Replace RSA by an abstract asymmetric key structure.
[paraslash.git] / crypt.c
1 /*
2 * Copyright (C) 2005-2011 Andre Noll <maan@systemlinux.org>
3 *
4 * Licensed under the GPL v2. For licencing details see COPYING.
5 */
6
7 /** \file crypt.c Openssl-based encryption/decryption routines. */
8
9 #include <regex.h>
10 #include <dirent.h>
11 #include <sys/types.h>
12 #include <sys/socket.h>
13 #include <openssl/rand.h>
14 #include <openssl/err.h>
15 #include <openssl/rc4.h>
16 #include <openssl/pem.h>
17
18 #include "para.h"
19 #include "error.h"
20 #include "string.h"
21 #include "crypt.h"
22 #include "fd.h"
23
24 struct asymmetric_key {
25 RSA *rsa;
26 };
27
28 /**
29 * Fill a buffer with random content.
30 *
31 * \param buf The buffer to fill.
32 * \param num The size of \a buf in bytes.
33 *
34 * This function puts \a num cryptographically strong pseudo-random bytes into
35 * buf. If libssl can not guarantee an unpredictable byte sequence (for example
36 * because the PRNG has not been seeded with enough randomness) the function
37 * logs an error message and calls exit().
38 */
39 void get_random_bytes_or_die(unsigned char *buf, int num)
40 {
41 unsigned long err;
42
43 /* RAND_bytes() returns 1 on success, 0 otherwise. */
44 if (RAND_bytes(buf, num) == 1)
45 return;
46 err = ERR_get_error();
47 PARA_EMERG_LOG("%s\n", ERR_reason_error_string(err));
48 exit(EXIT_FAILURE);
49 }
50
51 /**
52 * Seed pseudo random number generators.
53 *
54 * This function reads 64 bytes from /dev/urandom and adds them to the SSL
55 * PRNG. It also seeds the PRNG used by random() with a random seed obtained
56 * from SSL. If /dev/random could not be read, an error message is logged and
57 * the function calls exit().
58 *
59 * \sa RAND_load_file(3), \ref get_random_bytes_or_die(), srandom(3),
60 * random(3), \ref para_random().
61 */
62 void init_random_seed_or_die(void)
63 {
64 int seed, ret = RAND_load_file("/dev/urandom", 64);
65
66 if (ret != 64) {
67 PARA_EMERG_LOG("could not seed PRNG (ret = %d)\n", ret);
68 exit(EXIT_FAILURE);
69 }
70 get_random_bytes_or_die((unsigned char *)&seed, sizeof(seed));
71 srandom(seed);
72 }
73
74 static int check_key_file(const char *file, int private)
75 {
76 struct stat st;
77
78 if (stat(file, &st) != 0)
79 return -ERRNO_TO_PARA_ERROR(errno);
80 if (private != LOAD_PRIVATE_KEY)
81 return 0;
82 if ((st.st_uid == getuid()) && (st.st_mode & 077) != 0)
83 return -E_KEY_PERM;
84 return 1;
85 }
86
87 static EVP_PKEY *load_key(const char *file, int private)
88 {
89 BIO *key;
90 EVP_PKEY *pkey = NULL;
91 int ret = check_key_file(file, private);
92
93 if (ret < 0) {
94 PARA_ERROR_LOG("%s\n", para_strerror(-ret));
95 return NULL;
96 }
97 key = BIO_new(BIO_s_file());
98 if (!key)
99 return NULL;
100 if (BIO_read_filename(key, file) > 0) {
101 if (private == LOAD_PRIVATE_KEY)
102 pkey = PEM_read_bio_PrivateKey(key, NULL, NULL, NULL);
103 else
104 pkey = PEM_read_bio_PUBKEY(key, NULL, NULL, NULL);
105 }
106 BIO_free(key);
107 return pkey;
108 }
109
110 /**
111 * Read an asymmetric key from a file.
112 *
113 * \param key_file The file containing the key.
114 * \param private if non-zero, read the private key, otherwise the public key.
115 * \param result The key structure is returned here.
116 *
117 * \return The size of the key on success, negative on errors.
118 *
119 * \sa openssl(1), rsa(1).
120 */
121 int get_asymmetric_key(const char *key_file, int private,
122 struct asymmetric_key **result)
123 {
124 struct asymmetric_key *key;
125 RSA *rsa;
126 EVP_PKEY *pkey = load_key(key_file, private);
127
128 if (!pkey)
129 return (private == LOAD_PRIVATE_KEY)? -E_PRIVATE_KEY
130 : -E_PUBLIC_KEY;
131 rsa = EVP_PKEY_get1_RSA(pkey);
132 EVP_PKEY_free(pkey);
133 if (!rsa)
134 return -E_RSA;
135 key = para_malloc(sizeof(*key));
136 key->rsa = rsa;
137 *result = key;
138 return RSA_size(rsa);
139 }
140
141 /**
142 * Deallocate an asymmetric key structure.
143 *
144 * \param key Pointer to the key structure to free.
145 *
146 * This must be called for any key obtained by get_asymmetric_key().
147 */
148 void free_asymmetric_key(struct asymmetric_key *key)
149 {
150 if (!key)
151 return;
152 RSA_free(key->rsa);
153 free(key);
154 }
155
156 /**
157 * Decrypt a buffer using a private key.
158 *
159 * \param key_file Full path of the key.
160 * \param outbuf The output buffer.
161 * \param inbuf The encrypted input buffer.
162 * \param inlen The length of \a inbuf in bytes.
163 *
164 * The \a outbuf must be large enough to hold at least \a rsa_inlen bytes.
165 *
166 * \return The size of the recovered plaintext on success, negative on errors.
167 *
168 * \sa RSA_private_decrypt(3)
169 **/
170 int priv_decrypt(const char *key_file, unsigned char *outbuf,
171 unsigned char *inbuf, int inlen)
172 {
173 struct asymmetric_key *priv;
174 int ret;
175
176 if (inlen < 0)
177 return -E_RSA;
178 ret = get_asymmetric_key(key_file, LOAD_PRIVATE_KEY, &priv);
179 if (ret < 0)
180 return ret;
181 /*
182 * RSA is vulnerable to timing attacks. Generate a random blinding
183 * factor to protect against this kind of attack.
184 */
185 ret = -E_BLINDING;
186 if (RSA_blinding_on(priv->rsa, NULL) == 0)
187 goto out;
188 ret = RSA_private_decrypt(inlen, inbuf, outbuf, priv->rsa,
189 RSA_PKCS1_OAEP_PADDING);
190 RSA_blinding_off(priv->rsa);
191 if (ret <= 0)
192 ret = -E_DECRYPT;
193 out:
194 free_asymmetric_key(priv);
195 return ret;
196 }
197
198 /**
199 * Encrypt a buffer using an RSA key
200 *
201 * \param pub: The public key.
202 * \param inbuf The input buffer.
203 * \param len The length of \a inbuf.
204 * \param outbuf The output buffer.
205 *
206 * \return The size of the encrypted data on success, negative on errors.
207 *
208 * \sa RSA_public_encrypt(3)
209 */
210 int pub_encrypt(struct asymmetric_key *pub, unsigned char *inbuf,
211 unsigned len, unsigned char *outbuf)
212 {
213 int ret, flen = len; /* RSA_public_encrypt expects a signed int */
214
215 if (flen < 0)
216 return -E_ENCRYPT;
217 ret = RSA_public_encrypt(flen, inbuf, outbuf, pub->rsa,
218 RSA_PKCS1_OAEP_PADDING);
219 return ret < 0? -E_ENCRYPT : ret;
220 }
221
222 #define RC4_ALIGN 8
223
224 /**
225 * Encrypt and send a buffer.
226 *
227 * \param rc4c The rc4 crypt context.
228 * \param buf The buffer to send.
229 * \param len The size of \a buf in bytes.
230 *
231 * \return The return value of the underyling call to write_all().
232 *
233 * \sa \ref write_all(), RC4(3).
234 */
235 int rc4_send_bin_buffer(struct rc4_context *rc4c, const char *buf, size_t len)
236 {
237 int ret;
238 unsigned char *tmp;
239 static unsigned char remainder[RC4_ALIGN];
240 size_t l1 = ROUND_DOWN(len, RC4_ALIGN), l2 = ROUND_UP(len, RC4_ALIGN);
241
242 assert(len);
243 tmp = para_malloc(l2);
244 RC4(&rc4c->send_key, l1, (const unsigned char *)buf, tmp);
245 if (len > l1) {
246 memcpy(remainder, buf + l1, len - l1);
247 RC4(&rc4c->send_key, len - l1, remainder, tmp + l1);
248 }
249 ret = write_all(rc4c->fd, (char *)tmp, &len);
250 free(tmp);
251 return ret;
252 }
253
254 /**
255 * Encrypt and send a \p NULL-terminated buffer.
256 *
257 * \param rc4c The rc4 crypt context.
258 * \param buf The buffer to send.
259 *
260 * \return The return value of the underyling call to rc4_send_bin_buffer().
261 */
262 int rc4_send_buffer(struct rc4_context *rc4c, const char *buf)
263 {
264 return rc4_send_bin_buffer(rc4c, buf, strlen(buf));
265 }
266
267 /**
268 * Format, encrypt and send a buffer.
269 *
270 * \param rc4c The rc4 crypt context.
271 * \param fmt A format string.
272 *
273 * \return The return value of the underyling call to rc4_send_buffer().
274 */
275 __printf_2_3 int rc4_send_va_buffer(struct rc4_context *rc4c, const char *fmt, ...)
276 {
277 char *msg;
278 int ret;
279
280 PARA_VSPRINTF(fmt, msg);
281 ret = rc4_send_buffer(rc4c, msg);
282 free(msg);
283 return ret;
284 }
285
286 /**
287 * Receive a buffer and decrypt it.
288 *
289 * \param rc4c The rc4 crypt context.
290 * \param buf The buffer to write the decrypted data to.
291 * \param size The size of \a buf.
292 *
293 * \return The number of bytes received on success, negative on errors, zero if
294 * the peer has performed an orderly shutdown.
295 *
296 * \sa recv(2), RC4(3).
297 */
298 int rc4_recv_bin_buffer(struct rc4_context *rc4c, char *buf, size_t size)
299 {
300 unsigned char *tmp = para_malloc(size);
301 ssize_t ret = recv(rc4c->fd, tmp, size, 0);
302
303 if (ret > 0)
304 RC4(&rc4c->recv_key, ret, tmp, (unsigned char *)buf);
305 else if (ret < 0)
306 ret = -ERRNO_TO_PARA_ERROR(errno);
307 free(tmp);
308 return ret;
309 }
310
311 /**
312 * Receive a buffer, decrypt it and write terminating NULL byte.
313 *
314 * \param rc4c The rc4 crypt context.
315 * \param buf The buffer to write the decrypted data to.
316 * \param size The size of \a buf.
317 *
318 * Read at most \a size - 1 bytes from file descriptor given by \a rc4c,
319 * decrypt the received data and write a NULL byte at the end of the decrypted
320 * data.
321 *
322 * \return The return value of the underlying call to \ref
323 * rc4_recv_bin_buffer().
324 */
325 int rc4_recv_buffer(struct rc4_context *rc4c, char *buf, size_t size)
326 {
327 int n;
328
329 assert(size);
330 n = rc4_recv_bin_buffer(rc4c, buf, size - 1);
331 if (n >= 0)
332 buf[n] = '\0';
333 else
334 *buf = '\0';
335 return n;
336 }