Use RSA key blinding to protect against timing attacks.
[paraslash.git] / crypt.c
1 /*
2 * Copyright (C) 2005-2009 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 RSA 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
17 #include "para.h"
18 #include "error.h"
19 #include "string.h"
20 #include "crypt.h"
21 #include "fd.h"
22 /**
23 * Fill a buffer with random content.
24 *
25 * \param buf The buffer to fill.
26 * \param num The size of \a buf in bytes.
27 *
28 * This function puts \a num cryptographically strong pseudo-random bytes into
29 * buf. If libssl can not guarantee an unpredictable byte sequence (for example
30 * because the PRNG has not been seeded with enough randomness) the function
31 * logs an error message and calls exit().
32 */
33 void get_random_bytes_or_die(unsigned char *buf, int num)
34 {
35 unsigned long err;
36
37 /* RAND_bytes() returns 1 on success, 0 otherwise. */
38 if (RAND_bytes(buf, num) == 1)
39 return;
40 err = ERR_get_error();
41 PARA_EMERG_LOG("%s\n", ERR_reason_error_string(err));
42 exit(EXIT_FAILURE);
43 }
44
45 /**
46 * Seed pseudo random number generators.
47 *
48 * This function reads 64 bytes from /dev/urandom and adds them to the SSL
49 * PRNG. It also seeds the PRNG used by random() with a random seed obtained
50 * from SSL. If /dev/random could not be read, an error message is logged and
51 * the function calls exit().
52 *
53 * \sa RAND_load_file(3), \ref get_random_bytes_or_die(), srandom(3),
54 * random(3), \ref para_random().
55 */
56 void init_random_seed_or_die(void)
57 {
58 int seed, ret = RAND_load_file("/dev/urandom", 64);
59
60 if (ret != 64) {
61 PARA_EMERG_LOG("could not seed PRNG (ret = %d)\n", ret);
62 exit(EXIT_FAILURE);
63 }
64 get_random_bytes_or_die((unsigned char *)&seed, sizeof(seed));
65 srandom(seed);
66 }
67
68 static EVP_PKEY *load_key(const char *file, int private)
69 {
70 BIO *key;
71 EVP_PKEY *pkey = NULL;
72
73 key = BIO_new(BIO_s_file());
74 if (!key)
75 return NULL;
76 if (BIO_read_filename(key, file) > 0) {
77 if (private == LOAD_PRIVATE_KEY)
78 pkey = PEM_read_bio_PrivateKey(key, NULL, NULL, NULL);
79 else
80 pkey = PEM_read_bio_PUBKEY(key, NULL, NULL, NULL);
81 }
82 BIO_free(key);
83 return pkey;
84 }
85
86 /**
87 * read an RSA key from a file
88 *
89 * \param key_file the file containing the key
90 * \param rsa RSA structure is returned here
91 * \param private if non-zero, read the private key, otherwise the public key
92 *
93 * \return The size of the RSA key on success, negative on errors.
94 *
95 * \sa openssl(1), rsa(1).
96 */
97 int get_rsa_key(char *key_file, RSA **rsa, int private)
98 {
99 EVP_PKEY *key = load_key(key_file, private);
100
101 if (!key)
102 return (private == LOAD_PRIVATE_KEY)? -E_PRIVATE_KEY
103 : -E_PUBLIC_KEY;
104 *rsa = EVP_PKEY_get1_RSA(key);
105 EVP_PKEY_free(key);
106 if (!*rsa)
107 return -E_RSA;
108 return RSA_size(*rsa);
109 }
110
111 /**
112 * free an RSA structure
113 *
114 * \param rsa pointer to the RSA struct to free
115 *
116 * This must be called for any key obtained by get_rsa_key().
117 */
118 void rsa_free(RSA *rsa)
119 {
120 if (rsa)
121 RSA_free(rsa);
122 }
123
124 /**
125 * decrypt a buffer using an RSA key
126 *
127 * \param key_file full path of the rsa key
128 * \param outbuf the output buffer
129 * \param inbuf the encrypted input buffer
130 * \param rsa_inlen the length of \a inbuf
131 *
132 * The \a outbuf must be large enough to hold at least \a rsa_inlen bytes.
133 *
134 * \return The size of the recovered plaintext on success, negative on errors.
135 *
136 * \sa RSA_private_decrypt(3)
137 **/
138 int para_decrypt_buffer(char *key_file, unsigned char *outbuf, unsigned char *inbuf,
139 unsigned rsa_inlen)
140 {
141 RSA *rsa;
142 int ret, inlen = rsa_inlen;
143
144 if (inlen < 0)
145 return -E_RSA;
146 ret = get_rsa_key(key_file, &rsa, LOAD_PRIVATE_KEY);
147 if (ret < 0)
148 return ret;
149 /*
150 * RSA is vulnerable to timing attacks. Generate a random blinding
151 * factor to protect against this kind of attack.
152 */
153 ret = -E_BLINDING;
154 if (RSA_blinding_on(rsa, NULL) == 0)
155 goto out;
156 ret = RSA_private_decrypt(inlen, inbuf, outbuf, rsa, RSA_PKCS1_OAEP_PADDING);
157 RSA_blinding_off(rsa);
158 if (ret <= 0)
159 ret = -E_DECRYPT;
160 out:
161 rsa_free(rsa);
162 return ret;
163 }
164
165 /**
166 * encrypt a buffer using an RSA key
167 *
168 * \param rsa: public rsa key
169 * \param inbuf the input buffer
170 * \param len the length of \a inbuf
171 * \param outbuf the output buffer
172 *
173 * \return The size of the encrypted data on success, negative on errors
174 *
175 * \sa RSA_public_encrypt(3)
176 */
177 int para_encrypt_buffer(RSA *rsa, unsigned char *inbuf,
178 unsigned len, unsigned char *outbuf)
179 {
180 int ret, flen = len; /* RSA_public_encrypt expects a signed int */
181
182 if (flen < 0)
183 return -E_ENCRYPT;
184 ret = RSA_public_encrypt(flen, inbuf, outbuf, rsa, RSA_PKCS1_OAEP_PADDING);
185 return ret < 0? -E_ENCRYPT : ret;
186 }
187
188 /**
189 * Encrypt and send a buffer.
190 *
191 * \param rc4c The rc4 crypt context.
192 * \param buf The buffer to send.
193 * \param len The size of \a buf in bytes.
194 *
195 * \return The return value of the underyling call to write_all().
196 *
197 * \sa \ref write_all(), RC4(3).
198 */
199 int rc4_send_bin_buffer(struct rc4_context *rc4c, const char *buf, size_t len)
200 {
201 int ret;
202 unsigned char *tmp;
203
204 assert(len);
205 tmp = para_malloc(len);
206 RC4(&rc4c->send_key, len, (const unsigned char *)buf, tmp);
207 ret = write_all(rc4c->fd, (char *)tmp, &len);
208 free(tmp);
209 return ret;
210 }
211
212 /**
213 * Encrypt and send a \p NULL-terminated buffer.
214 *
215 * \param rc4c The rc4 crypt context.
216 * \param buf The buffer to send.
217 *
218 * \return The return value of the underyling call to rc4_send_bin_buffer().
219 */
220 int rc4_send_buffer(struct rc4_context *rc4c, const char *buf)
221 {
222 return rc4_send_bin_buffer(rc4c, buf, strlen(buf));
223 }
224
225 /**
226 * Format, encrypt and send a buffer.
227 *
228 * \param rc4c The rc4 crypt context.
229 * \param fmt A format string.
230 *
231 * \return The return value of the underyling call to rc4_send_buffer().
232 */
233 __printf_2_3 int rc4_send_va_buffer(struct rc4_context *rc4c, const char *fmt, ...)
234 {
235 char *msg;
236 int ret;
237
238 PARA_VSPRINTF(fmt, msg);
239 ret = rc4_send_buffer(rc4c, msg);
240 free(msg);
241 return ret;
242 }
243
244 /**
245 * Receive a buffer and decrypt it.
246 *
247 * \param rc4c The rc4 crypt context.
248 * \param buf The buffer to write the decrypted data to.
249 * \param size The size of \a buf.
250 *
251 * \return The number of bytes received on success, negative on errors, zero if
252 * the peer has performed an orderly shutdown.
253 *
254 * \sa recv(2), RC4(3).
255 */
256 int rc4_recv_bin_buffer(struct rc4_context *rc4c, char *buf, size_t size)
257 {
258 unsigned char *tmp = para_malloc(size);
259 ssize_t ret = recv(rc4c->fd, tmp, size, 0);
260
261 if (ret > 0)
262 RC4(&rc4c->recv_key, ret, tmp, (unsigned char *)buf);
263 else if (ret < 0)
264 ret = -ERRNO_TO_PARA_ERROR(errno);
265 free(tmp);
266 return ret;
267 }
268
269 /**
270 * Receive a buffer, decrypt it and write terminating NULL byte.
271 *
272 * \param rc4c The rc4 crypt context.
273 * \param buf The buffer to write the decrypted data to.
274 * \param size The size of \a buf.
275 *
276 * Read at most \a size - 1 bytes from file descriptor given by \a rc4c,
277 * decrypt the received data and write a NULL byte at the end of the decrypted
278 * data.
279 *
280 * \return The return value of the underlying call to \ref
281 * rc4_recv_bin_buffer().
282 */
283 int rc4_recv_buffer(struct rc4_context *rc4c, char *buf, size_t size)
284 {
285 int n;
286
287 assert(size);
288 n = rc4_recv_bin_buffer(rc4c, buf, size - 1);
289 if (n >= 0)
290 buf[n] = '\0';
291 else
292 *buf = '\0';
293 return n;
294 }