/*
 *  RSA/SHA-256 signature verification program
 *
 *  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.
 */

#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif

#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdio.h>
#include <stdlib.h>
#define mbedtls_printf          printf
#define mbedtls_snprintf        snprintf
#define mbedtls_exit            exit
#define MBEDTLS_EXIT_SUCCESS    EXIT_SUCCESS
#define MBEDTLS_EXIT_FAILURE    EXIT_FAILURE
#endif /* MBEDTLS_PLATFORM_C */

#if !defined(MBEDTLS_BIGNUM_C) || !defined(MBEDTLS_RSA_C) ||  \
    !defined(MBEDTLS_SHA256_C) || !defined(MBEDTLS_MD_C) || \
    !defined(MBEDTLS_FS_IO)
int main( void )
{
    mbedtls_printf("MBEDTLS_BIGNUM_C and/or MBEDTLS_RSA_C and/or "
            "MBEDTLS_MD_C and/or "
            "MBEDTLS_SHA256_C and/or MBEDTLS_FS_IO not defined.\n");
    mbedtls_exit( 0 );
}
#else

#include "mbedtls/rsa.h"
#include "mbedtls/md.h"

#include <stdio.h>
#include <string.h>


int main( int argc, char *argv[] )
{
    FILE *f;
    int ret = 1;
    unsigned c;
    int exit_code = MBEDTLS_EXIT_FAILURE;
    size_t i;
    mbedtls_rsa_context rsa;
    unsigned char hash[32];
    unsigned char buf[MBEDTLS_MPI_MAX_SIZE];
    char filename[512];

    mbedtls_rsa_init( &rsa );

    if( argc != 2 )
    {
        mbedtls_printf( "usage: rsa_verify <filename>\n" );

#if defined(_WIN32)
        mbedtls_printf( "\n" );
#endif

        goto exit;
    }

    mbedtls_printf( "\n  . Reading public key from rsa_pub.txt" );
    fflush( stdout );

    if( ( f = fopen( "rsa_pub.txt", "rb" ) ) == NULL )
    {
        mbedtls_printf( " failed\n  ! Could not open rsa_pub.txt\n" \
                "  ! Please run rsa_genkey first\n\n" );
        goto exit;
    }

    if( ( ret = mbedtls_mpi_read_file( &rsa.MBEDTLS_PRIVATE(N), 16, f ) ) != 0 ||
        ( ret = mbedtls_mpi_read_file( &rsa.MBEDTLS_PRIVATE(E), 16, f ) ) != 0 )
    {
        mbedtls_printf( " failed\n  ! mbedtls_mpi_read_file returned %d\n\n", ret );
        fclose( f );
        goto exit;
    }

    rsa.MBEDTLS_PRIVATE(len) = ( mbedtls_mpi_bitlen( &rsa.MBEDTLS_PRIVATE(N) ) + 7 ) >> 3;

    fclose( f );

    /*
     * Extract the RSA signature from the text file
     */
    mbedtls_snprintf( filename, sizeof(filename), "%s.sig", argv[1] );

    if( ( f = fopen( filename, "rb" ) ) == NULL )
    {
        mbedtls_printf( "\n  ! Could not open %s\n\n", filename );
        goto exit;
    }

    i = 0;
    while( fscanf( f, "%02X", (unsigned int*) &c ) > 0 &&
           i < (int) sizeof( buf ) )
        buf[i++] = (unsigned char) c;

    fclose( f );

    if( i != rsa.MBEDTLS_PRIVATE(len) )
    {
        mbedtls_printf( "\n  ! Invalid RSA signature format\n\n" );
        goto exit;
    }

    /*
     * Compute the SHA-256 hash of the input file and
     * verify the signature
     */
    mbedtls_printf( "\n  . Verifying the RSA/SHA-256 signature" );
    fflush( stdout );

    if( ( ret = mbedtls_md_file(
                    mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 ),
                    argv[1], hash ) ) != 0 )
    {
        mbedtls_printf( " failed\n  ! Could not open or read %s\n\n", argv[1] );
        goto exit;
    }

    if( ( ret = mbedtls_rsa_pkcs1_verify( &rsa, MBEDTLS_MD_SHA256,
                                          20, hash, buf ) ) != 0 )
    {
        mbedtls_printf( " failed\n  ! mbedtls_rsa_pkcs1_verify returned -0x%0x\n\n", (unsigned int) -ret );
        goto exit;
    }

    mbedtls_printf( "\n  . OK (the signature is valid)\n\n" );

    exit_code = MBEDTLS_EXIT_SUCCESS;

exit:

    mbedtls_rsa_free( &rsa );

#if defined(_WIN32)
    mbedtls_printf( "  + Press Enter to exit this program.\n" );
    fflush( stdout ); getchar();
#endif

    mbedtls_exit( exit_code );
}
#endif /* MBEDTLS_BIGNUM_C && MBEDTLS_RSA_C && MBEDTLS_SHA256_C &&
          MBEDTLS_FS_IO */