Added the finished first version

- Added lib.php file (function for generating the UUID)
- Added test.php file (file for testing the function)

Author: matiboux

lib.php

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+<?php
+/**
+ * Alternative UUID Generation Script
+ * 
+ * This is an alternative version of a randomly generated UUID, using both the timestamp and pseudo-random bytes.
+ * Maybe I'm wrong about all that but I thought mixing the UUID v1 and v4 methods would make the generated UUID more secure, as it ensures a zero-chance of collision of a single computer and a -really- low chance of collision on multiple computers (because of both probability and time).
+ * The UUID contains 62 randomly generated bits, so there is 2^62 different outcomes for that part of the generated UUID, which means you'd start geeting colisions after about 2^31 generations. That being said, that would only happen if you were able to generate that many UUIDs within 100 nanosecond to 1 microsecond (because the gettimeofday() function used here returns a microsecond-precise timestamp).
+ * 
+ * This generated UUID format is {oooooooo-oooo-Mooo-Nxxx-xxxxxxxxxxxx}, it concatenates:
+ * - o: The current timestamp (60 bits) (time_low, time_mid, time_high)
+ * - M: The version (4 bits)
+ * - N: The variant (2 bits)
+ * - x: Pseudo-random values (62 bits)
+ * 
+ * Based on:
+ * - Code from an UUID v1 Generation script. https://github.com/fredriklindberg/class.uuid.php/blob/c1de11110970c6df4f5d7743a11727851c7e5b5a/class.uuid.php#L220
+ * - Code from an UUID v4 Generation script. https://stackoverflow.com/a/15875555/5255556
+ * 
+ * @author Matiboux <[email protected]>
+ * @link https://github.com/matiboux/Time-Based-Random-UUID
+ * @version 1.0
+ * @return string Returns the generated UUID.
+ */
+function uuid($tp = null) {
+	if(!empty($tp)) {
+		if(is_array($tp)) $time = ($tp['sec'] * 10000000) + ($tp['usec'] * 10);
+		else if(is_numeric($tp)) $time = (int) ($tp * 10000000);
+		else return false;
+	} else $time = (int) (gettimeofday(true) * 10000000);
+	$time += 0x01B21DD213814000;
+	
+	$arr = str_split(dechex($time & 0xffffffff), 4); // time_low (32 bits)
+	$high = intval($time / 0xffffffff);
+	array_push($arr, dechex($high & 0xffff)); // time_mid (16 bits)
+	array_push($arr, dechex(0x4000 | (($high >> 16) & 0x0fff))); // Version (4 bits) + time_high (12 bits)
+	
+	// Variant (2 bits) + Cryptographically Secure Pseudo-Random Bytes (62 bits)
+	if(function_exists('random_bytes')) $random = random_bytes(8);
+	else $random = openssl_random_pseudo_bytes(8);
+	$random[0] = chr(ord($random[0]) & 0x3f | 0x80); // Apply variant: Set the two first bits of the random set to 10.
+	
+	$uuid = vsprintf('%s%s-%s-%s-%s-%s%s%s', array_merge($arr, str_split(bin2hex($random), 4)));
+	return strlen($uuid) == 36 ? $uuid : false;
+}
+?>

test.php

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+<?php
+header('Content-Type: text/plain');
+include 'lib.php';
+
+echo 'Fixed Date (2018-06-27 22:40:00): '; var_dump(uuid(strtotime('2018-06-27 22:25:00')));
+echo 'Right now: '; var_dump(uuid());
+?>