b61b428327292cf6bad504a44bdf824b26e2245f
[exim.git] / src / src / pdkim / signing.c
1 /*
2 * PDKIM - a RFC4871 (DKIM) implementation
3 *
4 * Copyright (C) 2017 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(uschar * privkey_pem, es_ctx * sign_ctx)
90 {
91 gnutls_datum_t k = { .data = 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(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-onl 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(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_EC
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. Could be incremental
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_SHA1: md = EVP_sha1(); break;
744 case HASH_SHA2_256: md = EVP_sha256(); break;
745 case HASH_SHA2_512: md = EVP_sha512(); break;
746 default: return US"nonhandled hash type";
747 }
748
749 /* Create the Message Digest Context */
750 /*XXX renamed to EVP_MD_CTX_new() in 1.1.0 */
751 if( (ctx = EVP_MD_CTX_create())
752
753 /* Initialise the DigestSign operation */
754 && EVP_DigestSignInit(ctx, NULL, md, NULL, sign_ctx->key) > 0
755
756 /* Call update with the message */
757 && EVP_DigestSignUpdate(ctx, data->data, data->len) > 0
758
759 /* Finalise the DigestSign operation */
760 /* First call EVP_DigestSignFinal with a NULL sig parameter to obtain the length of the
761 * signature. Length is returned in slen */
762 && EVP_DigestSignFinal(ctx, NULL, &siglen) > 0
763
764 /* Allocate memory for the signature based on size in slen */
765 && (sig->data = store_get(siglen))
766
767 /* Obtain the signature (slen could change here!) */
768 && EVP_DigestSignFinal(ctx, sig->data, &siglen) > 0
769 )
770 {
771 EVP_MD_CTX_destroy(ctx);
772 sig->len = siglen;
773 return NULL;
774 }
775
776 if (ctx) EVP_MD_CTX_destroy(ctx);
777 return US ERR_error_string(ERR_get_error(), NULL);
778 }
779
780
781
782 /* import public key (from blob in memory)
783 Return: NULL for success, or an error string */
784
785 const uschar *
786 exim_dkim_verify_init(blob * pubkey, keyformat fmt, ev_ctx * verify_ctx)
787 {
788 const uschar * s = pubkey->data;
789 uschar * ret = NULL;
790
791 if (fmt != KEYFMT_DER) return US"pubkey format not handled";
792 switch(fmt)
793 {
794 case KEYFMT_DER:
795 /*XXX ok, this fails for EC:
796 error:0609E09C:digital envelope routines:pkey_set_type:unsupported algorithm
797 */
798
799 /*XXX hmm, we never free this */
800 if (!(verify_ctx->key = d2i_PUBKEY(NULL, &s, pubkey->len)))
801 ret = US ERR_error_string(ERR_get_error(), NULL);
802 break;
803 #ifdef SIGN_HAVE_ED25519
804 case KEYFMT_ED25519_BARE:
805 {
806 BIGNUM * x;
807 EC_KEY * eck;
808 if ( !(x = BN_bin2bn(s, pubkey->len, NULL))
809 || !(eck = EC_KEY_new_by_curve_name(NID_ED25519))
810 || !EC_KEY_set_public_key_affine_coordinates(eck, x, NULL)
811 || !(verify_ctx->key = EVP_PKEY_new())
812 || !EVP_PKEY_assign_EC_KEY(verify_ctx->key, eck)
813 )
814 ret = US ERR_error_string(ERR_get_error(), NULL);
815 }
816 break;
817 #endif
818 default:
819 ret = US"pubkey format not handled";
820 break;
821 }
822
823 return ret;
824 }
825
826
827
828
829 /* verify signature (of hash)
830 (pre-EC coding; of data if "notyet" code, The latter could be incremental)
831 (given pubkey & alleged sig)
832 Return: NULL for success, or an error string */
833
834 const uschar *
835 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data, blob * sig)
836 {
837 const EVP_MD * md;
838
839 /*XXX OpenSSL does not seem to have Ed25519 support yet. Reportedly BoringSSL does,
840 but that's a nonstable API and not recommended (by its owner, Google) for external use. */
841
842 switch (hash)
843 {
844 case HASH_SHA1: md = EVP_sha1(); break;
845 case HASH_SHA2_256: md = EVP_sha256(); break;
846 case HASH_SHA2_512: md = EVP_sha512(); break;
847 default: return US"nonhandled hash type";
848 }
849
850 #ifdef notyet_SIGN_HAVE_ED25519
851 {
852 EVP_MD_CTX * ctx;
853
854 /*XXX renamed to EVP_MD_CTX_new() in 1.1.0 */
855 if (
856 (ctx = EVP_MD_CTX_create())
857
858 /* Initialize `key` with a public key */
859 && EVP_DigestVerifyInit(ctx, NULL, md, NULL, verify_ctx->key) > 0
860
861 /* add data to be hashed (call multiple times if needed) */
862
863 && EVP_DigestVerifyUpdate(ctx, data->data, data->len) > 0
864
865 /* finish off the hash and check the offered signature */
866
867 && EVP_DigestVerifyFinal(ctx, sig->data, sig->len) > 0
868 )
869 {
870 EVP_MD_CTX_destroy(ctx); /* renamed to _free in 1.1.0 */
871 return NULL;
872 }
873
874 if (ctx) EVP_MD_CTX_free(ctx);
875 return US ERR_error_string(ERR_get_error(), NULL);
876 }
877 #else
878 {
879 EVP_PKEY_CTX * ctx;
880
881 if ( (ctx = EVP_PKEY_CTX_new(verify_ctx->key, NULL))
882 && EVP_PKEY_verify_init(ctx) > 0
883 && EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) > 0
884 && EVP_PKEY_CTX_set_signature_md(ctx, md) > 0
885 && EVP_PKEY_verify(ctx, sig->data, sig->len,
886 data->data, data->len) == 1
887 )
888 { EVP_PKEY_CTX_free(ctx); return NULL; }
889
890 if (ctx) EVP_PKEY_CTX_free(ctx);
891 return US ERR_error_string(ERR_get_error(), NULL);
892 }
893 #endif
894 }
895
896
897
898 #endif
899 /******************************************************************************/
900
901 #endif /*DISABLE_DKIM*/
902 #endif /*MACRO_PREDEF*/
903 /* End of File */