vli_is_zero(r, ndigits) ||
116 vli_cmp(r, ctx->curve->n, ndigits) >= 0 ||
117 vli_is_zero(s, ndigits) ||
118 vli_cmp(s, ctx->curve->n, ndigits) >= 0)
119 return -EKEYREJECTED;
120
121 /* Step 2: calculate hash (h) of the message (passed as input) */
122 /* Step 3: calculate e = h \mod q */
123 vli_from_le64(e, digest, ndigits);
124 if (vli_cmp(e, ctx->curve->n, ndigits) >= 0)
125 vli_sub(e, e, ctx->curve->n, ndigits);
126 if (vli_is_zero(e, ndigits))
127 e[0] = 1;
128
129 /* Step 4: calculate v = e^{-1} \mod q */
130 vli_mod_inv(v, e, ctx->curve->n, ndigits);
131
132 /* Step 5: calculate z_1 = sv \mod q, z_2 = -rv \mod q */
133 vli_mod_mult_slow(z1, s, v, ctx->curve->n, ndigits);
134 vli_sub(_r, ctx->curve->n, r, ndigits);
135 vli_mod_mult_slow(z2, _r, v, ctx->curve->n, ndigits);
136
137 /* Step 6: calculate point C = z_1P + z_2Q, and R = x_c \mod q */
138 ecc_point_mult_shamir(&cc, z1, &ctx->curve->g, z2, &ctx->pub_key,
139 ctx->curve);
140 if (vli_cmp(cc.x, ctx->curve->n, ndigits) >= 0)
141 vli_sub(cc.x, cc.x, ctx->curve->n, ndigits);
142
143 /* Step 7: if R == r signature is valid */
144 if (!vli_cmp(cc.x, r, ndigits))
145 return 0;
146 else
147 return -EKEYREJECTED;
148 }
149
ecrdsa_param_curve(void * context,size_t hdrlen,unsigned char tag,const void * value,size_t vlen)150 int ecrdsa_param_curve(void *context, size_t hdrlen, unsigned char tag,
151 const void *value, size_t vlen)
152 {
153 struct ecrdsa_ctx *ctx = context;
154
155 ctx->curve_oid = look_up_OID(value, vlen);
156 if (!ctx->curve_oid)
157 return -EINVAL;
158 ctx->curve = get_curve_by_oid(ctx->curve_oid);
159 return 0;
160 }
161
162 /* 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)163 int ecrdsa_param_digest(void *context, size_t hdrlen, unsigned char tag,
164 const void *value, size_t vlen)
165 {
166 struct ecrdsa_ctx *ctx = context;
167 int digest_oid = look_up_OID(value, vlen);
168
169 if (digest_oid != ctx->digest_oid)
170 return -EINVAL;
171 return 0;
172 }
173
ecrdsa_parse_pub_key(void * context,size_t hdrlen,unsigned char tag,const void * value,size_t vlen)174 int ecrdsa_parse_pub_key(void *context, size_t hdrlen, unsigned char tag,
175 const void *value, size_t vlen)
176 {
177 struct ecrdsa_ctx *ctx = context;
178
179 ctx->key = value;
180 ctx->key_len = vlen;
181 return 0;
182 }
183
ecrdsa_unpack_u32(u32 * dst,void * src)184 static u8 *ecrdsa_unpack_u32(u32 *dst, void *src)
185 {
186 memcpy(dst, src, sizeof(u32));
187 return src + sizeof(u32);
188 }
189
190 /* Parse BER encoded subjectPublicKey. */
ecrdsa_set_pub_key(struct crypto_akcipher * tfm,const void * key,unsigned int keylen)191 static int ecrdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key,
192 unsigned int keylen)
193 {
194 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
195 unsigned int ndigits;
196 u32 algo, paramlen;
197 u8 *params;
198 int err;
199
200 err = asn1_ber_decoder(&ecrdsa_pub_key_decoder, ctx, key, keylen);
201 if (err < 0)
202 return err;
203
204 /* Key parameters is in the key after keylen. */
205 params = ecrdsa_unpack_u32(¶mlen,
206 ecrdsa_unpack_u32(&algo, (u8 *)key + keylen));
207
208 if (algo == OID_gost2012PKey256) {
209 ctx->digest = "streebog256";
210 ctx->digest_oid = OID_gost2012Digest256;
211 ctx->digest_len = 256 / 8;
212 } else if (algo == OID_gost2012PKey512) {
213 ctx->digest = "streebog512";
214 ctx->digest_oid = OID_gost2012Digest512;
215 ctx->digest_len = 512 / 8;
216 } else
217 return -ENOPKG;
218 ctx->algo_oid = algo;
219
220 /* Parse SubjectPublicKeyInfo.AlgorithmIdentifier.parameters. */
221 err = asn1_ber_decoder(&ecrdsa_params_decoder, ctx, params, paramlen);
222 if (err < 0)
223 return err;
224 /*
225 * Sizes of algo (set in digest_len) and curve should match
226 * each other.
227 */
228 if (!ctx->curve ||
229 ctx->curve->g.ndigits * sizeof(u64) != ctx->digest_len)
230 return -ENOPKG;
231 /*
232 * Key is two 256- or 512-bit coordinates which should match
233 * curve size.
234 */
235 if ((ctx->key_len != (2 * 256 / 8) &&
236 ctx->key_len != (2 * 512 / 8)) ||
237 ctx->key_len != ctx->curve->g.ndigits * sizeof(u64) * 2)
238 return -ENOPKG;
239
240 ndigits = ctx->key_len / sizeof(u64) / 2;
241 ctx->pub_key = ECC_POINT_INIT(ctx->_pubp[0], ctx->_pubp[1], ndigits);
242 vli_from_le64(ctx->pub_key.x, ctx->key, ndigits);
243 vli_from_le64(ctx->pub_key.y, ctx->key + ndigits * sizeof(u64),
244 ndigits);
245
246 if (ecc_is_pubkey_valid_partial(ctx->curve, &ctx->pub_key))
247 return -EKEYREJECTED;
248
249 return 0;
250 }
251
ecrdsa_max_size(struct crypto_akcipher * tfm)252 static unsigned int ecrdsa_max_size(struct crypto_akcipher *tfm)
253 {
254 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm);
255
256 /*
257 * Verify doesn't need any output, so it's just informational
258 * for keyctl to determine the key bit size.
259 */
260 return ctx->pub_key.ndigits * sizeof(u64);
261 }
262
ecrdsa_exit_tfm(struct crypto_akcipher * tfm)263 static void ecrdsa_exit_tfm(struct crypto_akcipher *tfm)
264 {
265 }
266
267 static struct akcipher_alg ecrdsa_alg = {
268 .verify = ecrdsa_verify,
269 .set_pub_key = ecrdsa_set_pub_key,
270 .max_size = ecrdsa_max_size,
271 .exit = ecrdsa_exit_tfm,
272 .base = {
273 .cra_name = "ecrdsa",
274 .cra_driver_name = "ecrdsa-generic",
275 .cra_priority = 100,
276 .cra_module = THIS_MODULE,
277 .cra_ctxsize = sizeof(struct ecrdsa_ctx),
278 },
279 };
280
ecrdsa_mod_init(void)281 static int __init ecrdsa_mod_init(void)
282 {
283 return crypto_register_akcipher(&ecrdsa_alg);
284 }
285
ecrdsa_mod_fini(void)286 static void __exit ecrdsa_mod_fini(void)
287 {
288 crypto_unregister_akcipher(&ecrdsa_alg);
289 }
290
291 module_init(ecrdsa_mod_init);
292 module_exit(ecrdsa_mod_fini);
293
294 MODULE_LICENSE("GPL");
295 MODULE_AUTHOR("Vitaly Chikunov <vt@altlinux.org>");
296 MODULE_DESCRIPTION("EC-RDSA generic algorithm");
297 MODULE_ALIAS_CRYPTO("ecrdsa-generic");
298