ts_rsp_verify.c

/* crypto/ts/ts_resp_verify.c */
/* Written by Zoltan Glozik (zglozik@stones.com) for the OpenSSL
 * project 2002.
 */
/* ====================================================================
 * Copyright (c) 2006 The OpenSSL Project.  All rights reserved.
 *
 * 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 above 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 acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    licensing@OpenSSL.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED 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 OpenSSL PROJECT OR
 * ITS 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.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
 * Hudson (tjh@cryptsoft.com).
 *
 */

#include <stdio.h>
#include "cryptlib.h"
#include <openssl/objects.h>
#include <openssl/ts.h>
#include <openssl/pkcs7.h>

/* Private function declarations. */

static int TS_verify_cert(X509_STORE *store, STACK_OF(X509) *untrusted,
			  X509 *signer, STACK_OF(X509) **chain);
static int TS_check_signing_certs(PKCS7_SIGNER_INFO *si, STACK_OF(X509) *chain);
static ESS_SIGNING_CERT *ESS_get_signing_cert(PKCS7_SIGNER_INFO *si);
static int TS_find_cert(STACK_OF(ESS_CERT_ID) *cert_ids, X509 *cert);
static int TS_issuer_serial_cmp(ESS_ISSUER_SERIAL *is, X509_CINF *cinfo);
static int int_TS_RESP_verify_token(TS_VERIFY_CTX *ctx, 
				 PKCS7 *token, TS_TST_INFO *tst_info);
static int TS_check_status_info(TS_RESP *response);
static char *TS_get_status_text(STACK_OF(ASN1_UTF8STRING) *text);
static int TS_check_policy(ASN1_OBJECT *req_oid, TS_TST_INFO *tst_info);
static int TS_compute_imprint(BIO *data, TS_TST_INFO *tst_info,
			      X509_ALGOR **md_alg, 
			      unsigned char **imprint, unsigned *imprint_len);
static int TS_check_imprints(X509_ALGOR *algor_a, 
			     unsigned char *imprint_a, unsigned len_a,
			     TS_TST_INFO *tst_info);
static int TS_check_nonces(const ASN1_INTEGER *a, TS_TST_INFO *tst_info);
static int TS_check_signer_name(GENERAL_NAME *tsa_name, X509 *signer);
static int TS_find_name(STACK_OF(GENERAL_NAME) *gen_names, GENERAL_NAME *name);

/*
 * Local mapping between response codes and descriptions.
 * Don't forget to change TS_STATUS_BUF_SIZE when modifying 
 * the elements of this array.
 */
static const char *TS_status_text[] =
	{ "granted",
	  "grantedWithMods",
	  "rejection",
	  "waiting",
	  "revocationWarning",
	  "revocationNotification" };

#define TS_STATUS_TEXT_SIZE	(sizeof(TS_status_text)/sizeof(*TS_status_text))

/*
 * This must be greater or equal to the sum of the strings in TS_status_text
 * plus the number of its elements.
 */
#define TS_STATUS_BUF_SIZE	256

static struct
	{
	int code;
	const char *text;
	} TS_failure_info[] =
		{ { TS_INFO_BAD_ALG, "badAlg" },
		  { TS_INFO_BAD_REQUEST, "badRequest" },
		  { TS_INFO_BAD_DATA_FORMAT, "badDataFormat" },
		  { TS_INFO_TIME_NOT_AVAILABLE, "timeNotAvailable" },
		  { TS_INFO_UNACCEPTED_POLICY, "unacceptedPolicy" },
		  { TS_INFO_UNACCEPTED_EXTENSION, "unacceptedExtension" },
		  { TS_INFO_ADD_INFO_NOT_AVAILABLE, "addInfoNotAvailable" },
		  { TS_INFO_SYSTEM_FAILURE, "systemFailure" } };

#define TS_FAILURE_INFO_SIZE	(sizeof(TS_failure_info) / \
				sizeof(*TS_failure_info))

/* Functions for verifying a signed TS_TST_INFO structure. */

/*
 * This function carries out the following tasks:
 *	- Checks if there is one and only one signer.
 *	- Search for the signing certificate in 'certs' and in the response.
 *	- Check the extended key usage and key usage fields of the signer
 *	certificate (done by the path validation).
 *	- Build and validate the certificate path.
 *	- Check if the certificate path meets the requirements of the
 *	SigningCertificate ESS signed attribute.
 *	- Verify the signature value.
 *	- Returns the signer certificate in 'signer', if 'signer' is not NULL.
 */
int TS_RESP_verify_signature(PKCS7 *token, STACK_OF(X509) *certs,
			     X509_STORE *store, X509 **signer_out)
	{
	STACK_OF(PKCS7_SIGNER_INFO) *sinfos = NULL;
	PKCS7_SIGNER_INFO *si;
	STACK_OF(X509) *signers = NULL;
	X509	*signer;
	STACK_OF(X509) *chain = NULL;
	char	buf[4096];
	int	i, j = 0, ret = 0;
	BIO	*p7bio = NULL;

	/* Some sanity checks first. */
	if (!token)
		{
		TSerr(TS_F_TS_RESP_VERIFY_SIGNATURE, TS_R_INVALID_NULL_POINTER);
		goto err;
		}

	/* Check for the correct content type */
	if(!PKCS7_type_is_signed(token))
		{
		TSerr(TS_F_TS_RESP_VERIFY_SIGNATURE, TS_R_WRONG_CONTENT_TYPE);
		goto err;
		}

	/* Check if there is one and only one signer. */
	sinfos = PKCS7_get_signer_info(token);
	if (!sinfos || sk_PKCS7_SIGNER_INFO_num(sinfos) != 1)
		{
		TSerr(TS_F_TS_RESP_VERIFY_SIGNATURE,
		      TS_R_THERE_MUST_BE_ONE_SIGNER);
		goto err;
		}
	si = sk_PKCS7_SIGNER_INFO_value(sinfos, 0);

	/* Check for no content: no data to verify signature. */
	if (PKCS7_get_detached(token))
		{
		TSerr(TS_F_TS_RESP_VERIFY_SIGNATURE, TS_R_NO_CONTENT);
		goto err;
		}
	
	/* Get hold of the signer certificate, search only internal
	   certificates if it was requested. */
	signers = PKCS7_get0_signers(token, certs, 0);
	if (!signers || sk_X509_num(signers) != 1) goto err;
	signer = sk_X509_value(signers, 0);

	/* Now verify the certificate. */
	if (!TS_verify_cert(store, certs, signer, &chain)) goto err;

	/* Check if the signer certificate is consistent with the
	   ESS extension. */
	if (!TS_check_signing_certs(si, chain)) goto err;

	/* Creating the message digest. */
	p7bio = PKCS7_dataInit(token, NULL);

	/* We now have to 'read' from p7bio to calculate digests etc. */
	while ((i = BIO_read(p7bio,buf,sizeof(buf))) > 0);

	/* Verifying the signature. */
	j = PKCS7_signatureVerify(p7bio, token, si, signer);
	if (j <= 0)
		{
		TSerr(TS_F_TS_RESP_VERIFY_SIGNATURE, TS_R_SIGNATURE_FAILURE);
		goto err;
		}

	/* Return the signer certificate if needed. */
	if (signer_out)
		{
		*signer_out = signer;
		CRYPTO_add(&signer->references, 1, CRYPTO_LOCK_X509);
		}

	ret = 1;

 err:
	BIO_free_all(p7bio);
	sk_X509_pop_free(chain, X509_free);
	sk_X509_free(signers);

	return ret;
	}

/*
 * The certificate chain is returned in chain. Caller is responsible for
 * freeing the vector.
 */
static int TS_verify_cert(X509_STORE *store, STACK_OF(X509) *untrusted,
			  X509 *signer, STACK_OF(X509) **chain)
	{
	X509_STORE_CTX	cert_ctx;
	int i;
	int ret = 1;

	/* chain is an out argument. */
	*chain = NULL;
	X509_STORE_CTX_init(&cert_ctx, store, signer, untrusted);
	X509_STORE_CTX_set_purpose(&cert_ctx, X509_PURPOSE_TIMESTAMP_SIGN);
	i = X509_verify_cert(&cert_ctx);
	if (i <= 0)
		{
		int j = X509_STORE_CTX_get_error(&cert_ctx);
		TSerr(TS_F_TS_VERIFY_CERT, TS_R_CERTIFICATE_VERIFY_ERROR);
		ERR_add_error_data(2, "Verify error:",
				   X509_verify_cert_error_string(j));
		ret = 0;
		}
	else
		{
		/* Get a copy of the certificate chain. */
		*chain = X509_STORE_CTX_get1_chain(&cert_ctx);
		}

	X509_STORE_CTX_cleanup(&cert_ctx);

	return ret;
	}

static int TS_check_signing_certs(PKCS7_SIGNER_INFO *si, STACK_OF(X509) *chain)
	{
	ESS_SIGNING_CERT *ss = ESS_get_signing_cert(si);
	STACK_OF(ESS_CERT_ID) *cert_ids = NULL;
	X509 *cert;
	int i = 0;
	int ret = 0;

	if (!ss) goto err;
	cert_ids = ss->cert_ids;
	/* The signer certificate must be the first in cert_ids. */
	cert = sk_X509_value(chain, 0);
	if (TS_find_cert(cert_ids, cert) != 0) goto err;
	
	/* Check the other certificates of the chain if there are more
	   than one certificate ids in cert_ids. */
	if (sk_ESS_CERT_ID_num(cert_ids) > 1)
		{
		/* All the certificates of the chain must be in cert_ids. */
		for (i = 1; i < sk_X509_num(chain); ++i)
			{
			cert = sk_X509_value(chain, i);
			if (TS_find_cert(cert_ids, cert) < 0) goto err;
			}
		}
	ret = 1;
 err:
	if (!ret)
		TSerr(TS_F_TS_CHECK_SIGNING_CERTS, 
		      TS_R_ESS_SIGNING_CERTIFICATE_ERROR);
	ESS_SIGNING_CERT_free(ss);
	return ret;
	}

static ESS_SIGNING_CERT *ESS_get_signing_cert(PKCS7_SIGNER_INFO *si)
	{
	ASN1_TYPE *attr;
	const unsigned char *p;
	attr = PKCS7_get_signed_attribute(si, 
					  NID_id_smime_aa_signingCertificate);
	if (!attr) return NULL;
	p = attr->value.sequence->data;
	return d2i_ESS_SIGNING_CERT(NULL, &p, attr->value.sequence->length);
	}

/* Returns < 0 if certificate is not found, certificate index otherwise. */
static int TS_find_cert(STACK_OF(ESS_CERT_ID) *cert_ids, X509 *cert)
	{
	int i;

	if (!cert_ids || !cert) return -1;

	/* Recompute SHA1 hash of certificate if necessary (side effect). */
	X509_check_purpose(cert, -1, 0);

	/* Look for cert in the cert_ids vector. */
	for (i = 0; i < sk_ESS_CERT_ID_num(cert_ids); ++i)
		{
		ESS_CERT_ID *cid = sk_ESS_CERT_ID_value(cert_ids, i);

		/* Check the SHA-1 hash first. */
		if (cid->hash->length == sizeof(cert->sha1_hash)
		    && !memcmp(cid->hash->data, cert->sha1_hash,
			       sizeof(cert->sha1_hash)))
			{
			/* Check the issuer/serial as well if specified. */
			ESS_ISSUER_SERIAL *is = cid->issuer_serial;
			if (!is || !TS_issuer_serial_cmp(is, cert->cert_info))
				return i;
			}
		}
	
	return -1;
	}

static int TS_issuer_serial_cmp(ESS_ISSUER_SERIAL *is, X509_CINF *cinfo)
	{
	GENERAL_NAME *issuer;

	if (!is || !cinfo || sk_GENERAL_NAME_num(is->issuer) != 1) return -1;

	/* Check the issuer first. It must be a directory name. */
	issuer = sk_GENERAL_NAME_value(is->issuer, 0);
	if (issuer->type != GEN_DIRNAME 
	    || X509_NAME_cmp(issuer->d.dirn, cinfo->issuer))
		return -1;

	/* Check the serial number, too. */
	if (ASN1_INTEGER_cmp(is->serial, cinfo->serialNumber))
		return -1;

	return 0;
	}

/*
 * Verifies whether 'response' contains a valid response with regards 
 * to the settings of the context:
 *	- Gives an error message if the TS_TST_INFO is not present.
 *	- Calls _TS_RESP_verify_token to verify the token content.
 */
int TS_RESP_verify_response(TS_VERIFY_CTX *ctx, TS_RESP *response)
	{
	PKCS7 *token = TS_RESP_get_token(response);
	TS_TST_INFO *tst_info = TS_RESP_get_tst_info(response);
	int ret = 0;

	/* Check if we have a successful TS_TST_INFO object in place. */
	if (!TS_check_status_info(response)) goto err;

	/* Check the contents of the time stamp token. */
	if (!int_TS_RESP_verify_token(ctx, token, tst_info))
		goto err;

	ret = 1;
 err:
	return ret;
	}

/*
 * Tries to extract a TS_TST_INFO structure from the PKCS7 token and
 * calls the internal int_TS_RESP_verify_token function for verifying it.
 */
int TS_RESP_verify_token(TS_VERIFY_CTX *ctx, PKCS7 *token)
	{
	TS_TST_INFO *tst_info = PKCS7_to_TS_TST_INFO(token);
	int ret = 0;
	if (tst_info)
		{
		ret = int_TS_RESP_verify_token(ctx, token, tst_info);
		TS_TST_INFO_free(tst_info);
		}
	return ret;
	}

/*
 * Verifies whether the 'token' contains a valid time stamp token 
 * with regards to the settings of the context. Only those checks are
 * carried out that are specified in the context:
 *	- Verifies the signature of the TS_TST_INFO.
 *	- Checks the version number of the response.
 *	- Check if the requested and returned policies math.
 *	- Check if the message imprints are the same.
 *	- Check if the nonces are the same.
 *	- Check if the TSA name matches the signer.
 *	- Check if the TSA name is the expected TSA.
 */
static int int_TS_RESP_verify_token(TS_VERIFY_CTX *ctx, 
				 PKCS7 *token, TS_TST_INFO *tst_info)
	{
	X509 *signer = NULL;
	GENERAL_NAME *tsa_name = TS_TST_INFO_get_tsa(tst_info);
	X509_ALGOR *md_alg = NULL;
	unsigned char *imprint = NULL;
	unsigned imprint_len = 0;
	int ret = 0;

	/* Verify the signature. */
	if ((ctx->flags & TS_VFY_SIGNATURE)
	    && !TS_RESP_verify_signature(token, ctx->certs, ctx->store,
					 &signer))
		goto err;
	
	/* Check version number of response. */
	if ((ctx->flags & TS_VFY_VERSION)
	    && TS_TST_INFO_get_version(tst_info) != 1)
		{
		TSerr(TS_F_INT_TS_RESP_VERIFY_TOKEN, TS_R_UNSUPPORTED_VERSION);
		goto err;
		}

	/* Check policies. */
	if ((ctx->flags & TS_VFY_POLICY)
	    && !TS_check_policy(ctx->policy, tst_info))
		goto err;
	
	/* Check message imprints. */
	if ((ctx->flags & TS_VFY_IMPRINT)
	    && !TS_check_imprints(ctx->md_alg, ctx->imprint, ctx->imprint_len,
				  tst_info)) 
		goto err;

	/* Compute and check message imprints. */
	if ((ctx->flags & TS_VFY_DATA)
	    && (!TS_compute_imprint(ctx->data, tst_info,
				    &md_alg, &imprint, &imprint_len)
	    || !TS_check_imprints(md_alg, imprint, imprint_len, tst_info)))
		goto err;

	/* Check nonces. */
	if ((ctx->flags & TS_VFY_NONCE)
	    && !TS_check_nonces(ctx->nonce, tst_info))
		goto err;

	/* Check whether TSA name and signer certificate match. */
	if ((ctx->flags & TS_VFY_SIGNER)
	    && tsa_name && !TS_check_signer_name(tsa_name, signer))
		{
		TSerr(TS_F_INT_TS_RESP_VERIFY_TOKEN, TS_R_TSA_NAME_MISMATCH);
		goto err;
		}

	/* Check whether the TSA is the expected one. */
	if ((ctx->flags & TS_VFY_TSA_NAME)
	    && !TS_check_signer_name(ctx->tsa_name, signer))
		{
		TSerr(TS_F_INT_TS_RESP_VERIFY_TOKEN, TS_R_TSA_UNTRUSTED);
		goto err;
		}

	ret = 1;
 err:
	X509_free(signer);
	X509_ALGOR_free(md_alg);
	OPENSSL_free(imprint);
	return ret;
	}

static int TS_check_status_info(TS_RESP *response)
	{
	TS_STATUS_INFO *info = TS_RESP_get_status_info(response);
	long status = ASN1_INTEGER_get(info->status);
	const char *status_text = NULL;
	char *embedded_status_text = NULL;
	char failure_text[TS_STATUS_BUF_SIZE] = "";

	/* Check if everything went fine. */
	if (status == 0 || status == 1) return 1;

	/* There was an error, get the description in status_text. */
	if (0 <= status && status < (long)TS_STATUS_TEXT_SIZE)
		status_text = TS_status_text[status];
	else
		status_text = "unknown code";

	/* Set the embedded_status_text to the returned description. */
	if (sk_ASN1_UTF8STRING_num(info->text) > 0
	    && !(embedded_status_text = TS_get_status_text(info->text)))
		return 0;
	
	/* Filling in failure_text with the failure information. */
	if (info->failure_info)
		{
		int i;
		int first = 1;
		for (i = 0; i < (int)TS_FAILURE_INFO_SIZE; ++i)
			{
			if (ASN1_BIT_STRING_get_bit(info->failure_info,
						    TS_failure_info[i].code))
				{
				if (!first)
					strcpy(failure_text, ",");
				else
					first = 0;
				strcat(failure_text, TS_failure_info[i].text);
				}
			}
		}
	if (failure_text[0] == '\0')
		strcpy(failure_text, "unspecified");

	/* Making up the error string. */
	TSerr(TS_F_TS_CHECK_STATUS_INFO, TS_R_NO_TIME_STAMP_TOKEN);
	ERR_add_error_data(6,
			   "status code: ", status_text,
			   ", status text: ", embedded_status_text ? 
			   embedded_status_text : "unspecified",
			   ", failure codes: ", failure_text);
	OPENSSL_free(embedded_status_text);

	return 0;
	}

static char *TS_get_status_text(STACK_OF(ASN1_UTF8STRING) *text)
	{
	int i;
	unsigned int length = 0;
	char *result = NULL;
	char *p;

	/* Determine length first. */
	for (i = 0; i < sk_ASN1_UTF8STRING_num(text); ++i)
		{
		ASN1_UTF8STRING *current = sk_ASN1_UTF8STRING_value(text, i);
		length += ASN1_STRING_length(current);
		length += 1;	/* separator character */
		}
	/* Allocate memory (closing '\0' included). */
	if (!(result = OPENSSL_malloc(length)))
		{
		TSerr(TS_F_TS_GET_STATUS_TEXT, ERR_R_MALLOC_FAILURE);
		return NULL;
		}
	/* Concatenate the descriptions. */
	for (i = 0, p = result; i < sk_ASN1_UTF8STRING_num(text); ++i)
		{
		ASN1_UTF8STRING *current = sk_ASN1_UTF8STRING_value(text, i);
		length = ASN1_STRING_length(current);
		if (i > 0) *p++ = '/';
		strncpy(p, (const char *)ASN1_STRING_data(current), length);
		p += length;
		}
	/* We do have space for this, too. */
	*p = '\0';
	
	return result;
	}

static int TS_check_policy(ASN1_OBJECT *req_oid, TS_TST_INFO *tst_info)
	{
	ASN1_OBJECT *resp_oid = TS_TST_INFO_get_policy_id(tst_info);

	if (OBJ_cmp(req_oid, resp_oid) != 0)
		{
		TSerr(TS_F_TS_CHECK_POLICY, TS_R_POLICY_MISMATCH);
		return 0;
		}

	return 1;
	}

static int TS_compute_imprint(BIO *data, TS_TST_INFO *tst_info,
			      X509_ALGOR **md_alg, 
			      unsigned char **imprint, unsigned *imprint_len)
	{
	TS_MSG_IMPRINT *msg_imprint = TS_TST_INFO_get_msg_imprint(tst_info);
	X509_ALGOR *md_alg_resp = TS_MSG_IMPRINT_get_algo(msg_imprint);
	const EVP_MD *md;
	EVP_MD_CTX md_ctx;
	unsigned char buffer[4096];
	int length;

	*md_alg = NULL;
	*imprint = NULL;

	/* Return the MD algorithm of the response. */
	if (!(*md_alg = X509_ALGOR_dup(md_alg_resp))) goto err;

	/* Getting the MD object. */
	if (!(md = EVP_get_digestbyobj((*md_alg)->algorithm)))
		{
		TSerr(TS_F_TS_COMPUTE_IMPRINT, TS_R_UNSUPPORTED_MD_ALGORITHM);
		goto err;
		}

	/* Compute message digest. */
	length = EVP_MD_size(md);
	if (length < 0)
	    goto err;
	*imprint_len = length;
	if (!(*imprint = OPENSSL_malloc(*imprint_len))) 
		{
		TSerr(TS_F_TS_COMPUTE_IMPRINT, ERR_R_MALLOC_FAILURE);
		goto err;
		}

	if (!EVP_DigestInit(&md_ctx, md))
		goto err;
	while ((length = BIO_read(data, buffer, sizeof(buffer))) > 0)
		{
		if (!EVP_DigestUpdate(&md_ctx, buffer, length))
			goto err;
		}
	if (!EVP_DigestFinal(&md_ctx, *imprint, NULL))
		goto err;

	return 1;
 err:
	X509_ALGOR_free(*md_alg);
	OPENSSL_free(*imprint);
	*imprint_len = 0;
	*imprint = NULL;
	return 0;
	}

static int TS_check_imprints(X509_ALGOR *algor_a, 
			     unsigned char *imprint_a, unsigned len_a,
			     TS_TST_INFO *tst_info)
	{
	TS_MSG_IMPRINT *b = TS_TST_INFO_get_msg_imprint(tst_info);
	X509_ALGOR *algor_b = TS_MSG_IMPRINT_get_algo(b);
	int ret = 0;

	/* algor_a is optional. */
	if (algor_a)
		{
		/* Compare algorithm OIDs. */
		if (OBJ_cmp(algor_a->algorithm, algor_b->algorithm)) goto err;

		/* The parameter must be NULL in both. */
		if ((algor_a->parameter 
		     && ASN1_TYPE_get(algor_a->parameter) != V_ASN1_NULL)
		    || (algor_b->parameter
			&& ASN1_TYPE_get(algor_b->parameter) != V_ASN1_NULL))
			goto err;
		}

	/* Compare octet strings. */
	ret = len_a == (unsigned) ASN1_STRING_length(b->hashed_msg) &&
		memcmp(imprint_a, ASN1_STRING_data(b->hashed_msg), len_a) == 0;
 err:
	if (!ret)
		TSerr(TS_F_TS_CHECK_IMPRINTS, TS_R_MESSAGE_IMPRINT_MISMATCH);
	return ret;
	}

static int TS_check_nonces(const ASN1_INTEGER *a, TS_TST_INFO *tst_info)
	{
	const ASN1_INTEGER *b = TS_TST_INFO_get_nonce(tst_info);

	/* Error if nonce is missing. */
	if (!b)
		{
		TSerr(TS_F_TS_CHECK_NONCES, TS_R_NONCE_NOT_RETURNED);
		return 0;
		}

	/* No error if a nonce is returned without being requested. */
	if (ASN1_INTEGER_cmp(a, b) != 0)
		{
		TSerr(TS_F_TS_CHECK_NONCES, TS_R_NONCE_MISMATCH);
		return 0;
		}

	return 1;
	}

/* Check if the specified TSA name matches either the subject
   or one of the subject alternative names of the TSA certificate. */
static int TS_check_signer_name(GENERAL_NAME *tsa_name, X509 *signer)
	{
	STACK_OF(GENERAL_NAME) *gen_names = NULL;
	int idx = -1;
	int found = 0;

	/* Check the subject name first. */
	if (tsa_name->type == GEN_DIRNAME 
	    && X509_name_cmp(tsa_name->d.dirn, signer->cert_info->subject) == 0)
		return 1;

	/* Check all the alternative names. */
	gen_names = X509_get_ext_d2i(signer, NID_subject_alt_name,
				     NULL, &idx);
	while (gen_names != NULL
	       && !(found = TS_find_name(gen_names, tsa_name) >= 0))
		{
		/* Get the next subject alternative name,
		   although there should be no more than one. */
		GENERAL_NAMES_free(gen_names);
		gen_names = X509_get_ext_d2i(signer, NID_subject_alt_name,
					     NULL, &idx);
		}
	if (gen_names) GENERAL_NAMES_free(gen_names);
	
	return found;
	}

/* Returns 1 if name is in gen_names, 0 otherwise. */
static int TS_find_name(STACK_OF(GENERAL_NAME) *gen_names, GENERAL_NAME *name)
	{
	int i, found;
	for (i = 0, found = 0; !found && i < sk_GENERAL_NAME_num(gen_names);
	     ++i)
		{
		GENERAL_NAME *current = sk_GENERAL_NAME_value(gen_names, i);
		found = GENERAL_NAME_cmp(current, name) == 0;
		}
	return found ? i - 1 : -1;
	}