[freenet-cvs] r15518 - in trunk/freenet/src/freenet: crypt node

[nextgens at freenetproject.org]

Author: nextgens
Date: 2007-10-24 09:19:44 +0000 (Wed, 24 Oct 2007)
New Revision: 15518

Modified:
   trunk/freenet/src/freenet/crypt/DiffieHellman.java
   trunk/freenet/src/freenet/node/FNPPacketMangler.java
Log:
JFK:
	Strengthen the verification of DH parameters.

See http://securitytracker.com/alerts/2005/Aug/1014739.html for details

Modified: trunk/freenet/src/freenet/crypt/DiffieHellman.java
===================================================================
--- trunk/freenet/src/freenet/crypt/DiffieHellman.java	2007-10-24 08:30:18 UTC (rev 15517)
+++ trunk/freenet/src/freenet/crypt/DiffieHellman.java	2007-10-24 09:19:44 UTC (rev 15518)
@@ -6,6 +6,7 @@
 
 package freenet.crypt;
 
+import java.math.BigInteger;
 import java.util.Random;
 import java.util.Stack;
 
@@ -36,6 +37,9 @@
 	private static Object precalcerWaitObj = new Object();
 
 	private static Thread precalcThread;
+	
+	public static final BigInteger MIN_EXPONENTIAL_VALUE = new BigInteger("2").pow(24);
+	public static final BigInteger MAX_EXPONENTIAL_VALUE = group.getP().subtract(MIN_EXPONENTIAL_VALUE);
 
 	static {
 		precalcThread = new PrecalcBufferFill();
@@ -139,10 +143,52 @@
 	private static NativeBigInteger[] genParams() {
 		NativeBigInteger params[] = new NativeBigInteger[2];
 		// Don't need NativeBigInteger?
-		params[0] = new NativeBigInteger(256, r);
-		params[1] = (NativeBigInteger) group.getG().modPow(params[0], group.getP());
+		
+		do {
+			params[0] = new NativeBigInteger(256, r);
+			params[1] = (NativeBigInteger) group.getG().modPow(params[0], group.getP());
+		} while(!DiffieHellman.checkDHExponentialValidity(DiffieHellman.class, params[1]));
+		
 		return params;
 	}
+	
+	/**
+	 * Check the validity of a DH exponential
+	 * 
+	 * @param a BigInteger: The exponential to test
+	 * @return a boolean: whether the DH exponential provided is acceptable or not
+	 * 
+	 * @see http://securitytracker.com/alerts/2005/Aug/1014739.html
+	 */
+	public static boolean checkDHExponentialValidity(Class caller, BigInteger exponential) {
+		int onesCount=0, zerosCount=0;
+		
+		// Ensure that we have at least 16 bits of each gender
+		for(int i=0; i < exponential.bitLength(); i++)
+			if(exponential.testBit(i))
+				onesCount++;
+			else
+				zerosCount++;
+		if((onesCount<16) || (zerosCount<16)) {
+			Logger.error(caller, "The provided exponential contains "+zerosCount+" zeros and "+onesCount+" ones wich is unacceptable!");
+			return false;
+		}
+		
+		//TODO: Shall we test if p-1 = -1 here ?
+		
+		// Ensure that g^x > 2^24
+		if(MIN_EXPONENTIAL_VALUE.compareTo(exponential) > -1) {
+			Logger.error(caller, "The provided exponential is smaller than 2^24 which is unacceptable!");
+			return false;
+		}
+		// Ensure that g^x < (p - 2^24)
+		if(MAX_EXPONENTIAL_VALUE.compareTo(exponential) < 1) {
+			Logger.error(DiffieHellman.class, "The provided exponential is bigger than (p - 2^24) which is unacceptable!");
+			return false;
+		}
+		
+		return true;
+	}
 
 	public static DHGroup getGroup() {
 		return group;

Modified: trunk/freenet/src/freenet/node/FNPPacketMangler.java
===================================================================
--- trunk/freenet/src/freenet/node/FNPPacketMangler.java	2007-10-24 08:30:18 UTC (rev 15517)
+++ trunk/freenet/src/freenet/node/FNPPacketMangler.java	2007-10-24 09:19:44 UTC (rev 15518)
@@ -492,10 +492,10 @@
 		byte[] hisExponential = new byte[DiffieHellman.modulusLengthInBytes()];
 		System.arraycopy(payload, offset, hisExponential, 0, DiffieHellman.modulusLengthInBytes());
 		NativeBigInteger _hisExponential = new NativeBigInteger(1,hisExponential);
-		if(_hisExponential.compareTo(NativeBigInteger.ONE) > 0) {
+		if(DiffieHellman.checkDHExponentialValidity(this.getClass(), _hisExponential)) {
 			sendJFKMessage2(nonceInitiator, hisExponential, pn, replyTo);
 		}else
-			Logger.error(this, "We can't accept the exponential "+pn+" sent us; it's smaller than 1!!");
+			Logger.error(this, "We can't accept the exponential "+pn+" sent us!!");
 
 		long t2=System.currentTimeMillis();
 		if((t2-t1)>500)
@@ -671,8 +671,8 @@
 			return;
 		}
 		
-		if(_hisExponential.compareTo(NativeBigInteger.ONE) < 1) {
-			Logger.error(this, "We can't accept the exponential "+pn+" sent us; it's smaller than 1!!");
+		if(!DiffieHellman.checkDHExponentialValidity(this.getClass(), _hisExponential)) {
+			Logger.error(this, "We can't accept the exponential "+pn+" sent us!!");
 			return;
 		}