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 "internal/cryptlib.h"
#include <openssl/objects.h>
#include <openssl/ts.h>
#include <openssl/pkcs7.h>
#include "ts_lcl.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 *cert);
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     OSSL_NELEM(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    OSSL_NELEM(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;
        X509_up_ref(signer);
    }

    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))
                return i;
        }
    }

    return -1;
}

static int ts_issuer_serial_cmp(ESS_ISSUER_SERIAL *is, X509 *cert)
{
    GENERAL_NAME *issuer;

    if (!is || !cert || 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, X509_get_issuer_name(cert)))
        return -1;

    /* Check the serial number, too. */
    if (ASN1_INTEGER_cmp(is->serial, X509_get_serialNumber(cert)))
        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 = response->token;
    TS_TST_INFO *tst_info = response->tst_info;
    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 = tst_info->tsa;
    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 = response->status_info;
    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)) == NULL)
        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)) == NULL) {
        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 = tst_info->policy_id;

    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 = tst_info->msg_imprint;
    X509_ALGOR *md_alg_resp = msg_imprint->hash_algo;
    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)) == NULL)
        goto err;

    /* Getting the MD object. */
    if ((md = EVP_get_digestbyobj((*md_alg)->algorithm)) == NULL) {
        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)) == NULL) {
        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 = 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 = tst_info->msg_imprint;
    X509_ALGOR *algor_b = b->hash_algo;
    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 = tst_info->nonce;

    /* 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, X509_get_subject_name(signer)) == 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;
        if (found)
            break;
        /*
         * 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);
    }
    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;
}