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 <stdbool.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 #include <openssl/sha.h>
  18 #include <openssl/bn.h>
  19
  20 #include "para.h"
  21 #include "error.h"
  22 #include "string.h"
  23 #include "crypt.h"
  24 #include "fd.h"
  25 #include "crypt_backend.h"
  26
  27 struct asymmetric_key {
  28         RSA *rsa;
  29 };
  30
  31 /**
  32  * Fill a buffer with random content.
  33  *
  34  * \param buf The buffer to fill.
  35  * \param num The size of \a buf in bytes.
  36  *
  37  * This function puts \a num cryptographically strong pseudo-random bytes into
  38  * buf. If libssl can not guarantee an unpredictable byte sequence (for example
  39  * because the PRNG has not been seeded with enough randomness) the function
  40  * logs an error message and calls exit().
  41  */
  42 void get_random_bytes_or_die(unsigned char *buf, int num)
  43 {
  44         unsigned long err;
  45
  46         /* RAND_bytes() returns 1 on success, 0 otherwise. */
  47         if (RAND_bytes(buf, num) == 1)
  48                 return;
  49         err = ERR_get_error();
  50         PARA_EMERG_LOG("%s\n", ERR_reason_error_string(err));
  51         exit(EXIT_FAILURE);
  52 }
  53
  54 /**
  55  * Seed pseudo random number generators.
  56  *
  57  * This function reads 64 bytes from /dev/urandom and adds them to the SSL
  58  * PRNG. It also seeds the PRNG used by random() with a random seed obtained
  59  * from SSL. If /dev/random could not be read, an error message is logged and
  60  * the function calls exit().
  61  *
  62  * \sa RAND_load_file(3), \ref get_random_bytes_or_die(), srandom(3),
  63  * random(3), \ref para_random().
  64  */
  65 void init_random_seed_or_die(void)
  66 {
  67         int seed, ret = RAND_load_file("/dev/urandom", 64);
  68
  69         if (ret != 64) {
  70                 PARA_EMERG_LOG("could not seed PRNG (ret = %d)\n", ret);
  71                 exit(EXIT_FAILURE);
  72         }
  73         get_random_bytes_or_die((unsigned char *)&seed, sizeof(seed));
  74         srandom(seed);
  75 }
  76
  77 static EVP_PKEY *load_key(const char *file, int private)
  78 {
  79         BIO *key;
  80         EVP_PKEY *pkey = NULL;
  81         int ret = check_key_file(file, private);
  82
  83         if (ret < 0) {
  84                 PARA_ERROR_LOG("%s\n", para_strerror(-ret));
  85                 return NULL;
  86         }
  87         key = BIO_new(BIO_s_file());
  88         if (!key)
  89                 return NULL;
  90         if (BIO_read_filename(key, file) > 0) {
  91                 if (private == LOAD_PRIVATE_KEY)
  92                         pkey = PEM_read_bio_PrivateKey(key, NULL, NULL, NULL);
  93                 else
  94                         pkey = PEM_read_bio_PUBKEY(key, NULL, NULL, NULL);
  95         }
  96         BIO_free(key);
  97         return pkey;
  98 }
  99
 100 static int get_openssl_key(const char *key_file, RSA **rsa, int private)
 101 {
 102         EVP_PKEY *key = load_key(key_file, private);
 103
 104         if (!key)
 105                 return (private == LOAD_PRIVATE_KEY)? -E_PRIVATE_KEY
 106                         : -E_PUBLIC_KEY;
 107         *rsa = EVP_PKEY_get1_RSA(key);
 108         EVP_PKEY_free(key);
 109         if (!*rsa)
 110                 return -E_RSA;
 111         return RSA_size(*rsa);
 112 }
 113
 114 /*
 115  * The public key loading functions below were inspired by corresponding code
 116  * of openssh-5.2p1, Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo,
 117  * Finland. However, not much of the original code remains.
 118  */
 119
 120 static int read_bignum(const unsigned char *buf, size_t len, BIGNUM **result)
 121 {
 122         const unsigned char *p = buf, *end = buf + len;
 123         uint32_t bnsize;
 124         BIGNUM *bn;
 125
 126         if (p + 4 < p)
 127                 return -E_BIGNUM;
 128         if (p + 4 > end)
 129                 return -E_BIGNUM;
 130         bnsize = read_ssh_u32(p);
 131         PARA_DEBUG_LOG("bnsize: %u\n", bnsize);
 132         p += 4;
 133         if (p + bnsize < p)
 134                 return -E_BIGNUM;
 135         if (p + bnsize > end)
 136                 return -E_BIGNUM;
 137         if (bnsize > 8192)
 138                 return -E_BIGNUM;
 139         bn = BN_bin2bn(p, bnsize, NULL);
 140         if (!bn)
 141                 return -E_BIGNUM;
 142         *result = bn;
 143         return bnsize + 4;
 144 }
 145
 146 static int read_rsa_bignums(const unsigned char *blob, int blen, RSA **result)
 147 {
 148         int ret;
 149         RSA *rsa;
 150         const unsigned char *p = blob, *end = blob + blen;
 151
 152         rsa = RSA_new();
 153         if (!rsa)
 154                 return -E_BIGNUM;
 155         ret = read_bignum(p, end - p, &rsa->e);
 156         if (ret < 0)
 157                 goto fail;
 158         p += ret;
 159         ret = read_bignum(p, end - p, &rsa->n);
 160         if (ret < 0)
 161                 goto fail;
 162         *result = rsa;
 163         return 1;
 164 fail:
 165         if (rsa)
 166                 RSA_free(rsa);
 167         return ret;
 168 }
 169
 170 /**
 171  * Read an asymmetric key from a file.
 172  *
 173  * \param key_file The file containing the key.
 174  * \param private if non-zero, read the private key, otherwise the public key.
 175  * \param result The key structure is returned here.
 176  *
 177  * \return The size of the key on success, negative on errors.
 178  *
 179  * \sa openssl(1), rsa(1).
 180  */
 181 int get_asymmetric_key(const char *key_file, int private,
 182                 struct asymmetric_key **result)
 183 {
 184         struct asymmetric_key *key = NULL;
 185         void *map = NULL;
 186         unsigned char *blob = NULL;
 187         size_t map_size, blob_size, decoded_size;
 188         int ret, ret2;
 189         char *cp;
 190
 191         key = para_malloc(sizeof(*key));
 192         if (private) {
 193                 ret = get_openssl_key(key_file, &key->rsa, LOAD_PRIVATE_KEY);
 194                 goto out;
 195         }
 196         ret = mmap_full_file(key_file, O_RDONLY, &map, &map_size, NULL);
 197         if (ret < 0)
 198                 goto out;
 199         ret = is_ssh_rsa_key(map, map_size);
 200         if (!ret) {
 201                 ret = para_munmap(map, map_size);
 202                 map = NULL;
 203                 if (ret < 0)
 204                         goto out;
 205                 ret = get_openssl_key(key_file, &key->rsa, LOAD_PUBLIC_KEY);
 206                 goto out;
 207         }
 208         cp = map + ret;
 209         PARA_INFO_LOG("decoding public rsa-ssh key %s\n", key_file);
 210         ret = -ERRNO_TO_PARA_ERROR(EOVERFLOW);
 211         if (map_size > INT_MAX / 4)
 212                 goto out;
 213         blob_size = 2 * map_size;
 214         blob = para_malloc(blob_size);
 215         ret = uudecode(cp, blob, blob_size);
 216         if (ret < 0)
 217                 goto out;
 218         decoded_size = ret;
 219         ret = check_ssh_key_header(blob, decoded_size);
 220         if (ret < 0)
 221                 goto out;
 222         ret = read_rsa_bignums(blob + ret, decoded_size - ret, &key->rsa);
 223         if (ret < 0)
 224                 goto out;
 225         ret = RSA_size(key->rsa);
 226 out:
 227         ret2 = para_munmap(map, map_size);
 228         if (ret >= 0 && ret2 < 0)
 229                 ret = ret2;
 230         if (ret < 0) {
 231                 free(key);
 232                 result = NULL;
 233                 PARA_ERROR_LOG("key %s: %s\n", key_file, para_strerror(-ret));
 234         } else
 235                 *result = key;
 236         free(blob);
 237         return ret;
 238 }
 239
 240 /**
 241  * Deallocate an asymmetric key structure.
 242  *
 243  * \param key Pointer to the key structure to free.
 244  *
 245  * This must be called for any key obtained by get_asymmetric_key().
 246  */
 247 void free_asymmetric_key(struct asymmetric_key *key)
 248 {
 249         if (!key)
 250                 return;
 251         RSA_free(key->rsa);
 252         free(key);
 253 }
 254
 255 /**
 256  * Decrypt a buffer using a private key.
 257  *
 258  * \param key_file Full path of the key.
 259  * \param outbuf The output buffer.
 260  * \param inbuf The encrypted input buffer.
 261  * \param inlen The length of \a inbuf in bytes.
 262  *
 263  * The \a outbuf must be large enough to hold at least \a rsa_inlen bytes.
 264  *
 265  * \return The size of the recovered plaintext on success, negative on errors.
 266  *
 267  * \sa RSA_private_decrypt(3)
 268  **/
 269 int priv_decrypt(const char *key_file, unsigned char *outbuf,
 270                 unsigned char *inbuf, int inlen)
 271 {
 272         struct asymmetric_key *priv;
 273         int ret;
 274
 275         if (inlen < 0)
 276                 return -E_RSA;
 277         ret = get_asymmetric_key(key_file, LOAD_PRIVATE_KEY, &priv);
 278         if (ret < 0)
 279                 return ret;
 280         /*
 281          * RSA is vulnerable to timing attacks. Generate a random blinding
 282          * factor to protect against this kind of attack.
 283          */
 284         ret = -E_BLINDING;
 285         if (RSA_blinding_on(priv->rsa, NULL) == 0)
 286                 goto out;
 287         ret = RSA_private_decrypt(inlen, inbuf, outbuf, priv->rsa,
 288                 RSA_PKCS1_OAEP_PADDING);
 289         RSA_blinding_off(priv->rsa);
 290         if (ret <= 0)
 291                 ret = -E_DECRYPT;
 292 out:
 293         free_asymmetric_key(priv);
 294         return ret;
 295 }
 296
 297 /**
 298  * Encrypt a buffer using an RSA key
 299  *
 300  * \param pub: The public key.
 301  * \param inbuf The input buffer.
 302  * \param len The length of \a inbuf.
 303  * \param outbuf The output buffer.
 304  *
 305  * \return The size of the encrypted data on success, negative on errors.
 306  *
 307  * \sa RSA_public_encrypt(3)
 308  */
 309 int pub_encrypt(struct asymmetric_key *pub, unsigned char *inbuf,
 310                 unsigned len, unsigned char *outbuf)
 311 {
 312         int ret, flen = len; /* RSA_public_encrypt expects a signed int */
 313
 314         if (flen < 0)
 315                 return -E_ENCRYPT;
 316         ret = RSA_public_encrypt(flen, inbuf, outbuf, pub->rsa,
 317                 RSA_PKCS1_OAEP_PADDING);
 318         return ret < 0? -E_ENCRYPT : ret;
 319 }
 320
 321 struct stream_cipher {
 322         RC4_KEY key;
 323 };
 324
 325 /**
 326  * Allocate and initialize a stream cipher structure.
 327  *
 328  * \param data The key.
 329  * \param len The size of the key.
 330  *
 331  * \return A new stream cipher structure.
 332  */
 333 struct stream_cipher *sc_new(const unsigned char *data, int len)
 334 {
 335         struct stream_cipher *sc = para_malloc(sizeof(*sc));
 336         RC4_set_key(&sc->key, len, data);
 337         return sc;
 338 }
 339
 340 /**
 341  * Deallocate a stream cipher structure.
 342  *
 343  * \param sc A stream cipher previously obtained by sc_new().
 344  */
 345 void sc_free(struct stream_cipher *sc)
 346 {
 347         free(sc);
 348 }
 349
 350 /**
 351  * The RC4() implementation of openssl apparently reads and writes data in
 352  * blocks of 8 bytes. So we have to make sure our buffer sizes are a multiple
 353  * of this.
 354  */
 355 #define RC4_ALIGN 8
 356
 357 /**
 358  * Encrypt and send a buffer.
 359  *
 360  * \param scc The context.
 361  * \param buf The buffer to send.
 362  * \param len The size of \a buf in bytes.
 363  *
 364  * \return The return value of the underyling call to write_all().
 365  *
 366  * \sa \ref write_all(), RC4(3).
 367  */
 368 int sc_send_bin_buffer(struct stream_cipher_context *scc, char *buf,
 369                 size_t len)
 370 {
 371         int ret;
 372         unsigned char *tmp;
 373         static unsigned char remainder[RC4_ALIGN];
 374         size_t l1 = ROUND_DOWN(len, RC4_ALIGN), l2 = ROUND_UP(len, RC4_ALIGN);
 375
 376         assert(len);
 377         tmp = para_malloc(l2);
 378         RC4(&scc->send->key, l1, (const unsigned char *)buf, tmp);
 379         if (len > l1) {
 380                 memcpy(remainder, buf + l1, len - l1);
 381                 RC4(&scc->send->key, len - l1, remainder, tmp + l1);
 382         }
 383         ret = write_all(scc->fd, (char *)tmp, &len);
 384         free(tmp);
 385         return ret;
 386 }
 387
 388 /**
 389  * Receive a buffer and decrypt it.
 390  *
 391  * \param scc The context.
 392  * \param buf The buffer to write the decrypted data to.
 393  * \param size The size of \a buf.
 394  *
 395  * \return The number of bytes received on success, negative on errors, zero if
 396  * the peer has performed an orderly shutdown.
 397  *
 398  * \sa recv(2), RC4(3).
 399  */
 400 int sc_recv_bin_buffer(struct stream_cipher_context *scc, char *buf,
 401                 size_t size)
 402 {
 403         unsigned char *tmp = para_malloc(size);
 404         ssize_t ret = recv(scc->fd, tmp, size, 0);
 405
 406         if (ret > 0)
 407                 RC4(&scc->recv->key, ret, tmp, (unsigned char *)buf);
 408         else if (ret < 0)
 409                 ret = -ERRNO_TO_PARA_ERROR(errno);
 410         free(tmp);
 411         return ret;
 412 }
 413
 414 /**
 415  * Compute the hash of the given input data.
 416  *
 417  * \param data Pointer to the data to compute the hash value from.
 418  * \param len The length of \a data in bytes.
 419  * \param hash Result pointer.
 420  *
 421  * \a hash must point to an area at least \p HASH_SIZE bytes large.
 422  *
 423  * \sa sha(3), openssl(1).
 424  * */
 425 void hash_function(const char *data, unsigned long len, unsigned char *hash)
 426 {
 427         SHA_CTX c;
 428         SHA1_Init(&c);
 429         SHA1_Update(&c, data, len);
 430         SHA1_Final(hash, &c);
 431 }