library/asn1write.c

/*
 * ASN.1 buffer writing functionality
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

#include "common.h"

#if defined(MBEDTLS_ASN1_WRITE_C)

#include "mbedtls/asn1write.h"
#include "mbedtls/error.h"

#include <string.h>

#include "mbedtls/platform.h"

int mbedtls_asn1_write_len( unsigned char **p, unsigned char *start, size_t len )
{
    if( len < 0x80 )
    {
        if( *p - start < 1 )
            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

        *--(*p) = (unsigned char) len;
        return( 1 );
    }

    if( len <= 0xFF )
    {
        if( *p - start < 2 )
            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

        *--(*p) = (unsigned char) len;
        *--(*p) = 0x81;
        return( 2 );
    }

    if( len <= 0xFFFF )
    {
        if( *p - start < 3 )
            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

        *--(*p) = MBEDTLS_BYTE_0( len );
        *--(*p) = MBEDTLS_BYTE_1( len );
        *--(*p) = 0x82;
        return( 3 );
    }

    if( len <= 0xFFFFFF )
    {
        if( *p - start < 4 )
            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

        *--(*p) = MBEDTLS_BYTE_0( len );
        *--(*p) = MBEDTLS_BYTE_1( len );
        *--(*p) = MBEDTLS_BYTE_2( len );
        *--(*p) = 0x83;
        return( 4 );
    }

    int len_valid = 1;
#if SIZE_MAX > 0xFFFFFFFF
    len_valid = ( len <= 0xFFFFFFFF );
#endif
    if( len_valid )
    {
        if( *p - start < 5 )
            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

        *--(*p) = MBEDTLS_BYTE_0( len );
        *--(*p) = MBEDTLS_BYTE_1( len );
        *--(*p) = MBEDTLS_BYTE_2( len );
        *--(*p) = MBEDTLS_BYTE_3( len );
        *--(*p) = 0x84;
        return( 5 );
    }
    else
    {
        return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
    }
}

int mbedtls_asn1_write_tag( unsigned char **p, unsigned char *start, unsigned char tag )
{
    if( *p - start < 1 )
        return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

    *--(*p) = tag;

    return( 1 );
}

int mbedtls_asn1_write_raw_buffer( unsigned char **p, unsigned char *start,
                           const unsigned char *buf, size_t size )
{
    size_t len = 0;

    if( *p < start || (size_t)( *p - start ) < size )
        return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

    len = size;
    (*p) -= len;
    memcpy( *p, buf, len );

    return( (int) len );
}

#if defined(MBEDTLS_BIGNUM_C)
int mbedtls_asn1_write_mpi( unsigned char **p, unsigned char *start, const mbedtls_mpi *X )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;

    // Write the MPI
    //
    len = mbedtls_mpi_size( X );

    /* DER represents 0 with a sign bit (0=nonnegative) and 7 value bits, not
     * as 0 digits. We need to end up with 020100, not with 0200. */
    if( len == 0 )
        len = 1;

    if( *p < start || (size_t)( *p - start ) < len )
        return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

    (*p) -= len;
    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( X, *p, len ) );

    // DER format assumes 2s complement for numbers, so the leftmost bit
    // should be 0 for positive numbers and 1 for negative numbers.
    //
    if( X->s ==1 && **p & 0x80 )
    {
        if( *p - start < 1 )
            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

        *--(*p) = 0x00;
        len += 1;
    }

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_INTEGER ) );

    ret = (int) len;

cleanup:
    return( ret );
}
#endif /* MBEDTLS_BIGNUM_C */

int mbedtls_asn1_write_null( unsigned char **p, unsigned char *start )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;

    // Write NULL
    //
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, 0) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_NULL ) );

    return( (int) len );
}

int mbedtls_asn1_write_oid( unsigned char **p, unsigned char *start,
                    const char *oid, size_t oid_len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
                                  (const unsigned char *) oid, oid_len ) );
    MBEDTLS_ASN1_CHK_ADD( len , mbedtls_asn1_write_len( p, start, len ) );
    MBEDTLS_ASN1_CHK_ADD( len , mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_OID ) );

    return( (int) len );
}

int mbedtls_asn1_write_algorithm_identifier( unsigned char **p, unsigned char *start,
                                     const char *oid, size_t oid_len,
                                     size_t par_len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;

    if( par_len == 0 )
        MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_null( p, start ) );
    else
        len += par_len;

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( p, start, oid, oid_len ) );

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start,
                                       MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) );

    return( (int) len );
}

int mbedtls_asn1_write_bool( unsigned char **p, unsigned char *start, int boolean )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;

    if( *p - start < 1 )
        return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

    *--(*p) = (boolean) ? 255 : 0;
    len++;

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_BOOLEAN ) );

    return( (int) len );
}

static int asn1_write_tagged_int( unsigned char **p, unsigned char *start, int val, int tag )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;

    do
    {
        if( *p - start < 1 )
            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
        len += 1;
        *--(*p) = val & 0xff;
        val >>= 8;
    }
    while( val > 0 );

    if( **p & 0x80 )
    {
        if( *p - start < 1 )
            return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
        *--(*p) = 0x00;
        len += 1;
    }

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, tag ) );

    return( (int) len );
}

int mbedtls_asn1_write_int( unsigned char **p, unsigned char *start, int val )
{
    return( asn1_write_tagged_int( p, start, val, MBEDTLS_ASN1_INTEGER ) );
}

int mbedtls_asn1_write_enum( unsigned char **p, unsigned char *start, int val )
{
    return( asn1_write_tagged_int( p, start, val, MBEDTLS_ASN1_ENUMERATED ) );
}

int mbedtls_asn1_write_tagged_string( unsigned char **p, unsigned char *start, int tag,
    const char *text, size_t text_len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
        (const unsigned char *) text, text_len ) );

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, tag ) );

    return( (int) len );
}

int mbedtls_asn1_write_utf8_string( unsigned char **p, unsigned char *start,
    const char *text, size_t text_len )
{
    return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_UTF8_STRING, text, text_len) );
}

int mbedtls_asn1_write_printable_string( unsigned char **p, unsigned char *start,
                                 const char *text, size_t text_len )
{
    return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_PRINTABLE_STRING, text, text_len) );
}

int mbedtls_asn1_write_ia5_string( unsigned char **p, unsigned char *start,
                           const char *text, size_t text_len )
{
    return( mbedtls_asn1_write_tagged_string(p, start, MBEDTLS_ASN1_IA5_STRING, text, text_len) );
}

int mbedtls_asn1_write_named_bitstring( unsigned char **p,
                                        unsigned char *start,
                                        const unsigned char *buf,
                                        size_t bits )
{
    size_t unused_bits, byte_len;
    const unsigned char *cur_byte;
    unsigned char cur_byte_shifted;
    unsigned char bit;

    byte_len = ( bits + 7 ) / 8;
    unused_bits = ( byte_len * 8 ) - bits;

    /*
     * Named bitstrings require that trailing 0s are excluded in the encoding
     * of the bitstring. Trailing 0s are considered part of the 'unused' bits
     * when encoding this value in the first content octet
     */
    if( bits != 0 )
    {
        cur_byte = buf + byte_len - 1;
        cur_byte_shifted = *cur_byte >> unused_bits;

        for( ; ; )
        {
            bit = cur_byte_shifted & 0x1;
            cur_byte_shifted >>= 1;

            if( bit != 0 )
                break;

            bits--;
            if( bits == 0 )
                break;

            if( bits % 8 == 0 )
                cur_byte_shifted = *--cur_byte;
        }
    }

    return( mbedtls_asn1_write_bitstring( p, start, buf, bits ) );
}

int mbedtls_asn1_write_bitstring( unsigned char **p, unsigned char *start,
                          const unsigned char *buf, size_t bits )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;
    size_t unused_bits, byte_len;

    byte_len = ( bits + 7 ) / 8;
    unused_bits = ( byte_len * 8 ) - bits;

    if( *p < start || (size_t)( *p - start ) < byte_len + 1 )
        return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );

    len = byte_len + 1;

    /* Write the bitstring. Ensure the unused bits are zeroed */
    if( byte_len > 0 )
    {
        byte_len--;
        *--( *p ) = buf[byte_len] & ~( ( 0x1 << unused_bits ) - 1 );
        ( *p ) -= byte_len;
        memcpy( *p, buf, byte_len );
    }

    /* Write unused bits */
    *--( *p ) = (unsigned char)unused_bits;

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_BIT_STRING ) );

    return( (int) len );
}

int mbedtls_asn1_write_octet_string( unsigned char **p, unsigned char *start,
                             const unsigned char *buf, size_t size )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t len = 0;

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start, buf, size ) );

    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
    MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_OCTET_STRING ) );

    return( (int) len );
}


/* This is a copy of the ASN.1 parsing function mbedtls_asn1_find_named_data(),
 * which is replicated to avoid a dependency ASN1_WRITE_C on ASN1_PARSE_C. */
static mbedtls_asn1_named_data *asn1_find_named_data(
                                               mbedtls_asn1_named_data *list,
                                               const char *oid, size_t len )
{
    while( list != NULL )
    {
        if( list->oid.len == len &&
            memcmp( list->oid.p, oid, len ) == 0 )
        {
            break;
        }

        list = list->next;
    }

    return( list );
}

mbedtls_asn1_named_data *mbedtls_asn1_store_named_data(
                                        mbedtls_asn1_named_data **head,
                                        const char *oid, size_t oid_len,
                                        const unsigned char *val,
                                        size_t val_len )
{
    mbedtls_asn1_named_data *cur;

    if( ( cur = asn1_find_named_data( *head, oid, oid_len ) ) == NULL )
    {
        // Add new entry if not present yet based on OID
        //
        cur = (mbedtls_asn1_named_data*)mbedtls_calloc( 1,
                                            sizeof(mbedtls_asn1_named_data) );
        if( cur == NULL )
            return( NULL );

        cur->oid.len = oid_len;
        cur->oid.p = mbedtls_calloc( 1, oid_len );
        if( cur->oid.p == NULL )
        {
            mbedtls_free( cur );
            return( NULL );
        }

        memcpy( cur->oid.p, oid, oid_len );

        cur->val.len = val_len;
        if( val_len != 0 )
        {
            cur->val.p = mbedtls_calloc( 1, val_len );
            if( cur->val.p == NULL )
            {
                mbedtls_free( cur->oid.p );
                mbedtls_free( cur );
                return( NULL );
            }
        }

        cur->next = *head;
        *head = cur;
    }
    else if( val_len == 0 )
    {
        mbedtls_free( cur->val.p );
        cur->val.p = NULL;
    }
    else if( cur->val.len != val_len )
    {
        /*
         * Enlarge existing value buffer if needed
         * Preserve old data until the allocation succeeded, to leave list in
         * a consistent state in case allocation fails.
         */
        void *p = mbedtls_calloc( 1, val_len );
        if( p == NULL )
            return( NULL );

        mbedtls_free( cur->val.p );
        cur->val.p = p;
        cur->val.len = val_len;
    }

    if( val != NULL && val_len != 0 )
        memcpy( cur->val.p, val, val_len );

    return( cur );
}
#endif /* MBEDTLS_ASN1_WRITE_C */