+return string_from_gstring(hdr);
+}
+
+
+/* -------------------------------------------------------------------------- */
+
+/* According to draft-ietf-dcrup-dkim-crypto-07 "keys are 256 bits" (referring
+to DNS, hence the pubkey). Check for more than 32 bytes; if so assume the
+alternate possible representation (still) being discussed: a
+SubjectPublickeyInfo wrapped key - and drop all but the trailing 32-bytes (it
+should be a DER, with exactly 12 leading bytes - but we could accept a BER also,
+which could be any size). We still rely on the crypto library for checking for
+undersize.
+
+When the RFC is published this should be re-addressed. */
+
+static void
+check_bare_ed25519_pubkey(pdkim_pubkey * p)
+{
+int excess = p->key.len - 32;
+if (excess > 0)
+ {
+ DEBUG(D_acl) debug_printf("DKIM: unexpected pubkey len %lu\n", p->key.len);
+ p->key.data += excess; p->key.len = 32;
+ }
+}
+
+
+static pdkim_pubkey *
+pdkim_key_from_dns(pdkim_ctx * ctx, pdkim_signature * sig, ev_ctx * vctx,
+ const uschar ** errstr)
+{
+uschar * dns_txt_name, * dns_txt_reply;
+pdkim_pubkey * p;
+
+/* Fetch public key for signing domain, from DNS */
+
+dns_txt_name = string_sprintf("%s._domainkey.%s.", sig->selector, sig->domain);
+
+if ( !(dns_txt_reply = ctx->dns_txt_callback(dns_txt_name))
+ || dns_txt_reply[0] == '\0'
+ )
+ {
+ sig->verify_status = PDKIM_VERIFY_INVALID;
+ sig->verify_ext_status = PDKIM_VERIFY_INVALID_PUBKEY_UNAVAILABLE;
+ return NULL;
+ }
+
+DEBUG(D_acl)
+ {
+ debug_printf(
+ "DKIM >> Parsing public key record >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n"
+ " %s\n"
+ " Raw record: ",
+ dns_txt_name);
+ pdkim_quoteprint(CUS dns_txt_reply, Ustrlen(dns_txt_reply));
+ }
+
+if ( !(p = pdkim_parse_pubkey_record(CUS dns_txt_reply))
+ || (Ustrcmp(p->srvtype, "*") != 0 && Ustrcmp(p->srvtype, "email") != 0)
+ )
+ {
+ sig->verify_status = PDKIM_VERIFY_INVALID;
+ sig->verify_ext_status = PDKIM_VERIFY_INVALID_PUBKEY_DNSRECORD;
+
+ DEBUG(D_acl)
+ {
+ if (p)
+ debug_printf(" Invalid public key service type '%s'\n", p->srvtype);
+ else
+ debug_printf(" Error while parsing public key record\n");
+ debug_printf(
+ "DKIM <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<\n");
+ }
+ return NULL;
+ }
+
+DEBUG(D_acl) debug_printf(
+ "DKIM <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<\n");
+
+/* Import public key */
+
+/* Normally we use the signature a= tag to tell us the pubkey format.
+When signing under debug we do a test-import of the pubkey, and at that
+time we do not have a signature so we must interpret the pubkey k= tag
+instead. Assume writing on the sig is ok in that case. */
+
+if (sig->keytype < 0)
+ if ((sig->keytype = pdkim_keyname_to_keytype(p->keytype)) < 0)
+ {
+ DEBUG(D_acl) debug_printf("verify_init: unhandled keytype %s\n", p->keytype);
+ sig->verify_status = PDKIM_VERIFY_INVALID;
+ sig->verify_ext_status = PDKIM_VERIFY_INVALID_PUBKEY_IMPORT;
+ return NULL;
+ }
+
+if (sig->keytype == KEYTYPE_ED25519)
+ check_bare_ed25519_pubkey(p);
+
+if ((*errstr = exim_dkim_verify_init(&p->key,
+ sig->keytype == KEYTYPE_ED25519 ? KEYFMT_ED25519_BARE : KEYFMT_DER,
+ vctx)))
+ {
+ DEBUG(D_acl) debug_printf("verify_init: %s\n", *errstr);
+ sig->verify_status = PDKIM_VERIFY_INVALID;
+ sig->verify_ext_status = PDKIM_VERIFY_INVALID_PUBKEY_IMPORT;
+ return NULL;
+ }
+
+vctx->keytype = sig->keytype;
+return p;
+}
+
+
+/* -------------------------------------------------------------------------- */
+/* Sort and filter the sigs developed from the message */
+
+static pdkim_signature *
+sort_sig_methods(pdkim_signature * siglist)
+{
+pdkim_signature * yield, ** ss;
+const uschar * prefs;
+uschar * ele;
+int sep;
+
+if (!siglist) return NULL;
+
+/* first select in order of hashtypes */
+DEBUG(D_acl) debug_printf("DKIM: dkim_verify_hashes '%s'\n", dkim_verify_hashes);
+for (prefs = dkim_verify_hashes, sep = 0, yield = NULL, ss = &yield;
+ ele = string_nextinlist(&prefs, &sep, NULL, 0); )
+ {
+ int i = pdkim_hashname_to_hashtype(CUS ele, 0);
+ for (pdkim_signature * s = siglist, * next, ** prev = &siglist; s;
+ s = next)
+ {
+ next = s->next;
+ if (s->hashtype == i)
+ { *prev = next; s->next = NULL; *ss = s; ss = &s->next; }
+ else
+ prev = &s->next;
+ }
+ }
+
+/* then in order of keytypes */
+siglist = yield;
+DEBUG(D_acl) debug_printf("DKIM: dkim_verify_keytypes '%s'\n", dkim_verify_keytypes);
+for (prefs = dkim_verify_keytypes, sep = 0, yield = NULL, ss = &yield;
+ ele = string_nextinlist(&prefs, &sep, NULL, 0); )
+ {
+ int i = pdkim_keyname_to_keytype(CUS ele);
+ for (pdkim_signature * s = siglist, * next, ** prev = &siglist; s;
+ s = next)
+ {
+ next = s->next;
+ if (s->keytype == i)
+ { *prev = next; s->next = NULL; *ss = s; ss = &s->next; }
+ else
+ prev = &s->next;
+ }
+ }
+
+DEBUG(D_acl) for (pdkim_signature * s = yield; s; s = s->next)
+ debug_printf(" retain d=%s s=%s a=%s\n",
+ s->domain, s->selector, dkim_sig_to_a_tag(s));
+return yield;
git://git.exim.org / exim.git / blobdiff