<?php
/*******
 * Helper for support of encrypt/decryption-related functionality.
 * @author jacob
 * 
 * NOTE: callers which include/require this class MUST also include/require the following:
 * - [moodle root]/config.php
 * - mod/turningtech/lib.php
 **/

/**
 * decrypt a single string for ResponseWare
 * @param $str the string to decrypt
 * @return string
 */
function decryptResponseWareString($str) {
  if( ! TURNINGTECH_ENABLE_DECRYPTION ) return $str;
  $crunch = new TurningTechEncryptionHelper();
  $crunch->key = base64_decode( 'iZRKTcYfw9G2DGrdymD23w==' );
  $crunch->iv = base64_decode( 'DvNdhsQOmHhMn6ZESNTTlw==' );
  $crunch->mode = MCRYPT_MODE_CBC;
  $crunch->dobase64 = false;
  $crunch->doPKCS5 = true;
  return $crunch->decryptString( $str );
}

/**
 * decrypt a list of strings for ResponseWare
 * @param $strings array
 * @return string array
 */
function decryptResponseWareStrings($strings) {
  if( ! TURNINGTECH_ENABLE_DECRYPTION ) return $strings;
  for($i= 0; $i<count($strings); $i++) {
    $strings[$i] = decryptResponseWareString($strings[$i]);
  }
  return $strings;
}

/**
 * encrypt a single string for ResponseWare
 * @param $str the string to encrypt
 * @return string
 */
function encryptResponseWareString($str) {
  if( ! TURNINGTECH_ENABLE_ENCRYPTION ) return $str;
  $crunch = new TurningTechEncryptionHelper();
  $crunch->key = base64_decode( 'iZRKTcYfw9G2DGrdymD23w==' );
  $crunch->iv = base64_decode( 'DvNdhsQOmHhMn6ZESNTTlw==' );
  $crunch->mode = MCRYPT_MODE_CBC;
  $crunch->dobase64 = false;
  $crunch->doPKCS5 = true;
  return $crunch->encryptString( $str );
}

/**
 * encrypt a list of strings for ResponseWare
 * @param $strings array
 * @return string array
 */
function encryptResponseWareStrings($strings) {
  if( ! TURNINGTECH_ENABLE_ENCRYPTION ) return $strings;
  for($i= 0; $i<count($strings); $i++) {
    $strings[$i] = encryptResponseWareString($strings[$i]);
  }
  return $strings;
}


/**
 * decrypt a single string for Web Services
 * @param $str the string to decrypt
 * @return string
 */
function decryptWebServicesString($str) {
  if( ! TURNINGTECH_ENABLE_DECRYPTION ) return $str;
  $crunch = new TurningTechEncryptionHelper();
  $crunch->key = base64_decode( 'Uepfjci/SJ7t+10kCtn2qA==' );
  $crunch->iv = $crunch->key;
  $crunch->mode = MCRYPT_MODE_ECB;
  return $crunch->decryptString( $str );
}

/**
 * decrypt a list of strings for Web Services
 * @param $strings array
 * @return string array
 */
function decryptWebServicesStrings($strings) {
  if( ! TURNINGTECH_ENABLE_DECRYPTION ) return $strings;
  for($i= 0; $i<count($strings); $i++) {
    $strings[$i] = decryptWebServicesString($strings[$i]);
  }
  return $strings;
}

/**
 * encrypt a single string for Web Services
 * @param $str the string to encrypt
 * @return string
 */
function encryptWebServicesString($str) {
  if( ! TURNINGTECH_ENABLE_ENCRYPTION ) return $str;
  $crunch = new TurningTechEncryptionHelper();
  $crunch->key = base64_decode( 'Uepfjci/SJ7t+10kCtn2qA==' );
  $crunch->iv = $crunch->key;
  $crunch->mode = MCRYPT_MODE_ECB;
  return $crunch->encryptString( $str );
}

/**
 * encrypt a list of strings for Web Services
 * @param $strings array
 * @return string array
 */
function encryptWebServicesStrings($strings) {
  if( ! TURNINGTECH_ENABLE_ENCRYPTION ) return $strings;
  for($i= 0; $i<count($strings); $i++) {
    $strings[$i] = encryptWebServicesString($strings[$i]);
  }
  return $strings;
}


/***
 * utility class that handles AES encryption/encoding
 */
class TurningTechEncryptionHelper {
  
  public $algorithm = MCRYPT_RIJNDAEL_128; // use MCRYPT_RIJNDAEL_128 for AES
  public $algorithm_directory = '';
  public $mode = MCRYPT_MODE_ECB;
  public $mode_directory = '';
  public $dobase64 = true;
  public $doPKCS5 = true;
  public $key = '';
  public $iv = ''; // NOTE: must be the same value for encrypt/decrypt
  
  const ENCRYPT = 1;
  const DECRYPT = 2;
  
  /**
   * decrypt a single string
   * @param $str the string to decrypt
   * @return string
   */
  public function decryptString($str) {
    if( ! TURNINGTECH_ENABLE_DECRYPTION ) return $str;
    return $this->processData( self::DECRYPT, $str );
  }
  
  /**
   * decrypt a list of strings
   * @param $strings array
   * @return string array
   */
  public function decryptStrings($strings) {
    if( ! TURNINGTECH_ENABLE_DECRYPTION ) return $strings;
    for($i= 0; $i<count($strings); $i++) {
      $strings[$i] = $this->decryptString($strings[$i]);
    }
    return $strings;
  }
  
  /**
   * encrypt a single string
   * @param $str the string to encrypt
   * @return string
   */
  public function encryptString($str) {
    if( ! TURNINGTECH_ENABLE_ENCRYPTION ) return $str;
    return $this->processData( self::ENCRYPT, $str );
  }
  
  /**
   * encrypt a list of strings
   * @param $strings array
   * @return string array
   */
  public function encryptStrings($strings) {
    if( ! TURNINGTECH_ENABLE_ENCRYPTION ) return $strings;
    for($i= 0; $i<count($strings); $i++) {
      $strings[$i] = $this->encryptString($strings[$i]);
    }
    return $strings;
  }
  
  /**
   * generic encrypt/decrypt logic
   * @param $direction pass in either self::ENCRYPT or self::DECRYPT
   * @param $str the data to encrypt/decrypt
   * @return string
   */
  protected function processData($direction, $str) {
    if( $direction != self::ENCRYPT && $direction != self::DECRYPT ) throw new TurningTechEncryptionHelperException( 'Unknown encryption request ' . $direction );
    $td = mcrypt_module_open( $this->algorithm, $this->algorithm_directory, $this->mode, $this->mode_directory );
    if( $td != false ) {
      if( $direction == self::ENCRYPT && $this->doPKCS5 ) $str = $this->padWithPKCS5( $str );
      if( $direction == self::DECRYPT && $this->dobase64 ) $str = base64_decode( $str );
      
      $ivsize = mcrypt_enc_get_iv_size( $td );
      if( $this->iv == '' ) $this->iv = mcrypt_create_iv( $ivsize ); // NOTE: must be the same value for encrypt/decrypt
      if( $ivsize != strlen( $this->iv ) ) throw new TurningTechEncryptionHelperException( 'size of given IV ' . strlen( $this->iv ) . ' does not match required size ' . $ivsize );
      
      $keysize = mcrypt_enc_get_key_size( $td );
      if( strlen( $this->key ) > $keysize ) throw new TurningTechEncryptionHelperException( 'size of key ' . strlen( $this->key ) . ' is greater than the maximum allowed size ' . $keysize );
      if( strlen( $this->key ) <= 0 ) throw new TurningTechEncryptionHelperException( 'size of key ' . strlen( $this->key ) . ' is too small' );
      
      $initstatus = mcrypt_generic_init( $td, $this->key, $this->iv );
      if( $initstatus === false || $initstatus < 0 ) throw new TurningTechEncryptionHelperException( 'mcrypt_generic_init() returned error code ' . $initstatus );

      if( $direction == self::ENCRYPT ) {
        $str = mcrypt_generic( $td, $str );
      } elseif( $direction == self::DECRYPT ) {
        $str = mdecrypt_generic( $td, $str );
      }

      if( ! mcrypt_generic_deinit( $td ) ) throw new TurningTechEncryptionHelperException( 'mcrypt_generic_deinit() returned FALSE' );
      //if( mcrypt_module_close( $td ) )  throw new EncryptionHelperException( 'mcrypt_module_close() returned FALSE' );
      mcrypt_module_close( $td ); // it returns false locally, for some unknown reason
      $td = false; // a pointer handling habit :)
      
      if( $direction == self::ENCRYPT && $this->dobase64 ) $str = base64_encode( $str );
      if( $direction == self::DECRYPT && $this->doPKCS5 ) $str = $this->unpadWithPKCS5( $str );
    } else {
      throw new TurningTechEncryptionHelperException( 'mcrypt_module_open() returned FALSE ' );
    }
    return $str;
  }
  
  /**
   * apply PKCS #5 padding to string
   * @param $s the string to pad
   * @return string
   */
  protected function padWithPKCS5( $s ) {
    $blocksize = mcrypt_get_block_size( $this->algorithm, $this->mode );
    $padsize = $blocksize - (strlen( $s ) % $blocksize);
    $s .= str_repeat( chr( $padsize ), $padsize );
    return $s;
  }

  /**
   * remove PKCS #5 padding from string
   * @param $s the string to de-pad
   * @return string
   */
  protected function unpadWithPKCS5( $s ) {
    $ssize = strlen( $s );
    $padsize = ord( $s[$ssize - 1] );
    if( $padsize <= $ssize && strspn( $s, chr( $padsize ), $ssize - $padsize ) == $padsize ) {
      $s = substr( $s, 0, -$padsize );
    }
    return $s;
  }
  
  
}


/**
 * Establish an exception namespace, add output to error_log()
*/
class TurningTechEncryptionHelperException extends Exception {
  public function __tostring() {
    if( TURNINGTECH_ENABLE_ENCRYPTION_EXCEPTIONS_IN_ERROR_LOG ) error_log( $this->getMessage() );
    return parent::__tostring();
  }
}

?>