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Random: expand on the explanations as to how things work

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This commit is contained in:
terrafrost 2012-12-17 08:41:47 -06:00
parent 885d7e0f24
commit 7f5e9f404a
1 changed files with 16 additions and 1 deletions
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17
phpseclib/Crypt/Random.php
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@ -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);