src/src/pdkim/signing.c

   1 /*
   2  *  PDKIM - a RFC4871 (DKIM) implementation
   3  *
   4  *  Copyright (C) 2016  Exim maintainers
   5  *
   6  *  signing/verification interface
   7  */
   8
   9 #include "../exim.h"
  10
  11 #ifndef DISABLE_DKIM    /* entire file */
  12
  13 #ifndef SUPPORT_TLS
  14 # error Need SUPPORT_TLS for DKIM
  15 #endif
  16
  17 #include "crypt_ver.h"
  18 #include "signing.h"
  19
  20
  21 /******************************************************************************/
  22 #ifdef SIGN_GNUTLS
  23
  24 void
  25 exim_dkim_init(void)
  26 {
  27 }
  28
  29
  30 /* accumulate data (gnutls-only).  String to be appended must be nul-terminated. */
  31 blob *
  32 exim_dkim_data_append(blob * b, int * alloc, uschar * s)
  33 {
  34 int len = b->len;
  35 b->data = string_append(b->data, alloc, &len, 1, s);
  36 b->len = len;
  37 return b;
  38 }
  39
  40
  41
  42 /* import private key from PEM string in memory.
  43 Return: NULL for success, or an error string */
  44
  45 const uschar *
  46 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
  47 {
  48 gnutls_datum_t k;
  49 int rc;
  50
  51 k.data = privkey_pem;
  52 k.size = strlen(privkey_pem);
  53
  54 if (  (rc = gnutls_x509_privkey_init(&sign_ctx->key)) != GNUTLS_E_SUCCESS
  55    || (rc = gnutls_x509_privkey_import(sign_ctx->key, &k,
  56           GNUTLS_X509_FMT_PEM)) != GNUTLS_E_SUCCESS
  57    )
  58   return gnutls_strerror(rc);
  59
  60 return NULL;
  61 }
  62
  63
  64
  65 /* allocate mem for signature (when signing) */
  66 /* sign data (gnutls_only)
  67 OR
  68 sign hash.
  69
  70 Return: NULL for success, or an error string */
  71
  72 const uschar *
  73 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
  74 {
  75 gnutls_digest_algorithm_t dig;
  76 gnutls_datum_t k;
  77 size_t sigsize = 0;
  78 int rc;
  79 const uschar * ret = NULL;
  80
  81 switch (hash)
  82   {
  83   case HASH_SHA1:       dig = GNUTLS_DIG_SHA1; break;
  84   case HASH_SHA2_256:   dig = GNUTLS_DIG_SHA256; break;
  85   case HASH_SHA2_512:   dig = GNUTLS_DIG_SHA512; break;
  86   default:              return US"nonhandled hash type";
  87   }
  88
  89 /* Allocate mem for signature */
  90 k.data = data->data;
  91 k.size = data->len;
  92 (void) gnutls_x509_privkey_sign_data(sign_ctx->key, dig,
  93   0, &k, NULL, &sigsize);
  94
  95 sig->data = store_get(sigsize);
  96 sig->len = sigsize;
  97
  98 /* Do signing */
  99 if ((rc = gnutls_x509_privkey_sign_data(sign_ctx->key, dig,
 100             0, &k, sig->data, &sigsize)) != GNUTLS_E_SUCCESS
 101    )
 102   ret = gnutls_strerror(rc);
 103
 104 gnutls_x509_privkey_deinit(sign_ctx->key);
 105 return ret;
 106 }
 107
 108
 109
 110 /* import public key (from DER in memory)
 111 Return: NULL for success, or an error string */
 112
 113 const uschar *
 114 exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx)
 115 {
 116 gnutls_datum_t k;
 117 int rc;
 118 const uschar * ret = NULL;
 119
 120 gnutls_pubkey_init(&verify_ctx->key);
 121
 122 k.data = pubkey_der->data;
 123 k.size = pubkey_der->len;
 124
 125 if ((rc = gnutls_pubkey_import(verify_ctx->key, &k, GNUTLS_X509_FMT_DER))
 126        != GNUTLS_E_SUCCESS)
 127   ret = gnutls_strerror(rc);
 128 return ret;
 129 }
 130
 131
 132 /* verify signature (of hash)  (given pubkey & alleged sig)
 133 Return: NULL for success, or an error string */
 134
 135 const uschar *
 136 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data_hash, blob * sig)
 137 {
 138 gnutls_sign_algorithm_t algo;
 139 gnutls_datum_t k, s;
 140 int rc;
 141 const uschar * ret = NULL;
 142
 143 /*XXX needs extension for non-rsa */
 144 switch (hash)
 145   {
 146   case HASH_SHA1:       algo = GNUTLS_SIGN_RSA_SHA1;   break;
 147   case HASH_SHA2_256:   algo = GNUTLS_SIGN_RSA_SHA256; break;
 148   case HASH_SHA2_512:   algo = GNUTLS_SIGN_RSA_SHA512; break;
 149   default:              return US"nonhandled hash type";
 150   }
 151
 152 k.data = data_hash->data;
 153 k.size = data_hash->len;
 154 s.data = sig->data;
 155 s.size = sig->len;
 156 if ((rc = gnutls_pubkey_verify_hash2(verify_ctx->key, algo, 0, &k, &s)) < 0)
 157   ret = gnutls_strerror(rc);
 158
 159 gnutls_pubkey_deinit(verify_ctx->key);
 160 return ret;
 161 }
 162
 163
 164
 165
 166 #elif defined(SIGN_GCRYPT)
 167 /******************************************************************************/
 168 /* This variant is used under pre-3.0.0 GnuTLS.  Only rsa-sha1 and rsa-sha256 */
 169
 170
 171 /* Internal service routine:
 172 Read and move past an asn.1 header, checking class & tag,
 173 optionally returning the data-length */
 174
 175 static int
 176 as_tag(blob * der, uschar req_cls, long req_tag, long * alen)
 177 {
 178 int rc;
 179 uschar tag_class;
 180 int taglen;
 181 long tag, len;
 182
 183 /* debug_printf_indent("as_tag: %02x %02x %02x %02x\n",
 184         der->data[0], der->data[1], der->data[2], der->data[3]); */
 185
 186 if ((rc = asn1_get_tag_der(der->data++, der->len--, &tag_class, &taglen, &tag))
 187     != ASN1_SUCCESS)
 188   return rc;
 189
 190 if (tag_class != req_cls || tag != req_tag) return ASN1_ELEMENT_NOT_FOUND;
 191
 192 if ((len = asn1_get_length_der(der->data, der->len, &taglen)) < 0)
 193   return ASN1_DER_ERROR;
 194 if (alen) *alen = len;
 195
 196 /* debug_printf_indent("as_tag:  tlen %d dlen %d\n", taglen, (int)len); */
 197
 198 der->data += taglen;
 199 der->len -= taglen;
 200 return rc;
 201 }
 202
 203 /* Internal service routine:
 204 Read and move over an asn.1 integer, setting an MPI to the value
 205 */
 206
 207 static uschar *
 208 as_mpi(blob * der, gcry_mpi_t * mpi)
 209 {
 210 long alen;
 211 int rc;
 212 gcry_error_t gerr;
 213
 214 /* integer; move past the header */
 215 if ((rc = as_tag(der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS)
 216   return US asn1_strerror(rc);
 217
 218 /* read to an MPI */
 219 if ((gerr = gcry_mpi_scan(mpi, GCRYMPI_FMT_STD, der->data, alen, NULL)))
 220   return US gcry_strerror(gerr);
 221
 222 /* move over the data */
 223 der->data += alen; der->len -= alen;
 224 return NULL;
 225 }
 226
 227
 228
 229 void
 230 exim_dkim_init(void)
 231 {
 232 /* Version check should be the very first call because it
 233 makes sure that important subsystems are initialized. */
 234 if (!gcry_check_version (GCRYPT_VERSION))
 235   {
 236   fputs ("libgcrypt version mismatch\n", stderr);
 237   exit (2);
 238   }
 239
 240 /* We don't want to see any warnings, e.g. because we have not yet
 241 parsed program options which might be used to suppress such
 242 warnings. */
 243 gcry_control (GCRYCTL_SUSPEND_SECMEM_WARN);
 244
 245 /* ... If required, other initialization goes here.  Note that the
 246 process might still be running with increased privileges and that
 247 the secure memory has not been initialized.  */
 248
 249 /* Allocate a pool of 16k secure memory.  This make the secure memory
 250 available and also drops privileges where needed.  */
 251 gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);
 252
 253 /* It is now okay to let Libgcrypt complain when there was/is
 254 a problem with the secure memory. */
 255 gcry_control (GCRYCTL_RESUME_SECMEM_WARN);
 256
 257 /* ... If required, other initialization goes here.  */
 258
 259 /* Tell Libgcrypt that initialization has completed. */
 260 gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
 261
 262 return;
 263 }
 264
 265
 266
 267
 268 /* Accumulate data (gnutls-only).
 269 String to be appended must be nul-terminated. */
 270
 271 blob *
 272 exim_dkim_data_append(blob * b, int * alloc, uschar * s)
 273 {
 274 return b;       /*dummy*/
 275 }
 276
 277
 278
 279 /* import private key from PEM string in memory.
 280 Return: NULL for success, or an error string */
 281
 282 const uschar *
 283 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
 284 {
 285 uschar * s1, * s2;
 286 blob der;
 287 long alen;
 288 int rc;
 289
 290 /*XXX will need extension to _spot_ as well as handle a
 291 non-RSA key?  I think... */
 292
 293 /*
 294  *  RSAPrivateKey ::= SEQUENCE
 295  *      version           Version,
 296  *      modulus           INTEGER,  -- n
 297  *      publicExponent    INTEGER,  -- e
 298  *      privateExponent   INTEGER,  -- d
 299  *      prime1            INTEGER,  -- p
 300  *      prime2            INTEGER,  -- q
 301  *      exponent1         INTEGER,  -- d mod (p-1)
 302  *      exponent2         INTEGER,  -- d mod (q-1)
 303  *      coefficient       INTEGER,  -- (inverse of q) mod p
 304  *      otherPrimeInfos   OtherPrimeInfos OPTIONAL
 305  */
 306
 307 if (  !(s1 = Ustrstr(CS privkey_pem, "-----BEGIN RSA PRIVATE KEY-----"))
 308    || !(s2 = Ustrstr(CS (s1+=31),    "-----END RSA PRIVATE KEY-----" ))
 309    )
 310   return US"Bad PEM wrapper";
 311
 312 *s2 = '\0';
 313
 314 if ((der.len = b64decode(s1, &der.data)) < 0)
 315   return US"Bad PEM-DER b64 decode";
 316
 317 /* untangle asn.1 */
 318
 319 /* sequence; just move past the header */
 320 if ((rc = as_tag(&der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
 321    != ASN1_SUCCESS) goto asn_err;
 322
 323 /* integer version; move past the header, check is zero */
 324 if ((rc = as_tag(&der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS)
 325   goto asn_err;
 326 if (alen != 1 || *der.data != 0)
 327   return US"Bad version number";
 328 der.data++; der.len--;
 329
 330 if (  (s1 = as_mpi(&der, &sign_ctx->n))
 331    || (s1 = as_mpi(&der, &sign_ctx->e))
 332    || (s1 = as_mpi(&der, &sign_ctx->d))
 333    || (s1 = as_mpi(&der, &sign_ctx->p))
 334    || (s1 = as_mpi(&der, &sign_ctx->q))
 335    || (s1 = as_mpi(&der, &sign_ctx->dp))
 336    || (s1 = as_mpi(&der, &sign_ctx->dq))
 337    || (s1 = as_mpi(&der, &sign_ctx->qp))
 338    )
 339   return s1;
 340
 341 #ifdef extreme_debug
 342 DEBUG(D_acl) debug_printf_indent("rsa_signing_init:\n");
 343   {
 344   uschar * s;
 345   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->n);
 346   debug_printf_indent(" N : %s\n", s);
 347   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->e);
 348   debug_printf_indent(" E : %s\n", s);
 349   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->d);
 350   debug_printf_indent(" D : %s\n", s);
 351   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->p);
 352   debug_printf_indent(" P : %s\n", s);
 353   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->q);
 354   debug_printf_indent(" Q : %s\n", s);
 355   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dp);
 356   debug_printf_indent(" DP: %s\n", s);
 357   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dq);
 358   debug_printf_indent(" DQ: %s\n", s);
 359   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->qp);
 360   debug_printf_indent(" QP: %s\n", s);
 361   }
 362 #endif
 363 return NULL;
 364
 365 asn_err: return US asn1_strerror(rc);
 366 }
 367
 368
 369
 370 /* allocate mem for signature (when signing) */
 371 /* sign data (gnutls_only)
 372 OR
 373 sign hash.
 374
 375 Return: NULL for success, or an error string */
 376
 377 const uschar *
 378 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
 379 {
 380 char * sexp_hash;
 381 gcry_sexp_t s_hash = NULL, s_key = NULL, s_sig = NULL;
 382 gcry_mpi_t m_sig;
 383 uschar * errstr;
 384 gcry_error_t gerr;
 385
 386 /*XXX will need extension for hash types (though, possibly, should
 387 be re-specced to not rehash but take an already-hashed value? Actually
 388 current impl looks WRONG - it _is_ given a hash so should not be
 389 re-hashing.  Has this been tested?
 390
 391 Will need extension for non-RSA sugning algos. */
 392
 393 switch (hash)
 394   {
 395   case HASH_SHA1:       sexp_hash = "(data(flags pkcs1)(hash sha1 %b))"; break;
 396   case HASH_SHA2_256:   sexp_hash = "(data(flags pkcs1)(hash sha256 %b))"; break;
 397   default:              return US"nonhandled hash type";
 398   }
 399
 400 #define SIGSPACE 128
 401 sig->data = store_get(SIGSPACE);
 402
 403 if (gcry_mpi_cmp (sign_ctx->p, sign_ctx->q) > 0)
 404   {
 405   gcry_mpi_swap (sign_ctx->p, sign_ctx->q);
 406   gcry_mpi_invm (sign_ctx->qp, sign_ctx->p, sign_ctx->q);
 407   }
 408
 409 if (  (gerr = gcry_sexp_build (&s_key, NULL,
 410                 "(private-key (rsa (n%m)(e%m)(d%m)(p%m)(q%m)(u%m)))",
 411                 sign_ctx->n, sign_ctx->e,
 412                 sign_ctx->d, sign_ctx->p,
 413                 sign_ctx->q, sign_ctx->qp))
 414    || (gerr = gcry_sexp_build (&s_hash, NULL, sexp_hash,
 415                 (int) data->len, CS data->data))
 416    ||  (gerr = gcry_pk_sign (&s_sig, s_hash, s_key))
 417    )
 418   return US gcry_strerror(gerr);
 419
 420 /* gcry_sexp_dump(s_sig); */
 421
 422 if (  !(s_sig = gcry_sexp_find_token(s_sig, "s", 0))
 423    )
 424   return US"no sig result";
 425
 426 m_sig = gcry_sexp_nth_mpi(s_sig, 1, GCRYMPI_FMT_USG);
 427
 428 #ifdef extreme_debug
 429 DEBUG(D_acl)
 430   {
 431   uschar * s;
 432   gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, m_sig);
 433   debug_printf_indent(" SG: %s\n", s);
 434   }
 435 #endif
 436
 437 gerr = gcry_mpi_print(GCRYMPI_FMT_USG, sig->data, SIGSPACE, &sig->len, m_sig);
 438 if (gerr)
 439   {
 440   debug_printf_indent("signature conversion from MPI to buffer failed\n");
 441   return US gcry_strerror(gerr);
 442   }
 443 #undef SIGSPACE
 444
 445 return NULL;
 446 }
 447
 448
 449 /* import public key (from DER in memory)
 450 Return: NULL for success, or an error string */
 451
 452 const uschar *
 453 exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx)
 454 {
 455 /*
 456 in code sequence per b81207d2bfa92 rsa_parse_public_key() and asn1_get_mpi()
 457 */
 458 uschar tag_class;
 459 int taglen;
 460 long alen;
 461 int rc;
 462 uschar * errstr;
 463 gcry_error_t gerr;
 464 uschar * stage = US"S1";
 465
 466 /*
 467 sequence
 468  sequence
 469   OBJECT:rsaEncryption
 470   NULL
 471  BIT STRING:RSAPublicKey
 472   sequence
 473    INTEGER:Public modulus
 474    INTEGER:Public exponent
 475
 476 openssl rsa -in aux-fixed/dkim/dkim.private -pubout -outform DER | od -t x1 | head;
 477 openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump;
 478 openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump -offset 22;
 479 */
 480
 481 /* sequence; just move past the header */
 482 if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
 483    != ASN1_SUCCESS) goto asn_err;
 484
 485 /* sequence; skip the entire thing */
 486 DEBUG(D_acl) stage = US"S2";
 487 if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, &alen))
 488    != ASN1_SUCCESS) goto asn_err;
 489 pubkey_der->data += alen; pubkey_der->len -= alen;
 490
 491
 492 /* bitstring: limit range to size of bitstring;
 493 move over header + content wrapper */
 494 DEBUG(D_acl) stage = US"BS";
 495 if ((rc = as_tag(pubkey_der, 0, ASN1_TAG_BIT_STRING, &alen)) != ASN1_SUCCESS)
 496   goto asn_err;
 497 pubkey_der->len = alen;
 498 pubkey_der->data++; pubkey_der->len--;
 499
 500 /* sequence; just move past the header */
 501 DEBUG(D_acl) stage = US"S3";
 502 if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
 503    != ASN1_SUCCESS) goto asn_err;
 504
 505 /* read two integers */
 506 DEBUG(D_acl) stage = US"MPI";
 507 if (  (errstr = as_mpi(pubkey_der, &verify_ctx->n))
 508    || (errstr = as_mpi(pubkey_der, &verify_ctx->e))
 509    )
 510   return errstr;
 511
 512 #ifdef extreme_debug
 513 DEBUG(D_acl) debug_printf_indent("rsa_verify_init:\n");
 514         {
 515         uschar * s;
 516         gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->n);
 517         debug_printf_indent(" N : %s\n", s);
 518         gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->e);
 519         debug_printf_indent(" E : %s\n", s);
 520         }
 521
 522 #endif
 523 return NULL;
 524
 525 asn_err:
 526 DEBUG(D_acl) return string_sprintf("%s: %s", stage, asn1_strerror(rc));
 527              return US asn1_strerror(rc);
 528 }
 529
 530
 531 /* verify signature (of hash)  (given pubkey & alleged sig)
 532 Return: NULL for success, or an error string */
 533
 534 const uschar *
 535 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data_hash, blob * sig)
 536 {
 537 /*
 538 cf. libgnutls 2.8.5 _wrap_gcry_pk_verify()
 539 */
 540 char * sexp_hash;
 541 gcry_mpi_t m_sig;
 542 gcry_sexp_t s_sig = NULL, s_hash = NULL, s_pkey = NULL;
 543 gcry_error_t gerr;
 544 uschar * stage;
 545
 546 /*XXX needs extension for SHA512 */
 547 switch (hash)
 548   {
 549   case HASH_SHA1:     sexp_hash = "(data(flags pkcs1)(hash sha1 %b))"; break;
 550   case HASH_SHA2_256: sexp_hash = "(data(flags pkcs1)(hash sha256 %b))"; break;
 551   default:            return US"nonhandled hash type";
 552   }
 553
 554 if (  (stage = US"pkey sexp build",
 555        gerr = gcry_sexp_build (&s_pkey, NULL, "(public-key(rsa(n%m)(e%m)))",
 556                         verify_ctx->n, verify_ctx->e))
 557    || (stage = US"data sexp build",
 558        gerr = gcry_sexp_build (&s_hash, NULL, sexp_hash,
 559                 (int) data_hash->len, CS data_hash->data))
 560    || (stage = US"sig mpi scan",
 561        gerr = gcry_mpi_scan(&m_sig, GCRYMPI_FMT_USG, sig->data, sig->len, NULL))
 562    || (stage = US"sig sexp build",
 563        gerr = gcry_sexp_build (&s_sig, NULL, "(sig-val(rsa(s%m)))", m_sig))
 564    || (stage = US"verify",
 565        gerr = gcry_pk_verify (s_sig, s_hash, s_pkey))
 566    )
 567   {
 568   DEBUG(D_acl) debug_printf_indent("verify: error in stage '%s'\n", stage);
 569   return US gcry_strerror(gerr);
 570   }
 571
 572 if (s_sig) gcry_sexp_release (s_sig);
 573 if (s_hash) gcry_sexp_release (s_hash);
 574 if (s_pkey) gcry_sexp_release (s_pkey);
 575 gcry_mpi_release (m_sig);
 576 gcry_mpi_release (verify_ctx->n);
 577 gcry_mpi_release (verify_ctx->e);
 578
 579 return NULL;
 580 }
 581
 582
 583
 584
 585 #elif defined(SIGN_OPENSSL)
 586 /******************************************************************************/
 587
 588 void
 589 exim_dkim_init(void)
 590 {
 591 ERR_load_crypto_strings();
 592 }
 593
 594
 595 /* accumulate data (gnutls-only) */
 596 blob *
 597 exim_dkim_data_append(blob * b, int * alloc, uschar * s)
 598 {
 599 return b;       /*dummy*/
 600 }
 601
 602
 603 /* import private key from PEM string in memory.
 604 Return: NULL for success, or an error string */
 605
 606 const uschar *
 607 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
 608 {
 609 BIO * bp = BIO_new_mem_buf(privkey_pem, -1);
 610
 611 if (!(sign_ctx->key = PEM_read_bio_PrivateKey(bp, NULL, NULL, NULL)))
 612   return US ERR_error_string(ERR_get_error(), NULL);
 613 return NULL;
 614 }
 615
 616
 617
 618 /* allocate mem for signature (when signing) */
 619 /* sign data (gnutls_only)
 620 OR
 621 sign hash.
 622
 623 Return: NULL for success with the signaature in the sig blob, or an error string */
 624
 625 const uschar *
 626 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
 627 {
 628 const EVP_MD * md;
 629 EVP_PKEY_CTX * ctx;
 630 size_t siglen;
 631
 632 switch (hash)
 633   {
 634   case HASH_SHA1:       md = EVP_sha1();   break;
 635   case HASH_SHA2_256:   md = EVP_sha256(); break;
 636   case HASH_SHA2_512:   md = EVP_sha512(); break;
 637   default:              return US"nonhandled hash type";
 638   }
 639
 640 if (  (ctx = EVP_PKEY_CTX_new(sign_ctx->key, NULL))
 641    && EVP_PKEY_sign_init(ctx) > 0
 642    && EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) > 0
 643    && EVP_PKEY_CTX_set_signature_md(ctx, md) > 0
 644    && EVP_PKEY_sign(ctx, NULL, &siglen, data->data, data->len) > 0
 645    )
 646   {
 647   /* Allocate mem for signature */
 648   sig->data = store_get(siglen);
 649
 650   if (EVP_PKEY_sign(ctx, sig->data, &siglen, data->data, data->len) > 0)
 651     {
 652     EVP_PKEY_CTX_free(ctx);
 653     sig->len = siglen;
 654     return NULL;
 655     }
 656   }
 657
 658 if (ctx) EVP_PKEY_CTX_free(ctx);
 659 return US ERR_error_string(ERR_get_error(), NULL);
 660 }
 661
 662
 663
 664 /* import public key (from DER in memory)
 665 Return: NULL for success, or an error string */
 666
 667 const uschar *
 668 exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx)
 669 {
 670 const uschar * s = pubkey_der->data;
 671
 672 /*XXX hmm, we never free this */
 673
 674 if ((verify_ctx->key = d2i_PUBKEY(NULL, &s, pubkey_der->len)))
 675   return NULL;
 676 return US ERR_error_string(ERR_get_error(), NULL);
 677 }
 678
 679
 680
 681
 682 /* verify signature (of hash)  (given pubkey & alleged sig)
 683 Return: NULL for success, or an error string */
 684
 685 const uschar *
 686 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data_hash, blob * sig)
 687 {
 688 const EVP_MD * md;
 689 EVP_PKEY_CTX * ctx;
 690
 691 switch (hash)
 692   {
 693   case HASH_SHA1:       md = EVP_sha1();   break;
 694   case HASH_SHA2_256:   md = EVP_sha256(); break;
 695   case HASH_SHA2_512:   md = EVP_sha512(); break;
 696   default:              return US"nonhandled hash type";
 697   }
 698
 699 if (  (ctx = EVP_PKEY_CTX_new(verify_ctx->key, NULL))
 700    && EVP_PKEY_verify_init(ctx) > 0
 701    && EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) > 0
 702    && EVP_PKEY_CTX_set_signature_md(ctx, md) > 0
 703    && EVP_PKEY_verify(ctx, sig->data, sig->len,
 704         data_hash->data, data_hash->len) == 1
 705    )
 706   { EVP_PKEY_CTX_free(ctx); return NULL; }
 707
 708 if (ctx) EVP_PKEY_CTX_free(ctx);
 709 return US ERR_error_string(ERR_get_error(), NULL);
 710 }
 711
 712
 713
 714 #endif
 715 /******************************************************************************/
 716
 717 #endif  /*DISABLE_DKIM*/
 718 /* End of File */