src/src/pdkim/signing.c

   1 /*
   2  *  PDKIM - a RFC4871 (DKIM) implementation
   3  *
   4  *  Copyright (C) 1995 - 2018  Exim maintainers
   5  *
   6  *  signing/verification interface
   7  */
   8
   9 #include "../exim.h"
  10 #include "crypt_ver.h"
  11 #include "signing.h"
  12
  13
  14 #ifdef MACRO_PREDEF
  15 # include "../macro_predef.h"
  16
  17 void
  18 features_crypto(void)
  19 {
  20 # ifdef SIGN_HAVE_ED25519
  21   builtin_macro_create(US"_CRYPTO_SIGN_ED25519");
  22 # endif
  23 # ifdef EXIM_HAVE_SHA3
  24   builtin_macro_create(US"_CRYPTO_HASH_SHA3");
  25 # endif
  26 }
  27 #else
  28
  29 #ifndef DISABLE_DKIM    /* rest of file */
  30
  31 #ifdef DISABLE_TLS
  32 # error Must no DISABLE_TLS, for DKIM
  33 #endif
  34
  35
  36 /******************************************************************************/
  37 #ifdef SIGN_GNUTLS
  38 # define EXIM_GNUTLS_LIBRARY_LOG_LEVEL 3
  39
  40
  41 /* Logging function which can be registered with
  42  *   gnutls_global_set_log_function()
  43  *   gnutls_global_set_log_level() 0..9
  44  */
  45 #if EXIM_GNUTLS_LIBRARY_LOG_LEVEL >= 0
  46 static void
  47 exim_gnutls_logger_cb(int level, const char *message)
  48 {
  49 size_t len = strlen(message);
  50 if (len < 1)
  51   {
  52   DEBUG(D_tls) debug_printf("GnuTLS<%d> empty debug message\n", level);
  53   return;
  54   }
  55 DEBUG(D_tls) debug_printf("GnuTLS<%d>: %s%s", level, message,
  56     message[len-1] == '\n' ? "" : "\n");
  57 }
  58 #endif
  59
  60
  61
  62 void
  63 exim_dkim_init(void)
  64 {
  65 #if EXIM_GNUTLS_LIBRARY_LOG_LEVEL >= 0
  66 DEBUG(D_tls)
  67   {
  68   gnutls_global_set_log_function(exim_gnutls_logger_cb);
  69   /* arbitrarily chosen level; bump upto 9 for more */
  70   gnutls_global_set_log_level(EXIM_GNUTLS_LIBRARY_LOG_LEVEL);
  71   }
  72 #endif
  73 }
  74
  75
  76 /* accumulate data (gnutls-only).  String to be appended must be nul-terminated. */
  77 gstring *
  78 exim_dkim_data_append(gstring * g, uschar * s)
  79 {
  80 return string_cat(g, s);
  81 }
  82
  83
  84
  85 /* import private key from PEM string in memory.
  86 Return: NULL for success, or an error string */
  87
  88 const uschar *
  89 exim_dkim_signing_init(const uschar * privkey_pem, es_ctx * sign_ctx)
  90 {
  91 gnutls_datum_t k = { .data = (void *)privkey_pem, .size = Ustrlen(privkey_pem) };
  92 gnutls_x509_privkey_t x509_key;
  93 const uschar * where;
  94 int rc;
  95
  96 if (  (where = US"internal init", rc = gnutls_x509_privkey_init(&x509_key))
  97    || (rc = gnutls_privkey_init(&sign_ctx->key))
  98    || (where = US"privkey PEM-block import",
  99        rc = gnutls_x509_privkey_import(x509_key, &k, GNUTLS_X509_FMT_PEM))
 100    || (where = US"internal privkey transfer",
 101        rc = gnutls_privkey_import_x509(sign_ctx->key, x509_key, 0))
 102    )
 103   return string_sprintf("%s: %s", where, gnutls_strerror(rc));
 104
 105 switch (rc = gnutls_privkey_get_pk_algorithm(sign_ctx->key, NULL))
 106   {
 107   case GNUTLS_PK_RSA:           sign_ctx->keytype = KEYTYPE_RSA;     break;
 108 #ifdef SIGN_HAVE_ED25519
 109   case GNUTLS_PK_EDDSA_ED25519: sign_ctx->keytype = KEYTYPE_ED25519; break;
 110 #endif
 111   default: return rc < 0
 112     ? CUS gnutls_strerror(rc)
 113     : string_sprintf("Unhandled key type: %d '%s'", rc, gnutls_pk_get_name(rc));
 114   }
 115
 116 return NULL;
 117 }
 118
 119
 120
 121 /* allocate mem for signature (when signing) */
 122 /* hash & sign data.   No way to do incremental.
 123
 124 Return: NULL for success, or an error string */
 125
 126 const uschar *
 127 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
 128 {
 129 gnutls_datum_t k_data = { .data = data->data, .size = data->len };
 130 gnutls_digest_algorithm_t dig;
 131 gnutls_datum_t k_sig;
 132 int rc;
 133
 134 switch (hash)
 135   {
 136   case HASH_SHA1:       dig = GNUTLS_DIG_SHA1; break;
 137   case HASH_SHA2_256:   dig = GNUTLS_DIG_SHA256; break;
 138   case HASH_SHA2_512:   dig = GNUTLS_DIG_SHA512; break;
 139   default:              return US"nonhandled hash type";
 140   }
 141
 142 if ((rc = gnutls_privkey_sign_data(sign_ctx->key, dig, 0, &k_data, &k_sig)))
 143   return CUS gnutls_strerror(rc);
 144
 145 /* Don't care about deinit for the key; shortlived process */
 146
 147 sig->data = k_sig.data;
 148 sig->len = k_sig.size;
 149 return NULL;
 150 }
 151
 152
 153
 154 /* import public key (from blob in memory)
 155 Return: NULL for success, or an error string */
 156
 157 const uschar *
 158 exim_dkim_verify_init(blob * pubkey, keyformat fmt, ev_ctx * verify_ctx)
 159 {
 160 gnutls_datum_t k;
 161 int rc;
 162 const uschar * ret = NULL;
 163
 164 gnutls_pubkey_init(&verify_ctx->key);
 165 k.data = pubkey->data;
 166 k.size = pubkey->len;
 167
 168 switch(fmt)
 169   {
 170   case KEYFMT_DER:
 171     if ((rc = gnutls_pubkey_import(verify_ctx->key, &k, GNUTLS_X509_FMT_DER)))
 172       ret = US gnutls_strerror(rc);
 173     break;
 174 #ifdef SIGN_HAVE_ED25519
 175   case KEYFMT_ED25519_BARE:
 176     if ((rc = gnutls_pubkey_import_ecc_raw(verify_ctx->key,
 177                                           GNUTLS_ECC_CURVE_ED25519, &k, NULL)))
 178       ret = US gnutls_strerror(rc);
 179     break;
 180 #endif
 181   default:
 182     ret = US"pubkey format not handled";
 183     break;
 184   }
 185 return ret;
 186 }
 187
 188
 189 /* verify signature (of hash if RSA sig, of data if EC sig.  No way to do incremental)
 190 (given pubkey & alleged sig)
 191 Return: NULL for success, or an error string */
 192
 193 const uschar *
 194 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data_hash, blob * sig)
 195 {
 196 gnutls_datum_t k = { .data = data_hash->data, .size = data_hash->len };
 197 gnutls_datum_t s = { .data = sig->data,       .size = sig->len };
 198 int rc;
 199 const uschar * ret = NULL;
 200
 201 #ifdef SIGN_HAVE_ED25519
 202 if (verify_ctx->keytype == KEYTYPE_ED25519)
 203   {
 204   if ((rc = gnutls_pubkey_verify_data2(verify_ctx->key,
 205                                       GNUTLS_SIGN_EDDSA_ED25519, 0, &k, &s)) < 0)
 206     ret = US gnutls_strerror(rc);
 207   }
 208 else
 209 #endif
 210   {
 211   gnutls_sign_algorithm_t algo;
 212   switch (hash)
 213     {
 214     case HASH_SHA1:     algo = GNUTLS_SIGN_RSA_SHA1;   break;
 215     case HASH_SHA2_256: algo = GNUTLS_SIGN_RSA_SHA256; break;
 216     case HASH_SHA2_512: algo = GNUTLS_SIGN_RSA_SHA512; break;
 217     default:            return US"nonhandled hash type";
 218     }
 219
 220   if ((rc = gnutls_pubkey_verify_hash2(verify_ctx->key, algo, 0, &k, &s)) < 0)
 221     ret = US gnutls_strerror(rc);
 222   }
 223
 224 gnutls_pubkey_deinit(verify_ctx->key);
 225 return ret;
 226 }
 227
 228
 229
 230
 231 #elif defined(SIGN_GCRYPT)
 232 /******************************************************************************/
 233 /* This variant is used under pre-3.0.0 GnuTLS.  Only rsa-sha1 and rsa-sha256 */
 234
 235
 236 /* Internal service routine:
 237 Read and move past an asn.1 header, checking class & tag,
 238 optionally returning the data-length */
 239
 240 static int
 241 as_tag(blob * der, uschar req_cls, long req_tag, long * alen)
 242 {
 243 int rc;
 244 uschar tag_class;
 245 int taglen;
 246 long tag, len;
 247
 248 debug_printf_indent("as_tag: %02x %02x %02x %02x\n",
 249         der->data[0], der->data[1], der->data[2], der->data[3]);
 250
 251 if ((rc = asn1_get_tag_der(der->data++, der->len--, &tag_class, &taglen, &tag))
 252     != ASN1_SUCCESS)
 253   return rc;
 254
 255 if (tag_class != req_cls || tag != req_tag) return ASN1_ELEMENT_NOT_FOUND;
 256
 257 if ((len = asn1_get_length_der(der->data, der->len, &taglen)) < 0)
 258   return ASN1_DER_ERROR;
 259 if (alen) *alen = len;
 260
 261 /* debug_printf_indent("as_tag:  tlen %d dlen %d\n", taglen, (int)len); */
 262
 263 der->data += taglen;
 264 der->len -= taglen;
 265 return rc;
 266 }
 267
 268 /* Internal service routine:
 269 Read and move over an asn.1 integer, setting an MPI to the value
 270 */
 271
 272 static uschar *
 273 as_mpi(blob * der, gcry_mpi_t * mpi)
 274 {
 275 long alen;
 276 int rc;
 277 gcry_error_t gerr;
 278
 279 debug_printf_indent("%s\n", __FUNCTION__);
 280
 281 /* integer; move past the header */
 282 if ((rc = as_tag(der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS)
 283   return US asn1_strerror(rc);
 284
 285 /* read to an MPI */
 286 if ((gerr = gcry_mpi_scan(mpi, GCRYMPI_FMT_STD, der->data, alen, NULL)))
 287   return US gcry_strerror(gerr);
 288
 289 /* move over the data */
 290 der->data += alen; der->len -= alen;
 291 return NULL;
 292 }
 293
 294
 295
 296 void
 297 exim_dkim_init(void)
 298 {
 299 /* Version check should be the very first call because it
 300 makes sure that important subsystems are initialized. */
 301 if (!gcry_check_version (GCRYPT_VERSION))
 302   {
 303   fputs ("libgcrypt version mismatch\n", stderr);
 304   exit (2);
 305   }
 306
 307 /* We don't want to see any warnings, e.g. because we have not yet
 308 parsed program options which might be used to suppress such
 309 warnings. */
 310 gcry_control (GCRYCTL_SUSPEND_SECMEM_WARN);
 311
 312 /* ... If required, other initialization goes here.  Note that the
 313 process might still be running with increased privileges and that
 314 the secure memory has not been initialized.  */
 315
 316 /* Allocate a pool of 16k secure memory.  This make the secure memory
 317 available and also drops privileges where needed.  */
 318 gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);
 319
 320 /* It is now okay to let Libgcrypt complain when there was/is
 321 a problem with the secure memory. */
 322 gcry_control (GCRYCTL_RESUME_SECMEM_WARN);
 323
 324 /* ... If required, other initialization goes here.  */
 325
 326 /* Tell Libgcrypt that initialization has completed. */
 327 gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
 328
 329 return;
 330 }
 331
 332
 333
 334
 335 /* Accumulate data (gnutls-only).
 336 String to be appended must be nul-terminated. */
 337
 338 gstring *
 339 exim_dkim_data_append(gstring * g, uschar * s)
 340 {
 341 return g;       /*dummy*/
 342 }
 343
 344
 345
 346 /* import private key from PEM string in memory.
 347 Only handles RSA keys.
 348 Return: NULL for success, or an error string */
 349
 350 const uschar *
 351 exim_dkim_signing_init(const uschar * privkey_pem, es_ctx * sign_ctx)
 352 {
 353 uschar * s1, * s2;
 354 blob der;
 355 long alen;
 356 int rc;
 357
 358 /*XXX will need extension to _spot_ as well as handle a
 359 non-RSA key?  I think...
 360 So... this is not a PrivateKeyInfo - which would have a field
 361 identifying the keytype - PrivateKeyAlgorithmIdentifier -
 362 but a plain RSAPrivateKey (wrapped in PEM-headers.  Can we
 363 use those as a type tag?  What forms are there?  "BEGIN EC PRIVATE KEY" (cf. ec(1ssl))
 364
 365 How does OpenSSL PEM_read_bio_PrivateKey() deal with it?
 366 gnutls_x509_privkey_import() ?
 367 */
 368
 369 /*
 370  *  RSAPrivateKey ::= SEQUENCE
 371  *      version           Version,
 372  *      modulus           INTEGER,  -- n
 373  *      publicExponent    INTEGER,  -- e
 374  *      privateExponent   INTEGER,  -- d
 375  *      prime1            INTEGER,  -- p
 376  *      prime2            INTEGER,  -- q
 377  *      exponent1         INTEGER,  -- d mod (p-1)
 378  *      exponent2         INTEGER,  -- d mod (q-1)
 379  *      coefficient       INTEGER,  -- (inverse of q) mod p
 380  *      otherPrimeInfos   OtherPrimeInfos OPTIONAL
 381
 382  * ECPrivateKey ::= SEQUENCE {
 383  *     version        INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
 384  *     privateKey     OCTET STRING,
 385  *     parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
 386  *     publicKey  [1] BIT STRING OPTIONAL
 387  *   }
 388  * Hmm, only 1 useful item, and not even an integer?  Wonder how we might use it...
 389
 390 - actually, gnutls_x509_privkey_import() appears to require a curve name parameter
 391         value for that is an OID? a local-only integer (it's an enum in GnuTLS)?
 392
 393
 394 Useful cmds:
 395   ssh-keygen -t ecdsa -f foo.privkey
 396   ssh-keygen -t ecdsa -b384 -f foo.privkey
 397   ssh-keygen -t ecdsa -b521 -f foo.privkey
 398   ssh-keygen -t ed25519 -f foo.privkey
 399
 400   < foo openssl pkcs8 -in /dev/stdin -inform PEM -nocrypt -topk8 -outform DER | od -x
 401
 402   openssl asn1parse -in foo -inform PEM -dump
 403   openssl asn1parse -in foo -inform PEM -dump -stroffset 24    (??)
 404 (not good for ed25519)
 405
 406  */
 407
 408 if (  !(s1 = Ustrstr(CS privkey_pem, "-----BEGIN RSA PRIVATE KEY-----"))
 409    || !(s2 = Ustrstr(CS (s1+=31),    "-----END RSA PRIVATE KEY-----" ))
 410    )
 411   return US"Bad PEM wrapper";
 412
 413 *s2 = '\0';
 414
 415 if ((rc = b64decode(s1, &der.data) < 0))
 416   return US"Bad PEM-DER b64 decode";
 417 der.len = rc;
 418
 419 /* untangle asn.1 */
 420
 421 /* sequence; just move past the header */
 422 if ((rc = as_tag(&der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
 423    != ASN1_SUCCESS) goto asn_err;
 424
 425 /* integer version; move past the header, check is zero */
 426 if ((rc = as_tag(&der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS)
 427   goto asn_err;
 428 if (alen != 1 || *der.data != 0)
 429   return US"Bad version number";
 430 der.data++; der.len--;
 431
 432 if (  (s1 = as_mpi(&der, &sign_ctx->n))
 433    || (s1 = as_mpi(&der, &sign_ctx->e))
 434    || (s1 = as_mpi(&der, &sign_ctx->d))
 435    || (s1 = as_mpi(&der, &sign_ctx->p))
 436    || (s1 = as_mpi(&der, &sign_ctx->q))
 437    || (s1 = as_mpi(&der, &sign_ctx->dp))
 438    || (s1 = as_mpi(&der, &sign_ctx->dq))
 439    || (s1 = as_mpi(&der, &sign_ctx->qp))
 440    )
 441   return s1;
 442
 443 #ifdef extreme_debug
 444 DEBUG(D_acl) debug_printf_indent("rsa_signing_init:\n");
 445   {
 446   uschar * s;
 447   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->n);
 448   debug_printf_indent(" N : %s\n", s);
 449   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->e);
 450   debug_printf_indent(" E : %s\n", s);
 451   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->d);
 452   debug_printf_indent(" D : %s\n", s);
 453   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->p);
 454   debug_printf_indent(" P : %s\n", s);
 455   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->q);
 456   debug_printf_indent(" Q : %s\n", s);
 457   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dp);
 458   debug_printf_indent(" DP: %s\n", s);
 459   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dq);
 460   debug_printf_indent(" DQ: %s\n", s);
 461   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->qp);
 462   debug_printf_indent(" QP: %s\n", s);
 463   }
 464 #endif
 465
 466 sign_ctx->keytype = KEYTYPE_RSA;
 467 return NULL;
 468
 469 asn_err: return US asn1_strerror(rc);
 470 }
 471
 472
 473
 474 /* allocate mem for signature (when signing) */
 475 /* sign already-hashed data.
 476
 477 Return: NULL for success, or an error string */
 478
 479 const uschar *
 480 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
 481 {
 482 char * sexp_hash;
 483 gcry_sexp_t s_hash = NULL, s_key = NULL, s_sig = NULL;
 484 gcry_mpi_t m_sig;
 485 uschar * errstr;
 486 gcry_error_t gerr;
 487
 488 /*XXX will need extension for hash types (though, possibly, should
 489 be re-specced to not rehash but take an already-hashed value? Actually
 490 current impl looks WRONG - it _is_ given a hash so should not be
 491 re-hashing.  Has this been tested?
 492
 493 Will need extension for non-RSA sugning algos. */
 494
 495 switch (hash)
 496   {
 497   case HASH_SHA1:       sexp_hash = "(data(flags pkcs1)(hash sha1 %b))"; break;
 498   case HASH_SHA2_256:   sexp_hash = "(data(flags pkcs1)(hash sha256 %b))"; break;
 499   default:              return US"nonhandled hash type";
 500   }
 501
 502 #define SIGSPACE 128
 503 sig->data = store_get(SIGSPACE, FALSE);
 504
 505 if (gcry_mpi_cmp (sign_ctx->p, sign_ctx->q) > 0)
 506   {
 507   gcry_mpi_swap (sign_ctx->p, sign_ctx->q);
 508   gcry_mpi_invm (sign_ctx->qp, sign_ctx->p, sign_ctx->q);
 509   }
 510
 511 if (  (gerr = gcry_sexp_build (&s_key, NULL,
 512                 "(private-key (rsa (n%m)(e%m)(d%m)(p%m)(q%m)(u%m)))",
 513                 sign_ctx->n, sign_ctx->e,
 514                 sign_ctx->d, sign_ctx->p,
 515                 sign_ctx->q, sign_ctx->qp))
 516    || (gerr = gcry_sexp_build (&s_hash, NULL, sexp_hash,
 517                 (int) data->len, CS data->data))
 518    ||  (gerr = gcry_pk_sign (&s_sig, s_hash, s_key))
 519    )
 520   return US gcry_strerror(gerr);
 521
 522 /* gcry_sexp_dump(s_sig); */
 523
 524 if (  !(s_sig = gcry_sexp_find_token(s_sig, "s", 0))
 525    )
 526   return US"no sig result";
 527
 528 m_sig = gcry_sexp_nth_mpi(s_sig, 1, GCRYMPI_FMT_USG);
 529
 530 #ifdef extreme_debug
 531 DEBUG(D_acl)
 532   {
 533   uschar * s;
 534   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, m_sig);
 535   debug_printf_indent(" SG: %s\n", s);
 536   }
 537 #endif
 538
 539 gerr = gcry_mpi_print(GCRYMPI_FMT_USG, sig->data, SIGSPACE, &sig->len, m_sig);
 540 if (gerr)
 541   {
 542   debug_printf_indent("signature conversion from MPI to buffer failed\n");
 543   return US gcry_strerror(gerr);
 544   }
 545 #undef SIGSPACE
 546
 547 return NULL;
 548 }
 549
 550
 551 /* import public key (from blob in memory)
 552 Return: NULL for success, or an error string */
 553
 554 const uschar *
 555 exim_dkim_verify_init(blob * pubkey, keyformat fmt, ev_ctx * verify_ctx)
 556 {
 557 /*
 558 in code sequence per b81207d2bfa92 rsa_parse_public_key() and asn1_get_mpi()
 559 */
 560 uschar tag_class;
 561 int taglen;
 562 long alen;
 563 int rc;
 564 uschar * errstr;
 565 gcry_error_t gerr;
 566 uschar * stage = US"S1";
 567
 568 if (fmt != KEYFMT_DER) return US"pubkey format not handled";
 569
 570 /*
 571 sequence
 572  sequence
 573   OBJECT:rsaEncryption
 574   NULL
 575  BIT STRING:RSAPublicKey
 576   sequence
 577    INTEGER:Public modulus
 578    INTEGER:Public exponent
 579
 580 openssl rsa -in aux-fixed/dkim/dkim.private -pubout -outform DER | od -t x1 | head;
 581 openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump;
 582 openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump -offset 22;
 583 */
 584
 585 /* sequence; just move past the header */
 586 if ((rc = as_tag(pubkey, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
 587    != ASN1_SUCCESS) goto asn_err;
 588
 589 /* sequence; skip the entire thing */
 590 DEBUG(D_acl) stage = US"S2";
 591 if ((rc = as_tag(pubkey, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, &alen))
 592    != ASN1_SUCCESS) goto asn_err;
 593 pubkey->data += alen; pubkey->len -= alen;
 594
 595
 596 /* bitstring: limit range to size of bitstring;
 597 move over header + content wrapper */
 598 DEBUG(D_acl) stage = US"BS";
 599 if ((rc = as_tag(pubkey, 0, ASN1_TAG_BIT_STRING, &alen)) != ASN1_SUCCESS)
 600   goto asn_err;
 601 pubkey->len = alen;
 602 pubkey->data++; pubkey->len--;
 603
 604 /* sequence; just move past the header */
 605 DEBUG(D_acl) stage = US"S3";
 606 if ((rc = as_tag(pubkey, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
 607    != ASN1_SUCCESS) goto asn_err;
 608
 609 /* read two integers */
 610 DEBUG(D_acl) stage = US"MPI";
 611 if (  (errstr = as_mpi(pubkey, &verify_ctx->n))
 612    || (errstr = as_mpi(pubkey, &verify_ctx->e))
 613    )
 614   return errstr;
 615
 616 #ifdef extreme_debug
 617 DEBUG(D_acl) debug_printf_indent("rsa_verify_init:\n");
 618         {
 619         uschar * s;
 620         gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->n);
 621         debug_printf_indent(" N : %s\n", s);
 622         gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->e);
 623         debug_printf_indent(" E : %s\n", s);
 624         }
 625
 626 #endif
 627 return NULL;
 628
 629 asn_err:
 630 DEBUG(D_acl) return string_sprintf("%s: %s", stage, asn1_strerror(rc));
 631              return US asn1_strerror(rc);
 632 }
 633
 634
 635 /* verify signature (of hash)
 636 XXX though we appear to be doing a hash, too!
 637 (given pubkey & alleged sig)
 638 Return: NULL for success, or an error string */
 639
 640 const uschar *
 641 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data_hash, blob * sig)
 642 {
 643 /*
 644 cf. libgnutls 2.8.5 _wrap_gcry_pk_verify()
 645 */
 646 char * sexp_hash;
 647 gcry_mpi_t m_sig;
 648 gcry_sexp_t s_sig = NULL, s_hash = NULL, s_pkey = NULL;
 649 gcry_error_t gerr;
 650 uschar * stage;
 651
 652 /*XXX needs extension for SHA512 */
 653 switch (hash)
 654   {
 655   case HASH_SHA1:     sexp_hash = "(data(flags pkcs1)(hash sha1 %b))"; break;
 656   case HASH_SHA2_256: sexp_hash = "(data(flags pkcs1)(hash sha256 %b))"; break;
 657   default:            return US"nonhandled hash type";
 658   }
 659
 660 if (  (stage = US"pkey sexp build",
 661        gerr = gcry_sexp_build (&s_pkey, NULL, "(public-key(rsa(n%m)(e%m)))",
 662                         verify_ctx->n, verify_ctx->e))
 663    || (stage = US"data sexp build",
 664        gerr = gcry_sexp_build (&s_hash, NULL, sexp_hash,
 665                 (int) data_hash->len, CS data_hash->data))
 666    || (stage = US"sig mpi scan",
 667        gerr = gcry_mpi_scan(&m_sig, GCRYMPI_FMT_USG, sig->data, sig->len, NULL))
 668    || (stage = US"sig sexp build",
 669        gerr = gcry_sexp_build (&s_sig, NULL, "(sig-val(rsa(s%m)))", m_sig))
 670    || (stage = US"verify",
 671        gerr = gcry_pk_verify (s_sig, s_hash, s_pkey))
 672    )
 673   {
 674   DEBUG(D_acl) debug_printf_indent("verify: error in stage '%s'\n", stage);
 675   return US gcry_strerror(gerr);
 676   }
 677
 678 if (s_sig) gcry_sexp_release (s_sig);
 679 if (s_hash) gcry_sexp_release (s_hash);
 680 if (s_pkey) gcry_sexp_release (s_pkey);
 681 gcry_mpi_release (m_sig);
 682 gcry_mpi_release (verify_ctx->n);
 683 gcry_mpi_release (verify_ctx->e);
 684
 685 return NULL;
 686 }
 687
 688
 689
 690
 691 #elif defined(SIGN_OPENSSL)
 692 /******************************************************************************/
 693
 694 void
 695 exim_dkim_init(void)
 696 {
 697 ERR_load_crypto_strings();
 698 }
 699
 700
 701 /* accumulate data (was gnutls-only but now needed for OpenSSL non-EC too
 702 because now using hash-and-sign interface) */
 703 gstring *
 704 exim_dkim_data_append(gstring * g, uschar * s)
 705 {
 706 return string_cat(g, s);
 707 }
 708
 709
 710 /* import private key from PEM string in memory.
 711 Return: NULL for success, or an error string */
 712
 713 const uschar *
 714 exim_dkim_signing_init(const uschar * privkey_pem, es_ctx * sign_ctx)
 715 {
 716 BIO * bp = BIO_new_mem_buf((void *)privkey_pem, -1);
 717
 718 if (!(sign_ctx->key = PEM_read_bio_PrivateKey(bp, NULL, NULL, NULL)))
 719   return string_sprintf("privkey PEM-block import: %s",
 720                         ERR_error_string(ERR_get_error(), NULL));
 721
 722 sign_ctx->keytype =
 723 #ifdef SIGN_HAVE_ED25519
 724         EVP_PKEY_type(EVP_PKEY_id(sign_ctx->key)) == EVP_PKEY_ED25519
 725           ? KEYTYPE_ED25519 : KEYTYPE_RSA;
 726 #else
 727         KEYTYPE_RSA;
 728 #endif
 729 return NULL;
 730 }
 731
 732
 733
 734 /* allocate mem for signature (when signing) */
 735 /* hash & sign data.  Incremental not supported.
 736
 737 Return: NULL for success with the signaature in the sig blob, or an error string */
 738
 739 const uschar *
 740 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
 741 {
 742 const EVP_MD * md;
 743 EVP_MD_CTX * ctx;
 744 size_t siglen;
 745
 746 switch (hash)
 747   {
 748   case HASH_NULL:       md = NULL;         break;       /* Ed25519 signing */
 749   case HASH_SHA1:       md = EVP_sha1();   break;
 750   case HASH_SHA2_256:   md = EVP_sha256(); break;
 751   case HASH_SHA2_512:   md = EVP_sha512(); break;
 752   default:              return US"nonhandled hash type";
 753   }
 754
 755 #ifdef SIGN_HAVE_ED25519
 756 if (  (ctx = EVP_MD_CTX_new())
 757    && EVP_DigestSignInit(ctx, NULL, md, NULL, sign_ctx->key) > 0
 758    && EVP_DigestSign(ctx, NULL, &siglen, NULL, 0) > 0
 759    && (sig->data = store_get(siglen, FALSE))
 760
 761    /* Obtain the signature (slen could change here!) */
 762    && EVP_DigestSign(ctx, sig->data, &siglen, data->data, data->len) > 0
 763    )
 764   {
 765   EVP_MD_CTX_destroy(ctx);
 766   sig->len = siglen;
 767   return NULL;
 768   }
 769 #else
 770 /*XXX renamed to EVP_MD_CTX_new() in 1.1.0 */
 771 if (  (ctx = EVP_MD_CTX_create())
 772    && EVP_DigestSignInit(ctx, NULL, md, NULL, sign_ctx->key) > 0
 773    && EVP_DigestSignUpdate(ctx, data->data, data->len) > 0
 774    && EVP_DigestSignFinal(ctx, NULL, &siglen) > 0
 775    && (sig->data = store_get(siglen, FALSE))
 776
 777    /* Obtain the signature (slen could change here!) */
 778    && EVP_DigestSignFinal(ctx, sig->data, &siglen) > 0
 779    )
 780   {
 781   EVP_MD_CTX_destroy(ctx);
 782   sig->len = siglen;
 783   return NULL;
 784   }
 785 #endif
 786
 787 if (ctx) EVP_MD_CTX_destroy(ctx);
 788 return US ERR_error_string(ERR_get_error(), NULL);
 789 }
 790
 791
 792
 793 /* import public key (from blob in memory)
 794 Return: NULL for success, or an error string */
 795
 796 const uschar *
 797 exim_dkim_verify_init(blob * pubkey, keyformat fmt, ev_ctx * verify_ctx)
 798 {
 799 const uschar * s = pubkey->data;
 800 uschar * ret = NULL;
 801
 802 switch(fmt)
 803   {
 804   case KEYFMT_DER:
 805     /*XXX hmm, we never free this */
 806     if (!(verify_ctx->key = d2i_PUBKEY(NULL, &s, pubkey->len)))
 807       ret = US ERR_error_string(ERR_get_error(), NULL);
 808     break;
 809 #ifdef SIGN_HAVE_ED25519
 810   case KEYFMT_ED25519_BARE:
 811     if (!(verify_ctx->key = EVP_PKEY_new_raw_public_key(EVP_PKEY_ED25519, NULL,
 812                                                         s, pubkey->len)))
 813       ret = US ERR_error_string(ERR_get_error(), NULL);
 814     break;
 815 #endif
 816   default:
 817     ret = US"pubkey format not handled";
 818     break;
 819   }
 820
 821 return ret;
 822 }
 823
 824
 825
 826
 827 /* verify signature (of hash, except Ed25519 where of-data)
 828 (given pubkey & alleged sig)
 829 Return: NULL for success, or an error string */
 830
 831 const uschar *
 832 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data, blob * sig)
 833 {
 834 const EVP_MD * md;
 835
 836 switch (hash)
 837   {
 838   case HASH_NULL:       md = NULL;         break;
 839   case HASH_SHA1:       md = EVP_sha1();   break;
 840   case HASH_SHA2_256:   md = EVP_sha256(); break;
 841   case HASH_SHA2_512:   md = EVP_sha512(); break;
 842   default:              return US"nonhandled hash type";
 843   }
 844
 845 #ifdef SIGN_HAVE_ED25519
 846 if (!md)
 847   {
 848   EVP_MD_CTX * ctx;
 849
 850   if ((ctx = EVP_MD_CTX_new()))
 851     {
 852     if (  EVP_DigestVerifyInit(ctx, NULL, md, NULL, verify_ctx->key) > 0
 853        && EVP_DigestVerify(ctx, sig->data, sig->len, data->data, data->len) > 0
 854        )
 855       { EVP_MD_CTX_free(ctx); return NULL; }
 856     EVP_MD_CTX_free(ctx);
 857     }
 858   }
 859 else
 860 #endif
 861   {
 862   EVP_PKEY_CTX * ctx;
 863
 864   if ((ctx = EVP_PKEY_CTX_new(verify_ctx->key, NULL)))
 865     {
 866     if (  EVP_PKEY_verify_init(ctx) > 0
 867        && EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) > 0
 868        && EVP_PKEY_CTX_set_signature_md(ctx, md) > 0
 869        && EVP_PKEY_verify(ctx, sig->data, sig->len,
 870                                       data->data, data->len) == 1
 871        )
 872       { EVP_PKEY_CTX_free(ctx); return NULL; }
 873     EVP_PKEY_CTX_free(ctx);
 874
 875     DEBUG(D_tls)
 876       if (Ustrcmp(ERR_reason_error_string(ERR_peek_error()), "wrong signature length") == 0)
 877         debug_printf("sig len (from msg hdr): %d, expected (from dns pubkey) %d\n",
 878          (int) sig->len, EVP_PKEY_size(verify_ctx->key));
 879     }
 880   }
 881
 882 return US ERR_error_string(ERR_get_error(), NULL);
 883 }
 884
 885
 886
 887 #endif
 888 /******************************************************************************/
 889
 890 #endif  /*DISABLE_DKIM*/
 891 #endif  /*MACRO_PREDEF*/
 892 /* End of File */