From 7f5e9f404a2c03b823d8b62b0fc9aa80732841be Mon Sep 17 00:00:00 2001 From: terrafrost Date: Mon, 17 Dec 2012 08:41:47 -0600 Subject: [PATCH] Random: expand on the explanations as to how things work --- phpseclib/Crypt/Random.php | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/phpseclib/Crypt/Random.php b/phpseclib/Crypt/Random.php index 27be6b4f..557742a3 100644 --- a/phpseclib/Crypt/Random.php +++ b/phpseclib/Crypt/Random.php @@ -105,7 +105,19 @@ function crypt_random_string($length) { // cascade entropy across multiple PHP instances by fixing the session and collecting all // environmental variables, including the previous session data and the current session - // data + // data. + // + // mt_rand seeds itself by looking at the PID and the time, both of which are (relatively) + // easy to guess at. linux uses mouse clicks, keyboard timings, etc, as entropy sources, but + // PHP isn't low level to be able to use those as sources and on a web server there's not likely + // going to be a ton of keyboard or mouse action. web servers do have one thing that we can use + // however. a ton of people visiting the website. obviously you don't want to base your seeding + // soley on parameters a potential attacker sends but (1) not everything in $_SERVER is controlled + // by the user and (2) this isn't just looking at the data sent by the current user - it's based + // on the data sent by all users. one user requests the page and a hash of their info is saved. + // another user visits the page and the serialization of their data is utilized along with the + // server envirnment stuff and a hash of the previous http request data (which itself utilizes + // a hash of the session data before that). static $crypto = false, $v; if ($crypto === false) { // save old session data @@ -166,6 +178,9 @@ function crypt_random_string($length) { $key = pack('H*', sha1($seed . 'A')); $iv = pack('H*', sha1($seed . 'C')); + // ciphers are used as per the nist.gov link below. also, see this link: + // + // http://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator#Designs_based_on_cryptographic_primitives switch (true) { case class_exists('Crypt_AES'): $crypto = new Crypt_AES(CRYPT_AES_MODE_CTR);