crypto/x509v3/v3_purp.c

/* v3_purp.c */
/*
 * Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL project
 * 2001.
 */
/* ====================================================================
 * Copyright (c) 1999-2004 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/buf.h>
#include <openssl/err.h>
#include <openssl/digest.h>
#include <openssl/mem.h>
#include <openssl/obj.h>
#include <openssl/thread.h>
#include <openssl/x509_vfy.h>
#include <openssl/x509v3.h>

#include "../internal.h"

#define V1_ROOT (EXFLAG_V1|EXFLAG_SS)
#define ku_reject(x, usage) \
        (((x)->ex_flags & EXFLAG_KUSAGE) && !((x)->ex_kusage & (usage)))
#define xku_reject(x, usage) \
        (((x)->ex_flags & EXFLAG_XKUSAGE) && !((x)->ex_xkusage & (usage)))
#define ns_reject(x, usage) \
        (((x)->ex_flags & EXFLAG_NSCERT) && !((x)->ex_nscert & (usage)))

static void x509v3_cache_extensions(X509 *x);

static int check_ssl_ca(const X509 *x);
static int check_purpose_ssl_client(const X509_PURPOSE *xp, const X509 *x,
                                    int ca);
static int check_purpose_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                    int ca);
static int check_purpose_ns_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                       int ca);
static int purpose_smime(const X509 *x, int ca);
static int check_purpose_smime_sign(const X509_PURPOSE *xp, const X509 *x,
                                    int ca);
static int check_purpose_smime_encrypt(const X509_PURPOSE *xp, const X509 *x,
                                       int ca);
static int check_purpose_crl_sign(const X509_PURPOSE *xp, const X509 *x,
                                  int ca);
static int check_purpose_timestamp_sign(const X509_PURPOSE *xp, const X509 *x,
                                        int ca);
static int no_check(const X509_PURPOSE *xp, const X509 *x, int ca);
static int ocsp_helper(const X509_PURPOSE *xp, const X509 *x, int ca);

static int xp_cmp(const X509_PURPOSE **a, const X509_PURPOSE **b);
static void xptable_free(X509_PURPOSE *p);

static X509_PURPOSE xstandard[] = {
    {X509_PURPOSE_SSL_CLIENT, X509_TRUST_SSL_CLIENT, 0,
     check_purpose_ssl_client, (char *)"SSL client", (char *)"sslclient",
     NULL},
    {X509_PURPOSE_SSL_SERVER, X509_TRUST_SSL_SERVER, 0,
     check_purpose_ssl_server, (char *)"SSL server", (char *)"sslserver",
     NULL},
    {X509_PURPOSE_NS_SSL_SERVER, X509_TRUST_SSL_SERVER, 0,
     check_purpose_ns_ssl_server, (char *)"Netscape SSL server",
     (char *)"nssslserver", NULL},
    {X509_PURPOSE_SMIME_SIGN, X509_TRUST_EMAIL, 0, check_purpose_smime_sign,
     (char *)"S/MIME signing", (char *)"smimesign", NULL},
    {X509_PURPOSE_SMIME_ENCRYPT, X509_TRUST_EMAIL, 0,
     check_purpose_smime_encrypt, (char *)"S/MIME encryption",
     (char *)"smimeencrypt", NULL},
    {X509_PURPOSE_CRL_SIGN, X509_TRUST_COMPAT, 0, check_purpose_crl_sign,
     (char *)"CRL signing", (char *)"crlsign", NULL},
    {X509_PURPOSE_ANY, X509_TRUST_DEFAULT, 0, no_check, (char *)"Any Purpose",
     (char *)"any", NULL},
    {X509_PURPOSE_OCSP_HELPER, X509_TRUST_COMPAT, 0, ocsp_helper,
     (char *)"OCSP helper", (char *)"ocsphelper", NULL},
    {X509_PURPOSE_TIMESTAMP_SIGN, X509_TRUST_TSA, 0,
     check_purpose_timestamp_sign, (char *)"Time Stamp signing",
     (char *)"timestampsign", NULL},
};

#define X509_PURPOSE_COUNT (sizeof(xstandard)/sizeof(X509_PURPOSE))

static STACK_OF(X509_PURPOSE) *xptable = NULL;

static int xp_cmp(const X509_PURPOSE **a, const X509_PURPOSE **b)
{
    return (*a)->purpose - (*b)->purpose;
}

/*
 * As much as I'd like to make X509_check_purpose use a "const" X509* I
 * really can't because it does recalculate hashes and do other non-const
 * things.
 */
int X509_check_purpose(X509 *x, int id, int ca)
{
    int idx;
    const X509_PURPOSE *pt;
    x509v3_cache_extensions(x);
    if (id == -1)
        return 1;
    idx = X509_PURPOSE_get_by_id(id);
    if (idx == -1)
        return -1;
    pt = X509_PURPOSE_get0(idx);
    return pt->check_purpose(pt, x, ca);
}

int X509_PURPOSE_set(int *p, int purpose)
{
    if (X509_PURPOSE_get_by_id(purpose) == -1) {
        OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_PURPOSE);
        return 0;
    }
    *p = purpose;
    return 1;
}

int X509_PURPOSE_get_count(void)
{
    if (!xptable)
        return X509_PURPOSE_COUNT;
    return sk_X509_PURPOSE_num(xptable) + X509_PURPOSE_COUNT;
}

X509_PURPOSE *X509_PURPOSE_get0(int idx)
{
    if (idx < 0)
        return NULL;
    if (idx < (int)X509_PURPOSE_COUNT)
        return xstandard + idx;
    return sk_X509_PURPOSE_value(xptable, idx - X509_PURPOSE_COUNT);
}

int X509_PURPOSE_get_by_sname(char *sname)
{
    int i;
    X509_PURPOSE *xptmp;
    for (i = 0; i < X509_PURPOSE_get_count(); i++) {
        xptmp = X509_PURPOSE_get0(i);
        if (!strcmp(xptmp->sname, sname))
            return i;
    }
    return -1;
}

int X509_PURPOSE_get_by_id(int purpose)
{
    X509_PURPOSE tmp;
    size_t idx;

    if ((purpose >= X509_PURPOSE_MIN) && (purpose <= X509_PURPOSE_MAX))
        return purpose - X509_PURPOSE_MIN;
    tmp.purpose = purpose;
    if (!xptable)
        return -1;

    if (!sk_X509_PURPOSE_find(xptable, &idx, &tmp))
        return -1;
    return idx + X509_PURPOSE_COUNT;
}

int X509_PURPOSE_add(int id, int trust, int flags,
                     int (*ck) (const X509_PURPOSE *, const X509 *, int),
                     char *name, char *sname, void *arg)
{
    int idx;
    X509_PURPOSE *ptmp;
    char *name_dup, *sname_dup;

    /*
     * This is set according to what we change: application can't set it
     */
    flags &= ~X509_PURPOSE_DYNAMIC;
    /* This will always be set for application modified trust entries */
    flags |= X509_PURPOSE_DYNAMIC_NAME;
    /* Get existing entry if any */
    idx = X509_PURPOSE_get_by_id(id);
    /* Need a new entry */
    if (idx == -1) {
        if (!(ptmp = OPENSSL_malloc(sizeof(X509_PURPOSE)))) {
            OPENSSL_PUT_ERROR(X509V3, ERR_R_MALLOC_FAILURE);
            return 0;
        }
        ptmp->flags = X509_PURPOSE_DYNAMIC;
    } else
        ptmp = X509_PURPOSE_get0(idx);

    /* Duplicate the supplied names. */
    name_dup = BUF_strdup(name);
    sname_dup = BUF_strdup(sname);
    if (name_dup == NULL || sname_dup == NULL) {
        OPENSSL_PUT_ERROR(X509V3, ERR_R_MALLOC_FAILURE);
        if (name_dup != NULL)
            OPENSSL_free(name_dup);
        if (sname_dup != NULL)
            OPENSSL_free(sname_dup);
        if (idx == -1)
            OPENSSL_free(ptmp);
        return 0;
    }

    /* OPENSSL_free existing name if dynamic */
    if (ptmp->flags & X509_PURPOSE_DYNAMIC_NAME) {
        OPENSSL_free(ptmp->name);
        OPENSSL_free(ptmp->sname);
    }
    /* dup supplied name */
    ptmp->name = name_dup;
    ptmp->sname = sname_dup;
    /* Keep the dynamic flag of existing entry */
    ptmp->flags &= X509_PURPOSE_DYNAMIC;
    /* Set all other flags */
    ptmp->flags |= flags;

    ptmp->purpose = id;
    ptmp->trust = trust;
    ptmp->check_purpose = ck;
    ptmp->usr_data = arg;

    /* If its a new entry manage the dynamic table */
    if (idx == -1) {
        if (!xptable && !(xptable = sk_X509_PURPOSE_new(xp_cmp))) {
            OPENSSL_PUT_ERROR(X509V3, ERR_R_MALLOC_FAILURE);
            xptable_free(ptmp);
            return 0;
        }
        if (!sk_X509_PURPOSE_push(xptable, ptmp)) {
            OPENSSL_PUT_ERROR(X509V3, ERR_R_MALLOC_FAILURE);
            xptable_free(ptmp);
            return 0;
        }
    }
    return 1;
}

static void xptable_free(X509_PURPOSE *p)
{
    if (!p)
        return;
    if (p->flags & X509_PURPOSE_DYNAMIC) {
        if (p->flags & X509_PURPOSE_DYNAMIC_NAME) {
            OPENSSL_free(p->name);
            OPENSSL_free(p->sname);
        }
        OPENSSL_free(p);
    }
}

void X509_PURPOSE_cleanup(void)
{
    unsigned int i;
    sk_X509_PURPOSE_pop_free(xptable, xptable_free);
    for (i = 0; i < X509_PURPOSE_COUNT; i++)
        xptable_free(xstandard + i);
    xptable = NULL;
}

int X509_PURPOSE_get_id(X509_PURPOSE *xp)
{
    return xp->purpose;
}

char *X509_PURPOSE_get0_name(X509_PURPOSE *xp)
{
    return xp->name;
}

char *X509_PURPOSE_get0_sname(X509_PURPOSE *xp)
{
    return xp->sname;
}

int X509_PURPOSE_get_trust(X509_PURPOSE *xp)
{
    return xp->trust;
}

static int nid_cmp(const void *void_a, const void *void_b)
{
    const int *a = void_a, *b = void_b;

    return *a - *b;
}

int X509_supported_extension(X509_EXTENSION *ex)
{
    /*
     * This table is a list of the NIDs of supported extensions: that is
     * those which are used by the verify process. If an extension is
     * critical and doesn't appear in this list then the verify process will
     * normally reject the certificate. The list must be kept in numerical
     * order because it will be searched using bsearch.
     */

    static const int supported_nids[] = {
        NID_netscape_cert_type, /* 71 */
        NID_key_usage,          /* 83 */
        NID_subject_alt_name,   /* 85 */
        NID_basic_constraints,  /* 87 */
        NID_certificate_policies, /* 89 */
        NID_ext_key_usage,      /* 126 */
        NID_policy_constraints, /* 401 */
        NID_proxyCertInfo,      /* 663 */
        NID_name_constraints,   /* 666 */
        NID_policy_mappings,    /* 747 */
        NID_inhibit_any_policy  /* 748 */
    };

    int ex_nid = OBJ_obj2nid(X509_EXTENSION_get_object(ex));

    if (ex_nid == NID_undef)
        return 0;

    if (bsearch
        (&ex_nid, supported_nids, sizeof(supported_nids) / sizeof(int),
         sizeof(int), nid_cmp) != NULL)
        return 1;
    return 0;
}

static void setup_dp(X509 *x, DIST_POINT *dp)
{
    X509_NAME *iname = NULL;
    size_t i;
    if (dp->reasons) {
        if (dp->reasons->length > 0)
            dp->dp_reasons = dp->reasons->data[0];
        if (dp->reasons->length > 1)
            dp->dp_reasons |= (dp->reasons->data[1] << 8);
        dp->dp_reasons &= CRLDP_ALL_REASONS;
    } else
        dp->dp_reasons = CRLDP_ALL_REASONS;
    if (!dp->distpoint || (dp->distpoint->type != 1))
        return;
    for (i = 0; i < sk_GENERAL_NAME_num(dp->CRLissuer); i++) {
        GENERAL_NAME *gen = sk_GENERAL_NAME_value(dp->CRLissuer, i);
        if (gen->type == GEN_DIRNAME) {
            iname = gen->d.directoryName;
            break;
        }
    }
    if (!iname)
        iname = X509_get_issuer_name(x);

    DIST_POINT_set_dpname(dp->distpoint, iname);

}

static void setup_crldp(X509 *x)
{
    size_t i;
    x->crldp = X509_get_ext_d2i(x, NID_crl_distribution_points, NULL, NULL);
    for (i = 0; i < sk_DIST_POINT_num(x->crldp); i++)
        setup_dp(x, sk_DIST_POINT_value(x->crldp, i));
}

static void x509v3_cache_extensions(X509 *x)
{
    BASIC_CONSTRAINTS *bs;
    PROXY_CERT_INFO_EXTENSION *pci;
    ASN1_BIT_STRING *usage;
    ASN1_BIT_STRING *ns;
    EXTENDED_KEY_USAGE *extusage;
    X509_EXTENSION *ex;
    size_t i;
    int j;

    CRYPTO_MUTEX_lock_read(&x->lock);
    const int is_set = x->ex_flags & EXFLAG_SET;
    CRYPTO_MUTEX_unlock_read(&x->lock);

    if (is_set) {
        return;
    }

    CRYPTO_MUTEX_lock_write(&x->lock);
    if (x->ex_flags & EXFLAG_SET) {
        CRYPTO_MUTEX_unlock_write(&x->lock);
        return;
    }

    X509_digest(x, EVP_sha1(), x->sha1_hash, NULL);
    /* V1 should mean no extensions ... */
    if (!X509_get_version(x))
        x->ex_flags |= EXFLAG_V1;
    /* Handle basic constraints */
    if ((bs = X509_get_ext_d2i(x, NID_basic_constraints, NULL, NULL))) {
        if (bs->ca)
            x->ex_flags |= EXFLAG_CA;
        if (bs->pathlen) {
            if ((bs->pathlen->type == V_ASN1_NEG_INTEGER)
                || !bs->ca) {
                x->ex_flags |= EXFLAG_INVALID;
                x->ex_pathlen = 0;
            } else
                x->ex_pathlen = ASN1_INTEGER_get(bs->pathlen);
        } else
            x->ex_pathlen = -1;
        BASIC_CONSTRAINTS_free(bs);
        x->ex_flags |= EXFLAG_BCONS;
    }
    /* Handle proxy certificates */
    if ((pci = X509_get_ext_d2i(x, NID_proxyCertInfo, NULL, NULL))) {
        if (x->ex_flags & EXFLAG_CA
            || X509_get_ext_by_NID(x, NID_subject_alt_name, -1) >= 0
            || X509_get_ext_by_NID(x, NID_issuer_alt_name, -1) >= 0) {
            x->ex_flags |= EXFLAG_INVALID;
        }
        if (pci->pcPathLengthConstraint) {
            x->ex_pcpathlen = ASN1_INTEGER_get(pci->pcPathLengthConstraint);
        } else
            x->ex_pcpathlen = -1;
        PROXY_CERT_INFO_EXTENSION_free(pci);
        x->ex_flags |= EXFLAG_PROXY;
    }
    /* Handle key usage */
    if ((usage = X509_get_ext_d2i(x, NID_key_usage, NULL, NULL))) {
        if (usage->length > 0) {
            x->ex_kusage = usage->data[0];
            if (usage->length > 1)
                x->ex_kusage |= usage->data[1] << 8;
        } else
            x->ex_kusage = 0;
        x->ex_flags |= EXFLAG_KUSAGE;
        ASN1_BIT_STRING_free(usage);
    }
    x->ex_xkusage = 0;
    if ((extusage = X509_get_ext_d2i(x, NID_ext_key_usage, NULL, NULL))) {
        x->ex_flags |= EXFLAG_XKUSAGE;
        for (i = 0; i < sk_ASN1_OBJECT_num(extusage); i++) {
            switch (OBJ_obj2nid(sk_ASN1_OBJECT_value(extusage, i))) {
            case NID_server_auth:
                x->ex_xkusage |= XKU_SSL_SERVER;
                break;

            case NID_client_auth:
                x->ex_xkusage |= XKU_SSL_CLIENT;
                break;

            case NID_email_protect:
                x->ex_xkusage |= XKU_SMIME;
                break;

            case NID_code_sign:
                x->ex_xkusage |= XKU_CODE_SIGN;
                break;

            case NID_ms_sgc:
            case NID_ns_sgc:
                x->ex_xkusage |= XKU_SGC;
                break;

            case NID_OCSP_sign:
                x->ex_xkusage |= XKU_OCSP_SIGN;
                break;

            case NID_time_stamp:
                x->ex_xkusage |= XKU_TIMESTAMP;
                break;

            case NID_dvcs:
                x->ex_xkusage |= XKU_DVCS;
                break;

            case NID_anyExtendedKeyUsage:
                x->ex_xkusage |= XKU_ANYEKU;
                break;
            }
        }
        sk_ASN1_OBJECT_pop_free(extusage, ASN1_OBJECT_free);
    }

    if ((ns = X509_get_ext_d2i(x, NID_netscape_cert_type, NULL, NULL))) {
        if (ns->length > 0)
            x->ex_nscert = ns->data[0];
        else
            x->ex_nscert = 0;
        x->ex_flags |= EXFLAG_NSCERT;
        ASN1_BIT_STRING_free(ns);
    }
    x->skid = X509_get_ext_d2i(x, NID_subject_key_identifier, NULL, NULL);
    x->akid = X509_get_ext_d2i(x, NID_authority_key_identifier, NULL, NULL);
    /* Does subject name match issuer ? */
    if (!X509_NAME_cmp(X509_get_subject_name(x), X509_get_issuer_name(x))) {
        x->ex_flags |= EXFLAG_SI;
        /* If SKID matches AKID also indicate self signed */
        if (X509_check_akid(x, x->akid) == X509_V_OK &&
            !ku_reject(x, KU_KEY_CERT_SIGN))
            x->ex_flags |= EXFLAG_SS;
    }
    x->altname = X509_get_ext_d2i(x, NID_subject_alt_name, NULL, NULL);
    x->nc = X509_get_ext_d2i(x, NID_name_constraints, &j, NULL);
    if (!x->nc && (j != -1))
        x->ex_flags |= EXFLAG_INVALID;
    setup_crldp(x);

    for (j = 0; j < X509_get_ext_count(x); j++) {
        ex = X509_get_ext(x, j);
        if (OBJ_obj2nid(X509_EXTENSION_get_object(ex))
            == NID_freshest_crl)
            x->ex_flags |= EXFLAG_FRESHEST;
        if (!X509_EXTENSION_get_critical(ex))
            continue;
        if (!X509_supported_extension(ex)) {
            x->ex_flags |= EXFLAG_CRITICAL;
            break;
        }
    }
    x->ex_flags |= EXFLAG_SET;

    CRYPTO_MUTEX_unlock_write(&x->lock);
}

/*
 * CA checks common to all purposes return codes: 0 not a CA 1 is a CA 2
 * basicConstraints absent so "maybe" a CA 3 basicConstraints absent but self
 * signed V1. 4 basicConstraints absent but keyUsage present and keyCertSign
 * asserted.
 */

static int check_ca(const X509 *x)
{
    /* keyUsage if present should allow cert signing */
    if (ku_reject(x, KU_KEY_CERT_SIGN))
        return 0;
    if (x->ex_flags & EXFLAG_BCONS) {
        if (x->ex_flags & EXFLAG_CA)
            return 1;
        /* If basicConstraints says not a CA then say so */
        else
            return 0;
    } else {
        /* we support V1 roots for...  uh, I don't really know why. */
        if ((x->ex_flags & V1_ROOT) == V1_ROOT)
            return 3;
        /*
         * If key usage present it must have certSign so tolerate it
         */
        else if (x->ex_flags & EXFLAG_KUSAGE)
            return 4;
        /* Older certificates could have Netscape-specific CA types */
        else if (x->ex_flags & EXFLAG_NSCERT && x->ex_nscert & NS_ANY_CA)
            return 5;
        /* can this still be regarded a CA certificate?  I doubt it */
        return 0;
    }
}

int X509_check_ca(X509 *x)
{
    x509v3_cache_extensions(x);
    return check_ca(x);
}

/* Check SSL CA: common checks for SSL client and server */
static int check_ssl_ca(const X509 *x)
{
    int ca_ret;
    ca_ret = check_ca(x);
    if (!ca_ret)
        return 0;
    /* check nsCertType if present */
    if (ca_ret != 5 || x->ex_nscert & NS_SSL_CA)
        return ca_ret;
    else
        return 0;
}

static int check_purpose_ssl_client(const X509_PURPOSE *xp, const X509 *x,
                                    int ca)
{
    if (xku_reject(x, XKU_SSL_CLIENT))
        return 0;
    if (ca)
        return check_ssl_ca(x);
    /* We need to do digital signatures or key agreement */
    if (ku_reject(x, KU_DIGITAL_SIGNATURE | KU_KEY_AGREEMENT))
        return 0;
    /* nsCertType if present should allow SSL client use */
    if (ns_reject(x, NS_SSL_CLIENT))
        return 0;
    return 1;
}

/*
 * Key usage needed for TLS/SSL server: digital signature, encipherment or
 * key agreement. The ssl code can check this more thoroughly for individual
 * key types.
 */
#define KU_TLS \
        (KU_DIGITAL_SIGNATURE|KU_KEY_ENCIPHERMENT|KU_KEY_AGREEMENT)

static int check_purpose_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                    int ca)
{
    if (xku_reject(x, XKU_SSL_SERVER | XKU_SGC))
        return 0;
    if (ca)
        return check_ssl_ca(x);

    if (ns_reject(x, NS_SSL_SERVER))
        return 0;
    if (ku_reject(x, KU_TLS))
        return 0;

    return 1;

}

static int check_purpose_ns_ssl_server(const X509_PURPOSE *xp, const X509 *x,
                                       int ca)
{
    int ret;
    ret = check_purpose_ssl_server(xp, x, ca);
    if (!ret || ca)
        return ret;
    /* We need to encipher or Netscape complains */
    if (ku_reject(x, KU_KEY_ENCIPHERMENT))
        return 0;
    return ret;
}

/* common S/MIME checks */
static int purpose_smime(const X509 *x, int ca)
{
    if (xku_reject(x, XKU_SMIME))
        return 0;
    if (ca) {
        int ca_ret;
        ca_ret = check_ca(x);
        if (!ca_ret)
            return 0;
        /* check nsCertType if present */
        if (ca_ret != 5 || x->ex_nscert & NS_SMIME_CA)
            return ca_ret;
        else
            return 0;
    }
    if (x->ex_flags & EXFLAG_NSCERT) {
        if (x->ex_nscert & NS_SMIME)
            return 1;
        /* Workaround for some buggy certificates */
        if (x->ex_nscert & NS_SSL_CLIENT)
            return 2;
        return 0;
    }
    return 1;
}

static int check_purpose_smime_sign(const X509_PURPOSE *xp, const X509 *x,
                                    int ca)
{
    int ret;
    ret = purpose_smime(x, ca);
    if (!ret || ca)
        return ret;
    if (ku_reject(x, KU_DIGITAL_SIGNATURE | KU_NON_REPUDIATION))
        return 0;
    return ret;
}

static int check_purpose_smime_encrypt(const X509_PURPOSE *xp, const X509 *x,
                                       int ca)
{
    int ret;
    ret = purpose_smime(x, ca);
    if (!ret || ca)
        return ret;
    if (ku_reject(x, KU_KEY_ENCIPHERMENT))
        return 0;
    return ret;
}

static int check_purpose_crl_sign(const X509_PURPOSE *xp, const X509 *x,
                                  int ca)
{
    if (ca) {
        int ca_ret;
        if ((ca_ret = check_ca(x)) != 2)
            return ca_ret;
        else
            return 0;
    }
    if (ku_reject(x, KU_CRL_SIGN))
        return 0;
    return 1;
}

/*
 * OCSP helper: this is *not* a full OCSP check. It just checks that each CA
 * is valid. Additional checks must be made on the chain.
 */

static int ocsp_helper(const X509_PURPOSE *xp, const X509 *x, int ca)
{
    /*
     * Must be a valid CA.  Should we really support the "I don't know" value
     * (2)?
     */
    if (ca)
        return check_ca(x);
    /* leaf certificate is checked in OCSP_verify() */
    return 1;
}

static int check_purpose_timestamp_sign(const X509_PURPOSE *xp, const X509 *x,
                                        int ca)
{
    int i_ext;

    /* If ca is true we must return if this is a valid CA certificate. */
    if (ca)
        return check_ca(x);

    /*
     * Check the optional key usage field:
     * if Key Usage is present, it must be one of digitalSignature
     * and/or nonRepudiation (other values are not consistent and shall
     * be rejected).
     */
    if ((x->ex_flags & EXFLAG_KUSAGE)
        && ((x->ex_kusage & ~(KU_NON_REPUDIATION | KU_DIGITAL_SIGNATURE)) ||
            !(x->ex_kusage & (KU_NON_REPUDIATION | KU_DIGITAL_SIGNATURE))))
        return 0;

    /* Only time stamp key usage is permitted and it's required. */
    if (!(x->ex_flags & EXFLAG_XKUSAGE) || x->ex_xkusage != XKU_TIMESTAMP)
        return 0;

    /* Extended Key Usage MUST be critical */
    i_ext = X509_get_ext_by_NID((X509 *)x, NID_ext_key_usage, -1);
    if (i_ext >= 0) {
        X509_EXTENSION *ext = X509_get_ext((X509 *)x, i_ext);
        if (!X509_EXTENSION_get_critical(ext))
            return 0;
    }

    return 1;
}

static int no_check(const X509_PURPOSE *xp, const X509 *x, int ca)
{
    return 1;
}

/*
 * Various checks to see if one certificate issued the second. This can be
 * used to prune a set of possible issuer certificates which have been looked
 * up using some simple method such as by subject name. These are: 1. Check
 * issuer_name(subject) == subject_name(issuer) 2. If akid(subject) exists
 * check it matches issuer 3. If key_usage(issuer) exists check it supports
 * certificate signing returns 0 for OK, positive for reason for mismatch,
 * reasons match codes for X509_verify_cert()
 */

int X509_check_issued(X509 *issuer, X509 *subject)
{
    if (X509_NAME_cmp(X509_get_subject_name(issuer),
                      X509_get_issuer_name(subject)))
        return X509_V_ERR_SUBJECT_ISSUER_MISMATCH;
    x509v3_cache_extensions(issuer);
    x509v3_cache_extensions(subject);

    if (subject->akid) {
        int ret = X509_check_akid(issuer, subject->akid);
        if (ret != X509_V_OK)
            return ret;
    }

    if (subject->ex_flags & EXFLAG_PROXY) {
        if (ku_reject(issuer, KU_DIGITAL_SIGNATURE))
            return X509_V_ERR_KEYUSAGE_NO_DIGITAL_SIGNATURE;
    } else if (ku_reject(issuer, KU_KEY_CERT_SIGN))
        return X509_V_ERR_KEYUSAGE_NO_CERTSIGN;
    return X509_V_OK;
}

int X509_check_akid(X509 *issuer, AUTHORITY_KEYID *akid)
{

    if (!akid)
        return X509_V_OK;

    /* Check key ids (if present) */
    if (akid->keyid && issuer->skid &&
        ASN1_OCTET_STRING_cmp(akid->keyid, issuer->skid))
        return X509_V_ERR_AKID_SKID_MISMATCH;
    /* Check serial number */
    if (akid->serial &&
        ASN1_INTEGER_cmp(X509_get_serialNumber(issuer), akid->serial))
        return X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH;
    /* Check issuer name */
    if (akid->issuer) {
        /*
         * Ugh, for some peculiar reason AKID includes SEQUENCE OF
         * GeneralName. So look for a DirName. There may be more than one but
         * we only take any notice of the first.
         */
        GENERAL_NAMES *gens;
        GENERAL_NAME *gen;
        X509_NAME *nm = NULL;
        size_t i;
        gens = akid->issuer;
        for (i = 0; i < sk_GENERAL_NAME_num(gens); i++) {
            gen = sk_GENERAL_NAME_value(gens, i);
            if (gen->type == GEN_DIRNAME) {
                nm = gen->d.dirn;
                break;
            }
        }
        if (nm && X509_NAME_cmp(nm, X509_get_issuer_name(issuer)))
            return X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH;
    }
    return X509_V_OK;
}