From 87953c4b9374764d80d9843c3b5de65290bbd8b5 Mon Sep 17 00:00:00 2001
From: zzz <zzz@mail.i2p>
Date: Wed, 27 May 2009 16:59:38 +0000
Subject: [PATCH] * Peer Selector: Make strict order opaque to hash value
---
.../tunnel/pool/TunnelPeerSelector.java | 24 +++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/router/java/src/net/i2p/router/tunnel/pool/TunnelPeerSelector.java b/router/java/src/net/i2p/router/tunnel/pool/TunnelPeerSelector.java
index 92e4545171..c515310051 100644
--- a/router/java/src/net/i2p/router/tunnel/pool/TunnelPeerSelector.java
+++ b/router/java/src/net/i2p/router/tunnel/pool/TunnelPeerSelector.java
@@ -11,6 +11,7 @@ import java.util.Set;
import java.util.StringTokenizer;
import net.i2p.I2PAppContext;
+import net.i2p.crypto.SHA256Generator;
import net.i2p.data.DataFormatException;
import net.i2p.data.Hash;
import net.i2p.data.RouterInfo;
@@ -477,6 +478,19 @@ public abstract class TunnelPeerSelector {
Collections.sort(rv, new HashComparator(hash));
}
+ /**
+ * Implement a deterministic comparison that cannot be predicted by
+ * others. A naive implementation (using the distance from a random key)
+ * allows an attacker who runs two routers with hashes far apart
+ * to maximize his chances of those two routers being at opposite
+ * ends of a tunnel.
+ *
+ * Previous:
+ * d(l, h) - d(r, h)
+ *
+ * Now:
+ * d((H(l+h), h) - d(H(r+h), h)
+ */
private class HashComparator implements Comparator {
private Hash _hash;
@@ -484,8 +498,14 @@ public abstract class TunnelPeerSelector {
_hash = h;
}
public int compare(Object l, Object r) {
- BigInteger ll = PeerSelector.getDistance(_hash, (Hash) l);
- BigInteger rr = PeerSelector.getDistance(_hash, (Hash) r);
+ byte[] data = new byte[2*Hash.HASH_LENGTH];
+ System.arraycopy(_hash.getData(), 0, data, Hash.HASH_LENGTH, Hash.HASH_LENGTH);
+ System.arraycopy(((Hash) l).getData(), 0, data, 0, Hash.HASH_LENGTH);
+ Hash lh = SHA256Generator.getInstance().calculateHash(data);
+ System.arraycopy(((Hash) r).getData(), 0, data, 0, Hash.HASH_LENGTH);
+ Hash rh = SHA256Generator.getInstance().calculateHash(data);
+ BigInteger ll = PeerSelector.getDistance(_hash, lh);
+ BigInteger rr = PeerSelector.getDistance(_hash, rh);
return ll.compareTo(rr);
}
}
--
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