x509.c

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/*
 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <errno.h>
#include <assert.h>
#include <ipxe/list.h>
#include <ipxe/base16.h>
#include <ipxe/asn1.h>
#include <ipxe/crypto.h>
#include <ipxe/md5.h>
#include <ipxe/sha1.h>
#include <ipxe/sha256.h>
#include <ipxe/rsa.h>
#include <ipxe/rootcert.h>
#include <ipxe/certstore.h>
#include <ipxe/privkey.h>
#include <ipxe/socket.h>
#include <ipxe/in.h>
#include <ipxe/image.h>
#include <ipxe/ocsp.h>
#include <ipxe/x509.h>
#include <config/crypto.h>

/** @file
 *
 * X.509 certificates
 *
 * The structure of X.509v3 certificates is documented in RFC 5280
 * section 4.1.
 */

/* Disambiguate the various error causes */
#define ENOTSUP_ALGORITHM \
        __einfo_error ( EINFO_ENOTSUP_ALGORITHM )
#define EINFO_ENOTSUP_ALGORITHM \
        __einfo_uniqify ( EINFO_ENOTSUP, 0x01, "Unsupported algorithm" )
#define ENOTSUP_EXTENSION \
        __einfo_error ( EINFO_ENOTSUP_EXTENSION )
#define EINFO_ENOTSUP_EXTENSION \
        __einfo_uniqify ( EINFO_ENOTSUP, 0x02, "Unsupported extension" )
#define EINVAL_ALGORITHM \
        __einfo_error ( EINFO_EINVAL_ALGORITHM )
#define EINFO_EINVAL_ALGORITHM \
        __einfo_uniqify ( EINFO_EINVAL, 0x01, "Invalid algorithm type" )
#define EINVAL_ALGORITHM_MISMATCH \
        __einfo_error ( EINFO_EINVAL_ALGORITHM_MISMATCH )
#define EINFO_EINVAL_ALGORITHM_MISMATCH \
        __einfo_uniqify ( EINFO_EINVAL, 0x04, "Signature algorithm mismatch" )
#define EINVAL_PATH_LEN \
        __einfo_error ( EINFO_EINVAL_PATH_LEN )
#define EINFO_EINVAL_PATH_LEN \
        __einfo_uniqify ( EINFO_EINVAL, 0x05, "Invalid pathLenConstraint" )
#define EINVAL_VERSION \
        __einfo_error ( EINFO_EINVAL_VERSION )
#define EINFO_EINVAL_VERSION \
        __einfo_uniqify ( EINFO_EINVAL, 0x06, "Invalid version" )
#define EACCES_WRONG_ISSUER \
        __einfo_error ( EINFO_EACCES_WRONG_ISSUER )
#define EINFO_EACCES_WRONG_ISSUER \
        __einfo_uniqify ( EINFO_EACCES, 0x01, "Wrong issuer" )
#define EACCES_NOT_CA \
        __einfo_error ( EINFO_EACCES_NOT_CA )
#define EINFO_EACCES_NOT_CA \
        __einfo_uniqify ( EINFO_EACCES, 0x02, "Not a CA certificate" )
#define EACCES_KEY_USAGE \
        __einfo_error ( EINFO_EACCES_KEY_USAGE )
#define EINFO_EACCES_KEY_USAGE \
        __einfo_uniqify ( EINFO_EACCES, 0x03, "Incorrect key usage" )
#define EACCES_EXPIRED \
        __einfo_error ( EINFO_EACCES_EXPIRED )
#define EINFO_EACCES_EXPIRED \
        __einfo_uniqify ( EINFO_EACCES, 0x04, "Expired (or not yet valid)" )
#define EACCES_PATH_LEN \
        __einfo_error ( EINFO_EACCES_PATH_LEN )
#define EINFO_EACCES_PATH_LEN \
        __einfo_uniqify ( EINFO_EACCES, 0x05, "Maximum path length exceeded" )
#define EACCES_UNTRUSTED \
        __einfo_error ( EINFO_EACCES_UNTRUSTED )
#define EINFO_EACCES_UNTRUSTED \
        __einfo_uniqify ( EINFO_EACCES, 0x06, "Untrusted root certificate" )
#define EACCES_OUT_OF_ORDER \
        __einfo_error ( EINFO_EACCES_OUT_OF_ORDER )
#define EINFO_EACCES_OUT_OF_ORDER \
        __einfo_uniqify ( EINFO_EACCES, 0x07, "Validation out of order" )
#define EACCES_EMPTY \
        __einfo_error ( EINFO_EACCES_EMPTY )
#define EINFO_EACCES_EMPTY \
        __einfo_uniqify ( EINFO_EACCES, 0x08, "Empty certificate chain" )
#define EACCES_OCSP_REQUIRED \
        __einfo_error ( EINFO_EACCES_OCSP_REQUIRED )
#define EINFO_EACCES_OCSP_REQUIRED \
        __einfo_uniqify ( EINFO_EACCES, 0x09, "OCSP check required" )
#define EACCES_WRONG_NAME \
        __einfo_error ( EINFO_EACCES_WRONG_NAME )
#define EINFO_EACCES_WRONG_NAME \
        __einfo_uniqify ( EINFO_EACCES, 0x0a, "Incorrect certificate name" )
#define EACCES_USELESS \
        __einfo_error ( EINFO_EACCES_USELESS )
#define EINFO_EACCES_USELESS \
        __einfo_uniqify ( EINFO_EACCES, 0x0b, "No usable certificates" )

/**
 * Free X.509 certificate
 *
 * @v refcnt            Reference count
 */
static void x509_free ( struct refcnt *refcnt ) {
        struct x509_certificate *cert =
                container_of ( refcnt, struct x509_certificate, refcnt );

        x509_root_put ( cert->root );
        free ( cert );
}

/**
 * Get X.509 certificate display name
 *
 * @v cert              X.509 certificate
 * @ret name            Display name
 */
const char * x509_name ( struct x509_certificate *cert ) {
        struct asn1_cursor *common_name = &cert->subject.common_name;
        struct digest_algorithm *digest = &sha1_algorithm;
        static char buf[64];
        uint8_t fingerprint[ digest->digestsize ];
        size_t len;

        len = common_name->len;
        if ( len ) {
                /* Certificate has a commonName: use that */
                if ( len > ( sizeof ( buf ) - 1 /* NUL */ ) )
                        len = ( sizeof ( buf ) - 1 /* NUL */ );
                memcpy ( buf, common_name->data, len );
                buf[len] = '\0';
        } else {
                /* Certificate has no commonName: use SHA-1 fingerprint */
                x509_fingerprint ( cert, digest, fingerprint );
                base16_encode ( fingerprint, sizeof ( fingerprint ),
                                buf, sizeof ( buf ) );
        }
        return buf;
}

/** "commonName" object identifier */
static uint8_t oid_common_name[] = { ASN1_OID_COMMON_NAME };

/** "commonName" object identifier cursor */
static struct asn1_cursor oid_common_name_cursor =
        ASN1_CURSOR ( oid_common_name );

/**
 * Parse X.509 certificate version
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_version ( struct x509_certificate *cert,
                                const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        int version;
        int rc;

        /* Enter version */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_EXPLICIT_TAG ( 0 ) );

        /* Parse integer */
        if ( ( rc = asn1_integer ( &cursor, &version ) ) != 0 ) {
                DBGC ( cert, "X509 %p cannot parse version: %s\n",
                       cert, strerror ( rc ) );
                DBGC_HDA ( cert, 0, raw->data, raw->len );
                return rc;
        }

        /* Sanity check */
        if ( version < 0 ) {
                DBGC ( cert, "X509 %p invalid version %d\n", cert, version );
                DBGC_HDA ( cert, 0, raw->data, raw->len );
                return -EINVAL_VERSION;
        }

        /* Record version */
        cert->version = version;
        DBGC2 ( cert, "X509 %p is a version %d certificate\n",
                cert, ( cert->version + 1 ) );

        return 0;
}

/**
 * Parse X.509 certificate serial number
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_serial ( struct x509_certificate *cert,
                               const struct asn1_cursor *raw ) {
        struct x509_serial *serial = &cert->serial;
        int rc;

        /* Record raw serial number */
        memcpy ( &serial->raw, raw, sizeof ( serial->raw ) );
        if ( ( rc = asn1_shrink ( &serial->raw, ASN1_INTEGER ) ) != 0 ) {
                DBGC ( cert, "X509 %p cannot shrink serialNumber: %s\n",
                       cert, strerror ( rc ) );
                return rc;
        }
        DBGC2 ( cert, "X509 %p issuer is:\n", cert );
        DBGC2_HDA ( cert, 0, serial->raw.data, serial->raw.len );

        return 0;
}

/**
 * Parse X.509 certificate issuer
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_issuer ( struct x509_certificate *cert,
                               const struct asn1_cursor *raw ) {
        struct x509_issuer *issuer = &cert->issuer;
        int rc;

        /* Record raw issuer */
        memcpy ( &issuer->raw, raw, sizeof ( issuer->raw ) );
        if ( ( rc = asn1_shrink ( &issuer->raw, ASN1_SEQUENCE ) ) != 0 ) {
                DBGC ( cert, "X509 %p cannot shrink issuer: %s\n",
                       cert, strerror ( rc ) );
                return rc;
        }
        DBGC2 ( cert, "X509 %p issuer is:\n", cert );
        DBGC2_HDA ( cert, 0, issuer->raw.data, issuer->raw.len );

        return 0;
}

/**
 * Parse X.509 certificate validity
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_validity ( struct x509_certificate *cert,
                                 const struct asn1_cursor *raw ) {
        struct x509_validity *validity = &cert->validity;
        struct x509_time *not_before = &validity->not_before;
        struct x509_time *not_after = &validity->not_after;
        struct asn1_cursor cursor;
        int rc;

        /* Enter validity */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse notBefore */
        if ( ( rc = asn1_generalized_time ( &cursor,
                                            &not_before->time ) ) != 0 ) {
                DBGC ( cert, "X509 %p cannot parse notBefore: %s\n",
                       cert, strerror ( rc ) );
                return rc;
        }
        DBGC2 ( cert, "X509 %p valid from time %lld\n",
                cert, not_before->time );
        asn1_skip_any ( &cursor );

        /* Parse notAfter */
        if ( ( rc = asn1_generalized_time ( &cursor,
                                            &not_after->time ) ) != 0 ) {
                DBGC ( cert, "X509 %p cannot parse notAfter: %s\n",
                       cert, strerror ( rc ) );
                return rc;
        }
        DBGC2 ( cert, "X509 %p valid until time %lld\n",
                cert, not_after->time );

        return 0;
}

/**
 * Parse X.509 certificate common name
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_common_name ( struct x509_certificate *cert,
                                    const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        struct asn1_cursor oid_cursor;
        struct asn1_cursor name_cursor;
        int rc;

        /* Enter name */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Scan through name list */
        for ( ; cursor.len ; asn1_skip_any ( &cursor ) ) {

                /* Check for "commonName" OID */
                memcpy ( &oid_cursor, &cursor, sizeof ( oid_cursor ) );
                asn1_enter ( &oid_cursor, ASN1_SET );
                asn1_enter ( &oid_cursor, ASN1_SEQUENCE );
                memcpy ( &name_cursor, &oid_cursor, sizeof ( name_cursor ) );
                asn1_enter ( &oid_cursor, ASN1_OID );
                if ( asn1_compare ( &oid_common_name_cursor, &oid_cursor ) != 0)
                        continue;
                asn1_skip_any ( &name_cursor );
                if ( ( rc = asn1_enter_any ( &name_cursor ) ) != 0 ) {
                        DBGC ( cert, "X509 %p cannot locate name:\n", cert );
                        DBGC_HDA ( cert, 0, raw->data, raw->len );
                        return rc;
                }

                /* Record common name */
                memcpy ( &cert->subject.common_name, &name_cursor,
                         sizeof ( cert->subject.common_name ) );

                return 0;
        }

        /* Certificates may not have a commonName */
        DBGC2 ( cert, "X509 %p no commonName found:\n", cert );
        return 0;
}

/**
 * Parse X.509 certificate subject
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_subject ( struct x509_certificate *cert,
                                const struct asn1_cursor *raw ) {
        struct x509_subject *subject = &cert->subject;
        int rc;

        /* Record raw subject */
        memcpy ( &subject->raw, raw, sizeof ( subject->raw ) );
        asn1_shrink_any ( &subject->raw );
        DBGC2 ( cert, "X509 %p subject is:\n", cert );
        DBGC2_HDA ( cert, 0, subject->raw.data, subject->raw.len );

        /* Parse common name */
        if ( ( rc = x509_parse_common_name ( cert, raw ) ) != 0 )
                return rc;
        DBGC2 ( cert, "X509 %p common name is \"%s\":\n", cert,
                x509_name ( cert ) );

        return 0;
}

/**
 * Parse X.509 certificate public key information
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_public_key ( struct x509_certificate *cert,
                                   const struct asn1_cursor *raw ) {
        struct x509_public_key *public_key = &cert->subject.public_key;
        struct asn1_algorithm **algorithm = &public_key->algorithm;
        struct asn1_bit_string *raw_bits = &public_key->raw_bits;
        struct asn1_cursor cursor;
        int rc;

        /* Record raw subjectPublicKeyInfo */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_shrink_any ( &cursor );
        memcpy ( &public_key->raw, &cursor, sizeof ( public_key->raw ) );
        DBGC2 ( cert, "X509 %p public key is:\n", cert );
        DBGC2_HDA ( cert, 0, public_key->raw.data, public_key->raw.len );

        /* Enter subjectPublicKeyInfo */
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse algorithm */
        if ( ( rc = asn1_pubkey_algorithm ( &cursor, algorithm ) ) != 0 ) {
                DBGC ( cert, "X509 %p could not parse public key algorithm: "
                       "%s\n", cert, strerror ( rc ) );
                return rc;
        }
        DBGC2 ( cert, "X509 %p public key algorithm is %s\n",
                cert, (*algorithm)->name );
        asn1_skip_any ( &cursor );

        /* Parse bit string */
        if ( ( rc = asn1_bit_string ( &cursor, raw_bits ) ) != 0 ) {
                DBGC ( cert, "X509 %p could not parse public key bits: %s\n",
                       cert, strerror ( rc ) );
                return rc;
        }

        return 0;
}

/**
 * Parse X.509 certificate basic constraints
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_basic_constraints ( struct x509_certificate *cert,
                                          const struct asn1_cursor *raw ) {
        struct x509_basic_constraints *basic = &cert->extensions.basic;
        struct asn1_cursor cursor;
        int ca = 0;
        int path_len;
        int rc;

        /* Enter basicConstraints */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse "cA", if present */
        if ( asn1_type ( &cursor ) == ASN1_BOOLEAN ) {
                ca = asn1_boolean ( &cursor );
                if ( ca < 0 ) {
                        rc = ca;
                        DBGC ( cert, "X509 %p cannot parse cA: %s\n",
                               cert, strerror ( rc ) );
                        DBGC_HDA ( cert, 0, raw->data, raw->len );
                        return rc;
                }
                asn1_skip_any ( &cursor );
        }
        basic->ca = ca;
        DBGC2 ( cert, "X509 %p is %sa CA certificate\n",
                cert, ( basic->ca ? "" : "not " ) );

        /* Ignore everything else unless "cA" is true */
        if ( ! ca )
                return 0;

        /* Parse "pathLenConstraint", if present and applicable */
        basic->path_len = X509_PATH_LEN_UNLIMITED;
        if ( asn1_type ( &cursor ) == ASN1_INTEGER ) {
                if ( ( rc = asn1_integer ( &cursor, &path_len ) ) != 0 ) {
                        DBGC ( cert, "X509 %p cannot parse pathLenConstraint: "
                               "%s\n", cert, strerror ( rc ) );
                        DBGC_HDA ( cert, 0, raw->data, raw->len );
                        return rc;
                }
                if ( path_len < 0 ) {
                        DBGC ( cert, "X509 %p invalid pathLenConstraint %d\n",
                               cert, path_len );
                        DBGC_HDA ( cert, 0, raw->data, raw->len );
                        return -EINVAL;
                }
                basic->path_len = path_len;
                DBGC2 ( cert, "X509 %p path length constraint is %d\n",
                        cert, basic->path_len );
        }

        return 0;
}

/**
 * Parse X.509 certificate key usage
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_key_usage ( struct x509_certificate *cert,
                                  const struct asn1_cursor *raw ) {
        struct x509_key_usage *usage = &cert->extensions.usage;
        struct asn1_bit_string bit_string;
        const uint8_t *bytes;
        size_t len;
        unsigned int i;
        int rc;

        /* Mark extension as present */
        usage->present = 1;

        /* Parse bit string */
        if ( ( rc = asn1_bit_string ( raw, &bit_string ) ) != 0 ) {
                DBGC ( cert, "X509 %p could not parse key usage: %s\n",
                       cert, strerror ( rc ) );
                return rc;
        }

        /* Parse key usage bits */
        bytes = bit_string.data;
        len = bit_string.len;
        if ( len > sizeof ( usage->bits ) )
                len = sizeof ( usage->bits );
        for ( i = 0 ; i < len ; i++ ) {
                usage->bits |= ( *(bytes++) << ( 8 * i ) );
        }
        DBGC2 ( cert, "X509 %p key usage is %08x\n", cert, usage->bits );

        return 0;
}

/** "id-kp-codeSigning" object identifier */
static uint8_t oid_code_signing[] = { ASN1_OID_CODESIGNING };

/** "id-kp-OCSPSigning" object identifier */
static uint8_t oid_ocsp_signing[] = { ASN1_OID_OCSPSIGNING };

/** Supported key purposes */
static struct x509_key_purpose x509_key_purposes[] = {
        {
                .name = "codeSigning",
                .bits = X509_CODE_SIGNING,
                .oid = ASN1_CURSOR ( oid_code_signing ),
        },
        {
                .name = "ocspSigning",
                .bits = X509_OCSP_SIGNING,
                .oid = ASN1_CURSOR ( oid_ocsp_signing ),
        },
};

/**
 * Parse X.509 certificate key purpose identifier
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_key_purpose ( struct x509_certificate *cert,
                                    const struct asn1_cursor *raw ) {
        struct x509_extended_key_usage *ext_usage = &cert->extensions.ext_usage;
        struct x509_key_purpose *purpose;
        struct asn1_cursor cursor;
        unsigned int i;
        int rc;

        /* Enter keyPurposeId */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        if ( ( rc = asn1_enter ( &cursor, ASN1_OID ) ) != 0 ) {
                DBGC ( cert, "X509 %p invalid keyPurposeId:\n", cert );
                DBGC_HDA ( cert, 0, raw->data, raw->len );
                return rc;
        }

        /* Identify key purpose */
        for ( i = 0 ; i < ( sizeof ( x509_key_purposes ) /
                            sizeof ( x509_key_purposes[0] ) ) ; i++ ) {
                purpose = &x509_key_purposes[i];
                if ( asn1_compare ( &cursor, &purpose->oid ) == 0 ) {
                        DBGC2 ( cert, "X509 %p has key purpose %s\n",
                                cert, purpose->name );
                        ext_usage->bits |= purpose->bits;
                        return 0;
                }
        }

        /* Ignore unrecognised key purposes */
        return 0;
}

/**
 * Parse X.509 certificate extended key usage
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_extended_key_usage ( struct x509_certificate *cert,
                                           const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        int rc;

        /* Enter extKeyUsage */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse each extended key usage in turn */
        while ( cursor.len ) {
                if ( ( rc = x509_parse_key_purpose ( cert, &cursor ) ) != 0 )
                        return rc;
                asn1_skip_any ( &cursor );
        }

        return 0;
}

/**
 * Parse X.509 certificate OCSP access method
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_ocsp ( struct x509_certificate *cert,
                             const struct asn1_cursor *raw ) {
        struct x509_ocsp_responder *ocsp = &cert->extensions.auth_info.ocsp;
        struct asn1_cursor *uri = &ocsp->uri;
        int rc;

        /* Enter accessLocation */
        memcpy ( uri, raw, sizeof ( *uri ) );
        if ( ( rc = asn1_enter ( uri, X509_GENERAL_NAME_URI ) ) != 0 ) {
                DBGC ( cert, "X509 %p OCSP does not contain "
                       "uniformResourceIdentifier:\n", cert );
                DBGC_HDA ( cert, 0, raw->data, raw->len );
                return rc;
        }
        DBGC2 ( cert, "X509 %p OCSP URI is:\n", cert );
        DBGC2_HDA ( cert, 0, uri->data, uri->len );

        return 0;
}

/** "id-ad-ocsp" object identifier */
static uint8_t oid_ad_ocsp[] = { ASN1_OID_OCSP };

/** Supported access methods */
static struct x509_access_method x509_access_methods[] = {
        {
                .name = "OCSP",
                .oid = ASN1_CURSOR ( oid_ad_ocsp ),
                .parse = x509_parse_ocsp,
        },
};

/**
 * Identify X.509 access method by OID
 *
 * @v oid               OID
 * @ret method          Access method, or NULL
 */
static struct x509_access_method *
x509_find_access_method ( const struct asn1_cursor *oid ) {
        struct x509_access_method *method;
        unsigned int i;

        for ( i = 0 ; i < ( sizeof ( x509_access_methods ) /
                            sizeof ( x509_access_methods[0] ) ) ; i++ ) {
                method = &x509_access_methods[i];
                if ( asn1_compare ( &method->oid, oid ) == 0 )
                        return method;
        }

        return NULL;
}

/**
 * Parse X.509 certificate access description
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_access_description ( struct x509_certificate *cert,
                                           const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        struct asn1_cursor subcursor;
        struct x509_access_method *method;
        int rc;

        /* Enter keyPurposeId */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Try to identify access method */
        memcpy ( &subcursor, &cursor, sizeof ( subcursor ) );
        asn1_enter ( &subcursor, ASN1_OID );
        method = x509_find_access_method ( &subcursor );
        asn1_skip_any ( &cursor );
        DBGC2 ( cert, "X509 %p found access method %s\n",
                cert, ( method ? method->name : "<unknown>" ) );

        /* Parse access location, if applicable */
        if ( method && ( ( rc = method->parse ( cert, &cursor ) ) != 0 ) )
                return rc;

        return 0;
}

/**
 * Parse X.509 certificate authority information access
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_authority_info_access ( struct x509_certificate *cert,
                                              const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        int rc;

        /* Enter authorityInfoAccess */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse each access description in turn */
        while ( cursor.len ) {
                if ( ( rc = x509_parse_access_description ( cert,
                                                            &cursor ) ) != 0 )
                        return rc;
                asn1_skip_any ( &cursor );
        }

        return 0;
}

/**
 * Parse X.509 certificate subject alternative name
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_subject_alt_name ( struct x509_certificate *cert,
                                         const struct asn1_cursor *raw ) {
        struct x509_subject_alt_name *alt_name = &cert->extensions.alt_name;
        struct asn1_cursor *names = &alt_name->names;
        int rc;

        /* Enter subjectAltName */
        memcpy ( names, raw, sizeof ( *names ) );
        if ( ( rc = asn1_enter ( names, ASN1_SEQUENCE ) ) != 0 ) {
                DBGC ( cert, "X509 %p invalid subjectAltName: %s\n",
                       cert, strerror ( rc ) );
                DBGC_HDA ( cert, 0, raw->data, raw->len );
                return rc;
        }
        DBGC2 ( cert, "X509 %p has subjectAltName:\n", cert );
        DBGC2_HDA ( cert, 0, names->data, names->len );

        return 0;
}

/** "id-ce-basicConstraints" object identifier */
static uint8_t oid_ce_basic_constraints[] =
        { ASN1_OID_BASICCONSTRAINTS };

/** "id-ce-keyUsage" object identifier */
static uint8_t oid_ce_key_usage[] =
        { ASN1_OID_KEYUSAGE };

/** "id-ce-extKeyUsage" object identifier */
static uint8_t oid_ce_ext_key_usage[] =
        { ASN1_OID_EXTKEYUSAGE };

/** "id-pe-authorityInfoAccess" object identifier */
static uint8_t oid_pe_authority_info_access[] =
        { ASN1_OID_AUTHORITYINFOACCESS };

/** "id-ce-subjectAltName" object identifier */
static uint8_t oid_ce_subject_alt_name[] =
        { ASN1_OID_SUBJECTALTNAME };

/** Supported certificate extensions */
static struct x509_extension x509_extensions[] = {
        {
                .name = "basicConstraints",
                .oid = ASN1_CURSOR ( oid_ce_basic_constraints ),
                .parse = x509_parse_basic_constraints,
        },
        {
                .name = "keyUsage",
                .oid = ASN1_CURSOR ( oid_ce_key_usage ),
                .parse = x509_parse_key_usage,
        },
        {
                .name = "extKeyUsage",
                .oid = ASN1_CURSOR ( oid_ce_ext_key_usage ),
                .parse = x509_parse_extended_key_usage,
        },
        {
                .name = "authorityInfoAccess",
                .oid = ASN1_CURSOR ( oid_pe_authority_info_access ),
                .parse = x509_parse_authority_info_access,
        },
        {
                .name = "subjectAltName",
                .oid = ASN1_CURSOR ( oid_ce_subject_alt_name ),
                .parse = x509_parse_subject_alt_name,
        },
};

/**
 * Identify X.509 extension by OID
 *
 * @v oid               OID
 * @ret extension       Extension, or NULL
 */
static struct x509_extension *
x509_find_extension ( const struct asn1_cursor *oid ) {
        struct x509_extension *extension;
        unsigned int i;

        for ( i = 0 ; i < ( sizeof ( x509_extensions ) /
                            sizeof ( x509_extensions[0] ) ) ; i++ ) {
                extension = &x509_extensions[i];
                if ( asn1_compare ( &extension->oid, oid ) == 0 )
                        return extension;
        }

        return NULL;
}

/**
 * Parse X.509 certificate extension
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_extension ( struct x509_certificate *cert,
                                  const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        struct asn1_cursor subcursor;
        struct x509_extension *extension;
        int is_critical = 0;
        int rc;

        /* Enter extension */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Try to identify extension */
        memcpy ( &subcursor, &cursor, sizeof ( subcursor ) );
        asn1_enter ( &subcursor, ASN1_OID );
        extension = x509_find_extension ( &subcursor );
        asn1_skip_any ( &cursor );
        DBGC2 ( cert, "X509 %p found extension %s\n",
                cert, ( extension ? extension->name : "<unknown>" ) );

        /* Identify criticality */
        if ( asn1_type ( &cursor ) == ASN1_BOOLEAN ) {
                is_critical = asn1_boolean ( &cursor );
                if ( is_critical < 0 ) {
                        rc = is_critical;
                        DBGC ( cert, "X509 %p cannot parse extension "
                               "criticality: %s\n", cert, strerror ( rc ) );
                        DBGC_HDA ( cert, 0, raw->data, raw->len );
                        return rc;
                }
                asn1_skip_any ( &cursor );
        }

        /* Handle unknown extensions */
        if ( ! extension ) {
                if ( is_critical ) {
                        /* Fail if we cannot handle a critical extension */
                        DBGC ( cert, "X509 %p cannot handle critical "
                               "extension:\n", cert );
                        DBGC_HDA ( cert, 0, raw->data, raw->len );
                        return -ENOTSUP_EXTENSION;
                } else {
                        /* Ignore unknown non-critical extensions */
                        return 0;
                }
        };

        /* Extract extnValue */
        if ( ( rc = asn1_enter ( &cursor, ASN1_OCTET_STRING ) ) != 0 ) {
                DBGC ( cert, "X509 %p extension missing extnValue:\n", cert );
                DBGC_HDA ( cert, 0, raw->data, raw->len );
                return rc;
        }

        /* Parse extension */
        if ( ( rc = extension->parse ( cert, &cursor ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Parse X.509 certificate extensions, if present
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_extensions ( struct x509_certificate *cert,
                                   const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        int rc;

        /* Enter extensions, if present */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_EXPLICIT_TAG ( 3 ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse each extension in turn */
        while ( cursor.len ) {
                if ( ( rc = x509_parse_extension ( cert, &cursor ) ) != 0 )
                        return rc;
                asn1_skip_any ( &cursor );
        }

        return 0;
}

/**
 * Parse X.509 certificate tbsCertificate
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int x509_parse_tbscertificate ( struct x509_certificate *cert,
                                       const struct asn1_cursor *raw ) {
        struct asn1_algorithm **algorithm = &cert->signature_algorithm;
        struct asn1_cursor cursor;
        int rc;

        /* Record raw tbsCertificate */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_shrink_any ( &cursor );
        memcpy ( &cert->tbs, &cursor, sizeof ( cert->tbs ) );

        /* Enter tbsCertificate */
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse version, if present */
        if ( asn1_type ( &cursor ) == ASN1_EXPLICIT_TAG ( 0 ) ) {
                if ( ( rc = x509_parse_version ( cert, &cursor ) ) != 0 )
                        return rc;
                asn1_skip_any ( &cursor );
        }

        /* Parse serialNumber */
        if ( ( rc = x509_parse_serial ( cert, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse signature */
        if ( ( rc = asn1_signature_algorithm ( &cursor, algorithm ) ) != 0 ) {
                DBGC ( cert, "X509 %p could not parse signature algorithm: "
                       "%s\n", cert, strerror ( rc ) );
                return rc;
        }
        DBGC2 ( cert, "X509 %p tbsCertificate signature algorithm is %s\n",
                cert, (*algorithm)->name );
        asn1_skip_any ( &cursor );

        /* Parse issuer */
        if ( ( rc = x509_parse_issuer ( cert, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse validity */
        if ( ( rc = x509_parse_validity ( cert, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse subject */
        if ( ( rc = x509_parse_subject ( cert, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse subjectPublicKeyInfo */
        if ( ( rc = x509_parse_public_key ( cert, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse extensions, if present */
        if ( ( rc = x509_parse_extensions ( cert, &cursor ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Parse X.509 certificate from ASN.1 data
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
int x509_parse ( struct x509_certificate *cert,
                 const struct asn1_cursor *raw ) {
        struct x509_signature *signature = &cert->signature;
        struct asn1_algorithm **signature_algorithm = &signature->algorithm;
        struct asn1_bit_string *signature_value = &signature->value;
        struct asn1_cursor cursor;
        int rc;

        /* Record raw certificate */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        memcpy ( &cert->raw, &cursor, sizeof ( cert->raw ) );

        /* Enter certificate */
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse tbsCertificate */
        if ( ( rc = x509_parse_tbscertificate ( cert, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse signatureAlgorithm */
        if ( ( rc = asn1_signature_algorithm ( &cursor,
                                               signature_algorithm ) ) != 0 ) {
                DBGC ( cert, "X509 %p could not parse signature algorithm: "
                       "%s\n", cert, strerror ( rc ) );
                return rc;
        }
        DBGC2 ( cert, "X509 %p signatureAlgorithm is %s\n",
                cert, (*signature_algorithm)->name );
        asn1_skip_any ( &cursor );

        /* Parse signatureValue */
        if ( ( rc = asn1_integral_bit_string ( &cursor,
                                               signature_value ) ) != 0 ) {
                DBGC ( cert, "X509 %p could not parse signature value: %s\n",
                       cert, strerror ( rc ) );
                return rc;
        }
        DBGC2 ( cert, "X509 %p signatureValue is:\n", cert );
        DBGC2_HDA ( cert, 0, signature_value->data, signature_value->len );

        /* Check that algorithm in tbsCertificate matches algorithm in
         * signature
         */
        if ( signature->algorithm != (*signature_algorithm) ) {
                DBGC ( cert, "X509 %p signature algorithm %s does not match "
                       "signatureAlgorithm %s\n",
                       cert, signature->algorithm->name,
                       (*signature_algorithm)->name );
                return -EINVAL_ALGORITHM_MISMATCH;
        }

        return 0;
}

/**
 * Create X.509 certificate
 *
 * @v data              Raw certificate data
 * @v len               Length of raw data
 * @ret cert            X.509 certificate
 * @ret rc              Return status code
 *
 * On success, the caller holds a reference to the X.509 certificate,
 * and is responsible for ultimately calling x509_put().
 */
int x509_certificate ( const void *data, size_t len,
                       struct x509_certificate **cert ) {
        struct asn1_cursor cursor;
        void *raw;
        int rc;

        /* Initialise cursor */
        cursor.data = data;
        cursor.len = len;
        asn1_shrink_any ( &cursor );

        /* Return stored certificate, if present */
        if ( ( *cert = x509_find ( NULL, &cursor ) ) != NULL ) {

                /* Add caller's reference */
                x509_get ( *cert );
                return 0;
        }

        /* Allocate and initialise certificate */
        *cert = zalloc ( sizeof ( **cert ) + cursor.len );
        if ( ! *cert )
                return -ENOMEM;
        ref_init ( &(*cert)->refcnt, x509_free );
        raw = ( *cert + 1 );

        /* Copy raw data */
        memcpy ( raw, cursor.data, cursor.len );
        cursor.data = raw;

        /* Parse certificate */
        if ( ( rc = x509_parse ( *cert, &cursor ) ) != 0 ) {
                x509_put ( *cert );
                *cert = NULL;
                return rc;
        }

        /* Add certificate to store */
        certstore_add ( *cert );

        return 0;
}

/**
 * Check X.509 certificate signature
 *
 * @v cert              X.509 certificate
 * @v public_key        X.509 public key
 * @ret rc              Return status code
 */
static int x509_check_signature ( struct x509_certificate *cert,
                                  struct x509_public_key *public_key ) {
        struct x509_signature *signature = &cert->signature;
        struct asn1_algorithm *algorithm = signature->algorithm;
        struct digest_algorithm *digest = algorithm->digest;
        struct pubkey_algorithm *pubkey = algorithm->pubkey;
        uint8_t digest_ctx[ digest->ctxsize ];
        uint8_t digest_out[ digest->digestsize ];
        int rc;

        /* Sanity check */
        assert ( cert->signature_algorithm == cert->signature.algorithm );

        /* Calculate certificate digest */
        digest_init ( digest, digest_ctx );
        digest_update ( digest, digest_ctx, cert->tbs.data, cert->tbs.len );
        digest_final ( digest, digest_ctx, digest_out );
        DBGC2 ( cert, "X509 %p \"%s\" digest:\n", cert, x509_name ( cert ) );
        DBGC2_HDA ( cert, 0, digest_out, sizeof ( digest_out ) );

        /* Check that signature public key algorithm matches signer */
        if ( public_key->algorithm->pubkey != pubkey ) {
                DBGC ( cert, "X509 %p \"%s\" signature algorithm %s does not "
                       "match signer's algorithm %s\n",
                       cert, x509_name ( cert ), algorithm->name,
                       public_key->algorithm->name );
                rc = -EINVAL_ALGORITHM_MISMATCH;
                goto err_mismatch;
        }

        /* Verify signature using signer's public key */
        if ( ( rc = pubkey_verify ( pubkey, &public_key->raw, digest,
                                    digest_out, signature->value.data,
                                    signature->value.len ) ) != 0 ) {
                DBGC ( cert, "X509 %p \"%s\" signature verification failed: "
                       "%s\n", cert, x509_name ( cert ), strerror ( rc ) );
                goto err_pubkey_verify;
        }

        /* Success */
        rc = 0;

 err_pubkey_verify:
 err_mismatch:
        return rc;
}

/**
 * Check X.509 certificate against issuer certificate
 *
 * @v cert              X.509 certificate
 * @v issuer            X.509 issuer certificate
 * @ret rc              Return status code
 */
int x509_check_issuer ( struct x509_certificate *cert,
                        struct x509_certificate *issuer ) {
        struct x509_public_key *public_key = &issuer->subject.public_key;
        int rc;

        /* Check issuer.  In theory, this should be a full X.500 DN
         * comparison, which would require support for a plethora of
         * abominations such as TeletexString (which allows the
         * character set to be changed mid-string using escape codes).
         * In practice, we assume that anyone who deliberately changes
         * the encoding of the issuer DN is probably a masochist who
         * will rather enjoy the process of figuring out exactly why
         * their certificate doesn't work.
         *
         * See http://www.cs.auckland.ac.nz/~pgut001/pubs/x509guide.txt
         * for some enjoyable ranting on this subject.
         */
        if ( asn1_compare ( &cert->issuer.raw, &issuer->subject.raw ) != 0 ) {
                DBGC ( cert, "X509 %p \"%s\" issuer does not match ",
                       cert, x509_name ( cert ) );
                DBGC ( cert, "X509 %p \"%s\" subject\n",
                       issuer, x509_name ( issuer ) );
                DBGC_HDA ( cert, 0, cert->issuer.raw.data,
                           cert->issuer.raw.len );
                DBGC_HDA ( issuer, 0, issuer->subject.raw.data,
                           issuer->subject.raw.len );
                return -EACCES_WRONG_ISSUER;
        }

        /* Check that issuer is allowed to sign certificates */
        if ( ! issuer->extensions.basic.ca ) {
                DBGC ( issuer, "X509 %p \"%s\" cannot sign ",
                       issuer, x509_name ( issuer ) );
                DBGC ( issuer, "X509 %p \"%s\": not a CA certificate\n",
                       cert, x509_name ( cert ) );
                return -EACCES_NOT_CA;
        }
        if ( issuer->extensions.usage.present &&
             ( ! ( issuer->extensions.usage.bits & X509_KEY_CERT_SIGN ) ) ) {
                DBGC ( issuer, "X509 %p \"%s\" cannot sign ",
                       issuer, x509_name ( issuer ) );
                DBGC ( issuer, "X509 %p \"%s\": no keyCertSign usage\n",
                       cert, x509_name ( cert ) );
                return -EACCES_KEY_USAGE;
        }

        /* Check signature */
        if ( ( rc = x509_check_signature ( cert, public_key ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Calculate X.509 certificate fingerprint
 *
 * @v cert              X.509 certificate
 * @v digest            Digest algorithm
 * @v fingerprint       Fingerprint buffer
 */
void x509_fingerprint ( struct x509_certificate *cert,
                        struct digest_algorithm *digest,
                        void *fingerprint ) {
        uint8_t ctx[ digest->ctxsize ];

        /* Calculate fingerprint */
        digest_init ( digest, ctx );
        digest_update ( digest, ctx, cert->raw.data, cert->raw.len );
        digest_final ( digest, ctx, fingerprint );
}

/**
 * Check X.509 root certificate
 *
 * @v cert              X.509 certificate
 * @v root              X.509 root certificate list
 * @ret rc              Return status code
 */
int x509_check_root ( struct x509_certificate *cert, struct x509_root *root ) {
        struct digest_algorithm *digest = root->digest;
        uint8_t fingerprint[ digest->digestsize ];
        const uint8_t *root_fingerprint = root->fingerprints;
        unsigned int i;

        /* Calculate certificate fingerprint */
        x509_fingerprint ( cert, digest, fingerprint );

        /* Check fingerprint against all root certificates */
        for ( i = 0 ; i < root->count ; i++ ) {
                if ( memcmp ( fingerprint, root_fingerprint,
                              sizeof ( fingerprint ) ) == 0 ) {
                        DBGC ( cert, "X509 %p \"%s\" is a root certificate\n",
                               cert, x509_name ( cert ) );
                        return 0;
                }
                root_fingerprint += sizeof ( fingerprint );
        }

        DBGC2 ( cert, "X509 %p \"%s\" is not a root certificate\n",
                cert, x509_name ( cert ) );
        return -ENOENT;
}

/**
 * Check X.509 certificate validity period
 *
 * @v cert              X.509 certificate
 * @v time              Time at which to check certificate
 * @ret rc              Return status code
 */
int x509_check_time ( struct x509_certificate *cert, time_t time ) {
        struct x509_validity *validity = &cert->validity;

        /* Check validity period */
        if ( validity->not_before.time > ( time + TIMESTAMP_ERROR_MARGIN ) ) {
                DBGC ( cert, "X509 %p \"%s\" is not yet valid (at time %lld)\n",
                       cert, x509_name ( cert ), time );
                return -EACCES_EXPIRED;
        }
        if ( validity->not_after.time < ( time - TIMESTAMP_ERROR_MARGIN ) ) {
                DBGC ( cert, "X509 %p \"%s\" has expired (at time %lld)\n",
                       cert, x509_name ( cert ), time );
                return -EACCES_EXPIRED;
        }

        DBGC2 ( cert, "X509 %p \"%s\" is valid (at time %lld)\n",
                cert, x509_name ( cert ), time );
        return 0;
}

/**
 * Check if X.509 certificate is valid
 *
 * @v cert              X.509 certificate
 * @v root              Root certificate list, or NULL to use default
 */
int x509_is_valid ( struct x509_certificate *cert, struct x509_root *root ) {

        /* Use default root certificate store if none specified */
        if ( ! root )
                root = &root_certificates;

        return ( cert->root == root );
}

/**
 * Set X.509 certificate as validated
 *
 * @v cert              X.509 certificate
 * @v issuer            Issuing X.509 certificate (or NULL)
 * @v root              Root certificate list
 */
static void x509_set_valid ( struct x509_certificate *cert,
                             struct x509_certificate *issuer,
                             struct x509_root *root ) {
        unsigned int max_path_remaining;

        /* Sanity checks */
        assert ( root != NULL );
        assert ( ( issuer == NULL ) || ( issuer->path_remaining >= 1 ) );

        /* Record validation root */
        x509_root_put ( cert->root );
        cert->root = x509_root_get ( root );

        /* Calculate effective path length */
        cert->path_remaining = ( cert->extensions.basic.path_len + 1 );
        if ( issuer ) {
                max_path_remaining = ( issuer->path_remaining - 1 );
                if ( cert->path_remaining > max_path_remaining )
                        cert->path_remaining = max_path_remaining;
        }
}

/**
 * Validate X.509 certificate
 *
 * @v cert              X.509 certificate
 * @v issuer            Issuing X.509 certificate (or NULL)
 * @v time              Time at which to validate certificate
 * @v root              Root certificate list, or NULL to use default
 * @ret rc              Return status code
 *
 * The issuing certificate must have already been validated.
 *
 * Validation results are cached: if a certificate has already been
 * successfully validated then @c issuer, @c time, and @c root will be
 * ignored.
 */
int x509_validate ( struct x509_certificate *cert,
                    struct x509_certificate *issuer,
                    time_t time, struct x509_root *root ) {
        int rc;

        /* Use default root certificate store if none specified */
        if ( ! root )
                root = &root_certificates;

        /* Return success if certificate has already been validated */
        if ( x509_is_valid ( cert, root ) )
                return 0;

        /* Fail if certificate is invalid at specified time */
        if ( ( rc = x509_check_time ( cert, time ) ) != 0 )
                return rc;

        /* Succeed if certificate is a trusted root certificate */
        if ( x509_check_root ( cert, root ) == 0 ) {
                x509_set_valid ( cert, NULL, root );
                return 0;
        }

        /* Fail unless we have an issuer */
        if ( ! issuer ) {
                DBGC2 ( cert, "X509 %p \"%s\" has no trusted issuer\n",
                        cert, x509_name ( cert ) );
                return -EACCES_UNTRUSTED;
        }

        /* Fail unless issuer has already been validated */
        if ( ! x509_is_valid ( issuer, root ) ) {
                DBGC ( cert, "X509 %p \"%s\" ", cert, x509_name ( cert ) );
                DBGC ( cert, "issuer %p \"%s\" has not yet been validated\n",
                       issuer, x509_name ( issuer ) );
                return -EACCES_OUT_OF_ORDER;
        }

        /* Fail if issuing certificate cannot validate this certificate */
        if ( ( rc = x509_check_issuer ( cert, issuer ) ) != 0 )
                return rc;

        /* Fail if path length constraint is violated */
        if ( issuer->path_remaining == 0 ) {
                DBGC ( cert, "X509 %p \"%s\" ", cert, x509_name ( cert ) );
                DBGC ( cert, "issuer %p \"%s\" path length exceeded\n",
                       issuer, x509_name ( issuer ) );
                return -EACCES_PATH_LEN;
        }

        /* Fail if OCSP is required */
        if ( ocsp_required ( cert ) ) {
                DBGC ( cert, "X509 %p \"%s\" requires an OCSP check\n",
                       cert, x509_name ( cert ) );
                return -EACCES_OCSP_REQUIRED;
        }

        /* Mark certificate as valid */
        x509_set_valid ( cert, issuer, root );

        DBGC ( cert, "X509 %p \"%s\" successfully validated using ",
               cert, x509_name ( cert ) );
        DBGC ( cert, "issuer %p \"%s\"\n", issuer, x509_name ( issuer ) );
        return 0;
}

/**
 * Check X.509 certificate alternative dNSName
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @v name              Name
 * @ret rc              Return status code
 */
static int x509_check_dnsname ( struct x509_certificate *cert,
                                const struct asn1_cursor *raw,
                                const char *name ) {
        const char *fullname = name;
        const char *dnsname = raw->data;
        size_t len = raw->len;

        /* Check for wildcards */
        if ( ( len >= 2 ) && ( dnsname[0] == '*' ) && ( dnsname[1] == '.' ) ) {

                /* Skip initial "*." */
                dnsname += 2;
                len -= 2;

                /* Skip initial portion of name to be tested */
                name = strchr ( name, '.' );
                if ( ! name )
                        return -ENOENT;
                name++;
        }

        /* Compare names */
        if ( ! ( ( strlen ( name ) == len ) &&
                 ( strncasecmp ( name, dnsname, len ) == 0 ) ) )
                return -ENOENT;

        if ( name != fullname ) {
                DBGC2 ( cert, "X509 %p \"%s\" found wildcard match for "
                        "\"*.%s\"\n", cert, x509_name ( cert ), name );
        }
        return 0;
}

/**
 * Check X.509 certificate alternative iPAddress
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @v name              Name
 * @ret rc              Return status code
 */
static int x509_check_ipaddress ( struct x509_certificate *cert,
                                  const struct asn1_cursor *raw,
                                  const char *name ) {
        struct sockaddr sa;
        sa_family_t family;
        const void *address;
        int rc;

        /* Determine address family */
        if ( raw->len == sizeof ( struct in_addr ) ) {
                struct sockaddr_in *sin = ( ( struct sockaddr_in * ) &sa );
                family = AF_INET;
                address = &sin->sin_addr;
        } else if ( raw->len == sizeof ( struct in6_addr ) ) {
                struct sockaddr_in6 *sin6 = ( ( struct sockaddr_in6 * ) &sa );
                family = AF_INET6;
                address = &sin6->sin6_addr;
        } else {
                DBGC ( cert, "X509 %p \"%s\" has iPAddress with unexpected "
                       "length %zd\n", cert, x509_name ( cert ), raw->len );
                DBGC_HDA ( cert, 0, raw->data, raw->len );
                return -EINVAL;
        }

        /* Attempt to convert name to a socket address */
        if ( ( rc = sock_aton ( name, &sa ) ) != 0 ) {
                DBGC2 ( cert, "X509 %p \"%s\" cannot parse \"%s\" as "
                        "iPAddress: %s\n", cert, x509_name ( cert ), name,
                        strerror ( rc ) );
                return rc;
        }
        if ( sa.sa_family != family )
                return -ENOENT;

        /* Compare addresses */
        if ( memcmp ( address, raw->data, raw->len ) != 0 )
                return -ENOENT;

        DBGC2 ( cert, "X509 %p \"%s\" found iPAddress match for \"%s\"\n",
                cert, x509_name ( cert ), sock_ntoa ( &sa ) );
        return 0;
}

/**
 * Check X.509 certificate alternative name
 *
 * @v cert              X.509 certificate
 * @v raw               ASN.1 cursor
 * @v name              Name
 * @ret rc              Return status code
 */
static int x509_check_alt_name ( struct x509_certificate *cert,
                                 const struct asn1_cursor *raw,
                                 const char *name ) {
        struct asn1_cursor alt_name;
        unsigned int type;

        /* Enter generalName */
        memcpy ( &alt_name, raw, sizeof ( alt_name ) );
        type = asn1_type ( &alt_name );
        asn1_enter_any ( &alt_name );

        /* Check this name */
        switch ( type ) {
        case X509_GENERAL_NAME_DNS :
                return x509_check_dnsname ( cert, &alt_name, name );
        case X509_GENERAL_NAME_IP :
                return x509_check_ipaddress ( cert, &alt_name, name );
        default:
                DBGC2 ( cert, "X509 %p \"%s\" unknown name of type %#02x:\n",
                        cert, x509_name ( cert ), type );
                DBGC2_HDA ( cert, 0, alt_name.data, alt_name.len );
                return -ENOTSUP;
        }
}

/**
 * Check X.509 certificate name
 *
 * @v cert              X.509 certificate
 * @v name              Name
 * @ret rc              Return status code
 */
int x509_check_name ( struct x509_certificate *cert, const char *name ) {
        struct asn1_cursor *common_name = &cert->subject.common_name;
        struct asn1_cursor alt_name;
        int rc;

        /* Check commonName */
        if ( x509_check_dnsname ( cert, common_name, name ) == 0 ) {
                DBGC2 ( cert, "X509 %p \"%s\" commonName matches \"%s\"\n",
                        cert, x509_name ( cert ), name );
                return 0;
        }

        /* Check any subjectAlternativeNames */
        memcpy ( &alt_name, &cert->extensions.alt_name.names,
                 sizeof ( alt_name ) );
        for ( ; alt_name.len ; asn1_skip_any ( &alt_name ) ) {
                if ( ( rc = x509_check_alt_name ( cert, &alt_name,
                                                  name ) ) == 0 ) {
                        DBGC2 ( cert, "X509 %p \"%s\" subjectAltName matches "
                                "\"%s\"\n", cert, x509_name ( cert ), name );
                        return 0;
                }
        }

        DBGC ( cert, "X509 %p \"%s\" does not match name \"%s\"\n",
               cert, x509_name ( cert ), name );
        return -EACCES_WRONG_NAME;
}

/**
 * Free X.509 certificate chain
 *
 * @v refcnt            Reference count
 */
static void x509_free_chain ( struct refcnt *refcnt ) {
        struct x509_chain *chain =
                container_of ( refcnt, struct x509_chain, refcnt );

        DBGC2 ( chain, "X509 chain %p freed\n", chain );

        /* Free chain */
        x509_truncate ( chain, NULL );
        assert ( list_empty ( &chain->links ) );
        free ( chain );
}

/**
 * Allocate X.509 certificate chain
 *
 * @ret chain           X.509 certificate chain, or NULL
 */
struct x509_chain * x509_alloc_chain ( void ) {
        struct x509_chain *chain;

        /* Allocate chain */
        chain = zalloc ( sizeof ( *chain ) );
        if ( ! chain )
                return NULL;

        /* Initialise chain */
        ref_init ( &chain->refcnt, x509_free_chain );
        INIT_LIST_HEAD ( &chain->links );

        DBGC2 ( chain, "X509 chain %p allocated\n", chain );
        return chain;
}

/**
 * Append X.509 certificate to X.509 certificate chain
 *
 * @v chain             X.509 certificate chain
 * @v cert              X.509 certificate
 * @ret rc              Return status code
 */
int x509_append ( struct x509_chain *chain, struct x509_certificate *cert ) {
        struct x509_link *link;

        /* Allocate link */
        link = zalloc ( sizeof ( *link ) );
        if ( ! link )
                return -ENOMEM;

        /* Add link to chain */
        link->cert = x509_get ( cert );
        list_add_tail ( &link->list, &chain->links );
        DBGC ( chain, "X509 chain %p added X509 %p \"%s\"\n",
               chain, cert, x509_name ( cert ) );

        return 0;
}

/**
 * Append X.509 certificate to X.509 certificate chain
 *
 * @v chain             X.509 certificate chain
 * @v data              Raw certificate data
 * @v len               Length of raw data
 * @ret rc              Return status code
 */
int x509_append_raw ( struct x509_chain *chain, const void *data,
                      size_t len ) {
        struct x509_certificate *cert;
        int rc;

        /* Parse certificate */
        if ( ( rc = x509_certificate ( data, len, &cert ) ) != 0 )
                goto err_parse;

        /* Append certificate to chain */
        if ( ( rc = x509_append ( chain, cert ) ) != 0 )
                goto err_append;

        /* Drop reference to certificate */
        x509_put ( cert );

        return 0;

 err_append:
        x509_put ( cert );
 err_parse:
        return rc;
}

/**
 * Truncate X.509 certificate chain
 *
 * @v chain             X.509 certificate chain
 * @v link              Link after which to truncate chain, or NULL
 */
void x509_truncate ( struct x509_chain *chain, struct x509_link *link ) {
        struct x509_link *tmp;

        /* Truncate entire chain if no link is specified */
        if ( ! link )
                link = list_entry ( &chain->links, struct x509_link, list );

        /* Free each link in the chain */
        list_for_each_entry_safe_continue ( link, tmp, &chain->links, list ) {
                x509_put ( link->cert );
                list_del ( &link->list );
                free ( link );
        }
}

/**
 * Mark X.509 certificate as found
 *
 * @v store             Certificate store
 * @v cert              X.509 certificate
 * @ret cert            X.509 certificate
 */
static struct x509_certificate * x509_found ( struct x509_chain *store,
                                              struct x509_certificate *cert ) {

        /* Sanity check */
        assert ( store != NULL );

        /* Mark as found, if applicable */
        if ( store->found )
                store->found ( store, cert );

        return cert;
}

/**
 * Identify X.509 certificate by raw certificate data
 *
 * @v store             Certificate store, or NULL to use default
 * @v raw               Raw certificate data
 * @ret cert            X.509 certificate, or NULL if not found
 */
struct x509_certificate * x509_find ( struct x509_chain *store,
                                      const struct asn1_cursor *raw ) {
        struct x509_link *link;
        struct x509_certificate *cert;

        /* Use default certificate store if none specified */
        if ( ! store )
                store = &certstore;

        /* Search for certificate within store */
        list_for_each_entry ( link, &store->links, list ) {

                /* Check raw certificate data */
                cert = link->cert;
                if ( asn1_compare ( raw, &cert->raw ) == 0 )
                        return x509_found ( store, cert );
        }

        return NULL;
}

/**
 * Identify X.509 certificate by subject
 *
 * @v store             Certificate store, or NULL to use default
 * @v subject           Subject
 * @ret cert            X.509 certificate, or NULL if not found
 */
struct x509_certificate *
x509_find_subject ( struct x509_chain *store,
                    const struct asn1_cursor *subject ) {
        struct x509_link *link;
        struct x509_certificate *cert;

        /* Use default certificate store if none specified */
        if ( ! store )
                store = &certstore;

        /* Scan through certificate list */
        list_for_each_entry ( link, &store->links, list ) {

                /* Check subject */
                cert = link->cert;
                if ( asn1_compare ( subject, &cert->subject.raw ) == 0 )
                        return x509_found ( store, cert );
        }

        return NULL;
}

/**
 * Identify X.509 certificate by issuer and serial number
 *
 * @v store             Certificate store, or NULL to use default
 * @v issuer            Issuer
 * @v serial            Serial number
 * @ret cert            X.509 certificate, or NULL if not found
 */
struct x509_certificate *
x509_find_issuer_serial ( struct x509_chain *store,
                          const struct asn1_cursor *issuer,
                          const struct asn1_cursor *serial ) {
        struct x509_link *link;
        struct x509_certificate *cert;

        /* Use default certificate store if none specified */
        if ( ! store )
                store = &certstore;

        /* Scan through certificate list */
        list_for_each_entry ( link, &store->links, list ) {

                /* Check issuer and serial number */
                cert = link->cert;
                if ( ( asn1_compare ( issuer, &cert->issuer.raw ) == 0 ) &&
                     ( asn1_compare ( serial, &cert->serial.raw ) == 0 ) )
                        return x509_found ( store, cert );
        }

        return NULL;
}

/**
 * Identify X.509 certificate by corresponding public key
 *
 * @v store             Certificate store, or NULL to use default
 * @v key               Private key
 * @ret cert            X.509 certificate, or NULL if not found
 */
struct x509_certificate * x509_find_key ( struct x509_chain *store,
                                          struct private_key *key ) {
        struct x509_link *link;
        struct x509_certificate *cert;

        /* Use default certificate store if none specified */
        if ( ! store )
                store = &certstore;

        /* Scan through certificate list */
        list_for_each_entry ( link, &store->links, list ) {

                /* Check public key */
                cert = link->cert;
                if ( pubkey_match ( cert->signature_algorithm->pubkey,
                                    privkey_cursor ( key ),
                                    &cert->subject.public_key.raw ) == 0 )
                        return x509_found ( store, cert );
        }

        return NULL;
}

/**
 * Append X.509 certificates to X.509 certificate chain
 *
 * @v chain             X.509 certificate chain
 * @v store             Certificate store, or NULL to use default
 * @ret rc              Return status code
 *
 * Certificates will be automatically appended to the chain based upon
 * the subject and issuer names.
 */
int x509_auto_append ( struct x509_chain *chain, struct x509_chain *store ) {
        struct x509_certificate *cert;
        struct x509_certificate *previous;
        int rc;

        /* Get current certificate */
        cert = x509_last ( chain );
        if ( ! cert ) {
                DBGC ( chain, "X509 chain %p has no certificates\n", chain );
                return -EACCES_EMPTY;
        }

        /* Append certificates, in order */
        while ( 1 ) {

                /* Find issuing certificate */
                previous = cert;
                cert = x509_find_subject ( store, &cert->issuer.raw );
                if ( ! cert )
                        break;
                if ( cert == previous )
                        break;

                /* Append certificate to chain */
                if ( ( rc = x509_append ( chain, cert ) ) != 0 )
                        return rc;
        }

        return 0;
}

/**
 * Validate X.509 certificate chain
 *
 * @v chain             X.509 certificate chain
 * @v time              Time at which to validate certificates
 * @v store             Certificate store, or NULL to use default
 * @v root              Root certificate list, or NULL to use default
 * @ret rc              Return status code
 */
int x509_validate_chain ( struct x509_chain *chain, time_t time,
                          struct x509_chain *store, struct x509_root *root ) {
        struct x509_certificate *issuer = NULL;
        struct x509_link *link;
        int rc;

        /* Append any applicable certificates from the certificate store */
        if ( ( rc = x509_auto_append ( chain, store ) ) != 0 )
                return rc;

        /* Find first certificate that can be validated as a
         * standalone (i.e.  is already valid, or can be validated as
         * a trusted root certificate).
         */
        list_for_each_entry ( link, &chain->links, list ) {

                /* Try validating this certificate as a standalone */
                if ( ( rc = x509_validate ( link->cert, NULL, time,
                                            root ) ) != 0 )
                        continue;

                /* Work back up to start of chain, performing pairwise
                 * validation.
                 */
                issuer = link->cert;
                list_for_each_entry_continue_reverse ( link, &chain->links,
                                                       list ) {

                        /* Validate this certificate against its issuer */
                        if ( ( rc = x509_validate ( link->cert, issuer, time,
                                                    root ) ) != 0 )
                                return rc;
                        issuer = link->cert;
                }

                return 0;
        }

        DBGC ( chain, "X509 chain %p found no usable certificates\n", chain );
        return -EACCES_USELESS;
}

/**
 * Extract X.509 certificate object from image
 *
 * @v image             Image
 * @v offset            Offset within image
 * @ret cert            X.509 certificate
 * @ret next            Offset to next image, or negative error
 *
 * On success, the caller holds a reference to the X.509 certificate,
 * and is responsible for ultimately calling x509_put().
 */
int image_x509 ( struct image *image, size_t offset,
                 struct x509_certificate **cert ) {
        struct asn1_cursor *cursor;
        int next;
        int rc;

        /* Get ASN.1 object */
        next = image_asn1 ( image, offset, &cursor );
        if ( next < 0 ) {
                rc = next;
                goto err_asn1;
        }

        /* Parse certificate */
        if ( ( rc = x509_certificate ( cursor->data, cursor->len,
                                       cert ) ) != 0 )
                goto err_certificate;

        /* Free ASN.1 object */
        free ( cursor );

        return next;

        x509_put ( *cert );
 err_certificate:
        free ( cursor );
 err_asn1:
        return rc;
}

/* Drag in objects via x509_validate() */
REQUIRING_SYMBOL ( x509_validate );

/* Drag in certificate store */
REQUIRE_OBJECT ( certstore );

/* Drag in crypto configuration */
REQUIRE_OBJECT ( config_crypto );