xref: /linux/crypto/sm2.c (revision 2da68a77) 
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * SM2 asymmetric public-key algorithm
4  * as specified by OSCCA GM/T 0003.1-2012 -- 0003.5-2012 SM2 and
5  * described at https://tools.ietf.org/html/draft-shen-sm2-ecdsa-02
6  *
7  * Copyright (c) 2020, Alibaba Group.
8  * Authors: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
9  */
10 
11 #include <linux/module.h>
12 #include <linux/mpi.h>
13 #include <crypto/internal/akcipher.h>
14 #include <crypto/akcipher.h>
15 #include <crypto/hash.h>
16 #include <crypto/sm3.h>
17 #include <crypto/rng.h>
18 #include <crypto/sm2.h>
19 #include "sm2signature.asn1.h"
20 
21 #define MPI_NBYTES(m)   ((mpi_get_nbits(m) + 7) / 8)
22 
23 struct ecc_domain_parms {
24 	const char *desc;           /* Description of the curve.  */
25 	unsigned int nbits;         /* Number of bits.  */
26 	unsigned int fips:1; /* True if this is a FIPS140-2 approved curve */
27 
28 	/* The model describing this curve.  This is mainly used to select
29 	 * the group equation.
30 	 */
31 	enum gcry_mpi_ec_models model;
32 
33 	/* The actual ECC dialect used.  This is used for curve specific
34 	 * optimizations and to select encodings etc.
35 	 */
36 	enum ecc_dialects dialect;
37 
38 	const char *p;              /* The prime defining the field.  */
39 	const char *a, *b;          /* The coefficients.  For Twisted Edwards
40 				     * Curves b is used for d.  For Montgomery
41 				     * Curves (a,b) has ((A-2)/4,B^-1).
42 				     */
43 	const char *n;              /* The order of the base point.  */
44 	const char *g_x, *g_y;      /* Base point.  */
45 	unsigned int h;             /* Cofactor.  */
46 };
47 
48 static const struct ecc_domain_parms sm2_ecp = {
49 	.desc = "sm2p256v1",
50 	.nbits = 256,
51 	.fips = 0,
52 	.model = MPI_EC_WEIERSTRASS,
53 	.dialect = ECC_DIALECT_STANDARD,
54 	.p   = "0xfffffffeffffffffffffffffffffffffffffffff00000000ffffffffffffffff",
55 	.a   = "0xfffffffeffffffffffffffffffffffffffffffff00000000fffffffffffffffc",
56 	.b   = "0x28e9fa9e9d9f5e344d5a9e4bcf6509a7f39789f515ab8f92ddbcbd414d940e93",
57 	.n   = "0xfffffffeffffffffffffffffffffffff7203df6b21c6052b53bbf40939d54123",
58 	.g_x = "0x32c4ae2c1f1981195f9904466a39c9948fe30bbff2660be1715a4589334c74c7",
59 	.g_y = "0xbc3736a2f4f6779c59bdcee36b692153d0a9877cc62a474002df32e52139f0a0",
60 	.h = 1
61 };
62 
63 static int sm2_ec_ctx_init(struct mpi_ec_ctx *ec)
64 {
65 	const struct ecc_domain_parms *ecp = &sm2_ecp;
66 	MPI p, a, b;
67 	MPI x, y;
68 	int rc = -EINVAL;
69 
70 	p = mpi_scanval(ecp->p);
71 	a = mpi_scanval(ecp->a);
72 	b = mpi_scanval(ecp->b);
73 	if (!p || !a || !b)
74 		goto free_p;
75 
76 	x = mpi_scanval(ecp->g_x);
77 	y = mpi_scanval(ecp->g_y);
78 	if (!x || !y)
79 		goto free;
80 
81 	rc = -ENOMEM;
82 
83 	ec->Q = mpi_point_new(0);
84 	if (!ec->Q)
85 		goto free;
86 
87 	/* mpi_ec_setup_elliptic_curve */
88 	ec->G = mpi_point_new(0);
89 	if (!ec->G) {
90 		mpi_point_release(ec->Q);
91 		goto free;
92 	}
93 
94 	mpi_set(ec->G->x, x);
95 	mpi_set(ec->G->y, y);
96 	mpi_set_ui(ec->G->z, 1);
97 
98 	rc = -EINVAL;
99 	ec->n = mpi_scanval(ecp->n);
100 	if (!ec->n) {
101 		mpi_point_release(ec->Q);
102 		mpi_point_release(ec->G);
103 		goto free;
104 	}
105 
106 	ec->h = ecp->h;
107 	ec->name = ecp->desc;
108 	mpi_ec_init(ec, ecp->model, ecp->dialect, 0, p, a, b);
109 
110 	rc = 0;
111 
112 free:
113 	mpi_free(x);
114 	mpi_free(y);
115 free_p:
116 	mpi_free(p);
117 	mpi_free(a);
118 	mpi_free(b);
119 
120 	return rc;
121 }
122 
123 static void sm2_ec_ctx_deinit(struct mpi_ec_ctx *ec)
124 {
125 	mpi_ec_deinit(ec);
126 
127 	memset(ec, 0, sizeof(*ec));
128 }
129 
130 /* RESULT must have been initialized and is set on success to the
131  * point given by VALUE.
132  */
133 static int sm2_ecc_os2ec(MPI_POINT result, MPI value)
134 {
135 	int rc;
136 	size_t n;
137 	unsigned char *buf;
138 	MPI x, y;
139 
140 	n = MPI_NBYTES(value);
141 	buf = kmalloc(n, GFP_KERNEL);
142 	if (!buf)
143 		return -ENOMEM;
144 
145 	rc = mpi_print(GCRYMPI_FMT_USG, buf, n, &n, value);
146 	if (rc)
147 		goto err_freebuf;
148 
149 	rc = -EINVAL;
150 	if (n < 1 || ((n - 1) % 2))
151 		goto err_freebuf;
152 	/* No support for point compression */
153 	if (*buf != 0x4)
154 		goto err_freebuf;
155 
156 	rc = -ENOMEM;
157 	n = (n - 1) / 2;
158 	x = mpi_read_raw_data(buf + 1, n);
159 	if (!x)
160 		goto err_freebuf;
161 	y = mpi_read_raw_data(buf + 1 + n, n);
162 	if (!y)
163 		goto err_freex;
164 
165 	mpi_normalize(x);
166 	mpi_normalize(y);
167 	mpi_set(result->x, x);
168 	mpi_set(result->y, y);
169 	mpi_set_ui(result->z, 1);
170 
171 	rc = 0;
172 
173 	mpi_free(y);
174 err_freex:
175 	mpi_free(x);
176 err_freebuf:
177 	kfree(buf);
178 	return rc;
179 }
180 
181 struct sm2_signature_ctx {
182 	MPI sig_r;
183 	MPI sig_s;
184 };
185 
186 int sm2_get_signature_r(void *context, size_t hdrlen, unsigned char tag,
187 				const void *value, size_t vlen)
188 {
189 	struct sm2_signature_ctx *sig = context;
190 
191 	if (!value || !vlen)
192 		return -EINVAL;
193 
194 	sig->sig_r = mpi_read_raw_data(value, vlen);
195 	if (!sig->sig_r)
196 		return -ENOMEM;
197 
198 	return 0;
199 }
200 
201 int sm2_get_signature_s(void *context, size_t hdrlen, unsigned char tag,
202 				const void *value, size_t vlen)
203 {
204 	struct sm2_signature_ctx *sig = context;
205 
206 	if (!value || !vlen)
207 		return -EINVAL;
208 
209 	sig->sig_s = mpi_read_raw_data(value, vlen);
210 	if (!sig->sig_s)
211 		return -ENOMEM;
212 
213 	return 0;
214 }
215 
216 static int sm2_z_digest_update(struct sm3_state *sctx,
217 			MPI m, unsigned int pbytes)
218 {
219 	static const unsigned char zero[32];
220 	unsigned char *in;
221 	unsigned int inlen;
222 
223 	in = mpi_get_buffer(m, &inlen, NULL);
224 	if (!in)
225 		return -EINVAL;
226 
227 	if (inlen < pbytes) {
228 		/* padding with zero */
229 		sm3_update(sctx, zero, pbytes - inlen);
230 		sm3_update(sctx, in, inlen);
231 	} else if (inlen > pbytes) {
232 		/* skip the starting zero */
233 		sm3_update(sctx, in + inlen - pbytes, pbytes);
234 	} else {
235 		sm3_update(sctx, in, inlen);
236 	}
237 
238 	kfree(in);
239 	return 0;
240 }
241 
242 static int sm2_z_digest_update_point(struct sm3_state *sctx,
243 		MPI_POINT point, struct mpi_ec_ctx *ec, unsigned int pbytes)
244 {
245 	MPI x, y;
246 	int ret = -EINVAL;
247 
248 	x = mpi_new(0);
249 	y = mpi_new(0);
250 
251 	if (!mpi_ec_get_affine(x, y, point, ec) &&
252 	    !sm2_z_digest_update(sctx, x, pbytes) &&
253 	    !sm2_z_digest_update(sctx, y, pbytes))
254 		ret = 0;
255 
256 	mpi_free(x);
257 	mpi_free(y);
258 	return ret;
259 }
260 
261 int sm2_compute_z_digest(struct crypto_akcipher *tfm,
262 			const unsigned char *id, size_t id_len,
263 			unsigned char dgst[SM3_DIGEST_SIZE])
264 {
265 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
266 	uint16_t bits_len;
267 	unsigned char entl[2];
268 	struct sm3_state sctx;
269 	unsigned int pbytes;
270 
271 	if (id_len > (USHRT_MAX / 8) || !ec->Q)
272 		return -EINVAL;
273 
274 	bits_len = (uint16_t)(id_len * 8);
275 	entl[0] = bits_len >> 8;
276 	entl[1] = bits_len & 0xff;
277 
278 	pbytes = MPI_NBYTES(ec->p);
279 
280 	/* ZA = H256(ENTLA | IDA | a | b | xG | yG | xA | yA) */
281 	sm3_init(&sctx);
282 	sm3_update(&sctx, entl, 2);
283 	sm3_update(&sctx, id, id_len);
284 
285 	if (sm2_z_digest_update(&sctx, ec->a, pbytes) ||
286 	    sm2_z_digest_update(&sctx, ec->b, pbytes) ||
287 	    sm2_z_digest_update_point(&sctx, ec->G, ec, pbytes) ||
288 	    sm2_z_digest_update_point(&sctx, ec->Q, ec, pbytes))
289 		return -EINVAL;
290 
291 	sm3_final(&sctx, dgst);
292 	return 0;
293 }
294 EXPORT_SYMBOL(sm2_compute_z_digest);
295 
296 static int _sm2_verify(struct mpi_ec_ctx *ec, MPI hash, MPI sig_r, MPI sig_s)
297 {
298 	int rc = -EINVAL;
299 	struct gcry_mpi_point sG, tP;
300 	MPI t = NULL;
301 	MPI x1 = NULL, y1 = NULL;
302 
303 	mpi_point_init(&sG);
304 	mpi_point_init(&tP);
305 	x1 = mpi_new(0);
306 	y1 = mpi_new(0);
307 	t = mpi_new(0);
308 
309 	/* r, s in [1, n-1] */
310 	if (mpi_cmp_ui(sig_r, 1) < 0 || mpi_cmp(sig_r, ec->n) > 0 ||
311 		mpi_cmp_ui(sig_s, 1) < 0 || mpi_cmp(sig_s, ec->n) > 0) {
312 		goto leave;
313 	}
314 
315 	/* t = (r + s) % n, t == 0 */
316 	mpi_addm(t, sig_r, sig_s, ec->n);
317 	if (mpi_cmp_ui(t, 0) == 0)
318 		goto leave;
319 
320 	/* sG + tP = (x1, y1) */
321 	rc = -EBADMSG;
322 	mpi_ec_mul_point(&sG, sig_s, ec->G, ec);
323 	mpi_ec_mul_point(&tP, t, ec->Q, ec);
324 	mpi_ec_add_points(&sG, &sG, &tP, ec);
325 	if (mpi_ec_get_affine(x1, y1, &sG, ec))
326 		goto leave;
327 
328 	/* R = (e + x1) % n */
329 	mpi_addm(t, hash, x1, ec->n);
330 
331 	/* check R == r */
332 	rc = -EKEYREJECTED;
333 	if (mpi_cmp(t, sig_r))
334 		goto leave;
335 
336 	rc = 0;
337 
338 leave:
339 	mpi_point_free_parts(&sG);
340 	mpi_point_free_parts(&tP);
341 	mpi_free(x1);
342 	mpi_free(y1);
343 	mpi_free(t);
344 
345 	return rc;
346 }
347 
348 static int sm2_verify(struct akcipher_request *req)
349 {
350 	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
351 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
352 	unsigned char *buffer;
353 	struct sm2_signature_ctx sig;
354 	MPI hash;
355 	int ret;
356 
357 	if (unlikely(!ec->Q))
358 		return -EINVAL;
359 
360 	buffer = kmalloc(req->src_len + req->dst_len, GFP_KERNEL);
361 	if (!buffer)
362 		return -ENOMEM;
363 
364 	sg_pcopy_to_buffer(req->src,
365 		sg_nents_for_len(req->src, req->src_len + req->dst_len),
366 		buffer, req->src_len + req->dst_len, 0);
367 
368 	sig.sig_r = NULL;
369 	sig.sig_s = NULL;
370 	ret = asn1_ber_decoder(&sm2signature_decoder, &sig,
371 				buffer, req->src_len);
372 	if (ret)
373 		goto error;
374 
375 	ret = -ENOMEM;
376 	hash = mpi_read_raw_data(buffer + req->src_len, req->dst_len);
377 	if (!hash)
378 		goto error;
379 
380 	ret = _sm2_verify(ec, hash, sig.sig_r, sig.sig_s);
381 
382 	mpi_free(hash);
383 error:
384 	mpi_free(sig.sig_r);
385 	mpi_free(sig.sig_s);
386 	kfree(buffer);
387 	return ret;
388 }
389 
390 static int sm2_set_pub_key(struct crypto_akcipher *tfm,
391 			const void *key, unsigned int keylen)
392 {
393 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
394 	MPI a;
395 	int rc;
396 
397 	/* include the uncompressed flag '0x04' */
398 	a = mpi_read_raw_data(key, keylen);
399 	if (!a)
400 		return -ENOMEM;
401 
402 	mpi_normalize(a);
403 	rc = sm2_ecc_os2ec(ec->Q, a);
404 	mpi_free(a);
405 
406 	return rc;
407 }
408 
409 static unsigned int sm2_max_size(struct crypto_akcipher *tfm)
410 {
411 	/* Unlimited max size */
412 	return PAGE_SIZE;
413 }
414 
415 static int sm2_init_tfm(struct crypto_akcipher *tfm)
416 {
417 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
418 
419 	return sm2_ec_ctx_init(ec);
420 }
421 
422 static void sm2_exit_tfm(struct crypto_akcipher *tfm)
423 {
424 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
425 
426 	sm2_ec_ctx_deinit(ec);
427 }
428 
429 static struct akcipher_alg sm2 = {
430 	.verify = sm2_verify,
431 	.set_pub_key = sm2_set_pub_key,
432 	.max_size = sm2_max_size,
433 	.init = sm2_init_tfm,
434 	.exit = sm2_exit_tfm,
435 	.base = {
436 		.cra_name = "sm2",
437 		.cra_driver_name = "sm2-generic",
438 		.cra_priority = 100,
439 		.cra_module = THIS_MODULE,
440 		.cra_ctxsize = sizeof(struct mpi_ec_ctx),
441 	},
442 };
443 
444 static int __init sm2_init(void)
445 {
446 	return crypto_register_akcipher(&sm2);
447 }
448 
449 static void __exit sm2_exit(void)
450 {
451 	crypto_unregister_akcipher(&sm2);
452 }
453 
454 subsys_initcall(sm2_init);
455 module_exit(sm2_exit);
456 
457 MODULE_LICENSE("GPL");
458 MODULE_AUTHOR("Tianjia Zhang <tianjia.zhang@linux.alibaba.com>");
459 MODULE_DESCRIPTION("SM2 generic algorithm");
460 MODULE_ALIAS_CRYPTO("sm2-generic");
461