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