[Uid] make UUIDv6 always return truly random nodes to prevent leaking the MAC of the host

nicolas-grekas · nicolas-grekas · commit 77c7a3b3917d · 2020-09-28T17:35:30.000+02:00
diff --git a/src/Symfony/Component/Uid/CHANGELOG.md b/src/Symfony/Component/Uid/CHANGELOG.md
@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+5.2.0
+-----
+
+ * made UUIDv6 always return truly random node fields to prevent leaking the MAC of the host
+
 5.1.0
 -----
 
diff --git a/src/Symfony/Component/Uid/Tests/UuidTest.php b/src/Symfony/Component/Uid/Tests/UuidTest.php
@@ -89,6 +89,14 @@ public function testV6()
         $this->assertSame('3499710062d0', $uuid->getNode());
     }
 
+    public function testV6IsRandom()
+    {
+        $uuid1 = Uuid::v6();
+        $uuid2 = Uuid::v6();
+
+        $this->assertNotSame(substr($uuid1, 24), substr($uuid2, 24));
+    }
+
     public function testBinary()
     {
         $uuid = new UuidV4(self::A_UUID_V4);
diff --git a/src/Symfony/Component/Uid/UuidV6.php b/src/Symfony/Component/Uid/UuidV6.php
@@ -14,6 +14,8 @@
 /**
  * A v6 UUID is lexicographically sortable and contains a 60-bit timestamp and 62 extra unique bits.
  *
+ * Unlike UUIDv1, this implementation of UUIDv6 doesn't leak the MAC address of the host.
+ *
  * @experimental in 5.1
  *
  * @author Nicolas Grekas <p@tchwork.com>
@@ -27,6 +29,16 @@ public function __construct(string $uuid = null)
         if (null === $uuid) {
             $uuid = uuid_create(\UUID_TYPE_TIME);
             $this->uid = substr($uuid, 15, 3).substr($uuid, 9, 4).$uuid[0].'-'.substr($uuid, 1, 4).'-6'.substr($uuid, 5, 3).substr($uuid, 18);
+
+            // uuid_create() returns a stable "node" that can leak the MAC of the host, but
+            // UUIDv6 prefers a truly random number here, let's XOR both to preserve the entropy
+
+            $rnd = unpack('N2', hex2bin('00'.substr($uuid, 24, 6)).hex2bin('00'.substr($uuid, 30)));
+
+            $this->uid = substr_replace($this->uid, sprintf('%06x%06x',
+                (random_int(0, 0xffffff) ^ $rnd[1]) | 0x010000,
+                random_int(0, 0xffffff) ^ $rnd[2]
+            ), 24);
         } else {
             parent::__construct($uuid);
         }

Original file line number	Diff line number	Diff line change
`@@ -89,6 +89,14 @@ public function testV6()`
`89`	`89`	`$this->assertSame('3499710062d0', $uuid->getNode());`
`90`	`90`	`}`
`91`	`91`
	`92`	`+ public function testV6IsRandom()`
	`93`	`+ {`
	`94`	`+ $uuid1 = Uuid::v6();`
	`95`	`+ $uuid2 = Uuid::v6();`
	`96`	`+`
	`97`	`+ $this->assertNotSame(substr($uuid1, 24), substr($uuid2, 24));`
	`98`	`+ }`
	`99`	`+`
`92`	`100`	`public function testBinary()`
`93`	`101`	`{`
`94`	`102`	`$uuid = new UuidV4(self::A_UUID_V4);`