Services/Sync/SimplifiedCrypto: Difference between revisions

Services/Sync/SimplifiedCrypto (view source)

Revision as of 08:48, 9 December 2010

526 bytes removed , 9 December 2010

→‎Deriving encryption and HMAC keys from the Sync Key

Philikon

canmove, Confirmed users

725

edits

@@ Line 42: / Line 42: @@
 First we base32-decode the syncKey from 26 characters to 16 bytes (128 bits). The base32 alphabet is the one specified in [http://tools.ietf.org/html/rfc4648 RFC 4648] except with '''l''' replaced by '''8''' and '''o''' replaced by '''9''':
-       let m = Utils.decodeKeyBase32(syncKey);
+       prk = decodeKeyBase32(syncKey)
-The resulting key is then expanded to an encryption and HMAC key using the algorithm described in [http://tools.ietf.org/html/rfc5869 RFC 5869]
+The resulting key is then expanded to an encryption key T(1) and HMAC key T(2) using the algorithm described in [http://tools.ietf.org/html/rfc5869 RFC 5869]
-      // Our extra input to SHA256-HMAC in generateEntry
-      // This includes the full crypto spec; change this when our algo changes.
-      HMAC_INPUT: "Sync-AES_256_CBC-HMAC256",
-      // Reuse the hasher.
-      let h = Utils.makeHMACHasher();
-      // First key.
-      let u = this.username;
-      let k1 = Utils.makeHMACKey("" + HMAC_INPUT + u + "\x01");
-      let enc = Utils.sha256HMACBytes(m, k1, h);
-      // Second key: depends on the output of the first run.
-      let k2 = Utils.makeHMACKey(enc + HMAC_INPUT + u + "\x02");
-      let hmac = Utils.sha256HMACBytes(m, k2, h);
-enc and hmac are the 256 bit encryption and HMAC keys, respectively.
+      info = "Sync-AES_256_CBC-HMAC256" + username
+      T(1) = HMAC-SHA256(prk, "" + info + 0x01)
+      T(2) = HMAC-SHA256(prk, T(1) + info + 0x02)
 ==== Upgrading existing Sync Keys to the new AES key ====