PhutilOpaqueEnvelope.php
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	<?php

	/**
	* Opaque reference to a string (like a password) that won't put any sensitive
	* data in stack traces, var_dump(), print_r(), error logs, etc. Usage:
	*
	* $envelope = new PhutilOpaqueEnvelope($password);
	* do_stuff($envelope);
	* // ...
	* $password = $envelope->openEnvelope();
	*
	* Any time you're passing sensitive data into a stack, you should obscure it
	* with an envelope to prevent it leaking if something goes wrong.
	*
	* The key for the envelope is stored elsewhere, in
	* @{class:PhutilOpaqueEnvelopeKey}. This prevents it from appearing in
	* any sort of logs related to the envelope, even if the logger is very
	* aggressive.
	*
	* @task envelope Using Opaque Envelopes
	* @task internal Internals
	*/
	final class PhutilOpaqueEnvelope {

	private $value;


	/* -( Using Opaque Envelopes )--------------------------------------------- */


	/**
	* @task envelope
	*/
	public function __construct($string) {
	$this->value = $this->mask($string, PhutilOpaqueEnvelopeKey::getKey());
	}


	/**
	* @task envelope
	*/
	public function openEnvelope() {
	return $this->mask($this->value, PhutilOpaqueEnvelopeKey::getKey());
	}


	/**
	* @task envelope
	*/
	public function __toString() {
	return '<opaque envelope>';
	}


	/* -( Internals )---------------------------------------------------------- */


	/**
	* @task internal
	*/
	private function mask($string, $noise) {
	$result = '';
	for ($ii = 0; $ii < strlen($string); $ii++) {
	$s = $string[$ii];
	$n = $noise[$ii % strlen($noise)];

	$result .= chr(ord($s) ^ ord($n));
	}
	return $result;
	}

	}