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