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source/com/hurlant/crypto/symmetric/IVMode.as

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+/**
+ * IVMode
+ * 
+ * An abstract class for confidentialy modes that rely on an initialization vector.
+ * Copyright (c) 2007 Henri Torgemane
+ * 
+ * See LICENSE.txt for full license information.
+ */
+package com.hurlant.crypto.symmetric
+{
+	import com.hurlant.crypto.prng.Random;
+	import com.hurlant.crypto.tests.TestCase;
+	import com.hurlant.util.Memory;
+	
+	import flash.utils.ByteArray;
+	
+	/**
+	 * An "abtract" class to avoid redundant code in subclasses
+	 */
+	public class IVMode
+	{
+		protected var key:ISymmetricKey;
+		protected var padding:IPad;
+		// random generator used to generate IVs
+		protected var prng:Random;
+		// optional static IV. used for testing only.
+		protected var iv:ByteArray;
+		// generated IV is stored here.
+		protected var lastIV:ByteArray;
+		protected var blockSize:uint;
+		
+		
+		public function IVMode(key:ISymmetricKey, padding:IPad = null) {
+			this.key = key;
+			blockSize = key.getBlockSize();
+			if (padding == null) {
+				padding = new PKCS5(blockSize);
+			}
+			this.padding = padding;
+			
+			prng = new Random;
+			iv = null;
+			lastIV = new ByteArray;
+		}
+		
+		public function getBlockSize():uint {
+			return key.getBlockSize();
+		}
+		public function dispose():void {
+			var i:uint;
+			if (iv != null) {
+				for (i=0;i<iv.length;i++) {
+					iv[i] = prng.nextByte();
+				}
+				iv.length=0;
+				iv = null;
+			}
+			if (lastIV != null) {
+				for (i=0;i<iv.length;i++) {
+					lastIV[i] = prng.nextByte();
+				}
+				lastIV.length=0;
+				lastIV=null;
+			}
+			key.dispose();
+			key = null;
+			padding = null;
+			prng.dispose();
+			prng = null;
+			Memory.gc();
+		}
+		/**
+		 * Optional function to force the IV value.
+		 * Normally, an IV gets generated randomly at every encrypt() call.
+		 * Also, use this to set the IV before calling decrypt()
+		 * (if not set before decrypt(), the IV is read from the beginning of the stream.)
+		 */
+		public function set IV(value:ByteArray):void {
+			iv = value;
+			lastIV.length=0;
+			lastIV.writeBytes(iv);
+		}
+		public function get IV():ByteArray {
+			return lastIV;
+		}
+		
+		protected function getIV4e():ByteArray {
+			var vec:ByteArray = new ByteArray;
+			if (iv) {
+				vec.writeBytes(iv);
+			} else {
+				prng.nextBytes(vec, blockSize);
+			}
+			lastIV.length=0;
+			lastIV.writeBytes(vec);
+			return vec;
+		}
+		protected function getIV4d():ByteArray {
+			var vec:ByteArray = new ByteArray;
+			if (iv) {
+				vec.writeBytes(iv);
+			} else {
+				throw new Error("an IV must be set before calling decrypt()");
+			}
+			return vec;
+		}
+	}
+}