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10  * Historical references: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) == 1 ||
117 	    vli_is_zero(s, ndigits) ||
118 	    vli_cmp(s, ctx->curve->n, ndigits) == 1)
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) == 1)
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) == 1)
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(&paramlen,
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