encrypt.php

<?php
function encrypt( $source, $key ) {

    /* calculate padding ... */
    $pad = 8 - ( strlen( $source ) % 8 );

    /* encrypt using MCrypt ... */
    return base64_encode( mcrypt_encrypt( 
        MCRYPT_DES ,$key, $source . str_repeat( chr( $pad ), $pad ), 
        MCRYPT_MODE_CBC, pack( 
            'c8', 1, 2, 3, 4, 5, 6, 7, 8 
            ) ) );

}

/* max length of key is 8 ... any longer is useless ... */
assert( true, 'sWql7JYSxGRhqgjOfx+9gQ==' == 
    encrypt( '371325751788249', 'SpanDivA' ) 
    );