f73fa9cc8f00631f0cd158abd6a854877afd7ffb
[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
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 # define EXIM_GNUTLS_LIBRARY_LOG_LEVEL 3
24
25
26 /* Logging function which can be registered with
27 * gnutls_global_set_log_function()
28 * gnutls_global_set_log_level() 0..9
29 */
30 #if EXIM_GNUTLS_LIBRARY_LOG_LEVEL >= 0
31 static void
32 exim_gnutls_logger_cb(int level, const char *message)
33 {
34 size_t len = strlen(message);
35 if (len < 1)
36 {
37 DEBUG(D_tls) debug_printf("GnuTLS<%d> empty debug message\n", level);
38 return;
39 }
40 DEBUG(D_tls) debug_printf("GnuTLS<%d>: %s%s", level, message,
41 message[len-1] == '\n' ? "" : "\n");
42 }
43 #endif
44
45
46
47 void
48 exim_dkim_init(void)
49 {
50 #if EXIM_GNUTLS_LIBRARY_LOG_LEVEL >= 0
51 DEBUG(D_tls)
52 {
53 gnutls_global_set_log_function(exim_gnutls_logger_cb);
54 /* arbitrarily chosen level; bump upto 9 for more */
55 gnutls_global_set_log_level(EXIM_GNUTLS_LIBRARY_LOG_LEVEL);
56 }
57 #endif
58 }
59
60
61 /* accumulate data (gnutls-only). String to be appended must be nul-terminated. */
62 gstring *
63 exim_dkim_data_append(gstring * g, uschar * s)
64 {
65 return string_cat(g, s);
66 }
67
68
69
70 /* import private key from PEM string in memory.
71 Return: NULL for success, or an error string */
72
73 const uschar *
74 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
75 {
76 gnutls_datum_t k = { .data = privkey_pem, .size = Ustrlen(privkey_pem) };
77 gnutls_x509_privkey_t x509_key;
78 int rc;
79
80 if ( (rc = gnutls_x509_privkey_init(&x509_key))
81 || (rc = gnutls_x509_privkey_import(x509_key, &k, GNUTLS_X509_FMT_PEM))
82 || (rc = gnutls_privkey_init(&sign_ctx->key))
83 || (rc = gnutls_privkey_import_x509(sign_ctx->key, x509_key, 0))
84 )
85 return CUS gnutls_strerror(rc);
86
87 switch (rc = gnutls_privkey_get_pk_algorithm(sign_ctx->key, NULL))
88 {
89 case GNUTLS_PK_RSA: sign_ctx->keytype = KEYTYPE_RSA; break;
90 #ifdef SIGN_HAVE_ED25519
91 case GNUTLS_PK_EDDSA_ED25519: sign_ctx->keytype = KEYTYPE_ED25519; break;
92 #endif
93 default: return rc < 0
94 ? CUS gnutls_strerror(rc)
95 : string_sprintf("Unhandled key type: %d '%s'", rc, gnutls_pk_get_name(rc));
96 }
97
98 return NULL;
99 }
100
101
102
103 /* allocate mem for signature (when signing) */
104 /* hash & sign data. No way to do incremental.
105
106 Return: NULL for success, or an error string */
107
108 const uschar *
109 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
110 {
111 gnutls_datum_t k_data = { .data = data->data, .size = data->len };
112 gnutls_digest_algorithm_t dig;
113 gnutls_datum_t k_sig;
114 int rc;
115
116 switch (hash)
117 {
118 case HASH_SHA1: dig = GNUTLS_DIG_SHA1; break;
119 case HASH_SHA2_256: dig = GNUTLS_DIG_SHA256; break;
120 case HASH_SHA2_512: dig = GNUTLS_DIG_SHA512; break;
121 default: return US"nonhandled hash type";
122 }
123
124 if ((rc = gnutls_privkey_sign_data(sign_ctx->key, dig, 0, &k_data, &k_sig)))
125 return CUS gnutls_strerror(rc);
126
127 /* Don't care about deinit for the key; shortlived process */
128
129 sig->data = k_sig.data;
130 sig->len = k_sig.size;
131 return NULL;
132 }
133
134
135
136 /* import public key (from blob in memory)
137 Return: NULL for success, or an error string */
138
139 const uschar *
140 exim_dkim_verify_init(blob * pubkey, keyformat fmt, ev_ctx * verify_ctx)
141 {
142 gnutls_datum_t k;
143 int rc;
144 const uschar * ret = NULL;
145
146 gnutls_pubkey_init(&verify_ctx->key);
147 k.data = pubkey->data;
148 k.size = pubkey->len;
149
150 switch(fmt)
151 {
152 case KEYFMT_DER:
153 if ((rc = gnutls_pubkey_import(verify_ctx->key, &k, GNUTLS_X509_FMT_DER)))
154 ret = gnutls_strerror(rc);
155 break;
156 #ifdef SIGN_HAVE_ED25519
157 case KEYFMT_ED25519_BARE:
158 if ((rc = gnutls_pubkey_import_ecc_raw(verify_ctx->key,
159 GNUTLS_ECC_CURVE_ED25519, &k, NULL)))
160 ret = gnutls_strerror(rc);
161 break;
162 #endif
163 default:
164 ret = US"pubkey format not handled";
165 break;
166 }
167 return ret;
168 }
169
170
171 /* verify signature (of hash if RSA sig, of data if EC sig. No way to do incremental)
172 (given pubkey & alleged sig)
173 Return: NULL for success, or an error string */
174
175 const uschar *
176 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data_hash, blob * sig)
177 {
178 gnutls_datum_t k = { .data = data_hash->data, .size = data_hash->len };
179 gnutls_datum_t s = { .data = sig->data, .size = sig->len };
180 int rc;
181 const uschar * ret = NULL;
182
183 #ifdef SIGN_HAVE_ED25519
184 if (verify_ctx->keytype == KEYTYPE_ED25519)
185 {
186 if ((rc = gnutls_pubkey_verify_data2(verify_ctx->key,
187 GNUTLS_SIGN_EDDSA_ED25519, 0, &k, &s)) < 0)
188 ret = gnutls_strerror(rc);
189 }
190 else
191 #endif
192 {
193 gnutls_sign_algorithm_t algo;
194 switch (hash)
195 {
196 case HASH_SHA1: algo = GNUTLS_SIGN_RSA_SHA1; break;
197 case HASH_SHA2_256: algo = GNUTLS_SIGN_RSA_SHA256; break;
198 case HASH_SHA2_512: algo = GNUTLS_SIGN_RSA_SHA512; break;
199 default: return US"nonhandled hash type";
200 }
201
202 if ((rc = gnutls_pubkey_verify_hash2(verify_ctx->key, algo, 0, &k, &s)) < 0)
203 ret = gnutls_strerror(rc);
204 }
205
206 gnutls_pubkey_deinit(verify_ctx->key);
207 return ret;
208 }
209
210
211
212
213 #elif defined(SIGN_GCRYPT)
214 /******************************************************************************/
215 /* This variant is used under pre-3.0.0 GnuTLS. Only rsa-sha1 and rsa-sha256 */
216
217
218 /* Internal service routine:
219 Read and move past an asn.1 header, checking class & tag,
220 optionally returning the data-length */
221
222 static int
223 as_tag(blob * der, uschar req_cls, long req_tag, long * alen)
224 {
225 int rc;
226 uschar tag_class;
227 int taglen;
228 long tag, len;
229
230 debug_printf_indent("as_tag: %02x %02x %02x %02x\n",
231 der->data[0], der->data[1], der->data[2], der->data[3]);
232
233 if ((rc = asn1_get_tag_der(der->data++, der->len--, &tag_class, &taglen, &tag))
234 != ASN1_SUCCESS)
235 return rc;
236
237 if (tag_class != req_cls || tag != req_tag) return ASN1_ELEMENT_NOT_FOUND;
238
239 if ((len = asn1_get_length_der(der->data, der->len, &taglen)) < 0)
240 return ASN1_DER_ERROR;
241 if (alen) *alen = len;
242
243 /* debug_printf_indent("as_tag: tlen %d dlen %d\n", taglen, (int)len); */
244
245 der->data += taglen;
246 der->len -= taglen;
247 return rc;
248 }
249
250 /* Internal service routine:
251 Read and move over an asn.1 integer, setting an MPI to the value
252 */
253
254 static uschar *
255 as_mpi(blob * der, gcry_mpi_t * mpi)
256 {
257 long alen;
258 int rc;
259 gcry_error_t gerr;
260
261 debug_printf_indent("%s\n", __FUNCTION__);
262
263 /* integer; move past the header */
264 if ((rc = as_tag(der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS)
265 return US asn1_strerror(rc);
266
267 /* read to an MPI */
268 if ((gerr = gcry_mpi_scan(mpi, GCRYMPI_FMT_STD, der->data, alen, NULL)))
269 return US gcry_strerror(gerr);
270
271 /* move over the data */
272 der->data += alen; der->len -= alen;
273 return NULL;
274 }
275
276
277
278 void
279 exim_dkim_init(void)
280 {
281 /* Version check should be the very first call because it
282 makes sure that important subsystems are initialized. */
283 if (!gcry_check_version (GCRYPT_VERSION))
284 {
285 fputs ("libgcrypt version mismatch\n", stderr);
286 exit (2);
287 }
288
289 /* We don't want to see any warnings, e.g. because we have not yet
290 parsed program options which might be used to suppress such
291 warnings. */
292 gcry_control (GCRYCTL_SUSPEND_SECMEM_WARN);
293
294 /* ... If required, other initialization goes here. Note that the
295 process might still be running with increased privileges and that
296 the secure memory has not been initialized. */
297
298 /* Allocate a pool of 16k secure memory. This make the secure memory
299 available and also drops privileges where needed. */
300 gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);
301
302 /* It is now okay to let Libgcrypt complain when there was/is
303 a problem with the secure memory. */
304 gcry_control (GCRYCTL_RESUME_SECMEM_WARN);
305
306 /* ... If required, other initialization goes here. */
307
308 /* Tell Libgcrypt that initialization has completed. */
309 gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
310
311 return;
312 }
313
314
315
316
317 /* Accumulate data (gnutls-only).
318 String to be appended must be nul-terminated. */
319
320 gstring *
321 exim_dkim_data_append(gstring * g, uschar * s)
322 {
323 return g; /*dummy*/
324 }
325
326
327
328 /* import private key from PEM string in memory.
329 Only handles RSA keys.
330 Return: NULL for success, or an error string */
331
332 const uschar *
333 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
334 {
335 uschar * s1, * s2;
336 blob der;
337 long alen;
338 int rc;
339
340 /*XXX will need extension to _spot_ as well as handle a
341 non-RSA key? I think...
342 So... this is not a PrivateKeyInfo - which would have a field
343 identifying the keytype - PrivateKeyAlgorithmIdentifier -
344 but a plain RSAPrivateKey (wrapped in PEM-headers. Can we
345 use those as a type tag? What forms are there? "BEGIN EC PRIVATE KEY" (cf. ec(1ssl))
346
347 How does OpenSSL PEM_read_bio_PrivateKey() deal with it?
348 gnutls_x509_privkey_import() ?
349 */
350
351 /*
352 * RSAPrivateKey ::= SEQUENCE
353 * version Version,
354 * modulus INTEGER, -- n
355 * publicExponent INTEGER, -- e
356 * privateExponent INTEGER, -- d
357 * prime1 INTEGER, -- p
358 * prime2 INTEGER, -- q
359 * exponent1 INTEGER, -- d mod (p-1)
360 * exponent2 INTEGER, -- d mod (q-1)
361 * coefficient INTEGER, -- (inverse of q) mod p
362 * otherPrimeInfos OtherPrimeInfos OPTIONAL
363
364 * ECPrivateKey ::= SEQUENCE {
365 * version INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
366 * privateKey OCTET STRING,
367 * parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
368 * publicKey [1] BIT STRING OPTIONAL
369 * }
370 * Hmm, only 1 useful item, and not even an integer? Wonder how we might use it...
371
372 - actually, gnutls_x509_privkey_import() appears to require a curve name parameter
373 value for that is an OID? a local-only integer (it's an enum in GnuTLS)?
374
375
376 Useful cmds:
377 ssh-keygen -t ecdsa -f foo.privkey
378 ssh-keygen -t ecdsa -b384 -f foo.privkey
379 ssh-keygen -t ecdsa -b521 -f foo.privkey
380 ssh-keygen -t ed25519 -f foo.privkey
381
382 < foo openssl pkcs8 -in /dev/stdin -inform PEM -nocrypt -topk8 -outform DER | od -x
383
384 openssl asn1parse -in foo -inform PEM -dump
385 openssl asn1parse -in foo -inform PEM -dump -stroffset 24 (??)
386 (not good for ed25519)
387
388 */
389
390 if ( !(s1 = Ustrstr(CS privkey_pem, "-----BEGIN RSA PRIVATE KEY-----"))
391 || !(s2 = Ustrstr(CS (s1+=31), "-----END RSA PRIVATE KEY-----" ))
392 )
393 return US"Bad PEM wrapper";
394
395 *s2 = '\0';
396
397 if ((der.len = b64decode(s1, &der.data)) < 0)
398 return US"Bad PEM-DER b64 decode";
399
400 /* untangle asn.1 */
401
402 /* sequence; just move past the header */
403 if ((rc = as_tag(&der, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
404 != ASN1_SUCCESS) goto asn_err;
405
406 /* integer version; move past the header, check is zero */
407 if ((rc = as_tag(&der, 0, ASN1_TAG_INTEGER, &alen)) != ASN1_SUCCESS)
408 goto asn_err;
409 if (alen != 1 || *der.data != 0)
410 return US"Bad version number";
411 der.data++; der.len--;
412
413 if ( (s1 = as_mpi(&der, &sign_ctx->n))
414 || (s1 = as_mpi(&der, &sign_ctx->e))
415 || (s1 = as_mpi(&der, &sign_ctx->d))
416 || (s1 = as_mpi(&der, &sign_ctx->p))
417 || (s1 = as_mpi(&der, &sign_ctx->q))
418 || (s1 = as_mpi(&der, &sign_ctx->dp))
419 || (s1 = as_mpi(&der, &sign_ctx->dq))
420 || (s1 = as_mpi(&der, &sign_ctx->qp))
421 )
422 return s1;
423
424 #ifdef extreme_debug
425 DEBUG(D_acl) debug_printf_indent("rsa_signing_init:\n");
426 {
427 uschar * s;
428 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->n);
429 debug_printf_indent(" N : %s\n", s);
430 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->e);
431 debug_printf_indent(" E : %s\n", s);
432 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->d);
433 debug_printf_indent(" D : %s\n", s);
434 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->p);
435 debug_printf_indent(" P : %s\n", s);
436 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->q);
437 debug_printf_indent(" Q : %s\n", s);
438 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dp);
439 debug_printf_indent(" DP: %s\n", s);
440 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->dq);
441 debug_printf_indent(" DQ: %s\n", s);
442 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, sign_ctx->qp);
443 debug_printf_indent(" QP: %s\n", s);
444 }
445 #endif
446
447 sign_ctx->keytype = KEYTYPE_RSA;
448 return NULL;
449
450 asn_err: return US asn1_strerror(rc);
451 }
452
453
454
455 /* allocate mem for signature (when signing) */
456 /* sign already-hashed data.
457
458 Return: NULL for success, or an error string */
459
460 const uschar *
461 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
462 {
463 char * sexp_hash;
464 gcry_sexp_t s_hash = NULL, s_key = NULL, s_sig = NULL;
465 gcry_mpi_t m_sig;
466 uschar * errstr;
467 gcry_error_t gerr;
468
469 /*XXX will need extension for hash types (though, possibly, should
470 be re-specced to not rehash but take an already-hashed value? Actually
471 current impl looks WRONG - it _is_ given a hash so should not be
472 re-hashing. Has this been tested?
473
474 Will need extension for non-RSA sugning algos. */
475
476 switch (hash)
477 {
478 case HASH_SHA1: sexp_hash = "(data(flags pkcs1)(hash sha1 %b))"; break;
479 case HASH_SHA2_256: sexp_hash = "(data(flags pkcs1)(hash sha256 %b))"; break;
480 default: return US"nonhandled hash type";
481 }
482
483 #define SIGSPACE 128
484 sig->data = store_get(SIGSPACE);
485
486 if (gcry_mpi_cmp (sign_ctx->p, sign_ctx->q) > 0)
487 {
488 gcry_mpi_swap (sign_ctx->p, sign_ctx->q);
489 gcry_mpi_invm (sign_ctx->qp, sign_ctx->p, sign_ctx->q);
490 }
491
492 if ( (gerr = gcry_sexp_build (&s_key, NULL,
493 "(private-key (rsa (n%m)(e%m)(d%m)(p%m)(q%m)(u%m)))",
494 sign_ctx->n, sign_ctx->e,
495 sign_ctx->d, sign_ctx->p,
496 sign_ctx->q, sign_ctx->qp))
497 || (gerr = gcry_sexp_build (&s_hash, NULL, sexp_hash,
498 (int) data->len, CS data->data))
499 || (gerr = gcry_pk_sign (&s_sig, s_hash, s_key))
500 )
501 return US gcry_strerror(gerr);
502
503 /* gcry_sexp_dump(s_sig); */
504
505 if ( !(s_sig = gcry_sexp_find_token(s_sig, "s", 0))
506 )
507 return US"no sig result";
508
509 m_sig = gcry_sexp_nth_mpi(s_sig, 1, GCRYMPI_FMT_USG);
510
511 #ifdef extreme_debug
512 DEBUG(D_acl)
513 {
514 uschar * s;
515 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, m_sig);
516 debug_printf_indent(" SG: %s\n", s);
517 }
518 #endif
519
520 gerr = gcry_mpi_print(GCRYMPI_FMT_USG, sig->data, SIGSPACE, &sig->len, m_sig);
521 if (gerr)
522 {
523 debug_printf_indent("signature conversion from MPI to buffer failed\n");
524 return US gcry_strerror(gerr);
525 }
526 #undef SIGSPACE
527
528 return NULL;
529 }
530
531
532 /* import public key (from blob in memory)
533 Return: NULL for success, or an error string */
534
535 const uschar *
536 exim_dkim_verify_init(blob * pubkey, keyformat fmt, ev_ctx * verify_ctx)
537 {
538 /*
539 in code sequence per b81207d2bfa92 rsa_parse_public_key() and asn1_get_mpi()
540 */
541 uschar tag_class;
542 int taglen;
543 long alen;
544 int rc;
545 uschar * errstr;
546 gcry_error_t gerr;
547 uschar * stage = US"S1";
548
549 if (fmt != KEYFMT_DER) return US"pubkey format not handled";
550
551 /*
552 sequence
553 sequence
554 OBJECT:rsaEncryption
555 NULL
556 BIT STRING:RSAPublicKey
557 sequence
558 INTEGER:Public modulus
559 INTEGER:Public exponent
560
561 openssl rsa -in aux-fixed/dkim/dkim.private -pubout -outform DER | od -t x1 | head;
562 openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump;
563 openssl rsa -in aux-fixed/dkim/dkim.private -pubout | openssl asn1parse -dump -offset 22;
564 */
565
566 /* sequence; just move past the header */
567 if ((rc = as_tag(pubkey, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
568 != ASN1_SUCCESS) goto asn_err;
569
570 /* sequence; skip the entire thing */
571 DEBUG(D_acl) stage = US"S2";
572 if ((rc = as_tag(pubkey, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, &alen))
573 != ASN1_SUCCESS) goto asn_err;
574 pubkey->data += alen; pubkey->len -= alen;
575
576
577 /* bitstring: limit range to size of bitstring;
578 move over header + content wrapper */
579 DEBUG(D_acl) stage = US"BS";
580 if ((rc = as_tag(pubkey, 0, ASN1_TAG_BIT_STRING, &alen)) != ASN1_SUCCESS)
581 goto asn_err;
582 pubkey->len = alen;
583 pubkey->data++; pubkey->len--;
584
585 /* sequence; just move past the header */
586 DEBUG(D_acl) stage = US"S3";
587 if ((rc = as_tag(pubkey, ASN1_CLASS_STRUCTURED, ASN1_TAG_SEQUENCE, NULL))
588 != ASN1_SUCCESS) goto asn_err;
589
590 /* read two integers */
591 DEBUG(D_acl) stage = US"MPI";
592 if ( (errstr = as_mpi(pubkey, &verify_ctx->n))
593 || (errstr = as_mpi(pubkey, &verify_ctx->e))
594 )
595 return errstr;
596
597 #ifdef extreme_debug
598 DEBUG(D_acl) debug_printf_indent("rsa_verify_init:\n");
599 {
600 uschar * s;
601 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->n);
602 debug_printf_indent(" N : %s\n", s);
603 gcry_mpi_aprint (GCRYMPI_FMT_HEX, &s, NULL, verify_ctx->e);
604 debug_printf_indent(" E : %s\n", s);
605 }
606
607 #endif
608 return NULL;
609
610 asn_err:
611 DEBUG(D_acl) return string_sprintf("%s: %s", stage, asn1_strerror(rc));
612 return US asn1_strerror(rc);
613 }
614
615
616 /* verify signature (of hash)
617 XXX though we appear to be doing a hash, too!
618 (given pubkey & alleged sig)
619 Return: NULL for success, or an error string */
620
621 const uschar *
622 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data_hash, blob * sig)
623 {
624 /*
625 cf. libgnutls 2.8.5 _wrap_gcry_pk_verify()
626 */
627 char * sexp_hash;
628 gcry_mpi_t m_sig;
629 gcry_sexp_t s_sig = NULL, s_hash = NULL, s_pkey = NULL;
630 gcry_error_t gerr;
631 uschar * stage;
632
633 /*XXX needs extension for SHA512 */
634 switch (hash)
635 {
636 case HASH_SHA1: sexp_hash = "(data(flags pkcs1)(hash sha1 %b))"; break;
637 case HASH_SHA2_256: sexp_hash = "(data(flags pkcs1)(hash sha256 %b))"; break;
638 default: return US"nonhandled hash type";
639 }
640
641 if ( (stage = US"pkey sexp build",
642 gerr = gcry_sexp_build (&s_pkey, NULL, "(public-key(rsa(n%m)(e%m)))",
643 verify_ctx->n, verify_ctx->e))
644 || (stage = US"data sexp build",
645 gerr = gcry_sexp_build (&s_hash, NULL, sexp_hash,
646 (int) data_hash->len, CS data_hash->data))
647 || (stage = US"sig mpi scan",
648 gerr = gcry_mpi_scan(&m_sig, GCRYMPI_FMT_USG, sig->data, sig->len, NULL))
649 || (stage = US"sig sexp build",
650 gerr = gcry_sexp_build (&s_sig, NULL, "(sig-val(rsa(s%m)))", m_sig))
651 || (stage = US"verify",
652 gerr = gcry_pk_verify (s_sig, s_hash, s_pkey))
653 )
654 {
655 DEBUG(D_acl) debug_printf_indent("verify: error in stage '%s'\n", stage);
656 return US gcry_strerror(gerr);
657 }
658
659 if (s_sig) gcry_sexp_release (s_sig);
660 if (s_hash) gcry_sexp_release (s_hash);
661 if (s_pkey) gcry_sexp_release (s_pkey);
662 gcry_mpi_release (m_sig);
663 gcry_mpi_release (verify_ctx->n);
664 gcry_mpi_release (verify_ctx->e);
665
666 return NULL;
667 }
668
669
670
671
672 #elif defined(SIGN_OPENSSL)
673 /******************************************************************************/
674
675 void
676 exim_dkim_init(void)
677 {
678 ERR_load_crypto_strings();
679 }
680
681
682 /* accumulate data (was gnutls-onl but now needed for OpenSSL non-EC too
683 because now using hash-and-sign interface) */
684 gstring *
685 exim_dkim_data_append(gstring * g, uschar * s)
686 {
687 return string_cat(g, s);
688 }
689
690
691 /* import private key from PEM string in memory.
692 Return: NULL for success, or an error string */
693
694 const uschar *
695 exim_dkim_signing_init(uschar * privkey_pem, es_ctx * sign_ctx)
696 {
697 BIO * bp = BIO_new_mem_buf(privkey_pem, -1);
698
699 if (!(sign_ctx->key = PEM_read_bio_PrivateKey(bp, NULL, NULL, NULL)))
700 return US ERR_error_string(ERR_get_error(), NULL);
701
702 sign_ctx->keytype =
703 #ifdef SIGN_HAVE_ED25519
704 EVP_PKEY_type(EVP_PKEY_id(sign_ctx->key)) == EVP_PKEY_EC
705 ? KEYTYPE_ED25519 : KEYTYPE_RSA;
706 #else
707 KEYTYPE_RSA;
708 #endif
709 return NULL;
710 }
711
712
713
714 /* allocate mem for signature (when signing) */
715 /* hash & sign data. Could be incremental
716
717 Return: NULL for success with the signaature in the sig blob, or an error string */
718
719 const uschar *
720 exim_dkim_sign(es_ctx * sign_ctx, hashmethod hash, blob * data, blob * sig)
721 {
722 const EVP_MD * md;
723 EVP_MD_CTX * ctx;
724 size_t siglen;
725
726 switch (hash)
727 {
728 case HASH_SHA1: md = EVP_sha1(); break;
729 case HASH_SHA2_256: md = EVP_sha256(); break;
730 case HASH_SHA2_512: md = EVP_sha512(); break;
731 default: return US"nonhandled hash type";
732 }
733
734 /* Create the Message Digest Context */
735 /*XXX renamed to EVP_MD_CTX_new() in 1.1.0 */
736 if( (ctx = EVP_MD_CTX_create())
737
738 /* Initialise the DigestSign operation */
739 && EVP_DigestSignInit(ctx, NULL, md, NULL, sign_ctx->key) > 0
740
741 /* Call update with the message */
742 && EVP_DigestSignUpdate(ctx, data->data, data->len) > 0
743
744 /* Finalise the DigestSign operation */
745 /* First call EVP_DigestSignFinal with a NULL sig parameter to obtain the length of the
746 * signature. Length is returned in slen */
747 && EVP_DigestSignFinal(ctx, NULL, &siglen) > 0
748
749 /* Allocate memory for the signature based on size in slen */
750 && (sig->data = store_get(siglen))
751
752 /* Obtain the signature (slen could change here!) */
753 && EVP_DigestSignFinal(ctx, sig->data, &siglen) > 0
754 )
755 {
756 EVP_MD_CTX_destroy(ctx);
757 sig->len = siglen;
758 return NULL;
759 }
760
761 if (ctx) EVP_MD_CTX_destroy(ctx);
762 return US ERR_error_string(ERR_get_error(), NULL);
763 }
764
765
766
767 /* import public key (from blob in memory)
768 Return: NULL for success, or an error string */
769
770 const uschar *
771 exim_dkim_verify_init(blob * pubkey, keyformat fmt, ev_ctx * verify_ctx)
772 {
773 const uschar * s = pubkey->data;
774 uschar * ret = NULL;
775
776 if (fmt != KEYFMT_DER) return US"pubkey format not handled";
777 switch(fmt)
778 {
779 case KEYFMT_DER:
780 /*XXX ok, this fails for EC:
781 error:0609E09C:digital envelope routines:pkey_set_type:unsupported algorithm
782 */
783
784 /*XXX hmm, we never free this */
785 if (!(verify_ctx->key = d2i_PUBKEY(NULL, &s, pubkey->len)))
786 ret = US ERR_error_string(ERR_get_error(), NULL);
787 break;
788 #ifdef SIGN_HAVE_ED25519
789 case KEYFMT_ED25519_BARE:
790 {
791 BIGNUM * x;
792 EC_KEY * eck;
793 if ( !(x = BN_bin2bn(s, pubkey->len, NULL))
794 || !(eck = EC_KEY_new_by_curve_name(NID_ED25519))
795 || !EC_KEY_set_public_key_affine_coordinates(eck, x, NULL)
796 || !(verify_ctx->key = EVP_PKEY_new())
797 || !EVP_PKEY_assign_EC_KEY(verify_ctx->key, eck)
798 )
799 ret = US ERR_error_string(ERR_get_error(), NULL);
800 }
801 break;
802 #endif
803 default:
804 ret = US"pubkey format not handled";
805 break;
806 }
807
808 return ret;
809 }
810
811
812
813
814 /* verify signature (of hash)
815 (pre-EC coding; of data if "notyet" code, The latter could be incremental)
816 (given pubkey & alleged sig)
817 Return: NULL for success, or an error string */
818
819 const uschar *
820 exim_dkim_verify(ev_ctx * verify_ctx, hashmethod hash, blob * data, blob * sig)
821 {
822 const EVP_MD * md;
823
824 /*XXX OpenSSL does not seem to have Ed25519 support yet. Reportedly BoringSSL does,
825 but that's a nonstable API and not recommended (by its owner, Google) for external use. */
826
827 switch (hash)
828 {
829 case HASH_SHA1: md = EVP_sha1(); break;
830 case HASH_SHA2_256: md = EVP_sha256(); break;
831 case HASH_SHA2_512: md = EVP_sha512(); break;
832 default: return US"nonhandled hash type";
833 }
834
835 #ifdef notyet_SIGN_HAVE_ED25519
836 {
837 EVP_MD_CTX * ctx;
838
839 /*XXX renamed to EVP_MD_CTX_new() in 1.1.0 */
840 if (
841 (ctx = EVP_MD_CTX_create())
842
843 /* Initialize `key` with a public key */
844 && EVP_DigestVerifyInit(ctx, NULL, md, NULL, verify_ctx->key) > 0
845
846 /* add data to be hashed (call multiple times if needed) */
847
848 && EVP_DigestVerifyUpdate(ctx, data->data, data->len) > 0
849
850 /* finish off the hash and check the offered signature */
851
852 && EVP_DigestVerifyFinal(ctx, sig->data, sig->len) > 0
853 )
854 {
855 EVP_MD_CTX_destroy(ctx); /* renamed to _free in 1.1.0 */
856 return NULL;
857 }
858
859 if (ctx) EVP_MD_CTX_free(ctx);
860 return US ERR_error_string(ERR_get_error(), NULL);
861 }
862 #else
863 {
864 EVP_PKEY_CTX * ctx;
865
866 if ( (ctx = EVP_PKEY_CTX_new(verify_ctx->key, NULL))
867 && EVP_PKEY_verify_init(ctx) > 0
868 && EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) > 0
869 && EVP_PKEY_CTX_set_signature_md(ctx, md) > 0
870 && EVP_PKEY_verify(ctx, sig->data, sig->len,
871 data->data, data->len) == 1
872 )
873 { EVP_PKEY_CTX_free(ctx); return NULL; }
874
875 if (ctx) EVP_PKEY_CTX_free(ctx);
876 return US ERR_error_string(ERR_get_error(), NULL);
877 }
878 #endif
879 }
880
881
882
883 #endif
884 /******************************************************************************/
885
886 #endif /*DISABLE_DKIM*/
887 /* End of File */