x509_vfy.c

/* crypto/x509/x509_vfy.c */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>
#include <time.h>
#include <errno.h>

#include "cryptlib.h"
#include <openssl/crypto.h>
#include <openssl/lhash.h>
#include <openssl/buffer.h>
#include <openssl/evp.h>
#include <openssl/asn1.h>
#include <openssl/x509.h>
#include <openssl/x509v3.h>
#include <openssl/objects.h>

/* CRL score values */

/* No unhandled critical extensions */

#define CRL_SCORE_NOCRITICAL	0x100

/* certificate is within CRL scope */

#define CRL_SCORE_SCOPE		0x080

/* CRL times valid */

#define CRL_SCORE_TIME		0x040

/* Issuer name matches certificate */

#define CRL_SCORE_ISSUER_NAME	0x020

/* If this score or above CRL is probably valid */

#define CRL_SCORE_VALID (CRL_SCORE_NOCRITICAL|CRL_SCORE_TIME|CRL_SCORE_SCOPE)

/* CRL issuer is certificate issuer */

#define CRL_SCORE_ISSUER_CERT	0x018

/* CRL issuer is on certificate path */

#define CRL_SCORE_SAME_PATH	0x008

/* CRL issuer matches CRL AKID */

#define CRL_SCORE_AKID		0x004

/* Have a delta CRL with valid times */

#define CRL_SCORE_TIME_DELTA	0x002

static int null_callback(int ok,X509_STORE_CTX *e);
static int check_issued(X509_STORE_CTX *ctx, X509 *x, X509 *issuer);
static X509 *find_issuer(X509_STORE_CTX *ctx, STACK_OF(X509) *sk, X509 *x);
static int check_chain_extensions(X509_STORE_CTX *ctx);
static int check_name_constraints(X509_STORE_CTX *ctx);
static int check_trust(X509_STORE_CTX *ctx);
static int check_revocation(X509_STORE_CTX *ctx);
static int check_cert(X509_STORE_CTX *ctx);
static int check_policy(X509_STORE_CTX *ctx);

static int get_crl_score(X509_STORE_CTX *ctx, X509 **pissuer,
			unsigned int *preasons,
			X509_CRL *crl, X509 *x);
static int get_crl_delta(X509_STORE_CTX *ctx,
				X509_CRL **pcrl, X509_CRL **pdcrl, X509 *x);
static void get_delta_sk(X509_STORE_CTX *ctx, X509_CRL **dcrl, int *pcrl_score,
			X509_CRL *base, STACK_OF(X509_CRL) *crls);
static void crl_akid_check(X509_STORE_CTX *ctx, X509_CRL *crl,
				X509 **pissuer, int *pcrl_score);
static int crl_crldp_check(X509 *x, X509_CRL *crl, int crl_score,
				unsigned int *preasons);
static int check_crl_path(X509_STORE_CTX *ctx, X509 *x);
static int check_crl_chain(X509_STORE_CTX *ctx,
			STACK_OF(X509) *cert_path,
			STACK_OF(X509) *crl_path);

static int internal_verify(X509_STORE_CTX *ctx);
const char X509_version[]="X.509" OPENSSL_VERSION_PTEXT;


static int null_callback(int ok, X509_STORE_CTX *e)
	{
	return ok;
	}

#if 0
static int x509_subject_cmp(X509 **a, X509 **b)
	{
	return X509_subject_name_cmp(*a,*b);
	}
#endif

int X509_verify_cert(X509_STORE_CTX *ctx)
	{
	X509 *x,*xtmp,*chain_ss=NULL;
	int bad_chain = 0;
	X509_VERIFY_PARAM *param = ctx->param;
	int depth,i,ok=0;
	int num;
	int (*cb)(int xok,X509_STORE_CTX *xctx);
	STACK_OF(X509) *sktmp=NULL;
	if (ctx->cert == NULL)
		{
		X509err(X509_F_X509_VERIFY_CERT,X509_R_NO_CERT_SET_FOR_US_TO_VERIFY);
		return -1;
		}

	cb=ctx->verify_cb;

	/* first we make sure the chain we are going to build is
	 * present and that the first entry is in place */
	if (ctx->chain == NULL)
		{
		if (	((ctx->chain=sk_X509_new_null()) == NULL) ||
			(!sk_X509_push(ctx->chain,ctx->cert)))
			{
			X509err(X509_F_X509_VERIFY_CERT,ERR_R_MALLOC_FAILURE);
			goto end;
			}
		CRYPTO_add(&ctx->cert->references,1,CRYPTO_LOCK_X509);
		ctx->last_untrusted=1;
		}

	/* We use a temporary STACK so we can chop and hack at it */
	if (ctx->untrusted != NULL
	    && (sktmp=sk_X509_dup(ctx->untrusted)) == NULL)
		{
		X509err(X509_F_X509_VERIFY_CERT,ERR_R_MALLOC_FAILURE);
		goto end;
		}

	num=sk_X509_num(ctx->chain);
	x=sk_X509_value(ctx->chain,num-1);
	depth=param->depth;


	for (;;)
		{
		/* If we have enough, we break */
		if (depth < num) break; /* FIXME: If this happens, we should take
		                         * note of it and, if appropriate, use the
		                         * X509_V_ERR_CERT_CHAIN_TOO_LONG error
		                         * code later.
		                         */

		/* If we are self signed, we break */
		if (ctx->check_issued(ctx, x,x)) break;

		/* If we were passed a cert chain, use it first */
		if (ctx->untrusted != NULL)
			{
			xtmp=find_issuer(ctx, sktmp,x);
			if (xtmp != NULL)
				{
				if (!sk_X509_push(ctx->chain,xtmp))
					{
					X509err(X509_F_X509_VERIFY_CERT,ERR_R_MALLOC_FAILURE);
					goto end;
					}
				CRYPTO_add(&xtmp->references,1,CRYPTO_LOCK_X509);
				(void)sk_X509_delete_ptr(sktmp,xtmp);
				ctx->last_untrusted++;
				x=xtmp;
				num++;
				/* reparse the full chain for
				 * the next one */
				continue;
				}
			}
		break;
		}

	/* at this point, chain should contain a list of untrusted
	 * certificates.  We now need to add at least one trusted one,
	 * if possible, otherwise we complain. */

	/* Examine last certificate in chain and see if it
 	 * is self signed.
 	 */

	i=sk_X509_num(ctx->chain);
	x=sk_X509_value(ctx->chain,i-1);
	if (ctx->check_issued(ctx, x, x))
		{
		/* we have a self signed certificate */
		if (sk_X509_num(ctx->chain) == 1)
			{
			/* We have a single self signed certificate: see if
			 * we can find it in the store. We must have an exact
			 * match to avoid possible impersonation.
			 */
			ok = ctx->get_issuer(&xtmp, ctx, x);
			if ((ok <= 0) || X509_cmp(x, xtmp)) 
				{
				ctx->error=X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT;
				ctx->current_cert=x;
				ctx->error_depth=i-1;
				if (ok == 1) X509_free(xtmp);
				bad_chain = 1;
				ok=cb(0,ctx);
				if (!ok) goto end;
				}
			else 
				{
				/* We have a match: replace certificate with store version
				 * so we get any trust settings.
				 */
				X509_free(x);
				x = xtmp;
				(void)sk_X509_set(ctx->chain, i - 1, x);
				ctx->last_untrusted=0;
				}
			}
		else
			{
			/* extract and save self signed certificate for later use */
			chain_ss=sk_X509_pop(ctx->chain);
			ctx->last_untrusted--;
			num--;
			x=sk_X509_value(ctx->chain,num-1);
			}
		}

	/* We now lookup certs from the certificate store */
	for (;;)
		{
		/* If we have enough, we break */
		if (depth < num) break;

		/* If we are self signed, we break */
		if (ctx->check_issued(ctx,x,x)) break;

		ok = ctx->get_issuer(&xtmp, ctx, x);

		if (ok < 0) return ok;
		if (ok == 0) break;

		x = xtmp;
		if (!sk_X509_push(ctx->chain,x))
			{
			X509_free(xtmp);
			X509err(X509_F_X509_VERIFY_CERT,ERR_R_MALLOC_FAILURE);
			return 0;
			}
		num++;
		}

	/* we now have our chain, lets check it... */

	/* Is last certificate looked up self signed? */
	if (!ctx->check_issued(ctx,x,x))
		{
		if ((chain_ss == NULL) || !ctx->check_issued(ctx, x, chain_ss))
			{
			if (ctx->last_untrusted >= num)
				ctx->error=X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY;
			else
				ctx->error=X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT;
			ctx->current_cert=x;
			}
		else
			{

			sk_X509_push(ctx->chain,chain_ss);
			num++;
			ctx->last_untrusted=num;
			ctx->current_cert=chain_ss;
			ctx->error=X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN;
			chain_ss=NULL;
			}

		ctx->error_depth=num-1;
		bad_chain = 1;
		ok=cb(0,ctx);
		if (!ok) goto end;
		}

	/* We have the chain complete: now we need to check its purpose */
	ok = check_chain_extensions(ctx);

	if (!ok) goto end;

	/* Check name constraints */

	ok = check_name_constraints(ctx);
	
	if (!ok) goto end;

	/* The chain extensions are OK: check trust */

	if (param->trust > 0) ok = check_trust(ctx);

	if (!ok) goto end;

	/* We may as well copy down any DSA parameters that are required */
	X509_get_pubkey_parameters(NULL,ctx->chain);

	/* Check revocation status: we do this after copying parameters
	 * because they may be needed for CRL signature verification.
	 */

	ok = ctx->check_revocation(ctx);
	if(!ok) goto end;

	/* At this point, we have a chain and need to verify it */
	if (ctx->verify != NULL)
		ok=ctx->verify(ctx);
	else
		ok=internal_verify(ctx);
	if(!ok) goto end;

#ifndef OPENSSL_NO_RFC3779
	/* RFC 3779 path validation, now that CRL check has been done */
	ok = v3_asid_validate_path(ctx);
	if (!ok) goto end;
	ok = v3_addr_validate_path(ctx);
	if (!ok) goto end;
#endif

	/* If we get this far evaluate policies */
	if (!bad_chain && (ctx->param->flags & X509_V_FLAG_POLICY_CHECK))
		ok = ctx->check_policy(ctx);
	if(!ok) goto end;
	if (0)
		{
end:
		X509_get_pubkey_parameters(NULL,ctx->chain);
		}
	if (sktmp != NULL) sk_X509_free(sktmp);
	if (chain_ss != NULL) X509_free(chain_ss);
	return ok;
	}


/* Given a STACK_OF(X509) find the issuer of cert (if any)
 */

static X509 *find_issuer(X509_STORE_CTX *ctx, STACK_OF(X509) *sk, X509 *x)
{
	int i;
	X509 *issuer;
	for (i = 0; i < sk_X509_num(sk); i++)
		{
		issuer = sk_X509_value(sk, i);
		if (ctx->check_issued(ctx, x, issuer))
			return issuer;
		}
	return NULL;
}

/* Given a possible certificate and issuer check them */

static int check_issued(X509_STORE_CTX *ctx, X509 *x, X509 *issuer)
{
	int ret;
	ret = X509_check_issued(issuer, x);
	if (ret == X509_V_OK)
		return 1;
	/* If we haven't asked for issuer errors don't set ctx */
	if (!(ctx->param->flags & X509_V_FLAG_CB_ISSUER_CHECK))
		return 0;

	ctx->error = ret;
	ctx->current_cert = x;
	ctx->current_issuer = issuer;
	return ctx->verify_cb(0, ctx);
	return 0;
}

/* Alternative lookup method: look from a STACK stored in other_ctx */

static int get_issuer_sk(X509 **issuer, X509_STORE_CTX *ctx, X509 *x)
{
	*issuer = find_issuer(ctx, ctx->other_ctx, x);
	if (*issuer)
		{
		CRYPTO_add(&(*issuer)->references,1,CRYPTO_LOCK_X509);
		return 1;
		}
	else
		return 0;
}
	

/* Check a certificate chains extensions for consistency
 * with the supplied purpose
 */

static int check_chain_extensions(X509_STORE_CTX *ctx)
{
#ifdef OPENSSL_NO_CHAIN_VERIFY
	return 1;
#else
	int i, ok=0, must_be_ca, plen = 0;
	X509 *x;
	int (*cb)(int xok,X509_STORE_CTX *xctx);
	int proxy_path_length = 0;
	int purpose;
	int allow_proxy_certs;
	cb=ctx->verify_cb;

	/* must_be_ca can have 1 of 3 values:
	   -1: we accept both CA and non-CA certificates, to allow direct
	       use of self-signed certificates (which are marked as CA).
	   0:  we only accept non-CA certificates.  This is currently not
	       used, but the possibility is present for future extensions.
	   1:  we only accept CA certificates.  This is currently used for
	       all certificates in the chain except the leaf certificate.
	*/
	must_be_ca = -1;

	/* CRL path validation */
	if (ctx->parent)
		{
		allow_proxy_certs = 0;
		purpose = X509_PURPOSE_CRL_SIGN;
		}
	else
		{
		allow_proxy_certs =
			!!(ctx->param->flags & X509_V_FLAG_ALLOW_PROXY_CERTS);
		/* A hack to keep people who don't want to modify their
		   software happy */
		if (getenv("OPENSSL_ALLOW_PROXY_CERTS"))
			allow_proxy_certs = 1;
		purpose = ctx->param->purpose;
		}

	/* Check all untrusted certificates */
	for (i = 0; i < ctx->last_untrusted; i++)
		{
		int ret;
		x = sk_X509_value(ctx->chain, i);
		if (!(ctx->param->flags & X509_V_FLAG_IGNORE_CRITICAL)
			&& (x->ex_flags & EXFLAG_CRITICAL))
			{
			ctx->error = X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION;
			ctx->error_depth = i;
			ctx->current_cert = x;
			ok=cb(0,ctx);
			if (!ok) goto end;
			}
		if (!allow_proxy_certs && (x->ex_flags & EXFLAG_PROXY))
			{
			ctx->error = X509_V_ERR_PROXY_CERTIFICATES_NOT_ALLOWED;
			ctx->error_depth = i;
			ctx->current_cert = x;
			ok=cb(0,ctx);
			if (!ok) goto end;
			}
		ret = X509_check_ca(x);
		switch(must_be_ca)
			{
		case -1:
			if ((ctx->param->flags & X509_V_FLAG_X509_STRICT)
				&& (ret != 1) && (ret != 0))
				{
				ret = 0;
				ctx->error = X509_V_ERR_INVALID_CA;
				}
			else
				ret = 1;
			break;
		case 0:
			if (ret != 0)
				{
				ret = 0;
				ctx->error = X509_V_ERR_INVALID_NON_CA;
				}
			else
				ret = 1;
			break;
		default:
			if ((ret == 0)
				|| ((ctx->param->flags & X509_V_FLAG_X509_STRICT)
					&& (ret != 1)))
				{
				ret = 0;
				ctx->error = X509_V_ERR_INVALID_CA;
				}
			else
				ret = 1;
			break;
			}
		if (ret == 0)
			{
			ctx->error_depth = i;
			ctx->current_cert = x;
			ok=cb(0,ctx);
			if (!ok) goto end;
			}
		if (ctx->param->purpose > 0)
			{
			ret = X509_check_purpose(x, purpose, must_be_ca > 0);
			if ((ret == 0)
				|| ((ctx->param->flags & X509_V_FLAG_X509_STRICT)
					&& (ret != 1)))
				{
				ctx->error = X509_V_ERR_INVALID_PURPOSE;
				ctx->error_depth = i;
				ctx->current_cert = x;
				ok=cb(0,ctx);
				if (!ok) goto end;
				}
			}
		/* Check pathlen if not self issued */
		if ((i > 1) && !(x->ex_flags & EXFLAG_SI)
			   && (x->ex_pathlen != -1)
			   && (plen > (x->ex_pathlen + proxy_path_length + 1)))
			{
			ctx->error = X509_V_ERR_PATH_LENGTH_EXCEEDED;
			ctx->error_depth = i;
			ctx->current_cert = x;
			ok=cb(0,ctx);
			if (!ok) goto end;
			}
		/* Increment path length if not self issued */
		if (!(x->ex_flags & EXFLAG_SI))
			plen++;
		/* If this certificate is a proxy certificate, the next
		   certificate must be another proxy certificate or a EE
		   certificate.  If not, the next certificate must be a
		   CA certificate.  */
		if (x->ex_flags & EXFLAG_PROXY)
			{
			if (x->ex_pcpathlen != -1 && i > x->ex_pcpathlen)
				{
				ctx->error =
					X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED;
				ctx->error_depth = i;
				ctx->current_cert = x;
				ok=cb(0,ctx);
				if (!ok) goto end;
				}
			proxy_path_length++;
			must_be_ca = 0;
			}
		else
			must_be_ca = 1;
		}
	ok = 1;
 end:
	return ok;
#endif
}

static int check_name_constraints(X509_STORE_CTX *ctx)
	{
	X509 *x;
	int i, j, rv;
	/* Check name constraints for all certificates */
	for (i = sk_X509_num(ctx->chain) - 1; i >= 0; i--)
		{
		x = sk_X509_value(ctx->chain, i);
		/* Ignore self issued certs unless last in chain */
		if (i && (x->ex_flags & EXFLAG_SI))
			continue;
		/* Check against constraints for all certificates higher in
		 * chain including trust anchor. Trust anchor not strictly
		 * speaking needed but if it includes constraints it is to be
		 * assumed it expects them to be obeyed.
		 */
		for (j = sk_X509_num(ctx->chain) - 1; j > i; j--)
			{
			NAME_CONSTRAINTS *nc = sk_X509_value(ctx->chain, j)->nc;
			if (nc)
				{
				rv = NAME_CONSTRAINTS_check(x, nc);
				if (rv != X509_V_OK)
					{
					ctx->error = rv;
					ctx->error_depth = i;
					ctx->current_cert = x;
					if (!ctx->verify_cb(0,ctx))
						return 0;
					}
				}
			}
		}
	return 1;
	}

static int check_trust(X509_STORE_CTX *ctx)
{
#ifdef OPENSSL_NO_CHAIN_VERIFY
	return 1;
#else
	int i, ok;
	X509 *x;
	int (*cb)(int xok,X509_STORE_CTX *xctx);
	cb=ctx->verify_cb;
/* For now just check the last certificate in the chain */
	i = sk_X509_num(ctx->chain) - 1;
	x = sk_X509_value(ctx->chain, i);
	ok = X509_check_trust(x, ctx->param->trust, 0);
	if (ok == X509_TRUST_TRUSTED)
		return 1;
	ctx->error_depth = i;
	ctx->current_cert = x;
	if (ok == X509_TRUST_REJECTED)
		ctx->error = X509_V_ERR_CERT_REJECTED;
	else
		ctx->error = X509_V_ERR_CERT_UNTRUSTED;
	ok = cb(0, ctx);
	return ok;
#endif
}

static int check_revocation(X509_STORE_CTX *ctx)
	{
	int i, last, ok;
	if (!(ctx->param->flags & X509_V_FLAG_CRL_CHECK))
		return 1;
	if (ctx->param->flags & X509_V_FLAG_CRL_CHECK_ALL)
		last = sk_X509_num(ctx->chain) - 1;
	else
		{
		/* If checking CRL paths this isn't the EE certificate */
		if (ctx->parent)
			return 1;
		last = 0;
		}
	for(i = 0; i <= last; i++)
		{
		ctx->error_depth = i;
		ok = check_cert(ctx);
		if (!ok) return ok;
		}
	return 1;
	}

static int check_cert(X509_STORE_CTX *ctx)
	{
	X509_CRL *crl = NULL, *dcrl = NULL;
	X509 *x;
	int ok, cnum;
	unsigned int last_reasons;
	cnum = ctx->error_depth;
	x = sk_X509_value(ctx->chain, cnum);
	ctx->current_cert = x;
	ctx->current_issuer = NULL;
	ctx->current_crl_score = 0;
	ctx->current_reasons = 0;
	while (ctx->current_reasons != CRLDP_ALL_REASONS)
		{
		last_reasons = ctx->current_reasons;
		/* Try to retrieve relevant CRL */
		if (ctx->get_crl)
			ok = ctx->get_crl(ctx, &crl, x);
		else
			ok = get_crl_delta(ctx, &crl, &dcrl, x);
		/* If error looking up CRL, nothing we can do except
		 * notify callback
		 */
		if(!ok)
			{
			ctx->error = X509_V_ERR_UNABLE_TO_GET_CRL;
			ok = ctx->verify_cb(0, ctx);
			goto err;
			}
		ctx->current_crl = crl;
		ok = ctx->check_crl(ctx, crl);
		if (!ok)
			goto err;

		if (dcrl)
			{
			ok = ctx->check_crl(ctx, dcrl);
			if (!ok)
				goto err;
			ok = ctx->cert_crl(ctx, dcrl, x);
			if (!ok)
				goto err;
			}
		else
			ok = 1;

		/* Don't look in full CRL if delta reason is removefromCRL */
		if (ok != 2)
			{
			ok = ctx->cert_crl(ctx, crl, x);
			if (!ok)
				goto err;
			}

		X509_CRL_free(crl);
		X509_CRL_free(dcrl);
		crl = NULL;
		dcrl = NULL;
		/* If reasons not updated we wont get anywhere by
		 * another iteration, so exit loop.
		 */
		if (last_reasons == ctx->current_reasons)
			{
			ctx->error = X509_V_ERR_UNABLE_TO_GET_CRL;
			ok = ctx->verify_cb(0, ctx);
			goto err;
			}
		}
	err:
	X509_CRL_free(crl);
	X509_CRL_free(dcrl);

	ctx->current_crl = NULL;
	return ok;

	}

/* Check CRL times against values in X509_STORE_CTX */

static int check_crl_time(X509_STORE_CTX *ctx, X509_CRL *crl, int notify)
	{
	time_t *ptime;
	int i;
	if (notify)
		ctx->current_crl = crl;
	if (ctx->param->flags & X509_V_FLAG_USE_CHECK_TIME)
		ptime = &ctx->param->check_time;
	else
		ptime = NULL;

	i=X509_cmp_time(X509_CRL_get_lastUpdate(crl), ptime);
	if (i == 0)
		{
		if (!notify)
			return 0;
		ctx->error=X509_V_ERR_ERROR_IN_CRL_LAST_UPDATE_FIELD;
		if (!ctx->verify_cb(0, ctx))
			return 0;
		}

	if (i > 0)
		{
		if (!notify)
			return 0;
		ctx->error=X509_V_ERR_CRL_NOT_YET_VALID;
		if (!ctx->verify_cb(0, ctx))
			return 0;
		}

	if(X509_CRL_get_nextUpdate(crl))
		{
		i=X509_cmp_time(X509_CRL_get_nextUpdate(crl), ptime);

		if (i == 0)
			{
			if (!notify)
				return 0;
			ctx->error=X509_V_ERR_ERROR_IN_CRL_NEXT_UPDATE_FIELD;
			if (!ctx->verify_cb(0, ctx))
				return 0;
			}
		/* Ignore expiry of base CRL is delta is valid */
		if ((i < 0) && !(ctx->current_crl_score & CRL_SCORE_TIME_DELTA))
			{
			if (!notify)
				return 0;
			ctx->error=X509_V_ERR_CRL_HAS_EXPIRED;
			if (!ctx->verify_cb(0, ctx))
				return 0;
			}
		}

	if (notify)
		ctx->current_crl = NULL;

	return 1;
	}

static int get_crl_sk(X509_STORE_CTX *ctx, X509_CRL **pcrl, X509_CRL **pdcrl,
			X509 **pissuer, int *pscore, unsigned int *preasons,
			STACK_OF(X509_CRL) *crls)
	{
	int i, crl_score, best_score = *pscore;
	unsigned int reasons, best_reasons = 0;
	X509 *x = ctx->current_cert;
	X509_CRL *crl, *best_crl = NULL;
	X509 *crl_issuer = NULL, *best_crl_issuer = NULL;

	for (i = 0; i < sk_X509_CRL_num(crls); i++)
		{
		crl = sk_X509_CRL_value(crls, i);
		reasons = *preasons;
		crl_score = get_crl_score(ctx, &crl_issuer, &reasons, crl, x);

		if (crl_score > best_score)
			{
			best_crl = crl;
			best_crl_issuer = crl_issuer;
			best_score = crl_score;
			best_reasons = reasons;
			}
		}

	if (best_crl)
		{
		if (*pcrl)
			X509_CRL_free(*pcrl);
		*pcrl = best_crl;
		*pissuer = best_crl_issuer;
		*pscore = best_score;
		*preasons = best_reasons;
		CRYPTO_add(&best_crl->references, 1, CRYPTO_LOCK_X509_CRL);
		if (*pdcrl)
			{
			X509_CRL_free(*pdcrl);
			*pdcrl = NULL;
			}
		get_delta_sk(ctx, pdcrl, pscore, best_crl, crls);
		}

	if (best_score >= CRL_SCORE_VALID)
		return 1;

	return 0;
	}

/* Compare two CRL extensions for delta checking purposes. They should be
 * both present or both absent. If both present all fields must be identical.
 */

static int crl_extension_match(X509_CRL *a, X509_CRL *b, int nid)
	{
	ASN1_OCTET_STRING *exta, *extb;
	int i;
	i = X509_CRL_get_ext_by_NID(a, nid, -1);
	if (i >= 0)
		{
		/* Can't have multiple occurrences */
		if (X509_CRL_get_ext_by_NID(a, nid, i) != -1)
			return 0;
		exta = X509_EXTENSION_get_data(X509_CRL_get_ext(a, i));
		}
	else
		exta = NULL;

	i = X509_CRL_get_ext_by_NID(b, nid, -1);

	if (i >= 0)
		{

		if (X509_CRL_get_ext_by_NID(b, nid, i) != -1)
			return 0;
		extb = X509_EXTENSION_get_data(X509_CRL_get_ext(b, i));
		}
	else
		extb = NULL;

	if (!exta && !extb)
		return 1;

	if (!exta || !extb)
		return 0;


	if (ASN1_OCTET_STRING_cmp(exta, extb))
		return 0;

	return 1;
	}

/* See if a base and delta are compatible */

static int check_delta_base(X509_CRL *delta, X509_CRL *base)
	{
	/* Delta CRL must be a delta */
	if (!delta->base_crl_number)
			return 0;
	/* Base must have a CRL number */
	if (!base->crl_number)
			return 0;
	/* Issuer names must match */
	if (X509_NAME_cmp(X509_CRL_get_issuer(base),
				X509_CRL_get_issuer(delta)))
		return 0;
	/* AKID and IDP must match */
	if (!crl_extension_match(delta, base, NID_authority_key_identifier))
			return 0;
	if (!crl_extension_match(delta, base, NID_issuing_distribution_point))
			return 0;
	/* Delta CRL base number must not exceed Full CRL number. */
	if (ASN1_INTEGER_cmp(delta->base_crl_number, base->crl_number) > 0)
			return 0;
	/* Delta CRL number must exceed full CRL number */
	if (ASN1_INTEGER_cmp(delta->crl_number, base->crl_number) > 0)
			return 1;
	return 0;
	}

/* For a given base CRL find a delta... maybe extend to delta scoring
 * or retrieve a chain of deltas...
 */

static void get_delta_sk(X509_STORE_CTX *ctx, X509_CRL **dcrl, int *pscore,
			X509_CRL *base, STACK_OF(X509_CRL) *crls)
	{
	X509_CRL *delta;
	int i;
	if (!(ctx->param->flags & X509_V_FLAG_USE_DELTAS))
		return;
	if (!((ctx->current_cert->ex_flags | base->flags) & EXFLAG_FRESHEST))
		return;
	for (i = 0; i < sk_X509_CRL_num(crls); i++)
		{
		delta = sk_X509_CRL_value(crls, i);
		if (check_delta_base(delta, base))
			{
			if (check_crl_time(ctx, delta, 0))
				*pscore |= CRL_SCORE_TIME_DELTA;
			CRYPTO_add(&delta->references, 1, CRYPTO_LOCK_X509_CRL);
			*dcrl = delta;
			return;
			}
		}
	*dcrl = NULL;
	}

/* For a given CRL return how suitable it is for the supplied certificate 'x'.
 * The return value is a mask of several criteria.
 * If the issuer is not the certificate issuer this is returned in *pissuer.
 * The reasons mask is also used to determine if the CRL is suitable: if
 * no new reasons the CRL is rejected, otherwise reasons is updated.
 */

static int get_crl_score(X509_STORE_CTX *ctx, X509 **pissuer,
			unsigned int *preasons,
			X509_CRL *crl, X509 *x)
	{

	int crl_score = 0;
	unsigned int tmp_reasons = *preasons, crl_reasons;

	/* First see if we can reject CRL straight away */

	/* Invalid IDP cannot be processed */
	if (crl->idp_flags & IDP_INVALID)
		return 0;
	/* Reason codes or indirect CRLs need extended CRL support */
	if (!(ctx->param->flags & X509_V_FLAG_EXTENDED_CRL_SUPPORT))
		{