2 * PDKIM - a RFC4871 (DKIM) implementation
4 * Copyright (C) 2016 Exim maintainers
6 * RSA signing/verification interface
7 XXX rename interfaces to cover all signature methods.
8 the method (algo) needs to be extracted from the supplied private-key
9 and not only stashed as needed in the sign- or verify- context, but
10 indicated to caller for protocol tag construction.
15 #ifndef DISABLE_DKIM /* entire file */
18 # error Need SUPPORT_TLS for DKIM
21 #include "crypt_ver.h"
25 /******************************************************************************/
34 /* accumulate data (gnutls-only). String to be appended must be nul-terminated. */
36 exim_dkim_data_append(blob * b, int * alloc, uschar * s)
39 b->data = string_append(b->data, alloc, &len, 1, s);
46 /* import private key from PEM string in memory.
47 Return: NULL for success, or an error string */
50 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
56 k.size = strlen(privkey_pem);
58 if ( (rc = gnutls_x509_privkey_init(&sign_ctx->rsa)) != GNUTLS_E_SUCCESS
59 || (rc = gnutls_x509_privkey_import(sign_ctx->rsa, &k,
60 GNUTLS_X509_FMT_PEM)) != GNUTLS_E_SUCCESS
62 return gnutls_strerror(rc);
69 /* allocate mem for signature (when signing) */
70 /* sign data (gnutls_only)
74 Return: NULL for success, or an error string */
77 exim_dkim_sign(es_ctx * sign_ctx, BOOL is_sha1, blob * data, blob * sig)
82 const uschar * ret = NULL;
84 /* Allocate mem for signature */
87 (void) gnutls_x509_privkey_sign_data(sign_ctx->rsa,
88 is_sha1 ? GNUTLS_DIG_SHA1 : GNUTLS_DIG_SHA256,
89 0, &k, NULL, &sigsize);
91 sig->data = store_get(sigsize);
95 /*XXX will need extension for hash type; looks ok for non-RSA algos
96 so long as the privkey_import stage got them. */
97 if ((rc = gnutls_x509_privkey_sign_data(sign_ctx->rsa,
98 is_sha1 ? GNUTLS_DIG_SHA1 : GNUTLS_DIG_SHA256,
99 0, &k, sig->data, &sigsize)) != GNUTLS_E_SUCCESS
101 ret = gnutls_strerror(rc);
103 gnutls_x509_privkey_deinit(sign_ctx->rsa);
109 /* import public key (from DER in memory)
110 Return: NULL for success, or an error string */
113 exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx)
117 const uschar * ret = NULL;
119 gnutls_pubkey_init(&verify_ctx->rsa);
121 k.data = pubkey_der->data;
122 k.size = pubkey_der->len;
124 if ((rc = gnutls_pubkey_import(verify_ctx->rsa, &k, GNUTLS_X509_FMT_DER))
126 ret = gnutls_strerror(rc);
131 /* verify signature (of hash) (given pubkey & alleged sig)
132 Return: NULL for success, or an error string */
135 exim_dkim_verify(ev_ctx * verify_ctx, BOOL is_sha1, blob * data_hash, blob * sig)
139 const uschar * ret = NULL;
141 k.data = data_hash->data;
142 k.size = data_hash->len;
145 if ((rc = gnutls_pubkey_verify_hash2(verify_ctx->rsa,
146 /*XXX needs extension for SHA512 */
147 is_sha1 ? GNUTLS_SIGN_RSA_SHA1 : GNUTLS_SIGN_RSA_SHA256,
149 ret = gnutls_strerror(rc);
151 gnutls_pubkey_deinit(verify_ctx->rsa);
158 #elif defined(RSA_GCRYPT)
159 /******************************************************************************/
162 /* Internal service routine:
163 Read and move past an asn.1 header, checking class & tag,
164 optionally returning the data-length */
167 as_tag(blob * der, uschar req_cls, long req_tag, long * alen)
174 /* debug_printf_indent("as_tag: %02x %02x %02x %02x\n",
175 der->data[0], der->data[1], der->data[2], der->data[3]); */
177 if ((rc = asn1_get_tag_der(der->data++, der->len--, &tag_class, &taglen, &tag))
181 if (tag_class != req_cls || tag != req_tag) return ASN1_ELEMENT_NOT_FOUND;
183 if ((len = asn1_get_length_der(der->data, der->len, &taglen)) < 0)
184 return ASN1_DER_ERROR;
185 if (alen) *alen = len;
187 /* debug_printf_indent("as_tag: tlen %d dlen %d\n", taglen, (int)len); */
194 /* Internal service routine:
195 Read and move over an asn.1 integer, setting an MPI to the value
199 as_mpi(blob * der, gcry_mpi_t * mpi)
205 /* integer; move past the header */
206 if ((rc = as_tag(der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS)
207 return US asn1_strerror(rc);
210 if ((gerr = gcry_mpi_scan(mpi, GCRYMPI_FMT_STD, der->data, alen, NULL)))
211 return US gcry_strerror(gerr);
213 /* move over the data */
214 der->data += alen; der->len -= alen;
223 /* Version check should be the very first call because it
224 makes sure that important subsystems are initialized. */
225 if (!gcry_check_version (GCRYPT_VERSION))
227 fputs ("libgcrypt version mismatch\n", stderr);
231 /* We don't want to see any warnings, e.g. because we have not yet
232 parsed program options which might be used to suppress such
234 gcry_control (GCRYCTL_SUSPEND_SECMEM_WARN);
236 /* ... If required, other initialization goes here. Note that the
237 process might still be running with increased privileges and that
238 the secure memory has not been initialized. */
240 /* Allocate a pool of 16k secure memory. This make the secure memory
241 available and also drops privileges where needed. */
242 gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);
244 /* It is now okay to let Libgcrypt complain when there was/is
245 a problem with the secure memory. */
246 gcry_control (GCRYCTL_RESUME_SECMEM_WARN);
248 /* ... If required, other initialization goes here. */
250 /* Tell Libgcrypt that initialization has completed. */
251 gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
259 /* Accumulate data (gnutls-only).
260 String to be appended must be nul-terminated. */
263 exim_dkim_data_append(blob * b, int * alloc, uschar * s)
270 /* import private key from PEM string in memory.
271 Return: NULL for success, or an error string */
274 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
281 /*XXX will need extension to _spot_ as well as handle a
282 non-RSA key? I think... */
285 * RSAPrivateKey ::= SEQUENCE
287 * modulus INTEGER, -- n
288 * publicExponent INTEGER, -- e
289 * privateExponent INTEGER, -- d
290 * prime1 INTEGER, -- p
291 * prime2 INTEGER, -- q
292 * exponent1 INTEGER, -- d mod (p-1)
293 * exponent2 INTEGER, -- d mod (q-1)
294 * coefficient INTEGER, -- (inverse of q) mod p
295 * otherPrimeInfos OtherPrimeInfos OPTIONAL
298 if ( !(s1 = Ustrstr(CS privkey_pem, "-----BEGIN RSA PRIVATE KEY-----"))
299 || !(s2 = Ustrstr(CS (s1+=31), "-----END RSA PRIVATE KEY-----" ))
301 return US"Bad PEM wrapper";
305 if ((der.len = b64decode(s1, &der.data)) < 0)
306 return US"Bad PEM-DER b64 decode";
310 /* sequence; just move past the header */
311 if ((rc = as_tag(&der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
312 != ASN1_SUCCESS) goto asn_err;
314 /* integer version; move past the header, check is zero */
315 if ((rc = as_tag(&der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS)
317 if (alen != 1 || *der.data != 0)
318 return US"Bad version number";
319 der.data++; der.len--;
321 if ( (s1 = as_mpi(&der, &sign_ctx->n))
322 || (s1 = as_mpi(&der, &sign_ctx->e))
323 || (s1 = as_mpi(&der, &sign_ctx->d))
324 || (s1 = as_mpi(&der, &sign_ctx->p))
325 || (s1 = as_mpi(&der, &sign_ctx->q))
326 || (s1 = as_mpi(&der, &sign_ctx->dp))
327 || (s1 = as_mpi(&der, &sign_ctx->dq))
328 || (s1 = as_mpi(&der, &sign_ctx->qp))
332 DEBUG(D_acl) debug_printf_indent("rsa_signing_init:\n");
335 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->n);
336 debug_printf_indent(" N : %s\n", s);
337 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->e);
338 debug_printf_indent(" E : %s\n", s);
339 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->d);
340 debug_printf_indent(" D : %s\n", s);
341 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->p);
342 debug_printf_indent(" P : %s\n", s);
343 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->q);
344 debug_printf_indent(" Q : %s\n", s);
345 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dp);
346 debug_printf_indent(" DP: %s\n", s);
347 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dq);
348 debug_printf_indent(" DQ: %s\n", s);
349 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->qp);
350 debug_printf_indent(" QP: %s\n", s);
354 asn_err: return US asn1_strerror(rc);
359 /* allocate mem for signature (when signing) */
360 /* sign data (gnutls_only)
364 Return: NULL for success, or an error string */
367 exim_dkim_sign(es_ctx * sign_ctx, BOOL is_sha1, blob * data, blob * sig)
369 gcry_sexp_t s_hash = NULL, s_key = NULL, s_sig = NULL;
374 /*XXX will need extension for hash types (though, possibly, should
375 be re-specced to not rehash but take an already-hashed value? Actually
376 current impl looks WRONG - it _is_ given a has so should not be
377 re-hashing. Has this been tested?
379 Will need extension for non-RSA sugning algos. */
382 sig->data = store_get(SIGSPACE);
384 if (gcry_mpi_cmp (sign_ctx->p, sign_ctx->q) > 0)
386 gcry_mpi_swap (sign_ctx->p, sign_ctx->q);
387 gcry_mpi_invm (sign_ctx->qp, sign_ctx->p, sign_ctx->q);
390 if ( (gerr = gcry_sexp_build (&s_key, NULL,
391 "(private-key (rsa (n%m)(e%m)(d%m)(p%m)(q%m)(u%m)))",
392 sign_ctx->n, sign_ctx->e,
393 sign_ctx->d, sign_ctx->p,
394 sign_ctx->q, sign_ctx->qp))
395 || (gerr = gcry_sexp_build (&s_hash, NULL,
397 ? "(data(flags pkcs1)(hash sha1 %b))"
398 : "(data(flags pkcs1)(hash sha256 %b))",
399 (int) data->len, CS data->data))
400 || (gerr = gcry_pk_sign (&s_sig, s_hash, s_key))
402 return US gcry_strerror(gerr);
404 /* gcry_sexp_dump(s_sig); */
406 if ( !(s_sig = gcry_sexp_find_token(s_sig, "s", 0))
408 return US"no sig result";
410 m_sig = gcry_sexp_nth_mpi(s_sig, 1, GCRYMPI_FMT_USG);
415 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, m_sig);
416 debug_printf_indent(" SG: %s\n", s);
419 gerr = gcry_mpi_print(GCRYMPI_FMT_USG, sig->data, SIGSPACE, &sig->len, m_sig);
422 debug_printf_indent("signature conversion from MPI to buffer failed\n");
423 return US gcry_strerror(gerr);
431 /* import public key (from DER in memory)
432 Return: NULL for success, or an error string */
435 exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx)
438 in code sequence per b81207d2bfa92 rsa_parse_public_key() and asn1_get_mpi()
446 uschar * stage = US"S1";
453 BIT STRING:RSAPublicKey
455 INTEGER:Public modulus
456 INTEGER:Public exponent
458 openssl rsa -in aux-fixed/dkim/dkim.private -pubout -outform DER | od -t x1 | head;
459 openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump;
460 openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump -offset 22;
463 /* sequence; just move past the header */
464 if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
465 != ASN1_SUCCESS) goto asn_err;
467 /* sequence; skip the entire thing */
468 DEBUG(D_acl) stage = US"S2";
469 if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, &alen))
470 != ASN1_SUCCESS) goto asn_err;
471 pubkey_der->data += alen; pubkey_der->len -= alen;
474 /* bitstring: limit range to size of bitstring;
475 move over header + content wrapper */
476 DEBUG(D_acl) stage = US"BS";
477 if ((rc = as_tag(pubkey_der, 0, ASN1_TAG_BIT_STRING, &alen)) != ASN1_SUCCESS)
479 pubkey_der->len = alen;
480 pubkey_der->data++; pubkey_der->len--;
482 /* sequence; just move past the header */
483 DEBUG(D_acl) stage = US"S3";
484 if ((rc = as_tag(pubkey_der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
485 != ASN1_SUCCESS) goto asn_err;
487 /* read two integers */
488 DEBUG(D_acl) stage = US"MPI";
489 if ( (errstr = as_mpi(pubkey_der, &verify_ctx->n))
490 || (errstr = as_mpi(pubkey_der, &verify_ctx->e))
494 DEBUG(D_acl) debug_printf_indent("rsa_verify_init:\n");
497 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->n);
498 debug_printf_indent(" N : %s\n", s);
499 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->e);
500 debug_printf_indent(" E : %s\n", s);
506 DEBUG(D_acl) return string_sprintf("%s: %s", stage, asn1_strerror(rc));
507 return US asn1_strerror(rc);
511 /* verify signature (of hash) (given pubkey & alleged sig)
512 Return: NULL for success, or an error string */
515 exim_dkim_verify(ev_ctx * verify_ctx, BOOL is_sha1, blob * data_hash, blob * sig)
518 cf. libgnutls 2.8.5 _wrap_gcry_pk_verify()
521 gcry_sexp_t s_sig = NULL, s_hash = NULL, s_pkey = NULL;
525 if ( (stage = US"pkey sexp build",
526 gerr = gcry_sexp_build (&s_pkey, NULL, "(public-key(rsa(n%m)(e%m)))",
527 verify_ctx->n, verify_ctx->e))
528 || (stage = US"data sexp build",
529 gerr = gcry_sexp_build (&s_hash, NULL,
530 /*XXX needs extension for SHA512 */
532 ? "(data(flags pkcs1)(hash sha1 %b))"
533 : "(data(flags pkcs1)(hash sha256 %b))",
534 (int) data_hash->len, CS data_hash->data))
535 || (stage = US"sig mpi scan",
536 gerr = gcry_mpi_scan(&m_sig, GCRYMPI_FMT_USG, sig->data, sig->len, NULL))
537 || (stage = US"sig sexp build",
538 gerr = gcry_sexp_build (&s_sig, NULL, "(sig-val(rsa(s%m)))", m_sig))
539 || (stage = US"verify",
540 gerr = gcry_pk_verify (s_sig, s_hash, s_pkey))
543 DEBUG(D_acl) debug_printf_indent("verify: error in stage '%s'\n", stage);
544 return US gcry_strerror(gerr);
547 if (s_sig) gcry_sexp_release (s_sig);
548 if (s_hash) gcry_sexp_release (s_hash);
549 if (s_pkey) gcry_sexp_release (s_pkey);
550 gcry_mpi_release (m_sig);
551 gcry_mpi_release (verify_ctx->n);
552 gcry_mpi_release (verify_ctx->e);
560 #elif defined(RSA_OPENSSL)
561 /******************************************************************************/
569 /* accumulate data (gnutls-only) */
571 exim_dkim_data_append(blob * b, int * alloc, uschar * s)
577 /* import private key from PEM string in memory.
578 Return: NULL for success, or an error string */
581 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
586 /*XXX maybe use PEM_read_bio_PrivateKey() ???
587 The sign_ctx would need to have an EVP_PKEY* */
589 /* Convert PEM to DER */
590 if ( !(p = Ustrstr(privkey_pem, "-----BEGIN RSA PRIVATE KEY-----"))
591 || !(q = Ustrstr(p+=31, "-----END RSA PRIVATE KEY-----"))
593 return US"Bad PEM wrapping";
596 if ((len = b64decode(p, &p)) < 0)
597 return US"b64decode failed";
599 if (!(sign_ctx->rsa = d2i_RSAPrivateKey(NULL, CUSS &p, len)))
601 char ssl_errstring[256];
602 ERR_load_crypto_strings(); /*XXX move to a startup routine */
603 ERR_error_string(ERR_get_error(), ssl_errstring);
604 return string_copy(US ssl_errstring);
612 /* allocate mem for signature (when signing) */
613 /* sign data (gnutls_only)
617 Return: NULL for success, or an error string */
620 exim_dkim_sign(es_ctx * sign_ctx, BOOL is_sha1, blob * data, blob * sig)
623 const uschar * ret = NULL;
625 /*XXX will need extension for non-RSA signing algo. Maybe use
626 https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_sign.html ??? */
628 /* Allocate mem for signature */
629 len = RSA_size(sign_ctx->rsa);
630 sig->data = store_get(len);
634 if (RSA_sign(is_sha1 ? NID_sha1 : NID_sha256,
635 CUS data->data, data->len,
636 US sig->data, &len, sign_ctx->rsa) != 1)
638 char ssl_errstring[256];
639 ERR_load_crypto_strings(); /*XXX move to a startup routine */
640 ERR_error_string(ERR_get_error(), ssl_errstring);
641 ret = string_copy(US ssl_errstring);
644 RSA_free(sign_ctx->rsa);
650 /* import public key (from DER in memory)
651 Return: NULL for success, or an error string */
654 exim_dkim_verify_init(blob * pubkey_der, ev_ctx * verify_ctx)
656 const uschar * p = CUS pubkey_der->data;
657 const uschar * ret = NULL;
659 /*XXX d2i_X509_PUBKEY, X509_get_pubkey(), and an EVP_PKEY* in verify_ctx. */
661 if (!(verify_ctx->rsa = d2i_RSA_PUBKEY(NULL, &p, (long) pubkey_der->len)))
663 char ssl_errstring[256];
664 ERR_load_crypto_strings(); /*XXX move to a startup routine */
665 ERR_error_string(ERR_get_error(), ssl_errstring);
666 ret = string_copy(CUS ssl_errstring);
674 /* verify signature (of hash) (given pubkey & alleged sig)
675 Return: NULL for success, or an error string */
678 exim_dkim_verify(ev_ctx * verify_ctx, BOOL is_sha1, blob * data_hash, blob * sig)
680 const uschar * ret = NULL;
682 /*XXX needs extension for SHA512, Possibly EVP_PKEY_verify() is all we need??? */
683 /* with EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING)
684 - see example code at https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_verify.html
685 and maybe also EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) though unclear
686 if that only sets a pad/type field byte value, or sets up for an actual hash operation...
687 Same on the signing side.
688 https://www.openssl.org/docs/manmaster/man3/EVP_PKEY_CTX_set_rsa_padding.html says it does what we want. */
690 if (RSA_verify(is_sha1 ? NID_sha1 : NID_sha256,
691 CUS data_hash->data, data_hash->len,
692 US sig->data, (uint) sig->len, verify_ctx->rsa) != 1)
694 char ssl_errstring[256];
695 ERR_load_crypto_strings(); /*XXX move to a startup routine */
696 ERR_error_string(ERR_get_error(), ssl_errstring);
697 ret = string_copy(US ssl_errstring);
704 /******************************************************************************/
706 #endif /*DISABLE_DKIM*/