diff options
author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 09:59:15 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 09:59:15 +0000 |
commit | 8de1ee1b2b676b0d07586f0752750dd6b0fb7511 (patch) | |
tree | dd46fd7dc3863045696cd0e48032d8a36fa0daf5 /dirmngr/validate.c | |
parent | Initial commit. (diff) | |
download | gnupg2-upstream.tar.xz gnupg2-upstream.zip |
Adding upstream version 2.2.27.upstream/2.2.27upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'dirmngr/validate.c')
-rw-r--r-- | dirmngr/validate.c | 1305 |
1 files changed, 1305 insertions, 0 deletions
diff --git a/dirmngr/validate.c b/dirmngr/validate.c new file mode 100644 index 0000000..901c165 --- /dev/null +++ b/dirmngr/validate.c @@ -0,0 +1,1305 @@ +/* validate.c - Validate a certificate chain. + * Copyright (C) 2001, 2003, 2004, 2008 Free Software Foundation, Inc. + * Copyright (C) 2004, 2006, 2008, 2017 g10 Code GmbH + * + * This file is part of DirMngr. + * + * DirMngr is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * DirMngr is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA + */ + +#include <config.h> + +#include <stdio.h> +#include <stdlib.h> +#include <errno.h> +#include <assert.h> +#include <ctype.h> + +#include "dirmngr.h" +#include "certcache.h" +#include "crlcache.h" +#include "validate.h" +#include "misc.h" + + +/* Mode parameters for cert_check_usage(). */ +enum cert_usage_modes + { + CERT_USAGE_MODE_SIGN, /* Usable for encryption. */ + CERT_USAGE_MODE_ENCR, /* Usable for signing. */ + CERT_USAGE_MODE_VRFY, /* Usable for verification. */ + CERT_USAGE_MODE_DECR, /* Usable for decryption. */ + CERT_USAGE_MODE_CERT, /* Usable for cert signing. */ + CERT_USAGE_MODE_OCSP, /* Usable for OCSP respone signing. */ + CERT_USAGE_MODE_CRL /* Usable for CRL signing. */ + }; + + +/* While running the validation function we need to keep track of the + certificates and the validation outcome of each. We use this type + for it. */ +struct chain_item_s +{ + struct chain_item_s *next; + ksba_cert_t cert; /* The certificate. */ + unsigned char fpr[20]; /* Fingerprint of the certificate. */ + int is_self_signed; /* This certificate is self-signed. */ + int is_valid; /* The certifiate is valid except for revocations. */ +}; +typedef struct chain_item_s *chain_item_t; + + +/* A couple of constants with Object Identifiers. */ +static const char oid_kp_serverAuth[] = "1.3.6.1.5.5.7.3.1"; +static const char oid_kp_clientAuth[] = "1.3.6.1.5.5.7.3.2"; +static const char oid_kp_codeSigning[] = "1.3.6.1.5.5.7.3.3"; +static const char oid_kp_emailProtection[]= "1.3.6.1.5.5.7.3.4"; +static const char oid_kp_timeStamping[] = "1.3.6.1.5.5.7.3.8"; +static const char oid_kp_ocspSigning[] = "1.3.6.1.5.5.7.3.9"; + + +/* Prototypes. */ +static gpg_error_t check_cert_sig (ksba_cert_t issuer_cert, ksba_cert_t cert); + + +/* Make sure that the values defined in the headers are correct. We + * can't use the preprocessor due to the use of enums. */ +static void +check_header_constants (void) +{ + log_assert (CERTTRUST_CLASS_SYSTEM == VALIDATE_FLAG_TRUST_SYSTEM); + log_assert (CERTTRUST_CLASS_CONFIG == VALIDATE_FLAG_TRUST_CONFIG); + log_assert (CERTTRUST_CLASS_HKP == VALIDATE_FLAG_TRUST_HKP); + log_assert (CERTTRUST_CLASS_HKPSPOOL == VALIDATE_FLAG_TRUST_HKPSPOOL); + +#undef X +#define X (VALIDATE_FLAG_TRUST_SYSTEM | VALIDATE_FLAG_TRUST_CONFIG \ + | VALIDATE_FLAG_TRUST_HKP | VALIDATE_FLAG_TRUST_HKPSPOOL) + +#if ( X & VALIDATE_FLAG_MASK_TRUST ) != X +# error VALIDATE_FLAG_MASK_TRUST is bad +#endif +#if ( ~X & VALIDATE_FLAG_MASK_TRUST ) +# error VALIDATE_FLAG_MASK_TRUST is bad +#endif + +#undef X +} + + +/* Check whether CERT contains critical extensions we don't know + about. */ +static gpg_error_t +unknown_criticals (ksba_cert_t cert) +{ + static const char *known[] = { + "2.5.29.15", /* keyUsage */ + "2.5.29.19", /* basic Constraints */ + "2.5.29.32", /* certificatePolicies */ + "2.5.29.37", /* extendedKeyUsage */ + NULL + }; + int i, idx, crit; + const char *oid; + int unsupported; + strlist_t sl; + gpg_error_t err, rc; + + rc = 0; + for (idx=0; !(err=ksba_cert_get_extension (cert, idx, + &oid, &crit, NULL, NULL));idx++) + { + if (!crit) + continue; + for (i=0; known[i] && strcmp (known[i],oid); i++) + ; + unsupported = !known[i]; + + /* If this critical extension is not supported, check the list + of to be ignored extensions to see whether we claim that it + is supported. */ + if (unsupported && opt.ignored_cert_extensions) + { + for (sl=opt.ignored_cert_extensions; + sl && strcmp (sl->d, oid); sl = sl->next) + ; + if (sl) + unsupported = 0; + } + + if (unsupported) + { + log_error (_("critical certificate extension %s is not supported"), + oid); + rc = gpg_error (GPG_ERR_UNSUPPORTED_CERT); + } + } + if (err && gpg_err_code (err) != GPG_ERR_EOF) + rc = err; /* Such an error takes precedence. */ + + return rc; +} + + +/* Basic check for supported policies. */ +static gpg_error_t +check_cert_policy (ksba_cert_t cert) +{ + static const char *allowed[] = { + "2.289.9.9", + NULL + }; + gpg_error_t err; + int idx; + char *p, *haystack; + char *policies; + int any_critical; + + err = ksba_cert_get_cert_policies (cert, &policies); + if (gpg_err_code (err) == GPG_ERR_NO_DATA) + return 0; /* No policy given. */ + if (err) + return err; + + /* STRING is a line delimited list of certifiate policies as stored + in the certificate. The line itself is colon delimited where the + first field is the OID of the policy and the second field either + N or C for normal or critical extension */ + if (opt.verbose > 1) + log_info ("certificate's policy list: %s\n", policies); + + /* The check is very minimal but won't give false positives */ + any_critical = !!strstr (policies, ":C"); + + /* See whether we find ALLOWED (which is an OID) in POLICIES */ + for (idx=0; allowed[idx]; idx++) + { + for (haystack=policies; (p=strstr (haystack, allowed[idx])); + haystack = p+1) + { + if ( !(p == policies || p[-1] == '\n') ) + continue; /* Does not match the begin of a line. */ + if (p[strlen (allowed[idx])] != ':') + continue; /* The length does not match. */ + /* Yep - it does match: Return okay. */ + ksba_free (policies); + return 0; + } + } + + if (!any_critical) + { + log_info (_("Note: non-critical certificate policy not allowed")); + err = 0; + } + else + { + log_info (_("certificate policy not allowed")); + err = gpg_error (GPG_ERR_NO_POLICY_MATCH); + } + + ksba_free (policies); + return err; +} + + +static gpg_error_t +allowed_ca (ksba_cert_t cert, int *chainlen) +{ + gpg_error_t err; + int flag; + + err = ksba_cert_is_ca (cert, &flag, chainlen); + if (err) + return err; + if (!flag) + { + if (!is_trusted_cert (cert, CERTTRUST_CLASS_CONFIG)) + { + /* The German SigG Root CA's certificate does not flag + itself as a CA; thus we relax this requirement if we + trust a root CA. I think this is reasonable. Note, that + gpgsm implements a far stricter scheme here. */ + if (chainlen) + *chainlen = 3; /* That is what the SigG implements. */ + if (opt.verbose) + log_info (_("accepting root CA not marked as a CA")); + } + else + { + log_error (_("issuer certificate is not marked as a CA")); + return gpg_error (GPG_ERR_BAD_CA_CERT); + } + } + return 0; +} + +/* Helper for validate_cert_chain. */ +static gpg_error_t +check_revocations (ctrl_t ctrl, chain_item_t chain) +{ + gpg_error_t err = 0; + int any_revoked = 0; + int any_no_crl = 0; + int any_crl_too_old = 0; + chain_item_t ci; + + log_assert (ctrl->check_revocations_nest_level >= 0); + log_assert (chain); + + if (ctrl->check_revocations_nest_level > 10) + { + log_error (_("CRL checking too deeply nested\n")); + return gpg_error(GPG_ERR_BAD_CERT_CHAIN); + } + ctrl->check_revocations_nest_level++; + + + for (ci=chain; ci; ci = ci->next) + { + assert (ci->cert); + if (ci == chain) + { + /* It does not make sense to check the root certificate for + revocations. In almost all cases this will lead to a + catch-22 as the root certificate is the final trust + anchor for the certificates and the CRLs. We expect the + user to remove root certificates from the list of trusted + certificates in case they have been revoked. */ + if (opt.verbose) + cert_log_name (_("not checking CRL for"), ci->cert); + continue; + } + + if (opt.verbose) + cert_log_name (_("checking CRL for"), ci->cert); + err = crl_cache_cert_isvalid (ctrl, ci->cert, 0); + if (gpg_err_code (err) == GPG_ERR_NO_CRL_KNOWN) + { + err = crl_cache_reload_crl (ctrl, ci->cert); + if (!err) + err = crl_cache_cert_isvalid (ctrl, ci->cert, 0); + } + switch (gpg_err_code (err)) + { + case 0: err = 0; break; + case GPG_ERR_CERT_REVOKED: any_revoked = 1; err = 0; break; + case GPG_ERR_NO_CRL_KNOWN: any_no_crl = 1; err = 0; break; + case GPG_ERR_CRL_TOO_OLD: any_crl_too_old = 1; err = 0; break; + default: break; + } + } + ctrl->check_revocations_nest_level--; + + + if (err) + ; + else if (any_revoked) + err = gpg_error (GPG_ERR_CERT_REVOKED); + else if (any_no_crl) + err = gpg_error (GPG_ERR_NO_CRL_KNOWN); + else if (any_crl_too_old) + err = gpg_error (GPG_ERR_CRL_TOO_OLD); + else + err = 0; + return err; +} + + +/* Check whether CERT is a root certificate. ISSUERDN and SUBJECTDN + are the DNs already extracted by the caller from CERT. Returns + True if this is the case. */ +static int +is_root_cert (ksba_cert_t cert, const char *issuerdn, const char *subjectdn) +{ + gpg_error_t err; + int result = 0; + ksba_sexp_t serialno; + ksba_sexp_t ak_keyid; + ksba_name_t ak_name; + ksba_sexp_t ak_sn; + const char *ak_name_str; + ksba_sexp_t subj_keyid = NULL; + + if (!issuerdn || !subjectdn) + return 0; /* No. */ + + if (strcmp (issuerdn, subjectdn)) + return 0; /* No. */ + + err = ksba_cert_get_auth_key_id (cert, &ak_keyid, &ak_name, &ak_sn); + if (err) + { + if (gpg_err_code (err) == GPG_ERR_NO_DATA) + return 1; /* Yes. Without a authorityKeyIdentifier this needs + to be the Root certificate (our trust anchor). */ + log_error ("error getting authorityKeyIdentifier: %s\n", + gpg_strerror (err)); + return 0; /* Well, it is broken anyway. Return No. */ + } + + serialno = ksba_cert_get_serial (cert); + if (!serialno) + { + log_error ("error getting serialno: %s\n", gpg_strerror (err)); + goto leave; + } + + /* Check whether the auth name's matches the issuer name+sn. If + that is the case this is a root certificate. */ + ak_name_str = ksba_name_enum (ak_name, 0); + if (ak_name_str + && !strcmp (ak_name_str, issuerdn) + && !cmp_simple_canon_sexp (ak_sn, serialno)) + { + result = 1; /* Right, CERT is self-signed. */ + goto leave; + } + + /* Similar for the ak_keyid. */ + if (ak_keyid && !ksba_cert_get_subj_key_id (cert, NULL, &subj_keyid) + && !cmp_simple_canon_sexp (ak_keyid, subj_keyid)) + { + result = 1; /* Right, CERT is self-signed. */ + goto leave; + } + + + leave: + ksba_free (subj_keyid); + ksba_free (ak_keyid); + ksba_name_release (ak_name); + ksba_free (ak_sn); + ksba_free (serialno); + return result; +} + + +/* Validate the certificate CHAIN up to the trust anchor. Optionally + return the closest expiration time in R_EXPTIME (this is useful for + caching issues). MODE is one of the VALIDATE_MODE_* constants. + + Note that VALIDATE_MODE_OCSP is not used due to the removal of the + system service in 2.1.15. Instead only the callback to gpgsm to + validate a certificate is used. + + If R_TRUST_ANCHOR is not NULL and the validation would fail only + because the root certificate is not trusted, the hexified + fingerprint of that root certificate is stored at R_TRUST_ANCHOR + and success is returned. The caller needs to free the value at + R_TRUST_ANCHOR; in all other cases NULL is stored there. */ +gpg_error_t +validate_cert_chain (ctrl_t ctrl, ksba_cert_t cert, ksba_isotime_t r_exptime, + unsigned int flags, char **r_trust_anchor) +{ + gpg_error_t err = 0; + int depth, maxdepth; + char *issuer = NULL; + char *subject = NULL; + ksba_cert_t subject_cert = NULL; + ksba_cert_t issuer_cert = NULL; + ksba_isotime_t current_time; + ksba_isotime_t exptime; + int any_expired = 0; + int any_no_policy_match = 0; + chain_item_t chain; + + check_header_constants (); + + if (r_exptime) + *r_exptime = 0; + *exptime = 0; + + if (r_trust_anchor) + *r_trust_anchor = NULL; + + if (DBG_X509) + dump_cert ("subject", cert); + + /* May the target certificate be used for this purpose? */ + if ((flags & VALIDATE_FLAG_OCSP) && (err = check_cert_use_ocsp (cert))) + return err; + if ((flags & VALIDATE_FLAG_CRL) && (err = check_cert_use_crl (cert))) + return err; + + /* If we already validated the certificate not too long ago, we can + avoid the excessive computations and lookups unless the caller + asked for the expiration time. */ + if (!r_exptime) + { + size_t buflen; + time_t validated_at; + + err = ksba_cert_get_user_data (cert, "validated_at", + &validated_at, sizeof (validated_at), + &buflen); + if (err || buflen != sizeof (validated_at) || !validated_at) + err = 0; /* Not available or other error. */ + else + { + /* If the validation is not older than 30 minutes we are ready. */ + if (validated_at < gnupg_get_time () + (30*60)) + { + if (opt.verbose) + log_info ("certificate is good (cached)\n"); + /* Note, that we can't jump to leave here as this would + falsely updated the validation timestamp. */ + return 0; + } + } + } + + /* Get the current time. */ + gnupg_get_isotime (current_time); + + /* We walk up the chain until we find a trust anchor. */ + subject_cert = cert; + maxdepth = 10; /* Sensible limit on the length of the chain. */ + chain = NULL; + depth = 0; + for (;;) + { + /* Get the subject and issuer name from the current + certificate. */ + ksba_free (issuer); + ksba_free (subject); + issuer = ksba_cert_get_issuer (subject_cert, 0); + subject = ksba_cert_get_subject (subject_cert, 0); + + if (!issuer) + { + log_error (_("no issuer found in certificate\n")); + err = gpg_error (GPG_ERR_BAD_CERT); + goto leave; + } + + /* Handle the notBefore and notAfter timestamps. */ + { + ksba_isotime_t not_before, not_after; + + err = ksba_cert_get_validity (subject_cert, 0, not_before); + if (!err) + err = ksba_cert_get_validity (subject_cert, 1, not_after); + if (err) + { + log_error (_("certificate with invalid validity: %s"), + gpg_strerror (err)); + err = gpg_error (GPG_ERR_BAD_CERT); + goto leave; + } + + /* Keep track of the nearest expiration time in EXPTIME. */ + if (*not_after) + { + if (!*exptime) + gnupg_copy_time (exptime, not_after); + else if (strcmp (not_after, exptime) < 0 ) + gnupg_copy_time (exptime, not_after); + } + + /* Check whether the certificate is already valid. */ + if (*not_before && strcmp (current_time, not_before) < 0 ) + { + log_error (_("certificate not yet valid")); + log_info ("(valid from "); + dump_isotime (not_before); + log_printf (")\n"); + err = gpg_error (GPG_ERR_CERT_TOO_YOUNG); + goto leave; + } + + /* Now check whether the certificate has expired. */ + if (*not_after && strcmp (current_time, not_after) > 0 ) + { + log_error (_("certificate has expired")); + log_info ("(expired at "); + dump_isotime (not_after); + log_printf (")\n"); + any_expired = 1; + } + } + + /* Do we have any critical extensions in the certificate we + can't handle? */ + err = unknown_criticals (subject_cert); + if (err) + goto leave; /* yes. */ + + /* Check that given policies are allowed. */ + err = check_cert_policy (subject_cert); + if (gpg_err_code (err) == GPG_ERR_NO_POLICY_MATCH) + { + any_no_policy_match = 1; + err = 0; + } + else if (err) + goto leave; + + /* Is this a self-signed certificate? */ + if (is_root_cert (subject_cert, issuer, subject)) + { + /* Yes, this is our trust anchor. */ + if (check_cert_sig (subject_cert, subject_cert) ) + { + log_error (_("selfsigned certificate has a BAD signature")); + err = gpg_error (depth? GPG_ERR_BAD_CERT_CHAIN + : GPG_ERR_BAD_CERT); + goto leave; + } + + /* Is this certificate allowed to act as a CA. */ + err = allowed_ca (subject_cert, NULL); + if (err) + goto leave; /* No. */ + + err = is_trusted_cert (subject_cert, + (flags & VALIDATE_FLAG_MASK_TRUST)); + if (!err) + ; /* Yes we trust this cert. */ + else if (gpg_err_code (err) == GPG_ERR_NOT_TRUSTED) + { + char *fpr; + + log_error (_("root certificate is not marked trusted")); + fpr = get_fingerprint_hexstring (subject_cert); + log_info (_("fingerprint=%s\n"), fpr? fpr : "?"); + dump_cert ("issuer", subject_cert); + if (r_trust_anchor) + { + /* Caller wants to do another trustiness check. */ + *r_trust_anchor = fpr; + err = 0; + } + else + xfree (fpr); + } + else + { + log_error (_("checking trustworthiness of " + "root certificate failed: %s\n"), + gpg_strerror (err)); + } + if (err) + goto leave; + + /* Prepend the certificate to our list. */ + { + chain_item_t ci; + + ci = xtrycalloc (1, sizeof *ci); + if (!ci) + { + err = gpg_error_from_errno (errno); + goto leave; + } + ksba_cert_ref (subject_cert); + ci->cert = subject_cert; + cert_compute_fpr (subject_cert, ci->fpr); + ci->next = chain; + chain = ci; + } + + if (opt.verbose) + { + if (r_trust_anchor && *r_trust_anchor) + log_info ("root certificate is good but not trusted\n"); + else + log_info ("root certificate is good and trusted\n"); + } + + break; /* Okay: a self-signed certificate is an end-point. */ + } + + /* To avoid loops, we use an arbitrary limit on the length of + the chain. */ + depth++; + if (depth > maxdepth) + { + log_error (_("certificate chain too long\n")); + err = gpg_error (GPG_ERR_BAD_CERT_CHAIN); + goto leave; + } + + /* Find the next cert up the tree. */ + ksba_cert_release (issuer_cert); issuer_cert = NULL; + err = find_issuing_cert (ctrl, subject_cert, &issuer_cert); + if (err) + { + if (gpg_err_code (err) == GPG_ERR_NOT_FOUND) + { + log_error (_("issuer certificate not found")); + log_info ("issuer certificate: #/"); + dump_string (issuer); + log_printf ("\n"); + } + else + log_error (_("issuer certificate not found: %s\n"), + gpg_strerror (err)); + /* Use a better understandable error code. */ + err = gpg_error (GPG_ERR_MISSING_ISSUER_CERT); + goto leave; + } + +/* try_another_cert: */ + if (DBG_X509) + { + log_debug ("got issuer's certificate:\n"); + dump_cert ("issuer", issuer_cert); + } + + /* Now check the signature of the certificate. FIXME: we should + * delay this until later so that faked certificates can't be + * turned into a DoS easily. */ + err = check_cert_sig (issuer_cert, subject_cert); + if (err) + { + log_error (_("certificate has a BAD signature")); +#if 0 + if (gpg_err_code (err) == GPG_ERR_BAD_SIGNATURE) + { + /* We now try to find other issuer certificates which + might have been used. This is required because some + CAs are reusing the issuer and subject DN for new + root certificates without using a authorityKeyIdentifier. */ + rc = find_up (kh, subject_cert, issuer, 1); + if (!rc) + { + ksba_cert_t tmp_cert; + + rc = keydb_get_cert (kh, &tmp_cert); + if (rc || !compare_certs (issuer_cert, tmp_cert)) + { + /* The find next did not work or returned an + identical certificate. We better stop here + to avoid infinite checks. */ + rc = gpg_error (GPG_ERR_BAD_SIGNATURE); + ksba_cert_release (tmp_cert); + } + else + { + do_list (0, lm, fp, _("found another possible matching " + "CA certificate - trying again")); + ksba_cert_release (issuer_cert); + issuer_cert = tmp_cert; + goto try_another_cert; + } + } + } +#endif + /* Return a more descriptive error code than the one + * returned from the signature checking. */ + err = gpg_error (GPG_ERR_BAD_CERT_CHAIN); + goto leave; + } + + /* Check that the length of the chain is not longer than allowed + * by the CA. */ + { + int chainlen; + + err = allowed_ca (issuer_cert, &chainlen); + if (err) + goto leave; + if (chainlen >= 0 && (depth - 1) > chainlen) + { + log_error (_("certificate chain longer than allowed by CA (%d)"), + chainlen); + err = gpg_error (GPG_ERR_BAD_CERT_CHAIN); + goto leave; + } + } + + /* May that certificate be used for certification? */ + err = check_cert_use_cert (issuer_cert); + if (err) + goto leave; /* No. */ + + /* Prepend the certificate to our list. */ + { + chain_item_t ci; + + ci = xtrycalloc (1, sizeof *ci); + if (!ci) + { + err = gpg_error_from_errno (errno); + goto leave; + } + ksba_cert_ref (subject_cert); + ci->cert = subject_cert; + cert_compute_fpr (subject_cert, ci->fpr); + ci->next = chain; + chain = ci; + } + + if (opt.verbose) + log_info (_("certificate is good\n")); + + /* Now to the next level up. */ + subject_cert = issuer_cert; + issuer_cert = NULL; + } + + /* Even if we have no error here we need to check whether we + * encountered an error somewhere during the checks. Set the error + * code to the most critical one. */ + if (!err) + { + if (any_expired) + err = gpg_error (GPG_ERR_CERT_EXPIRED); + else if (any_no_policy_match) + err = gpg_error (GPG_ERR_NO_POLICY_MATCH); + } + + if (!err && opt.verbose) + { + chain_item_t citem; + + log_info (_("certificate chain is good\n")); + for (citem = chain; citem; citem = citem->next) + cert_log_name (" certificate", citem->cert); + } + + /* Now check for revocations unless CRL checks are disabled or we + * are non-recursive CRL mode. */ + if (!err + && !(flags & VALIDATE_FLAG_NOCRLCHECK) + && !((flags & VALIDATE_FLAG_CRL) + && !(flags & VALIDATE_FLAG_RECURSIVE))) + { /* Now that everything is fine, walk the chain and check each + * certificate for revocations. + * + * 1. item in the chain - The root certificate. + * 2. item - the CA below the root + * last item - the target certificate. + * + * Now for each certificate in the chain check whether it has + * been included in a CRL and thus be revoked. We don't do OCSP + * here because this does not seem to make much sense. This + * might become a recursive process and we should better cache + * our validity results to avoid double work. Far worse a + * catch-22 may happen for an improper setup hierarchy and we + * need a way to break up such a deadlock. */ + err = check_revocations (ctrl, chain); + } + + if (!err && opt.verbose) + { + if (r_trust_anchor && *r_trust_anchor) + log_info ("target certificate may be valid\n"); + else + log_info ("target certificate is valid\n"); + } + else if (err && opt.verbose) + log_info ("target certificate is NOT valid\n"); + + + leave: + if (!err && !(r_trust_anchor && *r_trust_anchor)) + { + /* With no error we can update the validation cache. We do this + * for all certificates in the chain. Note that we can't use + * the cache if the caller requested to check the trustiness of + * the root certificate himself. Adding such a feature would + * require us to also store the fingerprint of root + * certificate. */ + chain_item_t citem; + time_t validated_at = gnupg_get_time (); + + for (citem = chain; citem; citem = citem->next) + { + err = ksba_cert_set_user_data (citem->cert, "validated_at", + &validated_at, sizeof (validated_at)); + if (err) + { + log_error ("set_user_data(validated_at) failed: %s\n", + gpg_strerror (err)); + err = 0; + } + } + } + + if (r_exptime) + gnupg_copy_time (r_exptime, exptime); + ksba_free (issuer); + ksba_free (subject); + ksba_cert_release (issuer_cert); + if (subject_cert != cert) + ksba_cert_release (subject_cert); + while (chain) + { + chain_item_t ci_next = chain->next; + if (chain->cert) + ksba_cert_release (chain->cert); + xfree (chain); + chain = ci_next; + } + if (err && r_trust_anchor && *r_trust_anchor) + { + xfree (*r_trust_anchor); + *r_trust_anchor = NULL; + } + return err; +} + + + +/* Return the public key algorithm id from the S-expression PKEY. + FIXME: libgcrypt should provide such a function. Note that this + implementation uses the names as used by libksba. */ +static int +pk_algo_from_sexp (gcry_sexp_t pkey) +{ + gcry_sexp_t l1, l2; + const char *name; + size_t n; + int algo; + + l1 = gcry_sexp_find_token (pkey, "public-key", 0); + if (!l1) + return 0; /* Not found. */ + l2 = gcry_sexp_cadr (l1); + gcry_sexp_release (l1); + + name = gcry_sexp_nth_data (l2, 0, &n); + if (!name) + algo = 0; /* Not found. */ + else if (n==3 && !memcmp (name, "rsa", 3)) + algo = GCRY_PK_RSA; + else if (n==3 && !memcmp (name, "dsa", 3)) + algo = GCRY_PK_DSA; + else if (n==13 && !memcmp (name, "ambiguous-rsa", 13)) + algo = GCRY_PK_RSA; + else + algo = 0; + gcry_sexp_release (l2); + return algo; +} + + +/* Return the hash algorithm's algo id from its name given in the + * non-null termnated string in (buffer,buflen). Returns 0 on failure + * or if the algo is not known. */ +static int +hash_algo_from_buffer (const void *buffer, size_t buflen) +{ + char *string; + int algo; + + string = xtrymalloc (buflen + 1); + if (!string) + { + log_error (_("out of core\n")); + return 0; + } + memcpy (string, buffer, buflen); + string[buflen] = 0; + algo = gcry_md_map_name (string); + if (!algo) + log_error ("unknown digest algorithm '%s' used in certificate\n", string); + xfree (string); + return algo; +} + + +/* Return an unsigned integer from the non-null termnated string + * (buffer,buflen). Returns 0 on failure. */ +static unsigned int +uint_from_buffer (const void *buffer, size_t buflen) +{ + char *string; + unsigned int val; + + string = xtrymalloc (buflen + 1); + if (!string) + { + log_error (_("out of core\n")); + return 0; + } + memcpy (string, buffer, buflen); + string[buflen] = 0; + val = strtoul (string, NULL, 10); + xfree (string); + return val; +} + + +/* Check the signature on CERT using the ISSUER_CERT. This function + * does only test the cryptographic signature and nothing else. It is + * assumed that the ISSUER_CERT is valid. */ +static gpg_error_t +check_cert_sig (ksba_cert_t issuer_cert, ksba_cert_t cert) +{ + gpg_error_t err; + const char *algoid; + gcry_md_hd_t md; + int algo; + ksba_sexp_t p; + size_t n; + gcry_sexp_t s_sig, s_hash, s_pkey; + const char *algo_name; /* hash algorithm name converted to lower case. */ + int digestlen; + unsigned char *digest; + int use_pss = 0; + unsigned int saltlen; + + /* Hash the target certificate using the algorithm from that certificate. */ + algoid = ksba_cert_get_digest_algo (cert); + algo = gcry_md_map_name (algoid); + if (!algo && algoid && !strcmp (algoid, "1.2.840.113549.1.1.10")) + use_pss = 1; + else if (!algo) + { + log_error (_("unknown hash algorithm '%s'\n"), algoid? algoid:"?"); + return gpg_error (GPG_ERR_GENERAL); + } + + /* Get the signature value out of the target certificate. */ + p = ksba_cert_get_sig_val (cert); + n = gcry_sexp_canon_len (p, 0, NULL, NULL); + if (!n) + { + log_error ("libksba did not return a proper S-Exp\n"); + ksba_free (p); + return gpg_error (GPG_ERR_BUG); + } + err = gcry_sexp_sscan ( &s_sig, NULL, p, n); + ksba_free (p); + if (err) + { + log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (err)); + return err; + } + if (DBG_CRYPTO) + gcry_log_debugsxp ("sigval", s_sig); + + if (use_pss) + { + /* Extract the hash algorithm and the salt length from the sigval. */ + gcry_buffer_t ioarray[2] = { {0}, {0} }; + + err = gcry_sexp_extract_param (s_sig, "sig-val", + "&'hash-algo''salt-length'", + ioarray+0, ioarray+1, NULL); + if (err) + { + gcry_sexp_release (s_sig); + log_error ("extracting params from PSS failed: %s\n", + gpg_strerror (err)); + return err; + } + algo = hash_algo_from_buffer (ioarray[0].data, ioarray[0].len); + saltlen = uint_from_buffer (ioarray[1].data, ioarray[1].len); + xfree (ioarray[0].data); + xfree (ioarray[1].data); + if (saltlen < 20) + { + log_error ("length of PSS salt too short\n"); + gcry_sexp_release (s_sig); + return gpg_error (GPG_ERR_DIGEST_ALGO); + } + if (!algo) + { + gcry_sexp_release (s_sig); + return gpg_error (GPG_ERR_DIGEST_ALGO); + } + /* Add some restrictions; see ../sm/certcheck.c for details. */ + switch (algo) + { + case GCRY_MD_SHA1: + case GCRY_MD_SHA256: + case GCRY_MD_SHA384: + case GCRY_MD_SHA512: + case GCRY_MD_SHA3_256: + case GCRY_MD_SHA3_384: + case GCRY_MD_SHA3_512: + break; + default: + log_error ("PSS hash algorithm '%s' rejected\n", + gcry_md_algo_name (algo)); + gcry_sexp_release (s_sig); + return gpg_error (GPG_ERR_DIGEST_ALGO); + } + + if (gcry_md_get_algo_dlen (algo) != saltlen) + { + log_error ("PSS hash algorithm '%s' rejected due to salt length %u\n", + gcry_md_algo_name (algo), saltlen); + gcry_sexp_release (s_sig); + return gpg_error (GPG_ERR_DIGEST_ALGO); + } + } + + algo_name = hash_algo_to_string (algo); + err = gcry_md_open (&md, algo, 0); + if (err) + { + log_error ("md_open failed: %s\n", gpg_strerror (err)); + gcry_sexp_release (s_sig); + return err; + } + if (DBG_HASHING) + gcry_md_debug (md, "hash.cert"); + + err = ksba_cert_hash (cert, 1, HASH_FNC, md); + if (err) + { + log_error ("ksba_cert_hash failed: %s\n", gpg_strerror (err)); + gcry_md_close (md); + gcry_sexp_release (s_sig); + return err; + } + gcry_md_final (md); + + /* Get the public key from the issuer certificate. */ + p = ksba_cert_get_public_key (issuer_cert); + n = gcry_sexp_canon_len (p, 0, NULL, NULL); + if (!n) + { + log_error ("libksba did not return a proper S-Exp\n"); + gcry_md_close (md); + ksba_free (p); + gcry_sexp_release (s_sig); + return gpg_error (GPG_ERR_BUG); + } + err = gcry_sexp_sscan ( &s_pkey, NULL, p, n); + ksba_free (p); + if (err) + { + log_error ("gcry_sexp_scan failed: %s\n", gpg_strerror (err)); + gcry_md_close (md); + gcry_sexp_release (s_sig); + return err; + } + + + /* Prepare the values for signature verification. At this point we + * have these values: + * + * S_PKEY - S-expression with the issuer's public key. + * S_SIG - Signature value as given in the certificate. + * MD - Finalized hash context with hash of the certificate. + * ALGO_NAME - Lowercase hash algorithm name + * SALTLEN - Salt length for rsaPSS. + */ + digestlen = gcry_md_get_algo_dlen (algo); + digest = gcry_md_read (md, algo); + if (use_pss) + { + err = gcry_sexp_build (&s_hash, NULL, + "(data (flags pss)" + "(hash %s %b)" + "(salt-length %u))", + algo_name, + (int)digestlen, + digest, + saltlen); + } + else if (pk_algo_from_sexp (s_pkey) == GCRY_PK_DSA) + { + /* NB.: We support only SHA-1 here because we had problems back + * then to get test data for DSA-2. Meanwhile DSA has been + * replaced by ECDSA which we do not yet support. */ + if (digestlen != 20) + { + log_error ("DSA requires the use of a 160 bit hash algorithm\n"); + gcry_md_close (md); + gcry_sexp_release (s_sig); + gcry_sexp_release (s_pkey); + return gpg_error (GPG_ERR_INTERNAL); + } + err = gcry_sexp_build (&s_hash, NULL, "(data(flags raw)(value %b))", + (int)digestlen, digest); + } + else /* Not DSA - we assume RSA */ + { + err = gcry_sexp_build (&s_hash, NULL, "(data(flags pkcs1)(hash %s %b))", + algo_name, (int)digestlen, digest); + } + + if (!err) + err = gcry_pk_verify (s_sig, s_hash, s_pkey); + if (DBG_X509) + log_debug ("gcry_pk_verify: %s\n", gpg_strerror (err)); + gcry_md_close (md); + gcry_sexp_release (s_sig); + gcry_sexp_release (s_hash); + gcry_sexp_release (s_pkey); + return err; +} + + + +/* Return 0 if CERT is usable for MODE. */ +static gpg_error_t +check_cert_usage (ksba_cert_t cert, enum cert_usage_modes mode) +{ + gpg_error_t err; + unsigned int use; + char *extkeyusages; + int have_ocsp_signing = 0; + + err = ksba_cert_get_ext_key_usages (cert, &extkeyusages); + if (gpg_err_code (err) == GPG_ERR_NO_DATA) + err = 0; /* No policy given. */ + if (!err) + { + unsigned int extusemask = ~0; /* Allow all. */ + + if (extkeyusages) + { + char *p, *pend; + int any_critical = 0; + + extusemask = 0; + + p = extkeyusages; + while (p && (pend=strchr (p, ':'))) + { + *pend++ = 0; + /* Only care about critical flagged usages. */ + if ( *pend == 'C' ) + { + any_critical = 1; + if ( !strcmp (p, oid_kp_serverAuth)) + extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE + | KSBA_KEYUSAGE_KEY_ENCIPHERMENT + | KSBA_KEYUSAGE_KEY_AGREEMENT); + else if ( !strcmp (p, oid_kp_clientAuth)) + extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE + | KSBA_KEYUSAGE_KEY_AGREEMENT); + else if ( !strcmp (p, oid_kp_codeSigning)) + extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE); + else if ( !strcmp (p, oid_kp_emailProtection)) + extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE + | KSBA_KEYUSAGE_NON_REPUDIATION + | KSBA_KEYUSAGE_KEY_ENCIPHERMENT + | KSBA_KEYUSAGE_KEY_AGREEMENT); + else if ( !strcmp (p, oid_kp_timeStamping)) + extusemask |= (KSBA_KEYUSAGE_DIGITAL_SIGNATURE + | KSBA_KEYUSAGE_NON_REPUDIATION); + } + + /* This is a hack to cope with OCSP. Note that we do + not yet fully comply with the requirements and that + the entire CRL/OCSP checking thing should undergo a + thorough review and probably redesign. */ + if ( !strcmp (p, oid_kp_ocspSigning)) + have_ocsp_signing = 1; + + if ((p = strchr (pend, '\n'))) + p++; + } + ksba_free (extkeyusages); + extkeyusages = NULL; + + if (!any_critical) + extusemask = ~0; /* Reset to the don't care mask. */ + } + + + err = ksba_cert_get_key_usage (cert, &use); + if (gpg_err_code (err) == GPG_ERR_NO_DATA) + { + err = 0; + if (opt.verbose && (mode == CERT_USAGE_MODE_SIGN + || mode == CERT_USAGE_MODE_ENCR)) + log_info (_("no key usage specified - assuming all usages\n")); + use = ~0; + } + + /* Apply extKeyUsage. */ + use &= extusemask; + + } + if (err) + { + log_error (_("error getting key usage information: %s\n"), + gpg_strerror (err)); + ksba_free (extkeyusages); + return err; + } + + switch (mode) + { + case CERT_USAGE_MODE_SIGN: + case CERT_USAGE_MODE_VRFY: + if ((use & (KSBA_KEYUSAGE_DIGITAL_SIGNATURE + | KSBA_KEYUSAGE_NON_REPUDIATION))) + return 0; + log_info (mode == CERT_USAGE_MODE_VRFY + ? _("certificate should not have been used for signing\n") + : _("certificate is not usable for signing\n")); + break; + + case CERT_USAGE_MODE_ENCR: + case CERT_USAGE_MODE_DECR: + if ((use & (KSBA_KEYUSAGE_KEY_ENCIPHERMENT + | KSBA_KEYUSAGE_DATA_ENCIPHERMENT))) + return 0; + log_info (mode == CERT_USAGE_MODE_DECR + ? _("certificate should not have been used for encryption\n") + : _("certificate is not usable for encryption\n")); + break; + + case CERT_USAGE_MODE_CERT: + if ((use & (KSBA_KEYUSAGE_KEY_CERT_SIGN))) + return 0; + log_info (_("certificate should not have " + "been used for certification\n")); + break; + + case CERT_USAGE_MODE_OCSP: + if (use != ~0 + && (have_ocsp_signing + || (use & (KSBA_KEYUSAGE_KEY_CERT_SIGN + |KSBA_KEYUSAGE_CRL_SIGN)))) + return 0; + log_info (_("certificate should not have " + "been used for OCSP response signing\n")); + break; + + case CERT_USAGE_MODE_CRL: + if ((use & (KSBA_KEYUSAGE_CRL_SIGN))) + return 0; + log_info (_("certificate should not have " + "been used for CRL signing\n")); + break; + } + + return gpg_error (GPG_ERR_WRONG_KEY_USAGE); +} + + +/* Return 0 if the certificate CERT is usable for certification. */ +gpg_error_t +check_cert_use_cert (ksba_cert_t cert) +{ + return check_cert_usage (cert, CERT_USAGE_MODE_CERT); +} + +/* Return 0 if the certificate CERT is usable for signing OCSP + responses. */ +gpg_error_t +check_cert_use_ocsp (ksba_cert_t cert) +{ + return check_cert_usage (cert, CERT_USAGE_MODE_OCSP); +} + +/* Return 0 if the certificate CERT is usable for signing CRLs. */ +gpg_error_t +check_cert_use_crl (ksba_cert_t cert) +{ + return check_cert_usage (cert, CERT_USAGE_MODE_CRL); +} |