From 95788cc1c63568e026644dacca73d731fe506f05 Mon Sep 17 00:00:00 2001
From: akwizgran <akwizgran@users.sourceforge.net>
Date: Fri, 12 Jul 2013 19:05:27 +0100
Subject: [PATCH] Simplified the KDF implementation, since one iteration is
enough.
We don't need to call HMAC-SHA-384 more than once to get 256 bits of key
material. The code will throw a RuntimeException if CIPHER_KEY_BYTES is
changed in future so that one iteration's no longer enough.
---
.../sf/briar/crypto/CryptoComponentImpl.java | 22 +++++++++----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/briar-core/src/net/sf/briar/crypto/CryptoComponentImpl.java b/briar-core/src/net/sf/briar/crypto/CryptoComponentImpl.java
index b765af8315..6cbf8b2349 100644
--- a/briar-core/src/net/sf/briar/crypto/CryptoComponentImpl.java
+++ b/briar-core/src/net/sf/briar/crypto/CryptoComponentImpl.java
@@ -403,26 +403,26 @@ class CryptoComponentImpl implements CryptoComponent {
throw new IllegalArgumentException();
if(Arrays.equals(secret, BLANK_SECRET))
throw new IllegalArgumentException();
+ // The label must be null-terminated
if(label[label.length - 1] != '\0')
throw new IllegalArgumentException();
+ // Initialise the PRF
Mac prf = new HMac(new SHA384Digest());
KeyParameter k = new KeyParameter(secret);
prf.init(k);
int macLength = prf.getMacSize();
+ // The output of the PRF must be long enough to use as a key
+ if(macLength < CIPHER_KEY_BYTES) throw new RuntimeException();
byte[] mac = new byte[macLength], output = new byte[CIPHER_KEY_BYTES];
+ prf.update((byte) 0); // Counter
+ prf.update(label, 0, label.length); // Null-terminated
byte[] contextBytes = new byte[4];
ByteUtils.writeUint32(context, contextBytes, 0);
- for(int i = 0; i * macLength < CIPHER_KEY_BYTES; i++) {
- prf.update((byte) i); // Counter
- prf.update(label, 0, label.length);
- prf.update(contextBytes, 0, contextBytes.length);
- prf.update((byte) CIPHER_KEY_BYTES); // Output length
- prf.doFinal(mac, 0);
- int bytesNeeded = CIPHER_KEY_BYTES - i * macLength;
- int bytesToUse = Math.min(bytesNeeded, macLength);
- System.arraycopy(mac, 0, output, i * macLength, bytesToUse);
- ByteUtils.erase(mac);
- }
+ prf.update(contextBytes, 0, contextBytes.length);
+ prf.update((byte) CIPHER_KEY_BYTES); // Output length
+ prf.doFinal(mac, 0);
+ System.arraycopy(mac, 0, output, 0, output.length);
+ ByteUtils.erase(mac);
ByteUtils.erase(k.getKey());
return output;
}
--
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