Erase keys after using them. (Copies created by ciphers, etc, may

still exist.)

api/net/sf/briar/api/crypto/ErasableKey.java

@@ -4,6 +4,9 @@ import javax.crypto.SecretKey;
 
 public interface ErasableKey extends SecretKey {
 
+	/** Returns a copy of the key. */
+	ErasableKey copy();
+
 	/** Erases the key from memory. */
 	void erase();
 }