hotp.php

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<?php
class HOTP {
    public static function generateByCounter( $key, $counter ) {
        // the counter value can be more than one byte long,
        // so we need to pack it down properly.
        $cur_counter = array( 0, 0, 0, 0, 0, 0, 0, 0 );
        for ( $i = 7; $i >= 0; $i-- ) {
            $cur_counter[$i] = pack( 'C*', $counter );
            $counter = $counter >> 8;
        }
 
        $bin_counter = implode( $cur_counter );
 
        // Pad to 8 chars
        if ( strlen( $bin_counter ) < 8 ) {
            $bin_counter = str_repeat( "\0", 8 - strlen( $bin_counter ) ) . $bin_counter;
        }
 
        // HMAC
        $hash = hash_hmac( 'sha1', $bin_counter, $key );
 
        return new HOTPResult( $hash );
    }
 
    public static function generateByTime( $key, $window, $timestamp = false ) {
        if ( !$timestamp && $timestamp !== 0 ) {
            $timestamp = HOTP::getTime();
        }
 
        $counter = (int)( $timestamp / $window );
 
        return HOTP::generateByCounter( $key, $counter );
    }
 
    public static function generateByTimeWindow( $key, $window, $min = -1,
        $max = 1, $timestamp = false
    ) {
        if ( !$timestamp && $timestamp !== 0 ) {
            $timestamp = HOTP::getTime();
        }
 
        $counter = (int)( $timestamp / $window );
        $window = range( $min, $max );
 
        $out = array();
        $length = count( $window );
        for ( $i = 0; $i < $length; $i++ ) {
            $shift_counter = $counter + $window[$i];
            $out[$shift_counter] = HOTP::generateByCounter($key, $shift_counter);
        }
 
        return $out;
    }
 
    public static function getTime() {
        return time(); // PHP's time is always UTC
    }
}
 
class HOTPResult {
    protected $hash;
    protected $binary;
    protected $decimal;
    protected $hex;
 
    public function __construct( $value ) {
        // store raw
        $this->hash = $value;
 
        // store calculate decimal
        $hmac_result = array();
 
        // Convert to decimal
        foreach ( str_split( $this->hash, 2 ) as $hex ) {
            $hmac_result[] = hexdec($hex);
        }
 
        $offset = $hmac_result[19] & 0xf;
 
        $this->decimal = (
            ( ( $hmac_result[$offset+0] & 0x7f ) << 24 ) |
            ( ( $hmac_result[$offset+1] & 0xff ) << 16 ) |
            ( ( $hmac_result[$offset+2] & 0xff ) << 8 ) |
            ( $hmac_result[$offset+3] & 0xff )
        );
 
        // calculate hex
        $this->hex = dechex( $this->decimal );
    }
 
    public function toString() {
        return $this->hash;
    }
 
    public function toHex() {
        return $this->hex;
    }
 
    public function toDec() {
        return $this->decimal;
    }
 
    public function toHOTP( $length ) {
        $str = str_pad( $this->toDec(), $length, "0", STR_PAD_LEFT );
        $str = substr( $str, ( -1 * $length ) );
 
        return $str;
    }
 
}