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gpg: Switch to a hash and CERT record based PKA system.
* common/dns-cert.c (get_dns_cert): Make r_key optional. * common/pka.c: Rewrite for the new hash based lookup. * common/t-pka.c: New. * configure.ac: Remove option --disable-dns-pka. (USE_DNS_PKA): Remove ac_define. * g10/getkey.c (parse_auto_key_locate): Always include PKA. -- Note that although PKA is now always build, it will only work if support for looking up via DNS has not been disabled. The new PKA only works with the IPGP DNS certtype and shall be used only to retrieve the fingerprint and optional the key for the first time. Due to the security problems with DNSSEC the former assumption to validate the key using DNSSEC is not anymore justified. Instead an additional layer (e.g. Trust-On-First-Use) needs to be implemented to track change to the key. Having a solid way of getting a key matching a mail address is however a must have. More work needs to go into a redefinition of the --verify-options pka-lookups and pka-trust-increase. The auto-key-locate mechanism should also be able to continue key fetching with another methods once the fingerprint has been retrieved with PKA. Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch
parent
af60152a46
commit
2fc27c8696
9 changed files with 144 additions and 315 deletions
343
common/pka.c
343
common/pka.c
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@ -33,307 +33,76 @@
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#include <stdlib.h>
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#include <string.h>
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#ifdef USE_DNS_PKA
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#include <sys/types.h>
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#ifdef _WIN32
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# ifdef HAVE_WINSOCK2_H
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# include <winsock2.h>
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# endif
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# include <windows.h>
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#else
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#include <netinet/in.h>
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#include <arpa/nameser.h>
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#include <resolv.h>
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#endif
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#endif /* USE_DNS_PKA */
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#ifdef USE_ADNS
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# include <adns.h>
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#endif
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#include "util.h"
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#include "host2net.h"
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#include "mbox-util.h"
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#include "dns-cert.h"
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#include "pka.h"
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#ifdef USE_DNS_PKA
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/* Parse the TXT resource record. Format is:
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v=pka1;fpr=a4d94e92b0986ab5ee9dcd755de249965b0358a2;uri=string
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For simplicity white spaces are not allowed. Because we expect to
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use a new RRTYPE for this in the future we define the TXT really
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strict for simplicity: No white spaces, case sensitivity of the
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names, order must be as given above. Only URI is optional.
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This function modifies BUFFER. On success 0 is returned, the 20
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byte fingerprint stored at FPR and BUFFER contains the URI or an
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empty string.
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*/
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static int
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parse_txt_record (char *buffer, unsigned char *fpr)
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{
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char *p, *pend;
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int i;
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p = buffer;
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pend = strchr (p, ';');
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if (!pend)
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return -1;
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*pend++ = 0;
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if (strcmp (p, "v=pka1"))
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return -1; /* Wrong or missing version. */
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p = pend;
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pend = strchr (p, ';');
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if (pend)
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*pend++ = 0;
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if (strncmp (p, "fpr=", 4))
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return -1; /* Missing fingerprint part. */
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p += 4;
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for (i=0; i < 20 && hexdigitp (p) && hexdigitp (p+1); i++, p += 2)
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fpr[i] = xtoi_2 (p);
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if (i != 20)
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return -1; /* Fingerprint consists not of exactly 40 hexbytes. */
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p = pend;
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if (!p || !*p)
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{
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*buffer = 0;
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return 0; /* Success (no URI given). */
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}
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if (strncmp (p, "uri=", 4))
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return -1; /* Unknown part. */
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p += 4;
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/* There is an URI, copy it to the start of the buffer. */
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while (*p)
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*buffer++ = *p++;
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*buffer = 0;
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return 0;
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}
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/* For the given email ADDRESS lookup the PKA information in the DNS.
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On success the 20 byte SHA-1 fingerprint is stored at FPR and the
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URI will be returned in an allocated buffer. Note that the URI
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might be an zero length string as this information is optional.
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Caller must xfree the returned string.
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On success the fingerprint is stored at FPRBUF and the URI will be
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returned in an allocated buffer. Note that the URI might be a zero
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length string as this information is optional. Caller must xfree
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the returned string. FPRBUFLEN gives the size of the expected
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fingerprint (usually 20).
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On error NULL is returned and the 20 bytes at FPR are not
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defined. */
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On error NULL is returned and the FPRBUF is not defined. */
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char *
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get_pka_info (const char *address, unsigned char *fpr)
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get_pka_info (const char *address, void *fprbuf, size_t fprbuflen)
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{
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#ifdef USE_ADNS
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int rc;
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adns_state state;
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const char *domain;
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char *name;
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adns_answer *answer = NULL;
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char *buffer = NULL;
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char *result = NULL;
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char *mbox;
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char *domain; /* Points to mbox. */
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char hashbuf[20];
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char *hash = NULL;
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char *name = NULL;
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unsigned char *fpr = NULL;
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size_t fpr_len;
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char *url = NULL;
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gpg_error_t err;
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domain = strrchr (address, '@');
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if (!domain || domain == address || !domain[1])
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return NULL; /* Invalid mail address given. */
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name = xtrymalloc (strlen (address) + 5 + 1);
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mbox = mailbox_from_userid (address);
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if (!mbox)
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goto leave;
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domain = strchr (mbox, '@');
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if (!domain)
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goto leave;
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*domain++ = 0;
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gcry_md_hash_buffer (GCRY_MD_SHA1, hashbuf, mbox, strlen (mbox));
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hash = zb32_encode (hashbuf, 8*20);
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if (!hash)
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goto leave;
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name = strconcat (hash, "._pka.", domain, NULL);
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if (!name)
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return NULL;
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memcpy (name, address, domain - address);
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strcpy (stpcpy (name + (domain-address), "._pka."), domain+1);
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goto leave;
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rc = adns_init (&state, adns_if_noerrprint, NULL);
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if (rc)
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if (get_dns_cert (name, DNS_CERTTYPE_IPGP, NULL, &fpr, &fpr_len, &url))
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goto leave;
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if (!fpr)
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goto leave;
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/* Return the fingerprint. */
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if (fpr_len != fprbuflen)
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{
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log_error ("error initializing adns: %s\n", strerror (errno));
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xfree (name);
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return NULL;
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/* fprintf (stderr, "get_dns_cert failed: fprlen (%zu/%zu)\n", */
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/* fpr_len, fprbuflen); */
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goto leave;
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}
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memcpy (fprbuf, fpr, fpr_len);
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rc = adns_synchronous (state, name, adns_r_txt, adns_qf_quoteok_query,
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&answer);
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/* We return the URL or an empty string. */
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if (!url)
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url = xtrycalloc (1, 1);
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result = url;
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url = NULL;
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leave:
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xfree (fpr);
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xfree (url);
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xfree (name);
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if (rc)
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{
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log_error ("DNS query failed: %s\n", strerror (errno));
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adns_finish (state);
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return NULL;
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}
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if (answer->status != adns_s_ok
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|| answer->type != adns_r_txt || !answer->nrrs)
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{
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log_error ("DNS query returned an error: %s (%s)\n",
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adns_strerror (answer->status),
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adns_errabbrev (answer->status));
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adns_free (answer);
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adns_finish (state);
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return NULL;
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}
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/* We use a PKA records iff there is exactly one record. */
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if (answer->nrrs == 1 && answer->rrs.manyistr[0]->i != -1)
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{
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buffer = xtrystrdup (answer->rrs.manyistr[0]->str);
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if (parse_txt_record (buffer, fpr))
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{
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xfree (buffer);
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buffer = NULL; /* Not a valid gpg trustdns RR. */
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}
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}
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adns_free (answer);
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adns_finish (state);
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return buffer;
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#else /*!USE_ADNS*/
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unsigned char answer[PACKETSZ];
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int anslen;
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int qdcount, ancount;
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int rc;
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unsigned char *p, *pend;
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const char *domain;
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char *name;
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HEADER header;
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domain = strrchr (address, '@');
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if (!domain || domain == address || !domain[1])
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return NULL; /* invalid mail address given. */
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name = xtrymalloc (strlen (address) + 5 + 1);
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if (!name)
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return NULL;
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memcpy (name, address, domain - address);
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strcpy (stpcpy (name + (domain-address), "._pka."), domain+1);
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anslen = res_query (name, C_IN, T_TXT, answer, PACKETSZ);
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xfree (name);
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if (anslen < sizeof(HEADER))
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return NULL; /* DNS resolver returned a too short answer. */
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/* Don't despair: A good compiler should optimize this away, as
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header is just 32 byte and constant at compile time. It's
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one way to comply with strict aliasing rules. */
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memcpy (&header, answer, sizeof (header));
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if ( (rc=header.rcode) != NOERROR )
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return NULL; /* DNS resolver returned an error. */
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/* We assume that PACKETSZ is large enough and don't do dynmically
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expansion of the buffer. */
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if (anslen > PACKETSZ)
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return NULL; /* DNS resolver returned a too long answer */
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qdcount = ntohs (header.qdcount);
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ancount = ntohs (header.ancount);
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if (!ancount)
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return NULL; /* Got no answer. */
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p = answer + sizeof (HEADER);
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pend = answer + anslen; /* Actually points directly behind the buffer. */
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while (qdcount-- && p < pend)
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{
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rc = dn_skipname (p, pend);
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if (rc == -1)
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return NULL;
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p += rc + QFIXEDSZ;
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}
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if (ancount > 1)
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return NULL; /* more than one possible gpg trustdns record - none used. */
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while (ancount-- && p <= pend)
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{
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unsigned int type, class, txtlen, n;
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char *buffer, *bufp;
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rc = dn_skipname (p, pend);
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if (rc == -1)
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return NULL;
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p += rc;
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if (p >= pend - 10)
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return NULL; /* RR too short. */
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type = buf16_to_uint (p);
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p += 2;
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class = buf16_to_uint (p);
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p += 2;
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p += 4;
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txtlen = buf16_to_uint (p);
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p += 2;
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if (type != T_TXT || class != C_IN)
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return NULL; /* Answer does not match the query. */
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buffer = bufp = xmalloc (txtlen + 1);
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while (txtlen && p < pend)
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{
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for (n = *p++, txtlen--; txtlen && n && p < pend; txtlen--, n--)
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*bufp++ = *p++;
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}
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*bufp = 0;
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if (parse_txt_record (buffer, fpr))
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{
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xfree (buffer);
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return NULL; /* Not a valid gpg trustdns RR. */
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}
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return buffer;
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}
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return NULL;
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#endif /*!USE_ADNS*/
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xfree (hash);
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xfree (mbox);
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return result;
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}
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#else /* !USE_DNS_PKA */
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/* Dummy version of the function if we can't use the resolver
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functions. */
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char *
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get_pka_info (const char *address, unsigned char *fpr)
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{
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(void)address;
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(void)fpr;
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return NULL;
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}
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#endif /* !USE_DNS_PKA */
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#ifdef TEST
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int
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main(int argc,char *argv[])
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{
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unsigned char fpr[20];
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char *uri;
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int i;
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if (argc < 2)
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{
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fprintf (stderr, "usage: pka mail-addresses\n");
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return 1;
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}
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argc--;
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argv++;
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for (; argc; argc--, argv++)
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{
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uri = get_pka_info ( *argv, fpr );
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printf ("%s", *argv);
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if (uri)
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{
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putchar (' ');
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for (i=0; i < 20; i++)
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printf ("%02X", fpr[i]);
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if (*uri)
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printf (" %s", uri);
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xfree (uri);
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}
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putchar ('\n');
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}
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return 0;
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}
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#endif /* TEST */
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/*
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Local Variables:
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compile-command: "cc -DUSE_DNS_PKA -DTEST -I.. -I../include -Wall -g -o pka pka.c -lresolv ../tools/no-libgcrypt.o ../jnlib/libjnlib.a"
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End:
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*/
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