gcrypt.c

   1 /*
   2  * Copyright (C) 2011-2013 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6
   7 /** \file gcrypt.c Libgrcypt-based encryption/decryption routines. */
   8
   9 #include <regex.h>
  10 #include <gcrypt.h>
  11
  12 #include "para.h"
  13 #include "error.h"
  14 #include "string.h"
  15 #include "crypt.h"
  16 #include "crypt_backend.h"
  17 #include "fd.h"
  18
  19 //#define GCRYPT_DEBUG 1
  20
  21 static bool libgcrypt_has_oaep;
  22 static const char *rsa_decrypt_sexp;
  23
  24 #ifdef GCRYPT_DEBUG
  25 static void dump_buffer(const char *msg, unsigned char *buf, int len)
  26 {
  27         int i;
  28
  29         fprintf(stderr, "%s (%u bytes): ", msg, len);
  30         for (i = 0; i < len; i++)
  31                 fprintf(stderr, "%02x ", buf[i]);
  32         fprintf(stderr, "\n");
  33 }
  34 #else
  35 /** Empty. Define GCRYPT_DEBUG to dump buffers. */
  36 #define dump_buffer(a, b, c)
  37 #endif
  38
  39 void hash_function(const char *data, unsigned long len, unsigned char *hash)
  40 {
  41         gcry_error_t gret;
  42         gcry_md_hd_t handle;
  43         unsigned char *md;
  44
  45         gret = gcry_md_open(&handle, GCRY_MD_SHA1, 0);
  46         assert(gret == 0);
  47         gcry_md_write(handle, data, (size_t)len);
  48         gcry_md_final(handle);
  49         md = gcry_md_read(handle, GCRY_MD_SHA1);
  50         assert(md);
  51         memcpy(hash, md, HASH_SIZE);
  52         gcry_md_close(handle);
  53 }
  54
  55 void get_random_bytes_or_die(unsigned char *buf, int num)
  56 {
  57         gcry_randomize(buf, (size_t)num, GCRY_STRONG_RANDOM);
  58 }
  59
  60 /*
  61  * This is called at the beginning of every program that uses libgcrypt. We
  62  * don't have to initialize any random seed here, but we must initialize the
  63  * gcrypt library. This task is performed by gcry_check_version() which can
  64  * also check that the gcrypt library version is at least the minimal required
  65  * version. This function also tells us whether we have to use our own OAEP
  66  * padding code.
  67  */
  68 void init_random_seed_or_die(void)
  69 {
  70         const char *ver, *req_ver;
  71
  72         ver = gcry_check_version(NULL);
  73         req_ver = "1.4.0";
  74         if (!gcry_check_version(req_ver)) {
  75                 PARA_EMERG_LOG("fatal: need at least libgcrypt-%s, have: %s\n",
  76                         req_ver, ver);
  77                 exit(EXIT_FAILURE);
  78         }
  79         req_ver = "1.5.0";
  80         if (gcry_check_version(req_ver)) {
  81                 libgcrypt_has_oaep = true;
  82                 rsa_decrypt_sexp = "(enc-val(flags oaep)(rsa(a %m)))";
  83         } else {
  84                 libgcrypt_has_oaep = false;
  85                 rsa_decrypt_sexp = "(enc-val(rsa(a %m)))";
  86         }
  87 }
  88
  89 /** S-expression for the public part of an RSA key. */
  90 #define RSA_PUBKEY_SEXP  "(public-key (rsa (n %m) (e %m)))"
  91 /** S-expression for a private RSA key. */
  92 #define RSA_PRIVKEY_SEXP "(private-key (rsa (n %m) (e %m) (d %m) (p %m) (q %m) (u %m)))"
  93
  94 /* rfc 3447, appendix B.2 */
  95 static void mgf1(unsigned char *seed, size_t seed_len, unsigned result_len,
  96                 unsigned char *result)
  97 {
  98         gcry_error_t gret;
  99         gcry_md_hd_t handle;
 100         size_t n;;
 101         unsigned char *md;
 102         unsigned char octet_string[4], *rp = result, *end = rp + result_len;
 103
 104         assert(result_len / HASH_SIZE < 1ULL << 31);
 105         gret = gcry_md_open(&handle, GCRY_MD_SHA1, 0);
 106         assert(gret == 0);
 107         for (n = 0; rp < end; n++) {
 108                 gcry_md_write(handle, seed, seed_len);
 109                 octet_string[0] = (unsigned char)((n >> 24) & 255);
 110                 octet_string[1] = (unsigned char)((n >> 16) & 255);
 111                 octet_string[2] = (unsigned char)((n >> 8)) & 255;
 112                 octet_string[3] = (unsigned char)(n & 255);
 113                 gcry_md_write(handle, octet_string, 4);
 114                 gcry_md_final(handle);
 115                 md = gcry_md_read(handle, GCRY_MD_SHA1);
 116                 memcpy(rp, md, PARA_MIN(HASH_SIZE, (int)(end - rp)));
 117                 rp += HASH_SIZE;
 118                 gcry_md_reset(handle);
 119         }
 120         gcry_md_close(handle);
 121 }
 122
 123 /** The sha1 hash of an empty file. */
 124 static const unsigned char empty_hash[HASH_SIZE] =
 125         "\xda" "\x39" "\xa3" "\xee" "\x5e"
 126         "\x6b" "\x4b" "\x0d" "\x32" "\x55"
 127         "\xbf" "\xef" "\x95" "\x60" "\x18"
 128         "\x90" "\xaf" "\xd8" "\x07" "\x09";
 129
 130 /* rfc3447, section 7.1.1 */
 131 static void pad_oaep(unsigned char *in, size_t in_len, unsigned char *out,
 132                 size_t out_len)
 133 {
 134         size_t ps_len = out_len - in_len - 2 * HASH_SIZE - 2;
 135         size_t n, mask_len = out_len - HASH_SIZE - 1;
 136         unsigned char *seed = out + 1, *db = seed + HASH_SIZE,
 137                 *ps = db + HASH_SIZE, *one = ps + ps_len;
 138         unsigned char *db_mask, seed_mask[HASH_SIZE];
 139
 140         assert(in_len <= out_len - 2 - 2 * HASH_SIZE);
 141         assert(out_len > 2 * HASH_SIZE + 2);
 142         PARA_DEBUG_LOG("padding %zu byte input -> %zu byte output\n",
 143                 in_len, out_len);
 144         dump_buffer("unpadded buffer", in, in_len);
 145
 146         out[0] = '\0';
 147         get_random_bytes_or_die(seed, HASH_SIZE);
 148         memcpy(db, empty_hash, HASH_SIZE);
 149         memset(ps, 0, ps_len);
 150         *one = 0x01;
 151         memcpy(one + 1, in, in_len);
 152         db_mask = para_malloc(mask_len);
 153         mgf1(seed, HASH_SIZE, mask_len, db_mask);
 154         for (n = 0; n < mask_len; n++)
 155                 db[n] ^= db_mask[n];
 156         mgf1(db, mask_len, HASH_SIZE, seed_mask);
 157         for (n = 0; n < HASH_SIZE; n++)
 158                 seed[n] ^= seed_mask[n];
 159         free(db_mask);
 160         dump_buffer("padded buffer", out, out_len);
 161 }
 162
 163 /* rfc 3447, section 7.1.2 */
 164 static int unpad_oaep(unsigned char *in, size_t in_len, unsigned char *out,
 165                 size_t *out_len)
 166 {
 167         unsigned char *masked_seed = in + 1;
 168         unsigned char *db = in + 1 + HASH_SIZE;
 169         unsigned char seed[HASH_SIZE], seed_mask[HASH_SIZE];
 170         unsigned char *db_mask, *p;
 171         size_t n, mask_len = in_len - HASH_SIZE - 1;
 172
 173         mgf1(db, mask_len, HASH_SIZE, seed_mask);
 174         for (n = 0; n < HASH_SIZE; n++)
 175                 seed[n] = masked_seed[n] ^ seed_mask[n];
 176         db_mask = para_malloc(mask_len);
 177         mgf1(seed, HASH_SIZE, mask_len, db_mask);
 178         for (n = 0; n < mask_len; n++)
 179                 db[n] ^= db_mask[n];
 180         free(db_mask);
 181         if (memcmp(db, empty_hash, HASH_SIZE))
 182                 return -E_OEAP;
 183         for (p = db + HASH_SIZE; p < in + in_len - 1; p++)
 184                 if (*p != '\0')
 185                         break;
 186         if (p >= in + in_len - 1)
 187                 return -E_OEAP;
 188         p++;
 189         *out_len = in + in_len - p;
 190         memcpy(out, p, *out_len);
 191         return 1;
 192 }
 193
 194 struct asymmetric_key {
 195         gcry_sexp_t sexp;
 196         int num_bytes;
 197 };
 198
 199 static const char *gcrypt_strerror(gcry_error_t gret)
 200 {
 201         return gcry_strerror(gcry_err_code(gret));
 202 }
 203
 204 static int decode_key(const char *key_file, const char *header_str,
 205                 const char *footer_str, unsigned char **result)
 206 {
 207         int ret, ret2, i, j;
 208         void *map;
 209         size_t map_size, key_size, blob_size;
 210         unsigned char *blob = NULL;
 211         char *begin, *footer, *key;
 212
 213         ret = mmap_full_file(key_file, O_RDONLY, &map, &map_size, NULL);
 214         if (ret < 0)
 215                 return ret;
 216         ret = -E_KEY_MARKER;
 217         if (strncmp(map, header_str, strlen(header_str)))
 218                 goto unmap;
 219         footer = strstr(map, footer_str);
 220         ret = -E_KEY_MARKER;
 221         if (!footer)
 222                 goto unmap;
 223         begin = map + strlen(header_str);
 224         /* skip whitespace at the beginning */
 225         for (; begin < footer; begin++) {
 226                 if (para_isspace(*begin))
 227                         continue;
 228                 break;
 229         }
 230         ret = -E_KEY_MARKER;
 231         if (begin >= footer)
 232                 goto unmap;
 233
 234         key_size = footer - begin;
 235         key = para_malloc(key_size + 1);
 236         for (i = 0, j = 0; begin + i < footer; i++) {
 237                 if (para_isspace(begin[i]))
 238                         continue;
 239                 key[j++] = begin[i];
 240         }
 241         key[j] = '\0';
 242         //PARA_CRIT_LOG("key: %s\n", key);
 243         blob_size = key_size * 2;
 244         blob = para_malloc(blob_size);
 245         ret = base64_decode(key, blob, blob_size);
 246         free(key);
 247         if (ret < 0)
 248                 goto free_unmap;
 249         goto unmap;
 250 free_unmap:
 251         free(blob);
 252         blob = NULL;
 253 unmap:
 254         ret2 = para_munmap(map, map_size);
 255         if (ret >= 0 && ret2 < 0)
 256                 ret = ret2;
 257         if (ret < 0) {
 258                 free(blob);
 259                 blob = NULL;
 260         }
 261         *result = blob;
 262         return ret;
 263 }
 264
 265 /** ASN Types and their code. */
 266 enum asn1_types {
 267         /** The next object is an integer. */
 268         ASN1_TYPE_INTEGER = 0x2,
 269         /** Bit string object. */
 270         ASN1_TYPE_BIT_STRING = 0x03,
 271         /** Keys start with one big type sequence. */
 272         ASN1_TYPE_SEQUENCE = 0x30,
 273 };
 274
 275 /* bit 6 has value 0 */
 276 static inline bool is_primitive(unsigned char c)
 277 {
 278         return ((c & (1<<6)) == 0);
 279 }
 280
 281 static inline bool is_primitive_integer(unsigned char c)
 282 {
 283         if (!is_primitive(c))
 284                 return false;
 285         return ((c & 0x1f) == ASN1_TYPE_INTEGER);
 286 }
 287
 288 /* Bit 8 is zero (and bits 7-1 give the length) */
 289 static inline bool is_short_form(unsigned char c)
 290 {
 291         return (c & 0x80) == 0;
 292 }
 293
 294 static inline int get_short_form_length(unsigned char c)
 295 {
 296         return c & 0x7f;
 297 }
 298
 299 static inline int get_long_form_num_length_bytes(unsigned char c)
 300 {
 301         return c & 0x7f;
 302 }
 303
 304 static int find_pubkey_bignum_offset(const unsigned char *data, int len)
 305 {
 306         const unsigned char *p = data, *end = data + len;
 307
 308         /* the whole thing istarts with one sequence */
 309         if (*p != ASN1_TYPE_SEQUENCE)
 310                 return -E_ASN1_PARSE;
 311         p++;
 312         if (p >= end)
 313                 return -E_ASN1_PARSE;
 314         if (is_short_form(*p))
 315                 p++;
 316         else
 317                 p += 1 + get_long_form_num_length_bytes(*p);
 318         if (p >= end)
 319                 return -E_ASN1_PARSE;
 320         /* another sequence containing the object id, skip it */
 321         if (*p != ASN1_TYPE_SEQUENCE)
 322                 return -E_ASN1_PARSE;
 323         p++;
 324         if (p >= end)
 325                 return -E_ASN1_PARSE;
 326         if (!is_short_form(*p))
 327                 return -E_ASN1_PARSE;
 328         p += 1 + get_short_form_length(*p);
 329         if (p >= end)
 330                 return -E_ASN1_PARSE;
 331         /* all numbers are wrapped in a bit string object that follows */
 332         if (*p != ASN1_TYPE_BIT_STRING)
 333                 return -E_ASN1_PARSE;
 334         p++;
 335         if (p >= end)
 336                 return -E_ASN1_PARSE;
 337         if (is_short_form(*p))
 338                 p++;
 339         else
 340                 p += 1 + get_long_form_num_length_bytes(*p);
 341         p++; /* skip number of unused bits in the bit string */
 342         if (p >= end)
 343                 return -E_ASN1_PARSE;
 344
 345         /* next, we have a sequence of two integers (n and e) */
 346         if (*p != ASN1_TYPE_SEQUENCE)
 347                 return -E_ASN1_PARSE;
 348         p++;
 349         if (p >= end)
 350                 return -E_ASN1_PARSE;
 351         if (is_short_form(*p))
 352                 p++;
 353         else
 354                 p += 1 + get_long_form_num_length_bytes(*p);
 355         if (p >= end)
 356                 return -E_ASN1_PARSE;
 357         if (*p != ASN1_TYPE_INTEGER)
 358                 return -E_ASN1_PARSE;
 359         return p - data;
 360 }
 361
 362 /*
 363  * Returns: Number of bytes scanned. This may differ from the value returned via
 364  * bn_bytes because the latter does not include the ASN.1 prefix and a leading
 365  * zero is not considered as an additional byte for bn_bytes.
 366  */
 367 static int read_bignum(unsigned char *start, unsigned char *end, gcry_mpi_t *bn,
 368                 int *bn_bytes)
 369 {
 370         int i, bn_size;
 371         gcry_error_t gret;
 372         unsigned char *cp = start;
 373
 374         if (!is_primitive_integer(*cp))
 375                 return -E_BAD_PRIVATE_KEY;
 376         cp++;
 377         if (is_short_form(*cp)) {
 378                 bn_size = get_short_form_length(*cp);
 379                 cp++;
 380         } else {
 381                 int num_bytes = get_long_form_num_length_bytes(*cp);
 382                 if (cp + num_bytes > end)
 383                         return -E_BAD_PRIVATE_KEY;
 384                 if (num_bytes > 4) /* nobody has such a large modulus */
 385                         return -E_BAD_PRIVATE_KEY;
 386                 cp++;
 387                 bn_size = 0;
 388                 for (i = 0; i < num_bytes; i++, cp++)
 389                         bn_size = (bn_size << 8) + *cp;
 390         }
 391         PARA_DEBUG_LOG("bn_size %d (0x%x)\n", bn_size, bn_size);
 392         gret = gcry_mpi_scan(bn, GCRYMPI_FMT_STD, cp, bn_size, NULL);
 393         if (gret) {
 394                 PARA_ERROR_LOG("%s while scanning n\n",
 395                         gcry_strerror(gcry_err_code(gret)));
 396                 return-E_MPI_SCAN;
 397         }
 398         /*
 399          * Don't take the first leading zero into account for the size of the
 400          * bignum.
 401          */
 402         if (*cp == '\0') {
 403                 cp++;
 404                 bn_size--;
 405         }
 406         if (bn_bytes)
 407                 *bn_bytes = bn_size;
 408         cp += bn_size;
 409 //      unsigned char *buf;
 410 //      gcry_mpi_aprint(GCRYMPI_FMT_HEX, &buf, NULL, *bn);
 411 //      PARA_CRIT_LOG("bn: %s\n", buf);
 412         return cp - start;
 413 }
 414
 415 static int find_privkey_bignum_offset(const unsigned char *data, int len)
 416 {
 417         const unsigned char *p = data, *end = data + len;
 418
 419         /* like the public key, the whole thing is contained in a sequence */
 420         if (*p != ASN1_TYPE_SEQUENCE)
 421                 return -E_ASN1_PARSE;
 422         p++;
 423         if (p >= end)
 424                 return -E_ASN1_PARSE;
 425         if (is_short_form(*p))
 426                 p++;
 427         else
 428                 p += 1 + get_long_form_num_length_bytes(*p);
 429         if (p >= end)
 430                 return -E_ASN1_PARSE;
 431
 432         /* Skip next integer  */
 433         if (*p != ASN1_TYPE_INTEGER)
 434                 return -E_ASN1_PARSE;
 435         p++;
 436         if (p >= end)
 437                 return -E_ASN1_PARSE;
 438         if (is_short_form(*p))
 439                 p += 1 + get_short_form_length(*p);
 440         else
 441                 p += 1 + get_long_form_num_length_bytes(*p);
 442         if (p >= end)
 443                 return -E_ASN1_PARSE;
 444         return p - data;
 445 }
 446
 447 /** Private keys start with this header. */
 448 #define PRIVATE_KEY_HEADER "-----BEGIN RSA PRIVATE KEY-----"
 449 /** Private keys end with this footer. */
 450 #define PRIVATE_KEY_FOOTER "-----END RSA PRIVATE KEY-----"
 451
 452 static int get_private_key(const char *key_file, struct asymmetric_key **result)
 453 {
 454         gcry_mpi_t n = NULL, e = NULL, d = NULL, p = NULL, q = NULL,
 455                 u = NULL;
 456         unsigned char *blob, *cp, *end;
 457         int blob_size, ret, n_size;
 458         gcry_error_t gret;
 459         size_t erroff;
 460         gcry_sexp_t sexp;
 461         struct asymmetric_key *key;
 462
 463         ret = decode_key(key_file, PRIVATE_KEY_HEADER, PRIVATE_KEY_FOOTER,
 464                 &blob);
 465         if (ret < 0)
 466                 return ret;
 467         blob_size = ret;
 468         end = blob + blob_size;
 469         ret = find_privkey_bignum_offset(blob, blob_size);
 470         if (ret < 0)
 471                 goto free_blob;
 472         PARA_INFO_LOG("reading RSA params at offset %d\n", ret);
 473         cp = blob + ret;
 474
 475         ret = read_bignum(cp, end, &n, &n_size);
 476         if (ret < 0)
 477                 goto free_blob;
 478         cp += ret;
 479
 480         ret = read_bignum(cp, end, &e, NULL);
 481         if (ret < 0)
 482                 goto release_n;
 483         cp += ret;
 484
 485         ret = read_bignum(cp, end, &d, NULL);
 486         if (ret < 0)
 487                 goto release_e;
 488         cp += ret;
 489
 490         ret = read_bignum(cp, end, &p, NULL);
 491         if (ret < 0)
 492                 goto release_d;
 493         cp += ret;
 494
 495         ret = read_bignum(cp, end, &q, NULL);
 496         if (ret < 0)
 497                 goto release_p;
 498         cp += ret;
 499         ret = read_bignum(cp, end, &u, NULL);
 500         if (ret < 0)
 501                 goto release_q;
 502         /*
 503          * OpenSSL uses slightly different parameters than gcrypt. To use these
 504          * parameters we need to swap the values of p and q and recompute u.
 505          */
 506         if (gcry_mpi_cmp(p, q) > 0) {
 507                 gcry_mpi_swap(p, q);
 508                 gcry_mpi_invm(u, p, q);
 509         }
 510         gret = gcry_sexp_build(&sexp, &erroff, RSA_PRIVKEY_SEXP,
 511                 n, e, d, p, q, u);
 512
 513         if (gret) {
 514                 PARA_ERROR_LOG("offset %zu: %s\n", erroff,
 515                         gcry_strerror(gcry_err_code(gret)));
 516                 ret = -E_SEXP_BUILD;
 517                 goto release_u;
 518         }
 519         key = para_malloc(sizeof(*key));
 520         key->sexp = sexp;
 521         *result = key;
 522         ret = n_size * 8;
 523         PARA_INFO_LOG("succesfully read %d bit private key\n", ret);
 524 release_u:
 525         gcry_mpi_release(u);
 526 release_q:
 527         gcry_mpi_release(q);
 528 release_p:
 529         gcry_mpi_release(p);
 530 release_d:
 531         gcry_mpi_release(d);
 532 release_e:
 533         gcry_mpi_release(e);
 534 release_n:
 535         gcry_mpi_release(n);
 536 free_blob:
 537         free(blob);
 538         return ret;
 539 }
 540
 541 /** Public keys start with this header. */
 542 #define PUBLIC_KEY_HEADER "-----BEGIN PUBLIC KEY-----"
 543 /** Public keys end with this footer. */
 544 #define PUBLIC_KEY_FOOTER "-----END PUBLIC KEY-----"
 545
 546 static int get_asn_public_key(const char *key_file, struct asymmetric_key **result)
 547 {
 548         gcry_mpi_t n = NULL, e = NULL;
 549         unsigned char *blob, *cp, *end;
 550         int blob_size, ret, n_size;
 551         gcry_error_t gret;
 552         size_t erroff;
 553         gcry_sexp_t sexp;
 554         struct asymmetric_key *key;
 555
 556         ret = decode_key(key_file, PUBLIC_KEY_HEADER, PUBLIC_KEY_FOOTER,
 557                 &blob);
 558         if (ret < 0)
 559                 return ret;
 560         blob_size = ret;
 561         end = blob + blob_size;
 562         ret = find_pubkey_bignum_offset(blob, blob_size);
 563         if (ret < 0)
 564                 goto free_blob;
 565         PARA_DEBUG_LOG("decoding public RSA params at offset %d\n", ret);
 566         cp = blob + ret;
 567
 568         ret = read_bignum(cp, end, &n, &n_size);
 569         if (ret < 0)
 570                 goto free_blob;
 571         cp += ret;
 572
 573         ret = read_bignum(cp, end, &e, NULL);
 574         if (ret < 0)
 575                 goto release_n;
 576
 577         gret = gcry_sexp_build(&sexp, &erroff, RSA_PUBKEY_SEXP, n, e);
 578         if (gret) {
 579                 PARA_ERROR_LOG("offset %zu: %s\n", erroff,
 580                         gcry_strerror(gcry_err_code(gret)));
 581                 ret = -E_SEXP_BUILD;
 582                 goto release_e;
 583         }
 584         key = para_malloc(sizeof(*key));
 585         key->sexp = sexp;
 586         *result = key;
 587         ret = n_size;
 588         PARA_INFO_LOG("successfully read %u bit asn public key\n", n_size * 8);
 589
 590 release_e:
 591         gcry_mpi_release(e);
 592 release_n:
 593         gcry_mpi_release(n);
 594 free_blob:
 595         free(blob);
 596         return ret;
 597 }
 598
 599 static int get_ssh_public_key(unsigned char *data, int size, gcry_sexp_t *result)
 600 {
 601         int ret;
 602         gcry_error_t gret;
 603         unsigned char *blob = NULL, *p, *end;
 604         size_t nr_scanned, erroff, decoded_size;
 605         gcry_mpi_t e = NULL, n = NULL;
 606
 607         PARA_DEBUG_LOG("decoding %d byte  public rsa-ssh key\n", size);
 608         if (size > INT_MAX / 4)
 609                 return -ERRNO_TO_PARA_ERROR(EOVERFLOW);
 610         blob = para_malloc(2 * size);
 611         ret = uudecode((char *)data, blob, 2 * size);
 612         if (ret < 0)
 613                 goto free_blob;
 614         decoded_size = ret;
 615         end = blob + decoded_size;
 616         dump_buffer("decoded key", blob, decoded_size);
 617         ret = check_ssh_key_header(blob, decoded_size);
 618         if (ret < 0)
 619                 goto free_blob;
 620         p = blob + ret;
 621         ret = -E_SSH_PARSE;
 622         if (p >= end)
 623                 goto free_blob;
 624         PARA_DEBUG_LOG("scanning modulus and public exponent\n");
 625         gret = gcry_mpi_scan(&e, GCRYMPI_FMT_SSH, p, end - p, &nr_scanned);
 626         if (gret) {
 627                 ret = -E_MPI_SCAN;
 628                 PARA_CRIT_LOG("%s\n", gcry_strerror(gcry_err_code(gret)));
 629                 goto free_blob;
 630         }
 631         PARA_DEBUG_LOG("scanned e (%zu bytes)\n", nr_scanned);
 632 //      gcry_mpi_aprint(GCRYMPI_FMT_HEX, &buf, NULL, rsa_e);
 633 //      PARA_CRIT_LOG("e: %s\n", buf);
 634         p += nr_scanned;
 635         if (p >= end)
 636                 goto release_e;
 637         gret = gcry_mpi_scan(&n, GCRYMPI_FMT_SSH, p, end - p, &nr_scanned);
 638         if (gret) {
 639                 ret = -E_MPI_SCAN;
 640                 PARA_ERROR_LOG("%s\n", gcry_strerror(gcry_err_code(gret)));
 641                 goto release_e;
 642         }
 643         PARA_DEBUG_LOG("scanned n (%zu bytes)\n", nr_scanned);
 644 //      gcry_mpi_aprint(GCRYMPI_FMT_HEX, &buf, NULL, rsa_n);
 645 //      PARA_CRIT_LOG("n: %s\n", buf);
 646         gret = gcry_sexp_build(result, &erroff, RSA_PUBKEY_SEXP, n, e);
 647         if (gret) {
 648                 PARA_ERROR_LOG("offset %zu: %s\n", erroff,
 649                         gcry_strerror(gcry_err_code(gret)));
 650                 ret = -E_SEXP_BUILD;
 651                 goto release_n;
 652         }
 653         ret = nr_scanned / 32 * 32;
 654         PARA_INFO_LOG("successfully read %u bit ssh public key\n", ret * 8);
 655 release_n:
 656         gcry_mpi_release(n);
 657 release_e:
 658         gcry_mpi_release(e);
 659 free_blob:
 660         free(blob);
 661         return ret;
 662 }
 663
 664 int get_asymmetric_key(const char *key_file, int private,
 665                 struct asymmetric_key **result)
 666 {
 667         int ret, ret2;
 668         void *map;
 669         size_t map_size;
 670         unsigned char *start, *end;
 671         gcry_sexp_t sexp;
 672         struct asymmetric_key *key;
 673
 674         if (private)
 675                 return get_private_key(key_file, result);
 676         ret = mmap_full_file(key_file, O_RDONLY, &map, &map_size, NULL);
 677         if (ret < 0)
 678                 return ret;
 679         ret = is_ssh_rsa_key(map, map_size);
 680         if (!ret) {
 681                 ret = para_munmap(map, map_size);
 682                 if (ret < 0)
 683                         return ret;
 684                 return get_asn_public_key(key_file, result);
 685         }
 686         start = map + ret;
 687         end = map + map_size;
 688         ret = -E_SSH_PARSE;
 689         if (start >= end)
 690                 goto unmap;
 691         ret = get_ssh_public_key(start, end - start, &sexp);
 692         if (ret < 0)
 693                 goto unmap;
 694         key = para_malloc(sizeof(*key));
 695         key->num_bytes = ret;
 696         key->sexp = sexp;
 697         *result = key;
 698 unmap:
 699         ret2 = para_munmap(map, map_size);
 700         if (ret >= 0 && ret2 < 0)
 701                 ret = ret2;
 702         return ret;
 703 }
 704
 705 void free_asymmetric_key(struct asymmetric_key *key)
 706 {
 707         if (!key)
 708                 return;
 709         gcry_sexp_release(key->sexp);
 710         free(key);
 711 }
 712
 713 static int decode_rsa(gcry_sexp_t sexp, int key_size, unsigned char *outbuf,
 714                 size_t *nbytes)
 715 {
 716         int ret;
 717         gcry_error_t gret;
 718         unsigned char oaep_buf[512];
 719         gcry_mpi_t out_mpi;
 720
 721         if (libgcrypt_has_oaep) {
 722                 const char *p = gcry_sexp_nth_data(sexp, 1, nbytes);
 723
 724                 if (!p) {
 725                         PARA_ERROR_LOG("could not get data from list\n");
 726                         return -E_OEAP;
 727                 }
 728                 memcpy(outbuf, p, *nbytes);
 729                 return 1;
 730         }
 731         out_mpi = gcry_sexp_nth_mpi(sexp, 0, GCRYMPI_FMT_USG);
 732         if (!out_mpi)
 733                 return -E_SEXP_FIND;
 734         gret = gcry_mpi_print(GCRYMPI_FMT_USG, oaep_buf, sizeof(oaep_buf),
 735                 nbytes, out_mpi);
 736         if (gret) {
 737                 PARA_ERROR_LOG("mpi_print: %s\n", gcrypt_strerror(gret));
 738                 ret = -E_MPI_PRINT;
 739                 goto out_mpi_release;
 740         }
 741         /*
 742          * An oaep-encoded buffer always starts with at least one zero byte.
 743          * However, leading zeroes in an mpi are omitted in the output of
 744          * gcry_mpi_print() when using the GCRYMPI_FMT_USG format. The
 745          * alternative, GCRYMPI_FMT_STD, does not work either because here the
 746          * leading zero(es) might also be omitted, depending on the value of
 747          * the second byte.
 748          *
 749          * To circumvent this, we shift the oaep buffer to the right. But first
 750          * we check that the buffer actually started with a zero byte, i.e. that
 751          * nbytes < key_size. Otherwise a decoding error occurred.
 752          */
 753         ret = -E_SEXP_DECRYPT;
 754         if (*nbytes >= key_size)
 755                 goto out_mpi_release;
 756         memmove(oaep_buf + key_size - *nbytes, oaep_buf, *nbytes);
 757         memset(oaep_buf, 0, key_size - *nbytes);
 758
 759         PARA_DEBUG_LOG("decrypted buffer before unpad (%d bytes):\n",
 760                 key_size);
 761         dump_buffer("non-unpadded decrypted buffer", oaep_buf, key_size);
 762         ret = unpad_oaep(oaep_buf, key_size, outbuf, nbytes);
 763         if (ret < 0)
 764                 goto out_mpi_release;
 765         PARA_DEBUG_LOG("decrypted buffer after unpad (%zu bytes):\n",
 766                 *nbytes);
 767         dump_buffer("unpadded decrypted buffer", outbuf, *nbytes);
 768         ret = 1;
 769 out_mpi_release:
 770         gcry_mpi_release(out_mpi);
 771         return ret;
 772 }
 773
 774 int priv_decrypt(const char *key_file, unsigned char *outbuf,
 775                 unsigned char *inbuf, int inlen)
 776 {
 777         gcry_error_t gret;
 778         int ret, key_size;
 779         struct asymmetric_key *priv;
 780         gcry_mpi_t in_mpi = NULL;
 781         gcry_sexp_t in, out, priv_key;
 782         size_t nbytes;
 783
 784         PARA_INFO_LOG("decrypting %d byte input\n", inlen);
 785         /* key_file -> asymmetric key priv */
 786         ret = get_private_key(key_file, &priv);
 787         if (ret < 0)
 788                 return ret;
 789         key_size = ret / 8;
 790
 791         /* asymmetric key priv -> sexp priv_key */
 792         ret = -E_SEXP_FIND;
 793         priv_key = gcry_sexp_find_token(priv->sexp, "private-key", 0);
 794         if (!priv_key)
 795                 goto free_key;
 796
 797         /* inbuf -> in_mpi */
 798         gret = gcry_mpi_scan(&in_mpi, GCRYMPI_FMT_USG, inbuf,
 799                 inlen, NULL);
 800         if (gret) {
 801                 PARA_ERROR_LOG("%s\n", gcrypt_strerror(gret));
 802                 ret = -E_MPI_SCAN;
 803                 goto key_release;
 804         }
 805         /* in_mpi -> in sexp */
 806         gret = gcry_sexp_build(&in, NULL, rsa_decrypt_sexp, in_mpi);
 807         if (gret) {
 808                 PARA_ERROR_LOG("%s\n", gcrypt_strerror(gret));
 809                 ret = -E_SEXP_BUILD;
 810                 goto in_mpi_release;
 811         }
 812
 813         /* rsa decryption: in sexp -> out sexp */
 814         gret = gcry_pk_decrypt(&out, in, priv_key);
 815         if (gret) {
 816                 PARA_ERROR_LOG("decrypt: %s\n", gcrypt_strerror(gret));
 817                 ret = -E_SEXP_DECRYPT;
 818                 goto in_release;
 819         }
 820         ret = decode_rsa(out, key_size, outbuf, &nbytes);
 821         if (ret < 0)
 822                 goto out_release;
 823         PARA_INFO_LOG("successfully decrypted %zu byte message\n", nbytes);
 824         ret = nbytes;
 825 out_release:
 826         gcry_sexp_release(out);
 827 in_release:
 828         gcry_sexp_release(in);
 829 in_mpi_release:
 830         gcry_mpi_release(in_mpi);
 831 key_release:
 832         gcry_sexp_release(priv_key);
 833 free_key:
 834         free_asymmetric_key(priv);
 835         return ret;
 836 }
 837
 838 int pub_encrypt(struct asymmetric_key *pub, unsigned char *inbuf,
 839                 unsigned len, unsigned char *outbuf)
 840 {
 841         gcry_error_t gret;
 842         gcry_sexp_t pub_key, in, out, out_a;
 843         gcry_mpi_t out_mpi = NULL;
 844         size_t nbytes;
 845         int ret;
 846
 847         PARA_INFO_LOG("encrypting %u byte input with %d-byte key\n", len, pub->num_bytes);
 848
 849         /* get pub key */
 850         pub_key = gcry_sexp_find_token(pub->sexp, "public-key", 0);
 851         if (!pub_key)
 852                 return -E_SEXP_FIND;
 853         if (libgcrypt_has_oaep) {
 854                 gret = gcry_sexp_build(&in, NULL,
 855                         "(data(flags oaep)(value %b))", len, inbuf);
 856         } else {
 857                 unsigned char padded_input[256];
 858                 const size_t pad_size = 256;
 859                 /* inbuf -> padded inbuf */
 860                 pad_oaep(inbuf, len, padded_input, pad_size);
 861                 /* padded inbuf -> in sexp */
 862                 gret = gcry_sexp_build(&in, NULL,
 863                         "(data(flags raw)(value %b))", pad_size, padded_input);
 864         }
 865         if (gret) {
 866                 PARA_ERROR_LOG("%s\n", gcrypt_strerror(gret));
 867                 ret = -E_SEXP_BUILD;
 868                 goto key_release;
 869         }
 870         /* rsa sexp encryption: in -> out */
 871         gret = gcry_pk_encrypt(&out, in, pub_key);
 872         if (gret) {
 873                 PARA_ERROR_LOG("%s\n", gcrypt_strerror(gret));
 874                 ret = -E_SEXP_ENCRYPT;
 875                 goto in_release;
 876         }
 877         /* extract a, an MPI with the result of the RSA operation */
 878         ret = -E_SEXP_FIND;
 879         out_a = gcry_sexp_find_token(out, "a", 0);
 880         if (!out_a)
 881                 goto out_release;
 882         /* convert sexp out_a -> out_mpi */
 883         out_mpi = gcry_sexp_nth_mpi(out_a, 1, GCRYMPI_FMT_USG);
 884         if (!out_mpi) {
 885                 ret = -E_SEXP_FIND;
 886                 goto out_a_release;
 887         }
 888         gret = gcry_mpi_print(GCRYMPI_FMT_USG, outbuf, 512 /* FIXME */, &nbytes, out_mpi);
 889         if (gret) {
 890                 PARA_ERROR_LOG("%s\n", gcrypt_strerror(gret));
 891                 ret = -E_SEXP_ENCRYPT;
 892                 goto out_mpi_release;
 893         }
 894         PARA_INFO_LOG("encrypted buffer is %zu bytes\n", nbytes);
 895         dump_buffer("enc buf", outbuf, nbytes);
 896         ret = nbytes;
 897
 898 out_mpi_release:
 899         gcry_mpi_release(out_mpi);
 900 out_a_release:
 901         gcry_sexp_release(out_a);
 902 out_release:
 903         gcry_sexp_release(out);
 904 in_release:
 905         gcry_sexp_release(in);
 906 key_release:
 907         gcry_sexp_release(pub_key);
 908         return ret;
 909 }
 910
 911 struct stream_cipher {
 912         gcry_cipher_hd_t handle;
 913 };
 914
 915 struct stream_cipher *sc_new(const unsigned char *data, int len)
 916 {
 917         gcry_error_t gret;
 918
 919         struct stream_cipher *sc = para_malloc(sizeof(*sc));
 920         gret = gcry_cipher_open(&sc->handle, GCRY_CIPHER_ARCFOUR,
 921                 GCRY_CIPHER_MODE_STREAM, 0);
 922         if (gret) {
 923                 PARA_ERROR_LOG("%s\n", gcrypt_strerror(gret));
 924                 free(sc);
 925                 return NULL;
 926         }
 927         gret = gcry_cipher_setkey(sc->handle, data, (size_t)len);
 928         assert(gret == 0);
 929         return sc;
 930 }
 931
 932 void sc_free(struct stream_cipher *sc)
 933 {
 934         if (!sc)
 935                 return;
 936         gcry_cipher_close(sc->handle);
 937         free(sc);
 938 }
 939
 940 void sc_crypt(struct stream_cipher *sc, struct iovec *src, struct iovec *dst)
 941 {
 942         gcry_cipher_hd_t handle = sc->handle;
 943         gcry_error_t gret;
 944
 945         /* perform in-place encryption */
 946         *dst = *src;
 947         gret = gcry_cipher_encrypt(handle, src->iov_base, src->iov_len,
 948                 NULL, 0);
 949         assert(gret == 0);
 950 }