tests/src/asn1_helpers.c

/** \file asn1_helpers.c
 *
 * \brief Helper functions for tests that manipulate ASN.1 data.
 */

/*
 *  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 <test/helpers.h>
#include <test/macros.h>

#if defined(MBEDTLS_ASN1_PARSE_C)

#include <mbedtls/asn1.h>

int mbedtls_test_asn1_skip_integer( unsigned char **p, const unsigned char *end,
                                    size_t min_bits, size_t max_bits,
                                    int must_be_odd )
{
    size_t len;
    size_t actual_bits;
    unsigned char msb;
    TEST_EQUAL( mbedtls_asn1_get_tag( p, end, &len,
                                      MBEDTLS_ASN1_INTEGER ),
                0 );

    /* Check if the retrieved length doesn't extend the actual buffer's size.
     * It is assumed here, that end >= p, which validates casting to size_t. */
    TEST_ASSERT( len <= (size_t)( end - *p) );

    /* Tolerate a slight departure from DER encoding:
     * - 0 may be represented by an empty string or a 1-byte string.
     * - The sign bit may be used as a value bit. */
    if( ( len == 1 && ( *p )[0] == 0 ) ||
        ( len > 1 && ( *p )[0] == 0 && ( ( *p )[1] & 0x80 ) != 0 ) )
    {
        ++( *p );
        --len;
    }
    if( min_bits == 0 && len == 0 )
        return( 1 );
    msb = ( *p )[0];
    TEST_ASSERT( msb != 0 );
    actual_bits = 8 * ( len - 1 );
    while( msb != 0 )
    {
        msb >>= 1;
        ++actual_bits;
    }
    TEST_ASSERT( actual_bits >= min_bits );
    TEST_ASSERT( actual_bits <= max_bits );
    if( must_be_odd )
        TEST_ASSERT( ( ( *p )[len-1] & 1 ) != 0 );
    *p += len;
    return( 1 );
exit:
    return( 0 );
}

#endif /* MBEDTLS_ASN1_PARSE_C */