xxtea可逆加密算法PHP实现：

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Class Xxtea {
	public function encrypt($s, $key) {
		return base64_encode(self :: xxtea_encrypt($s, $key));
	}
	public function decrypt($e, $key) {
		return self :: xxtea_decrypt(base64_decode($e), $key);
	}
	private function long2str($v, $w) {
		$len = count($v);
		$n = ($len -1) << 2;
		if ($w) {
			$m = $v[$len -1];
			if (($m < $n -3) || ($m > $n))
				return false;
			$n = $m;
		}
		$s = array ();
		for ($i = 0; $i < $len; $i++) {
			$s[$i] = pack("V", $v[$i]);
		}
		if ($w) {
			return substr(join('', $s), 0, $n);
		} else {
			return join('', $s);
		}
	}
	private function str2long($s, $w) {
		$v = unpack("V*", $s . str_repeat("\0", (4 - strlen($s) % 4) & 3));
		$v = array_values($v);
		if ($w) {
			$v[count($v)] = strlen($s);
		}
		return $v;
	}
	private function int32($n) {
		while ($n >= 2147483648)
			$n -= 4294967296;
		while ($n <= -2147483649)
			$n += 4294967296;
		return (int) $n;
	}
	private function xxtea_encrypt($str, $key) {
		if ($str == "") {
			return "";
		}
		$v = self :: str2long($str, true);
		$k = self :: str2long($key, false);
		if (count($k) < 4) {
			for ($i = count($k); $i < 4; $i++) {
				$k[$i] = 0;
			}
		}
		$n = count($v) - 1;
		$z = $v[$n];
		$y = $v[0];
		$delta = 0x9E3779B9;
		$q = floor(6 + 52 / ($n +1));
		$sum = 0;

		while (0 < $q--) {
			$sum = self :: int32($sum + $delta);
			$e = $sum >> 2 & 3;
			for ($p = 0; $p < $n; $p++) {
				$y = $v[$p +1];
				$mx = self :: int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self :: int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
				$z = $v[$p] = self :: int32($v[$p] + $mx);
			}
			$y = $v[0];
			$mx = self :: int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self :: int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
			$z = $v[$n] = self :: int32($v[$n] + $mx);
		}
		return self :: long2str($v, false);
	}
	private function xxtea_decrypt($str, $key) {
		if ($str == "") {
			return "";
		}
		$v = self :: str2long($str, false);
		$k = self :: str2long($key, false);
		if (count($k) < 4) {
			for ($i = count($k); $i < 4; $i++) {
				$k[$i] = 0;
			}
		}
		$n = count($v) - 1;

		$z = $v[$n];
		$y = $v[0];
		$delta = 0x9E3779B9;
		$q = floor(6 + 52 / ($n +1));
		$sum = self :: int32($q * $delta);

		while ($sum != 0) {
			$e = $sum >> 2 & 3;
			for ($p = $n; $p > 0; $p--) {
				$z = $v[$p -1];
				$mx = self :: int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self :: int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
				$y = $v[$p] = self :: int32($v[$p] - $mx);
			}
			$z = $v[$n];
			$mx = self :: int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self :: int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
			$y = $v[0] = self :: int32($v[0] - $mx);
			$sum = self :: int32($sum - $delta);
		}
		return self :: long2str($v, true);
	}
}

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使用方法：

加密：

Xxtea::encrypt(明文字符串, 密钥字符串);

解密：

Xxtea::decrypt(密文字符串, 密钥字符串);

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