xref: /openbmc/linux/crypto/sm2.c (revision 70a59dd8) 
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_base.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 	/* mpi_ec_setup_elliptic_curve */
83 	ec->G = mpi_point_new(0);
84 	if (!ec->G)
85 		goto free;
86 
87 	mpi_set(ec->G->x, x);
88 	mpi_set(ec->G->y, y);
89 	mpi_set_ui(ec->G->z, 1);
90 
91 	rc = -EINVAL;
92 	ec->n = mpi_scanval(ecp->n);
93 	if (!ec->n) {
94 		mpi_point_release(ec->G);
95 		goto free;
96 	}
97 
98 	ec->h = ecp->h;
99 	ec->name = ecp->desc;
100 	mpi_ec_init(ec, ecp->model, ecp->dialect, 0, p, a, b);
101 
102 	rc = 0;
103 
104 free:
105 	mpi_free(x);
106 	mpi_free(y);
107 free_p:
108 	mpi_free(p);
109 	mpi_free(a);
110 	mpi_free(b);
111 
112 	return rc;
113 }
114 
115 static void sm2_ec_ctx_deinit(struct mpi_ec_ctx *ec)
116 {
117 	mpi_ec_deinit(ec);
118 
119 	memset(ec, 0, sizeof(*ec));
120 }
121 
122 static int sm2_ec_ctx_reset(struct mpi_ec_ctx *ec)
123 {
124 	sm2_ec_ctx_deinit(ec);
125 	return sm2_ec_ctx_init(ec);
126 }
127 
128 /* RESULT must have been initialized and is set on success to the
129  * point given by VALUE.
130  */
131 static int sm2_ecc_os2ec(MPI_POINT result, MPI value)
132 {
133 	int rc;
134 	size_t n;
135 	const unsigned char *buf;
136 	unsigned char *buf_memory;
137 	MPI x, y;
138 
139 	n = (mpi_get_nbits(value)+7)/8;
140 	buf_memory = kmalloc(n, GFP_KERNEL);
141 	rc = mpi_print(GCRYMPI_FMT_USG, buf_memory, n, &n, value);
142 	if (rc) {
143 		kfree(buf_memory);
144 		return rc;
145 	}
146 	buf = buf_memory;
147 
148 	if (n < 1) {
149 		kfree(buf_memory);
150 		return -EINVAL;
151 	}
152 	if (*buf != 4) {
153 		kfree(buf_memory);
154 		return -EINVAL; /* No support for point compression.  */
155 	}
156 	if (((n-1)%2)) {
157 		kfree(buf_memory);
158 		return -EINVAL;
159 	}
160 	n = (n-1)/2;
161 	x = mpi_read_raw_data(buf + 1, n);
162 	if (!x) {
163 		kfree(buf_memory);
164 		return -ENOMEM;
165 	}
166 	y = mpi_read_raw_data(buf + 1 + n, n);
167 	kfree(buf_memory);
168 	if (!y) {
169 		mpi_free(x);
170 		return -ENOMEM;
171 	}
172 
173 	mpi_normalize(x);
174 	mpi_normalize(y);
175 
176 	mpi_set(result->x, x);
177 	mpi_set(result->y, y);
178 	mpi_set_ui(result->z, 1);
179 
180 	mpi_free(x);
181 	mpi_free(y);
182 
183 	return 0;
184 }
185 
186 struct sm2_signature_ctx {
187 	MPI sig_r;
188 	MPI sig_s;
189 };
190 
191 int sm2_get_signature_r(void *context, size_t hdrlen, unsigned char tag,
192 				const void *value, size_t vlen)
193 {
194 	struct sm2_signature_ctx *sig = context;
195 
196 	if (!value || !vlen)
197 		return -EINVAL;
198 
199 	sig->sig_r = mpi_read_raw_data(value, vlen);
200 	if (!sig->sig_r)
201 		return -ENOMEM;
202 
203 	return 0;
204 }
205 
206 int sm2_get_signature_s(void *context, size_t hdrlen, unsigned char tag,
207 				const void *value, size_t vlen)
208 {
209 	struct sm2_signature_ctx *sig = context;
210 
211 	if (!value || !vlen)
212 		return -EINVAL;
213 
214 	sig->sig_s = mpi_read_raw_data(value, vlen);
215 	if (!sig->sig_s)
216 		return -ENOMEM;
217 
218 	return 0;
219 }
220 
221 static int sm2_z_digest_update(struct shash_desc *desc,
222 			MPI m, unsigned int pbytes)
223 {
224 	static const unsigned char zero[32];
225 	unsigned char *in;
226 	unsigned int inlen;
227 
228 	in = mpi_get_buffer(m, &inlen, NULL);
229 	if (!in)
230 		return -EINVAL;
231 
232 	if (inlen < pbytes) {
233 		/* padding with zero */
234 		crypto_sm3_update(desc, zero, pbytes - inlen);
235 		crypto_sm3_update(desc, in, inlen);
236 	} else if (inlen > pbytes) {
237 		/* skip the starting zero */
238 		crypto_sm3_update(desc, in + inlen - pbytes, pbytes);
239 	} else {
240 		crypto_sm3_update(desc, in, inlen);
241 	}
242 
243 	kfree(in);
244 	return 0;
245 }
246 
247 static int sm2_z_digest_update_point(struct shash_desc *desc,
248 		MPI_POINT point, struct mpi_ec_ctx *ec, unsigned int pbytes)
249 {
250 	MPI x, y;
251 	int ret = -EINVAL;
252 
253 	x = mpi_new(0);
254 	y = mpi_new(0);
255 
256 	if (!mpi_ec_get_affine(x, y, point, ec) &&
257 		!sm2_z_digest_update(desc, x, pbytes) &&
258 		!sm2_z_digest_update(desc, y, pbytes))
259 		ret = 0;
260 
261 	mpi_free(x);
262 	mpi_free(y);
263 	return ret;
264 }
265 
266 int sm2_compute_z_digest(struct crypto_akcipher *tfm,
267 			const unsigned char *id, size_t id_len,
268 			unsigned char dgst[SM3_DIGEST_SIZE])
269 {
270 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
271 	uint16_t bits_len;
272 	unsigned char entl[2];
273 	SHASH_DESC_ON_STACK(desc, NULL);
274 	unsigned int pbytes;
275 
276 	if (id_len > (USHRT_MAX / 8) || !ec->Q)
277 		return -EINVAL;
278 
279 	bits_len = (uint16_t)(id_len * 8);
280 	entl[0] = bits_len >> 8;
281 	entl[1] = bits_len & 0xff;
282 
283 	pbytes = MPI_NBYTES(ec->p);
284 
285 	/* ZA = H256(ENTLA | IDA | a | b | xG | yG | xA | yA) */
286 	sm3_base_init(desc);
287 	crypto_sm3_update(desc, entl, 2);
288 	crypto_sm3_update(desc, id, id_len);
289 
290 	if (sm2_z_digest_update(desc, ec->a, pbytes) ||
291 		sm2_z_digest_update(desc, ec->b, pbytes) ||
292 		sm2_z_digest_update_point(desc, ec->G, ec, pbytes) ||
293 		sm2_z_digest_update_point(desc, ec->Q, ec, pbytes))
294 		return -EINVAL;
295 
296 	crypto_sm3_final(desc, dgst);
297 	return 0;
298 }
299 EXPORT_SYMBOL(sm2_compute_z_digest);
300 
301 static int _sm2_verify(struct mpi_ec_ctx *ec, MPI hash, MPI sig_r, MPI sig_s)
302 {
303 	int rc = -EINVAL;
304 	struct gcry_mpi_point sG, tP;
305 	MPI t = NULL;
306 	MPI x1 = NULL, y1 = NULL;
307 
308 	mpi_point_init(&sG);
309 	mpi_point_init(&tP);
310 	x1 = mpi_new(0);
311 	y1 = mpi_new(0);
312 	t = mpi_new(0);
313 
314 	/* r, s in [1, n-1] */
315 	if (mpi_cmp_ui(sig_r, 1) < 0 || mpi_cmp(sig_r, ec->n) > 0 ||
316 		mpi_cmp_ui(sig_s, 1) < 0 || mpi_cmp(sig_s, ec->n) > 0) {
317 		goto leave;
318 	}
319 
320 	/* t = (r + s) % n, t == 0 */
321 	mpi_addm(t, sig_r, sig_s, ec->n);
322 	if (mpi_cmp_ui(t, 0) == 0)
323 		goto leave;
324 
325 	/* sG + tP = (x1, y1) */
326 	rc = -EBADMSG;
327 	mpi_ec_mul_point(&sG, sig_s, ec->G, ec);
328 	mpi_ec_mul_point(&tP, t, ec->Q, ec);
329 	mpi_ec_add_points(&sG, &sG, &tP, ec);
330 	if (mpi_ec_get_affine(x1, y1, &sG, ec))
331 		goto leave;
332 
333 	/* R = (e + x1) % n */
334 	mpi_addm(t, hash, x1, ec->n);
335 
336 	/* check R == r */
337 	rc = -EKEYREJECTED;
338 	if (mpi_cmp(t, sig_r))
339 		goto leave;
340 
341 	rc = 0;
342 
343 leave:
344 	mpi_point_free_parts(&sG);
345 	mpi_point_free_parts(&tP);
346 	mpi_free(x1);
347 	mpi_free(y1);
348 	mpi_free(t);
349 
350 	return rc;
351 }
352 
353 static int sm2_verify(struct akcipher_request *req)
354 {
355 	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
356 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
357 	unsigned char *buffer;
358 	struct sm2_signature_ctx sig;
359 	MPI hash;
360 	int ret;
361 
362 	if (unlikely(!ec->Q))
363 		return -EINVAL;
364 
365 	buffer = kmalloc(req->src_len + req->dst_len, GFP_KERNEL);
366 	if (!buffer)
367 		return -ENOMEM;
368 
369 	sg_pcopy_to_buffer(req->src,
370 		sg_nents_for_len(req->src, req->src_len + req->dst_len),
371 		buffer, req->src_len + req->dst_len, 0);
372 
373 	sig.sig_r = NULL;
374 	sig.sig_s = NULL;
375 	ret = asn1_ber_decoder(&sm2signature_decoder, &sig,
376 				buffer, req->src_len);
377 	if (ret)
378 		goto error;
379 
380 	ret = -ENOMEM;
381 	hash = mpi_read_raw_data(buffer + req->src_len, req->dst_len);
382 	if (!hash)
383 		goto error;
384 
385 	ret = _sm2_verify(ec, hash, sig.sig_r, sig.sig_s);
386 
387 	mpi_free(hash);
388 error:
389 	mpi_free(sig.sig_r);
390 	mpi_free(sig.sig_s);
391 	kfree(buffer);
392 	return ret;
393 }
394 
395 static int sm2_set_pub_key(struct crypto_akcipher *tfm,
396 			const void *key, unsigned int keylen)
397 {
398 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
399 	MPI a;
400 	int rc;
401 
402 	rc = sm2_ec_ctx_reset(ec);
403 	if (rc)
404 		return rc;
405 
406 	ec->Q = mpi_point_new(0);
407 	if (!ec->Q)
408 		return -ENOMEM;
409 
410 	/* include the uncompressed flag '0x04' */
411 	rc = -ENOMEM;
412 	a = mpi_read_raw_data(key, keylen);
413 	if (!a)
414 		goto error;
415 
416 	mpi_normalize(a);
417 	rc = sm2_ecc_os2ec(ec->Q, a);
418 	mpi_free(a);
419 	if (rc)
420 		goto error;
421 
422 	return 0;
423 
424 error:
425 	mpi_point_release(ec->Q);
426 	ec->Q = NULL;
427 	return rc;
428 }
429 
430 static unsigned int sm2_max_size(struct crypto_akcipher *tfm)
431 {
432 	/* Unlimited max size */
433 	return PAGE_SIZE;
434 }
435 
436 static int sm2_init_tfm(struct crypto_akcipher *tfm)
437 {
438 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
439 
440 	return sm2_ec_ctx_init(ec);
441 }
442 
443 static void sm2_exit_tfm(struct crypto_akcipher *tfm)
444 {
445 	struct mpi_ec_ctx *ec = akcipher_tfm_ctx(tfm);
446 
447 	sm2_ec_ctx_deinit(ec);
448 }
449 
450 static struct akcipher_alg sm2 = {
451 	.verify = sm2_verify,
452 	.set_pub_key = sm2_set_pub_key,
453 	.max_size = sm2_max_size,
454 	.init = sm2_init_tfm,
455 	.exit = sm2_exit_tfm,
456 	.base = {
457 		.cra_name = "sm2",
458 		.cra_driver_name = "sm2-generic",
459 		.cra_priority = 100,
460 		.cra_module = THIS_MODULE,
461 		.cra_ctxsize = sizeof(struct mpi_ec_ctx),
462 	},
463 };
464 
465 static int sm2_init(void)
466 {
467 	return crypto_register_akcipher(&sm2);
468 }
469 
470 static void sm2_exit(void)
471 {
472 	crypto_unregister_akcipher(&sm2);
473 }
474 
475 subsys_initcall(sm2_init);
476 module_exit(sm2_exit);
477 
478 MODULE_LICENSE("GPL");
479 MODULE_AUTHOR("Tianjia Zhang <tianjia.zhang@linux.alibaba.com>");
480 MODULE_DESCRIPTION("SM2 generic algorithm");
481 MODULE_ALIAS_CRYPTO("sm2-generic");
482