cms.c

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/*
 * Copyright (C) 2012 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 );

/** @file
 *
 * Cryptographic Message Syntax (PKCS #7)
 *
 * The format of CMS messages is defined in RFC 5652.
 *
 */

#include <stdint.h>
#include <string.h>
#include <time.h>
#include <errno.h>
#include <ipxe/asn1.h>
#include <ipxe/x509.h>
#include <ipxe/image.h>
#include <ipxe/malloc.h>
#include <ipxe/privkey.h>
#include <ipxe/cms.h>

/* Disambiguate the various error causes */
#define EACCES_NON_SIGNING \
        __einfo_error ( EINFO_EACCES_NON_SIGNING )
#define EINFO_EACCES_NON_SIGNING \
        __einfo_uniqify ( EINFO_EACCES, 0x01, "Not a signing certificate" )
#define EACCES_NON_CODE_SIGNING \
        __einfo_error ( EINFO_EACCES_NON_CODE_SIGNING )
#define EINFO_EACCES_NON_CODE_SIGNING \
        __einfo_uniqify ( EINFO_EACCES, 0x02, "Not a code-signing certificate" )
#define EACCES_WRONG_NAME \
        __einfo_error ( EINFO_EACCES_WRONG_NAME )
#define EINFO_EACCES_WRONG_NAME \
        __einfo_uniqify ( EINFO_EACCES, 0x04, "Incorrect certificate name" )
#define EACCES_NO_SIGNATURES \
        __einfo_error ( EINFO_EACCES_NO_SIGNATURES )
#define EINFO_EACCES_NO_SIGNATURES \
        __einfo_uniqify ( EINFO_EACCES, 0x05, "No signatures present" )
#define EACCES_NO_RECIPIENTS \
        __einfo_error ( EINFO_EACCES_NO_RECIPIENTS )
#define EINFO_EACCES_NO_RECIPIENTS \
        __einfo_uniqify ( EINFO_EACCES, 0x06, "No usable recipients" )
#define EACCES_LEN \
        __einfo_error ( EINFO_EACCES_LEN )
#define EINFO_EACCES_LEN \
        __einfo_uniqify ( EINFO_EACCES, 0x07, "Bad file length" )
#define EACCES_PAD \
        __einfo_error ( EINFO_EACCES_PAD )
#define EINFO_EACCES_PAD \
        __einfo_uniqify ( EINFO_EACCES, 0x08, "Bad block padding" )
#define EACCES_MAC \
        __einfo_error ( EINFO_EACCES_MAC )
#define EINFO_EACCES_MAC \
        __einfo_uniqify ( EINFO_EACCES, 0x09, "Invalid MAC" )
#define ENOTSUP_TYPE \
        __einfo_error ( EINFO_ENOTSUP_TYPE )
#define EINFO_ENOTSUP_TYPE \
        __einfo_uniqify ( EINFO_ENOTSUP, 0x01, "Unrecognised message type" )

static int cms_parse_signed ( struct cms_message *cms,
                              const struct asn1_cursor *raw );
static int cms_parse_enveloped ( struct cms_message *cms,
                                 const struct asn1_cursor *raw );

/** "id-signedData" object identifier */
static uint8_t oid_signeddata[] = { ASN1_OID_SIGNEDDATA };

/** "id-envelopedData" object identifier */
static uint8_t oid_envelopeddata[] = { ASN1_OID_ENVELOPEDDATA };

/** "id-authEnvelopedData" object identifier */
static uint8_t oid_authenvelopeddata[] = { ASN1_OID_AUTHENVELOPEDDATA };

/** CMS message types */
static struct cms_type cms_types[] = {
        {
                .name = "signed",
                .oid = ASN1_CURSOR ( oid_signeddata ),
                .parse = cms_parse_signed,
        },
        {
                .name = "enveloped",
                .oid = ASN1_CURSOR ( oid_envelopeddata ),
                .parse = cms_parse_enveloped,
        },
        {
                .name = "authEnveloped",
                .oid = ASN1_CURSOR ( oid_authenvelopeddata ),
                .parse = cms_parse_enveloped,
        }
};

/**
 * Parse CMS message content type
 *
 * @v cms               CMS message
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_content_type ( struct cms_message *cms,
                                    const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        struct cms_type *type;
        unsigned int i;

        /* Enter contentType */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_OID );

        /* Check for a recognised OID */
        for ( i = 0 ; i < ( sizeof ( cms_types ) /
                            sizeof ( cms_types[0] ) ) ; i++ ) {
                type = &cms_types[i];
                if ( asn1_compare ( &cursor, &type->oid ) == 0 ) {
                        cms->type = type;
                        DBGC ( cms, "CMS %p contains %sData\n",
                               cms, type->name );
                        return 0;
                }
        }

        DBGC ( cms, "CMS %p is not a recognised message type:\n", cms );
        DBGC_HDA ( cms, 0, raw->data, raw->len );
        return -ENOTSUP_TYPE;
}

/**
 * Parse CMS message certificate list
 *
 * @v cms               CMS message
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_certificates ( struct cms_message *cms,
                                    const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        struct x509_certificate *cert;
        int rc;

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

        /* Add each certificate */
        while ( cursor.len ) {

                /* Add certificate to chain */
                if ( ( rc = x509_append_raw ( cms->certificates, cursor.data,
                                              cursor.len ) ) != 0 ) {
                        DBGC ( cms, "CMS %p could not append certificate: %s\n",
                               cms, strerror ( rc) );
                        DBGC_HDA ( cms, 0, cursor.data, cursor.len );
                        return rc;
                }
                cert = x509_last ( cms->certificates );
                DBGC ( cms, "CMS %p found certificate %s\n",
                       cms, x509_name ( cert ) );

                /* Move to next certificate */
                asn1_skip_any ( &cursor );
        }

        return 0;
}

/**
 * Parse CMS message participant identifier
 *
 * @v cms               CMS message
 * @v part              Participant information to fill in
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_identifier ( struct cms_message *cms,
                                  struct cms_participant *part,
                                  const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        struct asn1_cursor serial;
        struct asn1_cursor issuer;
        struct x509_certificate *cert;
        int rc;

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

        /* Identify issuer */
        memcpy ( &issuer, &cursor, sizeof ( issuer ) );
        if ( ( rc = asn1_shrink ( &issuer, ASN1_SEQUENCE ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not locate issuer: %s\n",
                       cms, part, strerror ( rc ) );
                DBGC_HDA ( cms, 0, raw->data, raw->len );
                return rc;
        }
        DBGC ( cms, "CMS %p/%p issuer is:\n", cms, part );
        DBGC_HDA ( cms, 0, issuer.data, issuer.len );
        asn1_skip_any ( &cursor );

        /* Identify serialNumber */
        memcpy ( &serial, &cursor, sizeof ( serial ) );
        if ( ( rc = asn1_shrink ( &serial, ASN1_INTEGER ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not locate serialNumber: %s\n",
                       cms, part, strerror ( rc ) );
                DBGC_HDA ( cms, 0, raw->data, raw->len );
                return rc;
        }
        DBGC ( cms, "CMS %p/%p serial number is:\n", cms, part );
        DBGC_HDA ( cms, 0, serial.data, serial.len );

        /* Identify certificate */
        cert = x509_find_issuer_serial ( cms->certificates, &issuer, &serial );
        if ( ! cert ) {
                DBGC ( cms, "CMS %p/%p could not identify certificate\n",
                       cms, part );
                return ( cms_is_signature ( cms ) ? -ENOENT : 0 );
        }

        /* Append certificate to chain */
        if ( ( rc = x509_append ( part->chain, cert ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not append certificate: %s\n",
                       cms, part, strerror ( rc ) );
                return rc;
        }

        /* Append remaining certificates to chain */
        if ( ( rc = x509_auto_append ( part->chain,
                                       cms->certificates ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not append certificates: %s\n",
                       cms, part, strerror ( rc ) );
                return rc;
        }

        return 0;
}

/**
 * Parse CMS message digest algorithm
 *
 * @v cms               CMS message
 * @v part              Participant information to fill in
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_digest_algorithm ( struct cms_message *cms,
                                        struct cms_participant *part,
                                        const struct asn1_cursor *raw ) {
        struct asn1_algorithm *algorithm;
        int rc;

        /* Identify algorithm */
        if ( ( rc = asn1_digest_algorithm ( raw, &algorithm ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not identify digest algorithm: "
                       "%s\n", cms, part, strerror ( rc ) );
                DBGC_HDA ( cms, 0, raw->data, raw->len );
                return rc;
        }

        /* Record digest algorithm */
        part->digest = algorithm->digest;
        DBGC ( cms, "CMS %p/%p digest algorithm is %s\n",
               cms, part, algorithm->name );

        return 0;
}

/**
 * Parse CMS message public-key algorithm
 *
 * @v cms               CMS message
 * @v part              Participant information to fill in
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_pubkey_algorithm ( struct cms_message *cms,
                                        struct cms_participant *part,
                                        const struct asn1_cursor *raw ) {
        struct asn1_algorithm *algorithm;
        int rc;

        /* Identify algorithm */
        if ( ( rc = asn1_pubkey_algorithm ( raw, &algorithm ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not identify public-key "
                       "algorithm: %s\n", cms, part, strerror ( rc ) );
                DBGC_HDA ( cms, 0, raw->data, raw->len );
                return rc;
        }

        /* Record public-key algorithm */
        part->pubkey = algorithm->pubkey;
        DBGC ( cms, "CMS %p/%p public-key algorithm is %s\n",
               cms, part, algorithm->name );

        return 0;
}

/**
 * Parse CMS message cipher algorithm
 *
 * @v cms               CMS message
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_cipher_algorithm ( struct cms_message *cms,
                                        const struct asn1_cursor *raw ) {
        struct asn1_algorithm *algorithm;
        int rc;

        /* Identify algorithm */
        if ( ( rc = asn1_cipher_algorithm ( raw, &algorithm,
                                            &cms->iv ) ) != 0 ) {
                DBGC ( cms, "CMS %p could not identify cipher algorithm: %s\n",
                       cms, strerror ( rc ) );
                DBGC_HDA ( cms, 0, raw->data, raw->len );
                return rc;
        }

        /* Record cipher */
        cms->cipher = algorithm->cipher;
        DBGC ( cms, "CMS %p cipher algorithm is %s\n", cms, algorithm->name );

        return 0;
}

/**
 * Parse CMS message signature or key value
 *
 * @v cms               CMS message
 * @v part              Participant information to fill in
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_value ( struct cms_message *cms,
                             struct cms_participant *part,
                             const struct asn1_cursor *raw ) {
        int rc;

        /* Enter signature or encryptedKey */
        memcpy ( &part->value, raw, sizeof ( part->value ) );
        if ( ( rc = asn1_enter ( &part->value, ASN1_OCTET_STRING ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not locate value:\n",
                       cms, part );
                DBGC_HDA ( cms, 0, raw->data, raw->len );
                return rc;
        }
        DBGC ( cms, "CMS %p/%p value is:\n", cms, part );
        DBGC_HDA ( cms, 0, part->value.data, part->value.len );

        return 0;
}

/**
 * Parse CMS message participant information
 *
 * @v cms               CMS message
 * @v part              Participant information to fill in
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_participant ( struct cms_message *cms,
                                   struct cms_participant *part,
                                   const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        int rc;

        /* Enter signerInfo or ktri */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Skip version */
        asn1_skip ( &cursor, ASN1_INTEGER );

        /* Parse sid or rid */
        if ( ( rc = cms_parse_identifier ( cms, part, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse signature-only objects */
        if ( cms_is_signature ( cms ) ) {

                /* Parse digestAlgorithm */
                if ( ( rc = cms_parse_digest_algorithm ( cms, part,
                                                         &cursor ) ) != 0 )
                        return rc;
                asn1_skip_any ( &cursor );

                /* Skip signedAttrs, if present */
                asn1_skip_if_exists ( &cursor, ASN1_EXPLICIT_TAG ( 0 ) );
        }

        /* Parse signatureAlgorithm or contentEncryptionAlgorithm */
        if ( ( rc = cms_parse_pubkey_algorithm ( cms, part, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse signature or encryptedKey */
        if ( ( rc = cms_parse_value ( cms, part, &cursor ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Parse CMS message participants information
 *
 * @v cms               CMS message
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_participants ( struct cms_message *cms,
                                    const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        struct cms_participant *part;
        int rc;

        /* Enter signerInfos or recipientInfos */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SET );

        /* Add each signerInfo or recipientInfo.  Errors are handled
         * by ensuring that cms_put() will always be able to free any
         * allocated memory.
         */
        while ( cursor.len ) {

                /* Allocate participant information block */
                part = zalloc ( sizeof ( *part ) );
                if ( ! part )
                        return -ENOMEM;
                list_add ( &part->list, &cms->participants );
                part->digest = &digest_null;
                part->pubkey = &pubkey_null;

                /* Allocate certificate chain */
                part->chain = x509_alloc_chain();
                if ( ! part->chain )
                        return -ENOMEM;

                /* Parse signerInfo or recipientInfo */
                if ( ( rc = cms_parse_participant ( cms, part,
                                                    &cursor ) ) != 0 )
                        return rc;
                asn1_skip_any ( &cursor );
        }

        return 0;
}

/**
 * Parse CMS message encrypted content information
 *
 * @v cms               CMS message
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_encrypted ( struct cms_message *cms,
                                 const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        int rc;

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

        /* Skip contentType */
        asn1_skip ( &cursor, ASN1_OID );

        /* Parse contentEncryptionAlgorithm */
        if ( ( rc = cms_parse_cipher_algorithm ( cms, &cursor ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Parse CMS message MAC
 *
 * @v cms               CMS message
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_mac ( struct cms_message *cms,
                           const struct asn1_cursor *raw ) {
        int rc;

        /* Enter mac */
        memcpy ( &cms->mac, raw, sizeof ( cms->mac ) );
        if ( ( rc = asn1_enter ( &cms->mac, ASN1_OCTET_STRING ) ) != 0 ) {
                DBGC ( cms, "CMS %p could not locate mac: %s\n",
                       cms, strerror ( rc ) );
                DBGC_HDA ( cms, 0, raw->data, raw->len );
                return rc;
        }
        DBGC ( cms, "CMS %p mac is:\n", cms );
        DBGC_HDA ( cms, 0, cms->mac.data, cms->mac.len );

        return 0;
}

/**
 * Parse CMS signed data
 *
 * @v cms               CMS message
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_signed ( struct cms_message *cms,
                              const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        int rc;

        /* Allocate certificate list */
        cms->certificates = x509_alloc_chain();
        if ( ! cms->certificates )
                return -ENOMEM;

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

        /* Skip version */
        asn1_skip ( &cursor, ASN1_INTEGER );

        /* Skip digestAlgorithms */
        asn1_skip ( &cursor, ASN1_SET );

        /* Skip encapContentInfo */
        asn1_skip ( &cursor, ASN1_SEQUENCE );

        /* Parse certificates */
        if ( ( rc = cms_parse_certificates ( cms, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Skip crls, if present */
        asn1_skip_if_exists ( &cursor, ASN1_EXPLICIT_TAG ( 1 ) );

        /* Parse signerInfos */
        if ( ( rc = cms_parse_participants ( cms, &cursor ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Parse CMS enveloped data
 *
 * @v cms               CMS message
 * @v raw               ASN.1 cursor
 * @ret rc              Return status code
 */
static int cms_parse_enveloped ( struct cms_message *cms,
                                 const struct asn1_cursor *raw ) {
        struct asn1_cursor cursor;
        int rc;

        /* Enter envelopedData or authEnvelopedData */
        memcpy ( &cursor, raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Skip version */
        asn1_skip ( &cursor, ASN1_INTEGER );

        /* Skip originatorInfo, if present */
        asn1_skip_if_exists ( &cursor, ASN1_IMPLICIT_TAG ( 0 ) );

        /* Parse recipientInfos */
        if ( ( rc = cms_parse_participants ( cms, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Parse encryptedContentInfo or authEncryptedContentInfo */
        if ( ( rc = cms_parse_encrypted ( cms, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );
        assert ( cms->cipher != NULL );

        /* Skip unprotectedAttrs or authAttrs, if present */
        asn1_skip_if_exists ( &cursor, ASN1_IMPLICIT_TAG ( 1 ) );

        /* Parse mac, if present */
        if ( ( cms->cipher->authsize != 0 ) &&
             ( ( rc = cms_parse_mac ( cms, &cursor ) ) != 0 ) )
                return rc;

        return 0;
}

/**
 * Parse CMS message from ASN.1 data
 *
 * @v cms               CMS message
 * @ret rc              Return status code
 */
static int cms_parse ( struct cms_message *cms ) {
        struct asn1_cursor cursor;
        int rc;

        /* Enter contentInfo */
        memcpy ( &cursor, cms->raw, sizeof ( cursor ) );
        asn1_enter ( &cursor, ASN1_SEQUENCE );

        /* Parse contentType */
        if ( ( rc = cms_parse_content_type ( cms, &cursor ) ) != 0 )
                return rc;
        asn1_skip_any ( &cursor );

        /* Enter content */
        asn1_enter ( &cursor, ASN1_EXPLICIT_TAG ( 0 ) );

        /* Parse type-specific content */
        if ( ( rc = cms->type->parse ( cms, &cursor ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Free CMS message
 *
 * @v refcnt            Reference count
 */
static void cms_free ( struct refcnt *refcnt ) {
        struct cms_message *cms =
                container_of ( refcnt, struct cms_message, refcnt );
        struct cms_participant *part;
        struct cms_participant *tmp;

        list_for_each_entry_safe ( part, tmp, &cms->participants, list ) {
                list_del ( &part->list );
                x509_chain_put ( part->chain );
                free ( part );
        }
        x509_chain_put ( cms->certificates );
        free ( cms->raw );
        free ( cms );
}

/**
 * Create CMS message
 *
 * @v image             Image
 * @ret sig             CMS message
 * @ret rc              Return status code
 *
 * On success, the caller holds a reference to the CMS message, and
 * is responsible for ultimately calling cms_put().
 */
int cms_message ( struct image *image, struct cms_message **cms ) {
        int next;
        int rc;

        /* Allocate and initialise message */
        *cms = zalloc ( sizeof ( **cms ) );
        if ( ! *cms ) {
                rc = -ENOMEM;
                goto err_alloc;
        }
        ref_init ( &(*cms)->refcnt, cms_free );
        INIT_LIST_HEAD ( &(*cms)->participants );
        (*cms)->cipher = &cipher_null;

        /* Get raw message data */
        next = image_asn1 ( image, 0, &(*cms)->raw );
        if ( next < 0 ) {
                rc = next;
                DBGC ( *cms, "CMS %p could not get raw ASN.1 data: %s\n",
                       *cms, strerror ( rc ) );
                goto err_asn1;
        }

        /* Use only first message in image */
        asn1_shrink_any ( (*cms)->raw );

        /* Parse message */
        if ( ( rc = cms_parse ( *cms ) ) != 0 )
                goto err_parse;

        return 0;

 err_parse:
 err_asn1:
        cms_put ( *cms );
 err_alloc:
        return rc;
}

/**
 * Calculate digest of CMS-signed data
 *
 * @v cms               CMS message
 * @v part              Participant information
 * @v data              Signed data
 * @v len               Length of signed data
 * @v out               Digest output
 */
static void cms_digest ( struct cms_message *cms,
                         struct cms_participant *part,
                         const void *data, size_t len, void *out ) {
        struct digest_algorithm *digest = part->digest;
        uint8_t ctx[ digest->ctxsize ];

        /* Calculate digest */
        digest_init ( digest, ctx );
        digest_update ( digest, ctx, data, len );
        digest_final ( digest, ctx, out );

        DBGC ( cms, "CMS %p/%p digest value:\n", cms, part );
        DBGC_HDA ( cms, 0, out, digest->digestsize );
}

/**
 * Verify digest of CMS-signed data
 *
 * @v cms               CMS message
 * @v part              Participant information
 * @v cert              Corresponding certificate
 * @v data              Signed data
 * @v len               Length of signed data
 * @ret rc              Return status code
 */
static int cms_verify_digest ( struct cms_message *cms,
                               struct cms_participant *part,
                               struct x509_certificate *cert,
                               const void *data, size_t len ) {
        struct digest_algorithm *digest = part->digest;
        struct pubkey_algorithm *pubkey = part->pubkey;
        const struct asn1_cursor *key = &cert->subject.public_key.raw;
        const struct asn1_cursor *value = &part->value;
        uint8_t digest_out[ digest->digestsize ];
        int rc;

        /* Generate digest */
        cms_digest ( cms, part, data, len, digest_out );

        /* Verify digest */
        if ( ( rc = pubkey_verify ( pubkey, key, digest, digest_out,
                                    value ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p signature verification failed: %s\n",
                       cms, part, strerror ( rc ) );
                return rc;
        }

        return 0;
}

/**
 * Verify CMS message signer
 *
 * @v cms               CMS message
 * @v part              Participant information
 * @v data              Signed data
 * @v len               Length of signed data
 * @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
 */
static int cms_verify_signer ( struct cms_message *cms,
                               struct cms_participant *part,
                               const void *data, size_t len,
                               time_t time, struct x509_chain *store,
                               struct x509_root *root ) {
        struct x509_certificate *cert;
        int rc;

        /* Validate certificate chain */
        if ( ( rc = x509_validate_chain ( part->chain, time, store,
                                          root ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not validate chain: %s\n",
                       cms, part, strerror ( rc ) );
                return rc;
        }

        /* Extract code-signing certificate */
        cert = x509_first ( part->chain );
        assert ( cert != NULL );

        /* Check that certificate can create digital signatures */
        if ( ! ( cert->extensions.usage.bits & X509_DIGITAL_SIGNATURE ) ) {
                DBGC ( cms, "CMS %p/%p certificate cannot create signatures\n",
                       cms, part );
                return -EACCES_NON_SIGNING;
        }

        /* Check that certificate can sign code */
        if ( ! ( cert->extensions.ext_usage.bits & X509_CODE_SIGNING ) ) {
                DBGC ( cms, "CMS %p/%p certificate is not code-signing\n",
                       cms, part );
                return -EACCES_NON_CODE_SIGNING;
        }

        /* Verify digest */
        if ( ( rc = cms_verify_digest ( cms, part, cert, data, len ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Verify CMS signature
 *
 * @v cms               CMS message
 * @v image             Signed image
 * @v name              Required common name, or NULL to check all signatures
 * @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 cms_verify ( struct cms_message *cms, struct image *image,
                 const char *name, time_t time, struct x509_chain *store,
                 struct x509_root *root ) {
        struct cms_participant *part;
        struct x509_certificate *cert;
        int count = 0;
        int rc;

        /* Mark image as untrusted */
        image_untrust ( image );

        /* Sanity check */
        if ( ! cms_is_signature ( cms ) )
                return -ENOTTY;

        /* Verify using all signers */
        list_for_each_entry ( part, &cms->participants, list ) {
                cert = x509_first ( part->chain );
                if ( name && ( x509_check_name ( cert, name ) != 0 ) )
                        continue;
                if ( ( rc = cms_verify_signer ( cms, part, image->data,
                                                image->len, time, store,
                                                root ) ) != 0 )
                        return rc;
                count++;
        }

        /* Check that we have verified at least one signature */
        if ( count == 0 ) {
                if ( name ) {
                        DBGC ( cms, "CMS %p had no signatures matching name "
                               "%s\n", cms, name );
                        return -EACCES_WRONG_NAME;
                } else {
                        DBGC ( cms, "CMS %p had no signatures\n", cms );
                        return -EACCES_NO_SIGNATURES;
                }
        }

        /* Mark image as trusted */
        image_trust ( image );

        return 0;
}

/**
 * Identify CMS recipient corresponding to private key
 *
 * @v cms               CMS message
 * @v private_key       Private key
 * @ret part            Participant information, or NULL if not found
 */
static struct cms_participant *
cms_recipient ( struct cms_message *cms, struct private_key *private_key ) {
        struct cms_participant *part;
        struct x509_certificate *cert;

        /* Identify certificate (if any) for which we have a private key */
        cert = x509_find_key ( NULL, private_key );
        if ( ! cert )
                return NULL;

        /* Identify corresponding recipient, if any */
        list_for_each_entry ( part, &cms->participants, list ) {
                if ( cert == x509_first ( part->chain ) )
                        return part;
        }

        return NULL;
}

/**
 * Set CMS cipher key
 *
 * @v cms               CMS message
 * @v part              Participant information
 * @v private_key       Private key
 * @v ctx               Cipher context
 * @ret rc              Return status code
 */
static int cms_cipher_key ( struct cms_message *cms,
                            struct cms_participant *part,
                            struct private_key *private_key, void *ctx ) {
        struct cipher_algorithm *cipher = cms->cipher;
        struct pubkey_algorithm *pubkey = part->pubkey;
        const struct asn1_cursor *key = privkey_cursor ( private_key );
        const struct asn1_cursor *value = &part->value;
        struct asn1_builder cipher_key = { NULL, 0 };
        int rc;

        /* Decrypt cipher key */
        if ( ( rc = pubkey_decrypt ( pubkey, key, value,
                                     &cipher_key ) ) != 0 ) {
                DBGC ( cms, "CMS %p/%p could not decrypt cipher key: %s\n",
                       cms, part, strerror ( rc ) );
                DBGC_HDA ( cms, 0, value->data, value->len );
                goto err_decrypt;
        }
        DBGC ( cms, "CMS %p/%p cipher key:\n", cms, part );
        DBGC_HDA ( cms, 0, cipher_key.data, cipher_key.len );

        /* Set cipher key */
        if ( ( rc = cipher_setkey ( cipher, ctx, cipher_key.data,
                                    cipher_key.len ) ) != 0 ) {
                DBGC ( cms, "CMS %p could not set cipher key: %s\n",
                       cms, strerror ( rc ) );
                goto err_setkey;
        }

        /* Set cipher initialization vector */
        cipher_setiv ( cipher, ctx, cms->iv.data, cms->iv.len );
        if ( cms->iv.len ) {
                DBGC ( cms, "CMS %p cipher IV:\n", cms );
                DBGC_HDA ( cms, 0, cms->iv.data, cms->iv.len );
        }

 err_setkey:
 err_decrypt:
        free ( cipher_key.data );
        return rc;
}

/**
 * Initialise cipher for CMS decryption
 *
 * @v cms               CMS message
 * @v private_key       Private key
 * @v ctx               Cipher context
 * @ret rc              Return status code
 */
static int cms_cipher ( struct cms_message *cms,
                        struct private_key *private_key, void *ctx ) {
        struct cms_participant *part;
        int rc;

        /* Identify a usable recipient */
        part = cms_recipient ( cms, private_key );
        if ( ! part ) {
                DBGC ( cms, "CMS %p had no usable recipients\n", cms );
                return -EACCES_NO_RECIPIENTS;
        }

        /* Decrypt and set cipher key */
        if ( ( rc = cms_cipher_key ( cms, part, private_key, ctx ) ) != 0 )
                return rc;

        return 0;
}

/**
 * Check CMS padding
 *
 * @v cms               CMS message
 * @v data              Final block
 * @v len               Final block length
 * @ret len             Padding length, or negative error
 */
static int cms_verify_padding ( struct cms_message *cms, const void *data,
                                size_t len ) {
        struct cipher_algorithm *cipher = cms->cipher;
        const uint8_t *pad;
        size_t pad_len;
        unsigned int i;

        /* Non-block ciphers do not use padding */
        if ( ! is_block_cipher ( cipher ) )
                return 0;

        /* Block padding can never produce an empty file */
        if ( len == 0 ) {
                DBGC ( cms, "CMS %p invalid empty padding\n", cms );
                return -EACCES_PAD;
        }

        /* Sanity check */
        assert ( len >= cipher->blocksize );

        /* Extract and verify padding */
        pad = ( data + len - 1 );
        pad_len = *pad;
        if ( ( pad_len == 0 ) || ( pad_len > len ) ) {
                DBGC ( cms, "CMS %p invalid padding length %zd\n",
                       cms, pad_len );
                return -EACCES_PAD;
        }
        for ( i = 0 ; i < pad_len ; i++ ) {
                if ( *(pad--) != pad_len ) {
                        DBGC ( cms, "CMS %p invalid padding\n", cms );
                        DBGC_HDA ( cms, 0, ( data + len - pad_len ), pad_len );
                        return -EACCES_PAD;
                }
        }

        return pad_len;
}

/**
 * Decrypt CMS message
 *
 * @v cms               CMS message
 * @v image             Image to decrypt
 * @v name              Decrypted image name, or NULL to use default
 * @v private_key       Private key
 * @ret rc              Return status code
 */
int cms_decrypt ( struct cms_message *cms, struct image *image,
                  const char *name, struct private_key *private_key ) {
        struct cipher_algorithm *cipher = cms->cipher;
        const unsigned int original_flags = image->flags;
        uint8_t ctx[ cipher->ctxsize ];
        uint8_t ctxdup[ cipher->ctxsize ];
        uint8_t auth[ cipher->authsize ];
        uint8_t final[ cipher->blocksize ];
        size_t final_len;
        size_t bulk_len;
        int pad_len;
        int rc;

        /* Check block size */
        if ( ( image->len & ( cipher->blocksize - 1 ) ) != 0 ) {
                DBGC ( cms, "CMS %p invalid length %zd\n", cms, image->len );
                rc = -EACCES_LEN;
                goto err_blocksize;
        }

        /* Initialise cipher */
        if ( ( rc = cms_cipher ( cms, private_key, ctx ) ) != 0 )
                goto err_cipher;

        /* Duplicate cipher context for potential reencryption on error */
        memcpy ( ctxdup, ctx, cipher->ctxsize );

        /* Clear trusted flag before modifying image */
        image_untrust ( image );

        /* Temporarily unregister image, if applicable */
        if ( original_flags & IMAGE_REGISTERED ) {
                image_get ( image );
                unregister_image ( image );
        }

        /* Decrypt all but the final block */
        final_len = ( ( image->len && is_block_cipher ( cipher ) ) ?
                      cipher->blocksize : 0 );
        bulk_len = ( image->len - final_len );
        cipher_decrypt ( cipher, ctx, image->data, image->rwdata, bulk_len );

        /* Decrypt final block */
        cipher_decrypt ( cipher, ctx, ( image->data + bulk_len ), final,
                         final_len );

        /* Check authentication tag, if applicable */
        cipher_auth ( cipher, ctx, auth );
        if ( ( cms->mac.len != cipher->authsize ) ||
             ( memcmp ( cms->mac.data, auth, cipher->authsize ) != 0 ) ) {
                DBGC ( cms, "CMS %p invalid authentication tag\n", cms );
                DBGC_HDA ( cms, 0, auth, cipher->authsize );
                rc = -EACCES_MAC;
                goto err_auth;
        }

        /* Check block padding, if applicable */
        if ( ( pad_len = cms_verify_padding ( cms, final, final_len ) ) < 0 ) {
                rc = pad_len;
                goto err_pad;
        }

        /* Update image name. Do this as the last possible failure, so
         * that we do not have to include any error-handling code path
         * to restore the original image name (which may itself fail).
         */
        if ( name ) {
                if ( ( rc = image_set_name ( image, name ) ) != 0 )
                        goto err_set_name;
        } else {
                image_strip_suffix ( image );
        }

        /* Overwrite final fragment and strip block padding.  Do this
         * only once no further failure paths exist, so that we do not
         * have to include include any error-handling code path to
         * reconstruct the block padding.
         */
        memcpy ( ( image->rwdata + bulk_len ), final, final_len );
        image->len -= pad_len;

        /* Clear image type and re-register image, if applicable */
        image->type = NULL;
        if ( original_flags & IMAGE_REGISTERED ) {
                register_image ( image );
                image_put ( image );
        }

        return 0;

 err_set_name:
 err_pad:
 err_auth:
        /* Reencrypt all overwritten portions.  This can be done since
         * we have deliberately not overwritten the final block
         * containing the potentially invalid (and therefore
         * unreproducible) block padding.
         */
        cipher_encrypt ( cipher, ctxdup, image->data, image->rwdata, bulk_len );
        if ( original_flags & IMAGE_REGISTERED ) {
                register_image ( image ); /* Cannot fail on re-registration */
                image_put ( image );
        }
        image->flags = original_flags;
 err_cipher:
 err_blocksize:
        return rc;
}