asn1.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 <stdint.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <errno.h>
#include <time.h>
#include <ipxe/tables.h>
#include <ipxe/image.h>
#include <ipxe/asn1.h>

/** @file
 *
 * ASN.1 encoding
 *
 */

/* Disambiguate the various error causes */
#define EINVAL_ASN1_EMPTY \
        __einfo_error ( EINFO_EINVAL_ASN1_EMPTY )
#define EINFO_EINVAL_ASN1_EMPTY \
        __einfo_uniqify ( EINFO_EINVAL, 0x01, "Empty or underlength cursor" )
#define EINVAL_ASN1_LEN_LEN \
        __einfo_error ( EINFO_EINVAL_ASN1_LEN_LEN )
#define EINFO_EINVAL_ASN1_LEN_LEN \
        __einfo_uniqify ( EINFO_EINVAL, 0x02, "Length field overruns cursor" )
#define EINVAL_ASN1_LEN \
        __einfo_error ( EINFO_EINVAL_ASN1_LEN )
#define EINFO_EINVAL_ASN1_LEN \
        __einfo_uniqify ( EINFO_EINVAL, 0x03, "Field overruns cursor" )
#define EINVAL_ASN1_BOOLEAN \
        __einfo_error ( EINFO_EINVAL_ASN1_BOOLEAN )
#define EINFO_EINVAL_ASN1_BOOLEAN \
        __einfo_uniqify ( EINFO_EINVAL, 0x04, "Invalid boolean" )
#define EINVAL_ASN1_INTEGER \
        __einfo_error ( EINFO_EINVAL_ASN1_INTEGER )
#define EINFO_EINVAL_ASN1_INTEGER \
        __einfo_uniqify ( EINFO_EINVAL, 0x04, "Invalid integer" )
#define EINVAL_ASN1_TIME \
        __einfo_error ( EINFO_EINVAL_ASN1_TIME )
#define EINFO_EINVAL_ASN1_TIME \
        __einfo_uniqify ( EINFO_EINVAL, 0x05, "Invalid time" )
#define EINVAL_ASN1_ALGORITHM \
        __einfo_error ( EINFO_EINVAL_ASN1_ALGORITHM )
#define EINFO_EINVAL_ASN1_ALGORITHM \
        __einfo_uniqify ( EINFO_EINVAL, 0x06, "Invalid algorithm" )
#define EINVAL_BIT_STRING \
        __einfo_error ( EINFO_EINVAL_BIT_STRING )
#define EINFO_EINVAL_BIT_STRING \
        __einfo_uniqify ( EINFO_EINVAL, 0x07, "Invalid bit string" )
#define ENOTSUP_ALGORITHM \
        __einfo_error ( EINFO_ENOTSUP_ALGORITHM )
#define EINFO_ENOTSUP_ALGORITHM \
        __einfo_uniqify ( EINFO_ENOTSUP, 0x01, "Unsupported algorithm" )
#define ENOTTY_ALGORITHM \
        __einfo_error ( EINFO_ENOTTY_ALGORITHM )
#define EINFO_ENOTTY_ALGORITHM \
        __einfo_uniqify ( EINFO_ENOTTY, 0x01, "Inappropriate algorithm" )

/**
 * Start parsing ASN.1 object
 *
 * @v cursor            ASN.1 object cursor
 * @v type              Expected type, or ASN1_ANY
 * @v extra             Additional length not present within partial cursor
 * @ret len             Length of object body, or negative error
 *
 * The object cursor will be updated to point to the start of the
 * object body (i.e. the first byte following the length byte(s)), and
 * the length of the object body (i.e. the number of bytes until the
 * following object tag, if any) is returned.
 */
int asn1_start ( struct asn1_cursor *cursor, unsigned int type, size_t extra ) {
        unsigned int len_len;
        unsigned int len;

        /* Sanity check */
        if ( cursor->len < 2 /* Tag byte and first length byte */ ) {
                if ( cursor->len )
                        DBGC ( cursor, "ASN1 %p too short\n", cursor );
                return -EINVAL_ASN1_EMPTY;
        }

        /* Check the tag byte */
        if ( ( type != ASN1_ANY ) && ( type != asn1_type ( cursor ) ) ) {
                DBGC ( cursor, "ASN1 %p type mismatch (expected %d, got %d)\n",
                       cursor, type, *( ( uint8_t * ) cursor->data ) );
                return -ENXIO;
        }
        cursor->data++;
        cursor->len--;

        /* Extract length of the length field and sanity check */
        len_len = *( ( uint8_t * ) cursor->data );
        if ( len_len & 0x80 ) {
                len_len = ( len_len & 0x7f );
                cursor->data++;
                cursor->len--;
        } else {
                len_len = 1;
        }
        if ( cursor->len < len_len ) {
                DBGC ( cursor, "ASN1 %p bad length field length %d (max "
                       "%zd)\n", cursor, len_len, cursor->len );
                return -EINVAL_ASN1_LEN_LEN;
        }

        /* Extract the length and sanity check */
        for ( len = 0 ; len_len ; len_len-- ) {
                len <<= 8;
                len |= *( ( uint8_t * ) cursor->data );
                cursor->data++;
                cursor->len--;
        }
        if ( ( cursor->len + extra ) < len ) {
                DBGC ( cursor, "ASN1 %p bad length %d (max %zd)\n",
                       cursor, len, ( cursor->len + extra ) );
                return -EINVAL_ASN1_LEN;
        }

        return len;
}

/**
 * Enter ASN.1 object
 *
 * @v cursor            ASN.1 object cursor
 * @v type              Expected type, or ASN1_ANY
 * @ret rc              Return status code
 *
 * The object cursor will be updated to point to the body of the
 * current ASN.1 object.  If any error occurs, the object cursor will
 * be invalidated.
 */
int asn1_enter ( struct asn1_cursor *cursor, unsigned int type ) {
        int len;

        len = asn1_start ( cursor, type, 0 );
        if ( len < 0 ) {
                asn1_invalidate_cursor ( cursor );
                return len;
        }

        cursor->len = len;
        DBGC ( cursor, "ASN1 %p entered object type %02x (len %x)\n",
               cursor, type, len );

        return 0;
}

/**
 * Skip ASN.1 object if present
 *
 * @v cursor            ASN.1 object cursor
 * @v type              Expected type, or ASN1_ANY
 * @ret rc              Return status code
 *
 * The object cursor will be updated to point to the next ASN.1
 * object.  If any error occurs, the object cursor will not be
 * modified.
 */
int asn1_skip_if_exists ( struct asn1_cursor *cursor, unsigned int type ) {
        int len;

        len = asn1_start ( cursor, type, 0 );
        if ( len < 0 )
                return len;

        cursor->data += len;
        cursor->len -= len;
        DBGC ( cursor, "ASN1 %p skipped object type %02x (len %x)\n",
               cursor, type, len );

        if ( ! cursor->len ) {
                DBGC ( cursor, "ASN1 %p reached end of object\n", cursor );
                return -ENOENT;
        }

        return 0;
}

/**
 * Skip ASN.1 object
 *
 * @v cursor            ASN.1 object cursor
 * @v type              Expected type, or ASN1_ANY
 * @ret rc              Return status code
 *
 * The object cursor will be updated to point to the next ASN.1
 * object.  If any error occurs, the object cursor will be
 * invalidated.
 */
int asn1_skip ( struct asn1_cursor *cursor, unsigned int type ) {
        int rc;

        if ( ( rc = asn1_skip_if_exists ( cursor, type ) ) != 0 ) {
                asn1_invalidate_cursor ( cursor );
                return rc;
        }

        return 0;
}

/**
 * Shrink ASN.1 cursor to fit object
 *
 * @v cursor            ASN.1 object cursor
 * @v type              Expected type, or ASN1_ANY
 * @ret rc              Return status code
 *
 * The object cursor will be shrunk to contain only the current ASN.1
 * object.  If any error occurs, the object cursor will be
 * invalidated.
 */
int asn1_shrink ( struct asn1_cursor *cursor, unsigned int type ) {
        struct asn1_cursor temp;
        const void *end;
        int len;

        /* Find end of object */
        memcpy ( &temp, cursor, sizeof ( temp ) );
        len = asn1_start ( &temp, type, 0 );
        if ( len < 0 ) {
                asn1_invalidate_cursor ( cursor );
                return len;
        }
        end = ( temp.data + len );

        /* Shrink original cursor to contain only its first object */
        cursor->len = ( end - cursor->data );

        return 0;
}

/**
 * Enter ASN.1 object of any type
 *
 * @v cursor            ASN.1 object cursor
 * @ret rc              Return status code
 */
int asn1_enter_any ( struct asn1_cursor *cursor ) {
        return asn1_enter ( cursor, ASN1_ANY );
}

/**
 * Skip ASN.1 object of any type
 *
 * @v cursor            ASN.1 object cursor
 * @ret rc              Return status code
 */
int asn1_skip_any ( struct asn1_cursor *cursor ) {
        return asn1_skip ( cursor, ASN1_ANY );
}

/**
 * Shrink ASN.1 object of any type
 *
 * @v cursor            ASN.1 object cursor
 * @ret rc              Return status code
 */
int asn1_shrink_any ( struct asn1_cursor *cursor ) {
        return asn1_shrink ( cursor, ASN1_ANY );
}

/**
 * Parse value of ASN.1 boolean
 *
 * @v cursor            ASN.1 object cursor
 * @ret value           Value, or negative error
 */
int asn1_boolean ( const struct asn1_cursor *cursor ) {
        struct asn1_cursor contents;
        const struct {
                uint8_t value;
        } __attribute__ (( packed )) *boolean;

        /* Enter boolean */
        memcpy ( &contents, cursor, sizeof ( contents ) );
        asn1_enter ( &contents, ASN1_BOOLEAN );
        if ( contents.len != sizeof ( *boolean ) )
                return -EINVAL_ASN1_BOOLEAN;

        /* Extract value */
        boolean = contents.data;
        return boolean->value;
}

/**
 * Parse value of ASN.1 integer
 *
 * @v cursor            ASN.1 object cursor
 * @v value             Value to fill in
 * @ret rc              Return status code
 */
int asn1_integer ( const struct asn1_cursor *cursor, int *value ) {
        struct asn1_cursor contents;
        uint8_t high_byte;
        int rc;

        /* Enter integer */
        memcpy ( &contents, cursor, sizeof ( contents ) );
        if ( ( rc = asn1_enter ( &contents, ASN1_INTEGER ) ) != 0 )
                return rc;
        if ( contents.len < 1 )
                return -EINVAL_ASN1_INTEGER;

        /* Initialise value according to sign byte */
        *value = *( ( int8_t * ) contents.data );
        contents.data++;
        contents.len--;

        /* Process value */
        while ( contents.len ) {
                high_byte = ( (*value) >> ( 8 * ( sizeof ( *value ) - 1 ) ) );
                if ( ( high_byte != 0x00 ) && ( high_byte != 0xff ) ) {
                        DBGC ( cursor, "ASN1 %p integer overflow\n", cursor );
                        return -EINVAL_ASN1_INTEGER;
                }
                *value = ( ( *value << 8 ) | *( ( uint8_t * ) contents.data ) );
                contents.data++;
                contents.len--;
        }

        return 0;
}

/**
 * Parse ASN.1 bit string
 *
 * @v cursor            ASN.1 cursor
 * @v bits              Bit string to fill in
 * @ret rc              Return status code
 */
int asn1_bit_string ( const struct asn1_cursor *cursor,
                      struct asn1_bit_string *bits ) {
        struct asn1_cursor contents;
        const struct {
                uint8_t unused;
                uint8_t data[0];
        } __attribute__ (( packed )) *bit_string;
        size_t len;
        unsigned int unused;
        uint8_t unused_mask;
        const uint8_t *last;
        int rc;

        /* Enter bit string */
        memcpy ( &contents, cursor, sizeof ( contents ) );
        if ( ( rc = asn1_enter ( &contents, ASN1_BIT_STRING ) ) != 0 ) {
                DBGC ( cursor, "ASN1 %p cannot locate bit string:\n", cursor );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return rc;
        }

        /* Validity checks */
        if ( contents.len < sizeof ( *bit_string ) ) {
                DBGC ( cursor, "ASN1 %p invalid bit string:\n", cursor );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -EINVAL_BIT_STRING;
        }
        bit_string = contents.data;
        len = ( contents.len - offsetof ( typeof ( *bit_string ), data ) );
        unused = bit_string->unused;
        unused_mask = ( 0xff >> ( 8 - unused ) );
        last = ( bit_string->data + len - 1 );
        if ( ( unused >= 8 ) ||
             ( ( unused > 0 ) && ( len == 0 ) ) ||
             ( ( *last & unused_mask ) != 0 ) ) {
                DBGC ( cursor, "ASN1 %p invalid bit string:\n", cursor );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -EINVAL_BIT_STRING;
        }

        /* Populate bit string */
        bits->data = &bit_string->data;
        bits->len = len;
        bits->unused = unused;

        return 0;
}

/**
 * Parse ASN.1 bit string that must be an integral number of bytes
 *
 * @v cursor            ASN.1 cursor
 * @v bits              Bit string to fill in
 * @ret rc              Return status code
 */
int asn1_integral_bit_string ( const struct asn1_cursor *cursor,
                               struct asn1_bit_string *bits ) {
        int rc;

        /* Parse bit string */
        if ( ( rc = asn1_bit_string ( cursor, bits ) ) != 0 )
                return rc;

        /* Check that there are no unused bits at end of string */
        if ( bits->unused ) {
                DBGC ( cursor, "ASN1 %p invalid integral bit string:\n",
                       cursor );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -EINVAL_BIT_STRING;
        }

        return 0;
}

/**
 * Compare two ASN.1 objects
 *
 * @v cursor1           ASN.1 object cursor
 * @v cursor2           ASN.1 object cursor
 * @ret difference      Difference as returned by memcmp()
 *
 * Note that invalid and empty cursors will compare as equal with each
 * other.
 */
int asn1_compare ( const struct asn1_cursor *cursor1,
                   const struct asn1_cursor *cursor2 ) {
        int difference;

        difference = ( cursor2->len - cursor1->len );
        return ( difference ? difference :
                 memcmp ( cursor1->data, cursor2->data, cursor1->len ) );
}

/**
 * Identify ASN.1 algorithm by OID
 *
 * @v cursor            ASN.1 object cursor

 * @ret algorithm       Algorithm, or NULL
 */
static struct asn1_algorithm *
asn1_find_algorithm ( const struct asn1_cursor *cursor ) {
        struct asn1_algorithm *algorithm;

        for_each_table_entry ( algorithm, ASN1_ALGORITHMS ) {
                if ( asn1_compare ( &algorithm->oid, cursor ) == 0 )
                        return algorithm;
        }

        return NULL;
}

/**
 * Parse ASN.1 OID-identified algorithm
 *
 * @v cursor            ASN.1 object cursor
 * @ret algorithm       Algorithm
 * @ret rc              Return status code
 */
int asn1_algorithm ( const struct asn1_cursor *cursor,
                     struct asn1_algorithm **algorithm ) {
        struct asn1_cursor contents;
        int rc;

        /* Enter signatureAlgorithm */
        memcpy ( &contents, cursor, sizeof ( contents ) );
        asn1_enter ( &contents, ASN1_SEQUENCE );

        /* Enter algorithm */
        if ( ( rc = asn1_enter ( &contents, ASN1_OID ) ) != 0 ) {
                DBGC ( cursor, "ASN1 %p cannot locate algorithm OID:\n",
                       cursor );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -EINVAL_ASN1_ALGORITHM;
        }

        /* Identify algorithm */
        *algorithm = asn1_find_algorithm ( &contents );
        if ( ! *algorithm ) {
                DBGC ( cursor, "ASN1 %p unrecognised algorithm:\n", cursor );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -ENOTSUP_ALGORITHM;
        }

        return 0;
}

/**
 * Parse ASN.1 OID-identified public-key algorithm
 *
 * @v cursor            ASN.1 object cursor
 * @ret algorithm       Algorithm
 * @ret rc              Return status code
 */
int asn1_pubkey_algorithm ( const struct asn1_cursor *cursor,
                            struct asn1_algorithm **algorithm ) {
        int rc;

        /* Parse algorithm */
        if ( ( rc = asn1_algorithm ( cursor, algorithm ) ) != 0 )
                return rc;

        /* Check algorithm has a public key */
        if ( ! (*algorithm)->pubkey ) {
                DBGC ( cursor, "ASN1 %p algorithm %s is not a public-key "
                       "algorithm:\n", cursor, (*algorithm)->name );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -ENOTTY_ALGORITHM;
        }

        return 0;
}

/**
 * Parse ASN.1 OID-identified digest algorithm
 *
 * @v cursor            ASN.1 object cursor
 * @ret algorithm       Algorithm
 * @ret rc              Return status code
 */
int asn1_digest_algorithm ( const struct asn1_cursor *cursor,
                            struct asn1_algorithm **algorithm ) {
        int rc;

        /* Parse algorithm */
        if ( ( rc = asn1_algorithm ( cursor, algorithm ) ) != 0 )
                return rc;

        /* Check algorithm has a digest */
        if ( ! (*algorithm)->digest ) {
                DBGC ( cursor, "ASN1 %p algorithm %s is not a digest "
                       "algorithm:\n", cursor, (*algorithm)->name );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -ENOTTY_ALGORITHM;
        }

        return 0;
}

/**
 * Parse ASN.1 OID-identified signature algorithm
 *
 * @v cursor            ASN.1 object cursor
 * @ret algorithm       Algorithm
 * @ret rc              Return status code
 */
int asn1_signature_algorithm ( const struct asn1_cursor *cursor,
                               struct asn1_algorithm **algorithm ) {
        int rc;

        /* Parse algorithm */
        if ( ( rc = asn1_algorithm ( cursor, algorithm ) ) != 0 )
                return rc;

        /* Check algorithm has a public key */
        if ( ! (*algorithm)->pubkey ) {
                DBGC ( cursor, "ASN1 %p algorithm %s is not a signature "
                       "algorithm:\n", cursor, (*algorithm)->name );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -ENOTTY_ALGORITHM;
        }

        /* Check algorithm has a digest */
        if ( ! (*algorithm)->digest ) {
                DBGC ( cursor, "ASN1 %p algorithm %s is not a signature "
                       "algorithm:\n", cursor, (*algorithm)->name );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -ENOTTY_ALGORITHM;
        }

        return 0;
}

/**
 * Parse ASN.1 GeneralizedTime
 *
 * @v cursor            ASN.1 cursor
 * @v time              Time to fill in
 * @ret rc              Return status code
 *
 * RFC 5280 section 4.1.2.5 places several restrictions on the allowed
 * formats for UTCTime and GeneralizedTime, and mandates the
 * interpretation of centuryless year values.
 */
int asn1_generalized_time ( const struct asn1_cursor *cursor, time_t *time ) {
        struct asn1_cursor contents;
        unsigned int have_century;
        unsigned int type;
        union {
                struct {
                        uint8_t century;
                        uint8_t year;
                        uint8_t month;
                        uint8_t day;
                        uint8_t hour;
                        uint8_t minute;
                        uint8_t second;
                } __attribute__ (( packed )) named;
                uint8_t raw[7];
        } pairs;
        struct tm tm;
        const uint8_t *data;
        size_t remaining;
        unsigned int tens;
        unsigned int units;
        unsigned int i;
        int rc;

        /* Determine time format utcTime/generalizedTime */
        memcpy ( &contents, cursor, sizeof ( contents ) );
        type = asn1_type ( &contents );
        switch ( type ) {
        case ASN1_UTC_TIME:
                have_century = 0;
                break;
        case ASN1_GENERALIZED_TIME:
                have_century = 1;
                break;
        default:
                DBGC ( cursor, "ASN1 %p invalid time type %02x\n",
                       cursor, type );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -EINVAL_ASN1_TIME;
        }

        /* Enter utcTime/generalizedTime */
        if ( ( rc = asn1_enter ( &contents, type ) ) != 0 ) {
                DBGC ( cursor, "ASN1 %p cannot locate %s time:\n", cursor,
                       ( ( type == ASN1_UTC_TIME ) ? "UTC" : "generalized" ) );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return rc;
        }

        /* Parse digit string a pair at a time */
        memset ( &pairs, 0, sizeof ( pairs ) );
        data = contents.data;
        remaining = contents.len;
        for ( i = ( have_century ? 0 : 1 ) ; i < sizeof ( pairs.raw ) ; i++ ) {
                if ( remaining < 2 ) {
                        /* Some certificates violate the X.509 RFC by
                         * omitting the "seconds" value.
                         */
                        if ( i == ( sizeof ( pairs.raw ) - 1 ) )
                                break;
                        DBGC ( cursor, "ASN1 %p invalid time:\n", cursor );
                        DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                        return -EINVAL_ASN1_TIME;
                }
                tens = data[0];
                units = data[1];
                if ( ! ( isdigit ( tens ) && isdigit ( units ) ) ) {
                        DBGC ( cursor, "ASN1 %p invalid time:\n", cursor );
                        DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                        return -EINVAL_ASN1_TIME;
                }
                pairs.raw[i] = ( ( 10 * ( tens - '0' ) ) + ( units - '0' ) );
                data += 2;
                remaining -= 2;
        }

        /* Determine century if applicable */
        if ( ! have_century )
                pairs.named.century = ( ( pairs.named.year >= 50 ) ? 19 : 20 );

        /* Check for trailing "Z" */
        if ( ( remaining != 1 ) || ( data[0] != 'Z' ) ) {
                DBGC ( cursor, "ASN1 %p invalid time:\n", cursor );
                DBGC_HDA ( cursor, 0, cursor->data, cursor->len );
                return -EINVAL_ASN1_TIME;
        }

        /* Fill in time */
        tm.tm_year = ( ( ( pairs.named.century - 19 ) * 100 ) +
                       pairs.named.year );
        tm.tm_mon = ( pairs.named.month - 1 );
        tm.tm_mday = pairs.named.day;
        tm.tm_hour = pairs.named.hour;
        tm.tm_min = pairs.named.minute;
        tm.tm_sec = pairs.named.second;

        /* Convert to seconds since the Epoch */
        *time = mktime ( &tm );

        return 0;
}

/**
 * Construct ASN.1 header
 *
 * @v header            ASN.1 builder header
 * @v type              Type
 * @v len               Content length
 * @ret header_len      Header length
 */
static size_t asn1_header ( struct asn1_builder_header *header,
                            unsigned int type, size_t len ) {
        unsigned int header_len = 2;
        unsigned int len_len = 0;
        size_t temp;

        /* Construct header */
        header->type = type;
        if ( len < 0x80 ) {
                header->length[0] = len;
        } else {
                for ( temp = len ; temp ; temp >>= 8 )
                        len_len++;
                header->length[0] = ( 0x80 | len_len );
                header_len += len_len;
                for ( temp = len ; temp ; temp >>= 8 )
                        header->length[len_len--] = ( temp & 0xff );
        }

        return header_len;
}

/**
 * Grow ASN.1 builder
 *
 * @v builder           ASN.1 builder
 * @v extra             Extra space to prepend
 * @ret rc              Return status code
 */
int asn1_grow ( struct asn1_builder *builder, size_t extra ) {
        size_t new_len;
        void *new;

        /* As with the ASN1 parsing functions, make errors permanent */
        if ( builder->len && ! builder->data )
                return -ENOMEM;

        /* Reallocate data buffer */
        new_len = ( builder->len + extra );
        new = realloc ( builder->data, new_len );
        if ( ! new ) {
                free ( builder->data );
                builder->data = NULL;
                return -ENOMEM;
        }
        builder->data = new;

        /* Move existing data to end of buffer */
        memmove ( ( builder->data + extra ), builder->data, builder->len );
        builder->len = new_len;

        return 0;
}

/**
 * Prepend raw data to ASN.1 builder
 *
 * @v builder           ASN.1 builder
 * @v data              Data to prepend
 * @v len               Length of data to prepend
 * @ret rc              Return status code
 */
int asn1_prepend_raw ( struct asn1_builder *builder, const void *data,
                       size_t len ) {
        int rc;

        /* Grow buffer */
        if ( ( rc = asn1_grow ( builder, len ) ) != 0 )
                return rc;

        /* Populate data buffer */
        memcpy ( builder->data, data, len );

        return 0;
}

/**
 * Prepend data to ASN.1 builder
 *
 * @v builder           ASN.1 builder
 * @v type              Type
 * @v data              Data to prepend
 * @v len               Length of data to prepend
 * @ret rc              Return status code
 */
int asn1_prepend ( struct asn1_builder *builder, unsigned int type,
                   const void *data, size_t len ) {
        struct asn1_builder_header header;
        size_t header_len;
        int rc;

        /* Construct header */
        header_len = asn1_header ( &header, type, len );

        /* Grow buffer */
        if ( ( rc = asn1_grow ( builder, header_len + len ) ) != 0 )
                return rc;

        /* Populate data buffer */
        memcpy ( builder->data, &header, header_len );
        memcpy ( ( builder->data + header_len ), data, len );

        return 0;
}

/**
 * Wrap ASN.1 builder
 *
 * @v builder           ASN.1 builder
 * @v type              Type
 * @ret rc              Return status code
 */
int asn1_wrap ( struct asn1_builder *builder, unsigned int type ) {
        struct asn1_builder_header header;
        size_t header_len;
        int rc;

        /* Construct header */
        header_len = asn1_header ( &header, type, builder->len );

        /* Grow buffer */
        if ( ( rc = asn1_grow ( builder, header_len ) ) != 0 )
                return rc;

        /* Populate data buffer */
        memcpy ( builder->data, &header, header_len );

        return 0;
}

/**
 * Extract ASN.1 object from image
 *
 * @v image             Image
 * @v offset            Offset within image
 * @v cursor            ASN.1 cursor to fill in
 * @ret next            Offset to next image, or negative error
 *
 * The caller is responsible for eventually calling free() on the
 * allocated ASN.1 cursor.
 */
int image_asn1 ( struct image *image, size_t offset,
                 struct asn1_cursor **cursor ) {
        int next;
        int rc;

        /* Sanity check */
        assert ( offset <= image->len );

        /* Check that this image can be used to extract an ASN.1 object */
        if ( ! ( image->type && image->type->asn1 ) )
                return -ENOTSUP;

        /* Try creating ASN.1 cursor */
        next = image->type->asn1 ( image, offset, cursor );
        if ( next < 0 ) {
                rc = next;
                DBGC ( image, "IMAGE %s could not extract ASN.1 object: %s\n",
                       image->name, strerror ( rc ) );
                return rc;
        }

        return next;
}

/* Drag in objects via image_asn1() */
REQUIRING_SYMBOL ( image_asn1 );

/* Drag in ASN.1 image formats */
REQUIRE_OBJECT ( config_asn1 );