xref: /linux/lib/digsig.c (revision ff6092a8)
1 /*
2  * Copyright (C) 2011 Nokia Corporation
3  * Copyright (C) 2011 Intel Corporation
4  *
5  * Author:
6  * Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
7  *                 <dmitry.kasatkin@intel.com>
8  *
9  * This program is free software; you can redistribute it and/or modify
10  * it under the terms of the GNU General Public License as published by
11  * the Free Software Foundation, version 2 of the License.
12  *
13  * File: sign.c
14  *	implements signature (RSA) verification
15  *	pkcs decoding is based on LibTomCrypt code
16  */
17 
18 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
19 
20 #include <linux/err.h>
21 #include <linux/module.h>
22 #include <linux/slab.h>
23 #include <linux/key.h>
24 #include <linux/crypto.h>
25 #include <crypto/hash.h>
26 #include <crypto/sha.h>
27 #include <keys/user-type.h>
28 #include <linux/mpi.h>
29 #include <linux/digsig.h>
30 
31 static struct crypto_shash *shash;
32 
33 static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
34 						unsigned long  msglen,
35 						unsigned long  modulus_bitlen,
36 						unsigned long *outlen)
37 {
38 	unsigned long modulus_len, ps_len, i;
39 
40 	modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
41 
42 	/* test message size */
43 	if ((msglen > modulus_len) || (modulus_len < 11))
44 		return NULL;
45 
46 	/* separate encoded message */
47 	if (msg[0] != 0x00 || msg[1] != 0x01)
48 		return NULL;
49 
50 	for (i = 2; i < modulus_len - 1; i++)
51 		if (msg[i] != 0xFF)
52 			break;
53 
54 	/* separator check */
55 	if (msg[i] != 0)
56 		/* There was no octet with hexadecimal value 0x00
57 		to separate ps from m. */
58 		return NULL;
59 
60 	ps_len = i - 2;
61 
62 	*outlen = (msglen - (2 + ps_len + 1));
63 
64 	return msg + 2 + ps_len + 1;
65 }
66 
67 /*
68  * RSA Signature verification with public key
69  */
70 static int digsig_verify_rsa(struct key *key,
71 		    const char *sig, int siglen,
72 		       const char *h, int hlen)
73 {
74 	int err = -EINVAL;
75 	unsigned long len;
76 	unsigned long mlen, mblen;
77 	unsigned nret, l;
78 	int head, i;
79 	unsigned char *out1 = NULL;
80 	const char *m;
81 	MPI in = NULL, res = NULL, pkey[2];
82 	uint8_t *p, *datap, *endp;
83 	struct user_key_payload *ukp;
84 	struct pubkey_hdr *pkh;
85 
86 	down_read(&key->sem);
87 	ukp = key->payload.data;
88 
89 	if (ukp->datalen < sizeof(*pkh))
90 		goto err1;
91 
92 	pkh = (struct pubkey_hdr *)ukp->data;
93 
94 	if (pkh->version != 1)
95 		goto err1;
96 
97 	if (pkh->algo != PUBKEY_ALGO_RSA)
98 		goto err1;
99 
100 	if (pkh->nmpi != 2)
101 		goto err1;
102 
103 	datap = pkh->mpi;
104 	endp = ukp->data + ukp->datalen;
105 
106 	err = -ENOMEM;
107 
108 	for (i = 0; i < pkh->nmpi; i++) {
109 		unsigned int remaining = endp - datap;
110 		pkey[i] = mpi_read_from_buffer(datap, &remaining);
111 		if (!pkey[i])
112 			goto err;
113 		datap += remaining;
114 	}
115 
116 	mblen = mpi_get_nbits(pkey[0]);
117 	mlen = DIV_ROUND_UP(mblen, 8);
118 
119 	if (mlen == 0)
120 		goto err;
121 
122 	out1 = kzalloc(mlen, GFP_KERNEL);
123 	if (!out1)
124 		goto err;
125 
126 	nret = siglen;
127 	in = mpi_read_from_buffer(sig, &nret);
128 	if (!in)
129 		goto err;
130 
131 	res = mpi_alloc(mpi_get_nlimbs(in) * 2);
132 	if (!res)
133 		goto err;
134 
135 	err = mpi_powm(res, in, pkey[1], pkey[0]);
136 	if (err)
137 		goto err;
138 
139 	if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
140 		err = -EINVAL;
141 		goto err;
142 	}
143 
144 	p = mpi_get_buffer(res, &l, NULL);
145 	if (!p) {
146 		err = -EINVAL;
147 		goto err;
148 	}
149 
150 	len = mlen;
151 	head = len - l;
152 	memset(out1, 0, head);
153 	memcpy(out1 + head, p, l);
154 
155 	kfree(p);
156 
157 	m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
158 
159 	if (!m || len != hlen || memcmp(m, h, hlen))
160 		err = -EINVAL;
161 
162 err:
163 	mpi_free(in);
164 	mpi_free(res);
165 	kfree(out1);
166 	while (--i >= 0)
167 		mpi_free(pkey[i]);
168 err1:
169 	up_read(&key->sem);
170 
171 	return err;
172 }
173 
174 /**
175  * digsig_verify() - digital signature verification with public key
176  * @keyring:	keyring to search key in
177  * @sig:	digital signature
178  * @sigen:	length of the signature
179  * @data:	data
180  * @datalen:	length of the data
181  * @return:	0 on success, -EINVAL otherwise
182  *
183  * Verifies data integrity against digital signature.
184  * Currently only RSA is supported.
185  * Normally hash of the content is used as a data for this function.
186  *
187  */
188 int digsig_verify(struct key *keyring, const char *sig, int siglen,
189 						const char *data, int datalen)
190 {
191 	int err = -ENOMEM;
192 	struct signature_hdr *sh = (struct signature_hdr *)sig;
193 	struct shash_desc *desc = NULL;
194 	unsigned char hash[SHA1_DIGEST_SIZE];
195 	struct key *key;
196 	char name[20];
197 
198 	if (siglen < sizeof(*sh) + 2)
199 		return -EINVAL;
200 
201 	if (sh->algo != PUBKEY_ALGO_RSA)
202 		return -ENOTSUPP;
203 
204 	sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
205 
206 	if (keyring) {
207 		/* search in specific keyring */
208 		key_ref_t kref;
209 		kref = keyring_search(make_key_ref(keyring, 1UL),
210 						&key_type_user, name);
211 		if (IS_ERR(kref))
212 			key = ERR_CAST(kref);
213 		else
214 			key = key_ref_to_ptr(kref);
215 	} else {
216 		key = request_key(&key_type_user, name, NULL);
217 	}
218 	if (IS_ERR(key)) {
219 		pr_err("key not found, id: %s\n", name);
220 		return PTR_ERR(key);
221 	}
222 
223 	desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
224 		       GFP_KERNEL);
225 	if (!desc)
226 		goto err;
227 
228 	desc->tfm = shash;
229 	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
230 
231 	crypto_shash_init(desc);
232 	crypto_shash_update(desc, data, datalen);
233 	crypto_shash_update(desc, sig, sizeof(*sh));
234 	crypto_shash_final(desc, hash);
235 
236 	kfree(desc);
237 
238 	/* pass signature mpis address */
239 	err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
240 			     hash, sizeof(hash));
241 
242 err:
243 	key_put(key);
244 
245 	return err ? -EINVAL : 0;
246 }
247 EXPORT_SYMBOL_GPL(digsig_verify);
248 
249 static int __init digsig_init(void)
250 {
251 	shash = crypto_alloc_shash("sha1", 0, 0);
252 	if (IS_ERR(shash)) {
253 		pr_err("shash allocation failed\n");
254 		return  PTR_ERR(shash);
255 	}
256 
257 	return 0;
258 
259 }
260 
261 static void __exit digsig_cleanup(void)
262 {
263 	crypto_free_shash(shash);
264 }
265 
266 module_init(digsig_init);
267 module_exit(digsig_cleanup);
268 
269 MODULE_LICENSE("GPL");
270