openpgp-php/lib/OpenPgP/Crypt/Symmetric.php

<?php

namespace Leenooks\OpenPGP\Crypt;

use phpseclib\Crypt\AES as Crypt_AES;
use phpseclib\Crypt\Blowfish as Crypt_Blowfish;
use phpseclib\Crypt\TripleDES as Crypt_TripleDES;
use phpseclib\Crypt\Twofish as Crypt_Twofish;
use phpseclib\Crypt\Random;

use Leenooks\OpenPGP;

class Symmetric
{
	protected static $DEBUG = FALSE;

	public static function encrypt($passphrases_and_keys,$message,$symmetric_algorithm=9): OpenPGP\Message
	{
		if (static::$DEBUG)
			dump(['In METHOD: '=>__METHOD__,'passphrases_and_keys'=>$passphrases_and_keys,'symmetric_algorithm'=>$symmetric_algorithm]);

		list($cipher,$key_bytes,$key_block_bytes) = self::getCipher($symmetric_algorithm);
		if (static::$DEBUG)
			dump(['cipher'=>$cipher,'key_bytes'=>$key_bytes,'key_block_bytes'=>$key_block_bytes]);

		if (! $cipher)
			throw new Exception("Unsupported cipher");

		$prefix = Random::string($key_block_bytes);
		$prefix .= substr($prefix, -2);

		$key = Random::string($key_bytes);
		$cipher->setKey($key);

		$to_encrypt = $prefix.$message;

		$mdc = new OpenPGP\ModificationDetectionCodePacket(hash('sha1',$to_encrypt."\xD3\x14",true));
		$to_encrypt .= (string)$mdc;

		if (static::$DEBUG)
			dump(['to_encrypt'=>$to_encrypt]);

		$encrypted = [new OpenPGP\IntegrityProtectedDataPacket($cipher->encrypt($to_encrypt))];

		if (static::$DEBUG)
			dump(['encrypted'=>$encrypted]);

		if (! is_array($passphrases_and_keys) && ! ($passphrases_and_keys instanceof \IteratorAggregate)) {
			$passphrases_and_keys = (array)$passphrases_and_keys;
		}

		if (static::$DEBUG)
			dump(['pk'=>$passphrases_and_keys]);

		foreach ($passphrases_and_keys as $pass) {
			if ($pass instanceof OpenPGP\PublicKeyPacket) {
				if (static::$DEBUG)
					dump(['pass'=>$pass,'instanceof'=>'Leenooks\OpenPGP\PublicKeyPacket']);

				if (! in_array($pass->algorithm,[1,2,3]))
					throw new Exception("Only RSA keys are supported.");

				$crypt_rsa = new RSA($pass);
				$rsa = $crypt_rsa->public_key();

				if (static::$DEBUG)
					dump(['public_key'=>$rsa]);

				$rsa->setEncryptionMode(CRYPT_RSA_ENCRYPTION_PKCS1);
				$esk = $rsa->encrypt(chr($symmetric_algorithm).$key.pack('n', self::checksum($key)));
				$esk = pack('n',OpenPGP::bitlength($esk)).$esk;

				array_unshift($encrypted, new OpenPGP\AsymmetricSessionKeyPacket($pass->algorithm,$pass->fingerprint(),$esk));

			} elseif (is_string($pass)) {
				$s2k = new OpenPGP\S2K(Random::string(8));

				$cipher->setKey($s2k->make_key($pass, $key_bytes));
				$esk = $cipher->encrypt(chr($symmetric_algorithm) . $key);

				array_unshift($encrypted, new OpenPGP\SymmetricSessionKeyPacket($s2k, $esk, $symmetric_algorithm));
			}
		}

		if (static::$DEBUG)
			dump(['Out METHOD: '=>__METHOD__,'encrypted'=>$encrypted,'message'=>(new OpenPGP\Message($encrypted))]);

		return new OpenPGP\Message($encrypted);
	}

	public static function decryptSymmetric($pass,$m)
	{
		$epacket = self::getEncryptedData($m);

		foreach ($m as $p) {
			if ($p instanceof OpenPGP\SymmetricSessionKeyPacket) {
				if (strlen($p->encrypted_data) > 0) {
					list ($cipher,$key_bytes,$key_block_bytes) = self::getCipher($p->symmetric_algorithm);

					if (! $cipher)
						continue;

					$cipher->setKey($p->s2k->make_key($pass, $key_bytes));
					$padAmount = $key_block_bytes - (strlen($p->encrypted_data) % $key_block_bytes);
					$data = substr($cipher->decrypt($p->encrypted_data . str_repeat("\0", $padAmount)), 0, strlen($p->encrypted_data));
					$decrypted = self::decryptPacket($epacket, ord($data[0]), substr($data, 1));

				} else {
					list($cipher,$key_bytes,$key_block_bytes) = self::getCipher($p->symmetric_algorithm);

					$decrypted = self::decryptPacket($epacket,$p->symmetric_algorithm,$p->s2k->make_key($pass,$key_bytes));
				}

				if ($decrypted)
					return $decrypted;
			}
		}

		return NULL; /* If we get here, we failed */
	}

	public static function encryptSecretKey($pass,$packet,$symmetric_algorithm=9)
	{
		$packet = clone $packet; // Do not mutate original
		$packet->s2k_useage = 254;
		$packet->symmetric_algorithm = $symmetric_algorithm;

		list($cipher,$key_bytes,$key_block_bytes) = self::getCipher($packet->symmetric_algorithm);
		if (! $cipher)
			throw new Exception("Unsupported cipher");

		$material = '';
		foreach (OpenPGP\SecretKeyPacket::$secret_key_fields[$packet->algorithm] as $field) {
			$f = $packet->key[$field];
			$material .= pack('n',OpenPGP::bitlength($f)).$f;
			unset($packet->key[$field]);
		}
		$material .= hash('sha1',$material,true);

		$iv = Random::string($key_block_bytes);
		if (! $packet->s2k)
			$packet->s2k = new OpenPGP\S2K(Random::string(8));

		$cipher->setKey($packet->s2k->make_key($pass, $key_bytes));
		$cipher->setIV($iv);
		$packet->encrypted_data = $iv.$cipher->encrypt($material);

		return $packet;
	}

	public static function decryptSecretKey($pass,$packet)
	{
		$packet = clone $packet; // Do not mutate orinigal

		list($cipher,$key_bytes,$key_block_bytes) = self::getCipher($packet->symmetric_algorithm);
		if (! $cipher)
			throw new Exception("Unsupported cipher");

		$cipher->setKey($packet->s2k->make_key($pass, $key_bytes));
		$cipher->setIV(substr($packet->encrypted_data, 0, $key_block_bytes));
		$material = $cipher->decrypt(substr($packet->encrypted_data, $key_block_bytes));

		if ($packet->s2k_useage == 254) {
			$chk = substr($material, -20);
			$material = substr($material, 0, -20);
			if ($chk != hash('sha1', $material, true))
				return NULL;

		} else {
			$chk = unpack('n', substr($material, -2));
			$chk = reset($chk);
			$material = substr($material, 0, -2);

			$mkChk = self::checksum($material);
			if ($chk != $mkChk)
				return NULL;
		}

		$packet->s2k = NULL;
		$packet->s2k_useage = 0;
		$packet->symmetric_algorithm = 0;
		$packet->encrypted_data = NULL;
		$packet->input = $material;
		$packet->key_from_input();
		unset($packet->input);

		return $packet;
	}

	public static function decryptPacket($epacket, $symmetric_algorithm, $key)
	{
		list($cipher,$key_bytes,$key_block_bytes) = self::getCipher($symmetric_algorithm);
		if (! $cipher)
			return NULL;

		$cipher->setKey($key);

		if ($epacket instanceof OpenPGP\IntegrityProtectedDataPacket) {
			$padAmount = $key_block_bytes - (strlen($epacket->data) % $key_block_bytes);
			$data = substr($cipher->decrypt($epacket->data . str_repeat("\0", $padAmount)), 0, strlen($epacket->data));
			$prefix = substr($data, 0, $key_block_bytes + 2);
			$mdc = substr(substr($data, -22, 22), 2);
			$data = substr($data, $key_block_bytes + 2, -22);

			$mkMDC = hash("sha1", $prefix . $data . "\xD3\x14", true);
			if ($mkMDC !== $mdc)
				return false;

			try {
				$msg = OpenPGP\Message::parse($data);

			} catch (Exception $ex) {
				$msg = NULL;
			}

			if ($msg)
				return $msg; /* Otherwise keep trying */

		} else {
			// No MDC mean decrypt with resync
			$iv = substr($epacket->data, 2, $key_block_bytes);
			$edata = substr($epacket->data, $key_block_bytes + 2);
			$padAmount = $key_block_bytes - (strlen($edata) % $key_block_bytes);

			$cipher->setIV($iv);
			$data = substr($cipher->decrypt($edata . str_repeat("\0", $padAmount)), 0, strlen($edata));

			try {
				$msg = OpenPGP\Message::parse($data);

			} catch (Exception $ex) {
				$msg = NULL;
			}

			if ($msg)
				return $msg; /* Otherwise keep trying */
		}

		return NULL; /* Failed */
	}

	public static function getCipher($algo) {
		$cipher = NULL;

		switch($algo) {
			case NULL:
			case 0:
				throw new \Exception("Data is already unencrypted");

			case 2:
				$cipher = new Crypt_TripleDES(Crypt_TripleDES::MODE_CFB);
				$key_bytes = 24;
				$key_block_bytes = 8;
				break;

			case 3:
				if (class_exists('OpenSSLWrapper')) {
					$cipher = new \OpenSSLWrapper("CAST5-CFB");
				} else if(defined('MCRYPT_CAST_128')) {
					$cipher = new \MCryptWrapper(MCRYPT_CAST_128);
				}
				break;

			case 4:
				$cipher = new Crypt_Blowfish(Crypt_Blowfish::MODE_CFB);
				$key_bytes = 16;
				$key_block_bytes = 8;
				break;

			case 7:
				$cipher = new Crypt_AES(Crypt_AES::MODE_CFB);
				$cipher->setKeyLength(128);
				break;

			case 8:
				$cipher = new Crypt_AES(Crypt_AES::MODE_CFB);
				$cipher->setKeyLength(192);
				break;

			case 9:
				$cipher = new Crypt_AES(Crypt_AES::MODE_CFB);
				$cipher->setKeyLength(256);
				break;

			case 10:
				$cipher = new Crypt_Twofish(Crypt_Twofish::MODE_CFB);
				if (method_exists($cipher, 'setKeyLength')) {
					$cipher->setKeyLength(256);
				} else {
					$cipher = NULL;
				}
				break;
		}

		// Unsupported cipher
		if (! $cipher)
			return [NULL,NULL,NULL];

		if (! isset($key_bytes))
			$key_bytes = isset($cipher->key_size)?$cipher->key_size:$cipher->key_length;

		if (! isset($key_block_bytes))
			$key_block_bytes = $cipher->block_size;

		return [$cipher,$key_bytes,$key_block_bytes];
	}

	public static function getEncryptedData($m)
	{
		foreach ($m as $p) {
			if ($p instanceof OpenPGP\EncryptedDataPacket)
				return $p;
		}

		throw new Exception("Can only decrypt EncryptedDataPacket");
	}

	public static function checksum($s) {
		$mkChk = 0;

		for($i = 0; $i < strlen($s); $i++) {
			$mkChk = ($mkChk + ord($s[$i])) % 65536;
		}

		return $mkChk;
	}
}