From bb38911dc82fd8ad38bdab4a858737255f8d550e Mon Sep 17 00:00:00 2001
From: akwizgran <akwizgran@users.sourceforge.net>
Date: Fri, 21 Mar 2014 15:04:55 +0000
Subject: [PATCH] SecureRandom impl that XORs the outputs of other impls (not
yet used).
This can be used to combine e.g. the platform's SecureRandom
implementation with our own, so that a weakness in either source doesn't
harm security as long as the other source is strong.
---
.../crypto/CombinedSecureRandom.java | 67 +++++++++++++++++++
1 file changed, 67 insertions(+)
create mode 100644 briar-core/src/org/briarproject/crypto/CombinedSecureRandom.java
diff --git a/briar-core/src/org/briarproject/crypto/CombinedSecureRandom.java b/briar-core/src/org/briarproject/crypto/CombinedSecureRandom.java
new file mode 100644
index 0000000000..7f36bb7c4e
--- /dev/null
+++ b/briar-core/src/org/briarproject/crypto/CombinedSecureRandom.java
@@ -0,0 +1,67 @@
+package org.briarproject.crypto;
+
+import java.security.Provider;
+import java.security.SecureRandom;
+import java.security.SecureRandomSpi;
+
+/**
+ * A {@link java.security.SecureRandom SecureRandom} implementation that
+ * combines the outputs of two or more other implementations using XOR.
+ */
+class CombinedSecureRandom extends SecureRandom {
+
+ private static final long serialVersionUID = -605269609862397104L;
+ private static final Provider PROVIDER = new CombinedProvider();
+
+ CombinedSecureRandom(SecureRandom... randoms) {
+ super(new CombinedSecureRandomSpi(randoms), PROVIDER);
+ }
+
+ private static class CombinedSecureRandomSpi extends SecureRandomSpi {
+
+ private static final long serialVersionUID = 483801767899979081L;
+
+ private final SecureRandom[] randoms;
+
+ private CombinedSecureRandomSpi(SecureRandom... randoms) {
+ if(randoms.length < 2) throw new IllegalArgumentException();
+ this.randoms = randoms;
+ }
+
+ @Override
+ protected byte[] engineGenerateSeed(int numBytes) {
+ byte[] combined = new byte[numBytes];
+ for(SecureRandom random : randoms) {
+ byte[] b = random.generateSeed(numBytes);
+ int length = Math.min(numBytes, b.length);
+ for(int i = 0; i < length; i++)
+ combined[i] = (byte) (combined[i] ^ b[i]);
+ }
+ return combined;
+ }
+
+ @Override
+ protected void engineNextBytes(byte[] b) {
+ byte[] temp = new byte[b.length];
+ for(SecureRandom random : randoms) {
+ random.nextBytes(temp);
+ for(int i = 0; i < b.length; i++)
+ b[i] = (byte) (b[i] ^ temp[i]);
+ }
+ }
+
+ @Override
+ protected void engineSetSeed(byte[] seed) {
+ for(SecureRandom random : randoms) random.setSeed(seed);
+ }
+ }
+
+ private static class CombinedProvider extends Provider {
+
+ private static final long serialVersionUID = -4678501890053703844L;
+
+ private CombinedProvider() {
+ super("Combined", 1.0, "");
+ }
+ }
+}
--
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