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* Peer Selector: Make strict order opaque to hash value

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zzz
2009-05-27 16:59:38 +00:00
parent be480d577c
commit 87953c4b93
1 changed files with 22 additions and 2 deletions
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24
router/java/src/net/i2p/router/tunnel/pool/TunnelPeerSelector.java
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@ -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);
}
}