Import LibreSSL v2.4.2 to vendor branch

[dragonfly.git] / crypto / libressl / crypto / ts / ts_rsp_verify.c

/* $OpenBSD: ts_rsp_verify.c,v 1.15 2015/07/19 05:42:55 miod Exp $ */
/* 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 <string.h>

#include <openssl/err.h>
#include <openssl/objects.h>
#include <openssl/pkcs7.h>
#include <openssl/ts.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 = 0;

        /* chain is an out argument. */
        *chain = NULL;
        if (X509_STORE_CTX_init(&cert_ctx, store, signer, untrusted) == 0) {
                TSerr(TS_F_TS_VERIFY_CERT, ERR_R_X509_LIB);
                goto err;
        }
        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_asprintf_error_data("Verify error:%s",
                    X509_verify_cert_error_string(j));
                goto err;
        } else {
                /* Get a copy of the certificate chain. */
                *chain = X509_STORE_CTX_get1_chain(&cert_ctx);
                ret = 1;
        }

err:
        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;
        if (attr->type != V_ASN1_SEQUENCE)
                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);
        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)
                                        strlcat(failure_text, ",",
                                            TS_STATUS_BUF_SIZE);
                                else
                                        first = 0;
                                strlcat(failure_text, TS_failure_info[i].text,
                                    TS_STATUS_BUF_SIZE);
                        }
                }
        }
        if (failure_text[0] == '\0')
                strlcpy(failure_text, "unspecified", TS_STATUS_BUF_SIZE);

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

        /* 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 = malloc(length))) {
                TSerr(TS_F_TS_GET_STATUS_TEXT, ERR_R_MALLOC_FAILURE);
                return NULL;
        }
        /* Concatenate the descriptions. */
        result[0] = '\0';
        for (i = 0; i < sk_ASN1_UTF8STRING_num(text); ++i) {
                ASN1_UTF8STRING *current = sk_ASN1_UTF8STRING_value(text, i);
                if (i > 0)
                        strlcat(result, "/", length);
                strlcat(result, (const char *)ASN1_STRING_data(current), length);
        }
        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 = 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);
        free(*imprint);
        *imprint = NULL;
        *imprint_len = 0;
        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;

        if (signer == NULL)
                return 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;
}