/**
* Decrypt the contents of a file handle $inputHandle and store the results
* in $outputHandle using HKDF of $key to decrypt then verify
*
* @param resource $inputHandle
* @param resource $outputHandle
* @param Key $key
* @return boolean
*/
public static function decryptResource($inputHandle, $outputHandle, Key $key)
{
// Because we don't have strict typing in PHP 5
if (!\is_resource($inputHandle)) {
throw new Ex\InvalidInput('Input handle must be a resource!');
}
if (!\is_resource($outputHandle)) {
throw new Ex\InvalidInput('Output handle must be a resource!');
}
// Parse the header.
$header = self::readBytes($inputHandle, Core::HEADER_VERSION_SIZE);
$config = self::getFileVersionConfigFromHeader($header, Core::CURRENT_FILE_VERSION);
// Let's add this check before anything
if (!\in_array($config->hashFunctionName(), \hash_algos())) {
throw new Ex\CannotPerformOperationException('The specified hash function does not exist');
}
// Let's grab the file salt.
$file_salt = self::readBytes($inputHandle, $config->saltByteSize());
// For storing MACs of each buffer chunk
$macs = [];
/**
* 1. We need to decode some values from our files
*/
/**
* Let's split our keys
*
* $ekey -- Encryption Key -- used for AES
*/
$ekey = Core::HKDF($config->hashFunctionName(), $key->getRawBytes(), $config->keyByteSize(), $config->encryptionInfoString(), $file_salt, $config);
/**
* $akey -- Authentication Key -- used for HMAC
*/
$akey = Core::HKDF($config->hashFunctionName(), $key->getRawBytes(), $config->keyByteSize(), $config->authenticationInfoString(), $file_salt, $config);
/**
* Grab our IV from the encrypted message
*
* It should be the first N blocks of the file (N = 16)
*/
$ivsize = \openssl_cipher_iv_length($config->cipherMethod());
$iv = self::readBytes($inputHandle, $ivsize);
// How much do we increase the counter after each buffered encryption to prevent nonce reuse
$inc = $config->bufferByteSize() / $config->blockByteSize();
$thisIv = $iv;
/**
* Let's grab our MAC
*
* It should be the last N blocks of the file (N = 32)
*/
if (\fseek($inputHandle, -1 * $config->macByteSize(), SEEK_END) === false) {
throw new Ex\CannotPerformOperationException('Cannot seek to beginning of MAC within input file');
}
// Grab our last position of ciphertext before we read the MAC
$cipher_end = \ftell($inputHandle);
if ($cipher_end === false) {
throw new Ex\CannotPerformOperationException('Cannot read input file');
}
--$cipher_end;
// We need to subtract one
// We keep our MAC stored in this variable
$stored_mac = self::readBytes($inputHandle, $config->macByteSize());
/**
* We begin recalculating the HMAC for the entire file...
*/
$hmac = \hash_init($config->hashFunctionName(), HASH_HMAC, $akey);
if ($hmac === false) {
throw new Ex\CannotPerformOperationException('Cannot initialize a hash context');
}
/**
* Reset file pointer to the beginning of the file after the header
*/
if (\fseek($inputHandle, Core::HEADER_VERSION_SIZE, SEEK_SET) === false) {
throw new Ex\CannotPerformOperationException('Cannot read seek within input file');
}
/**
* Set it to the first non-salt and non-IV byte
*/
if (\fseek($inputHandle, $config->saltByteSize() + $ivsize, SEEK_CUR) === false) {
throw new Ex\CannotPerformOperationException('Cannot read seek input file to beginning of ciphertext');
}
/**
* 2. Let's recalculate the MAC
*/
/**
* Let's initialize our $hmac hasher with our Salt and IV
*/
\hash_update($hmac, $header);
\hash_update($hmac, $file_salt);
\hash_update($hmac, $iv);
$hmac2 = \hash_copy($hmac);
$break = false;
while (!$break) {
/**
* First, grab the current position
*/
$pos = \ftell($inputHandle);
if ($pos === false) {
throw new Ex\CannotPerformOperationException('Could not get current position in input file during decryption');
}
/**
* Would a full DBUFFER read put it past the end of the
* ciphertext? If so, only return a portion of the file.
*/
if ($pos + $config->bufferByteSize() >= $cipher_end) {
$break = true;
$read = self::readBytes($inputHandle, $cipher_end - $pos + 1);
} else {
$read = self::readBytes($inputHandle, $config->bufferByteSize());
}
if ($read === false) {
throw new Ex\CannotPerformOperationException('Could not read input file during decryption');
}
/**
* We're updating our HMAC and nothing else
*/
\hash_update($hmac, $read);
/**
* Store a MAC of each chunk
*/
$chunkMAC = \hash_copy($hmac);
if ($chunkMAC === false) {
throw new Ex\CannotPerformOperationException('Cannot duplicate a hash context');
}
$macs[] = \hash_final($chunkMAC);
}
/**
* We should now have enough data to generate an identical HMAC
*/
$finalHMAC = \hash_final($hmac, true);
/**
* 3. Did we match?
*/
if (!Core::hashEquals($finalHMAC, $stored_mac)) {
throw new Ex\InvalidCiphertextException('Message Authentication failure; tampering detected.');
}
/**
* 4. Okay, let's begin decrypting
*/
/**
* Return file pointer to the first non-header, non-IV byte in the file
*/
if (\fseek($inputHandle, $config->saltByteSize() + $ivsize + Core::HEADER_VERSION_SIZE, SEEK_SET) === false) {
throw new Ex\CannotPerformOperationException('Could not move the input file pointer during decryption');
}
/**
* Should we break the writing?
*/
$breakW = false;
/**
* This loop writes plaintext to the destination file:
*/
while (!$breakW) {
/**
* Get the current position
*/
$pos = \ftell($inputHandle);
if ($pos === false) {
throw new Ex\CannotPerformOperationException('Could not get current position in input file during decryption');
}
/**
* Would a full BUFFER read put it past the end of the
* ciphertext? If so, only return a portion of the file.
*/
if ($pos + $config->bufferByteSize() >= $cipher_end) {
$breakW = true;
$read = self::readBytes($inputHandle, $cipher_end - $pos + 1);
} else {
$read = self::readBytes($inputHandle, $config->bufferByteSize());
}
/**
* Recalculate the MAC, compare with the one stored in the $macs
* array to ensure attackers couldn't tamper with the file
* after MAC verification
*/
\hash_update($hmac2, $read);
$calcMAC = \hash_copy($hmac2);
if ($calcMAC === false) {
throw new Ex\CannotPerformOperationException('Cannot duplicate a hash context');
}
$calc = \hash_final($calcMAC);
if (empty($macs)) {
throw new Ex\InvalidCiphertextException('File was modified after MAC verification');
} elseif (!Core::hashEquals(\array_shift($macs), $calc)) {
throw new Ex\InvalidCiphertextException('File was modified after MAC verification');
}
$thisIv = Core::incrementCounter($thisIv, $inc, $config);
/**
* Perform the AES decryption. Decrypts the message.
*/
$decrypted = \openssl_decrypt($read, $config->cipherMethod(), $ekey, OPENSSL_RAW_DATA, $thisIv);
/**
* Test for decryption faulure
*/
if ($decrypted === false) {
throw new Ex\CannotPerformOperationException('OpenSSL decryption error');
}
/**
* Write the plaintext out to the output file
*/
self::writeBytes($outputHandle, $decrypted, Core::ourStrlen($decrypted));
}
return true;
}
