From fd9e0cbb0b03c030cc098c58bbf68e533ff08186 Mon Sep 17 00:00:00 2001
From: Peter Dettman <peter.dettman@bouncycastle.org>
Date: Tue, 15 Aug 2023 09:46:51 +0700
Subject: Explicitly set IV to zeros when no ParametersWithIV

---
 crypto/src/crypto/modes/CbcBlockCipher.cs        | 15 +++++++++------
 crypto/src/crypto/parameters/ParametersWithIV.cs |  8 ++++++++
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/crypto/src/crypto/modes/CbcBlockCipher.cs b/crypto/src/crypto/modes/CbcBlockCipher.cs
index 8e2b3c2a4..0423af242 100644
--- a/crypto/src/crypto/modes/CbcBlockCipher.cs
+++ b/crypto/src/crypto/modes/CbcBlockCipher.cs
@@ -1,6 +1,7 @@
 using System;
 
 using Org.BouncyCastle.Crypto.Parameters;
+using Org.BouncyCastle.Utilities;
 
 namespace Org.BouncyCastle.Crypto.Modes
 {
@@ -56,19 +57,21 @@ namespace Org.BouncyCastle.Crypto.Modes
 
             if (parameters is ParametersWithIV ivParam)
             {
-                byte[] iv = ivParam.GetIV();
-
-                if (iv.Length != blockSize)
+                if (ivParam.IVLength != blockSize)
                     throw new ArgumentException("initialisation vector must be the same length as block size");
 
-                Array.Copy(iv, 0, IV, 0, iv.Length);
+                ivParam.CopyIVTo(IV, 0, blockSize);
 
-				parameters = ivParam.Parameters;
+                parameters = ivParam.Parameters;
+            }
+            else
+            {
+                Arrays.Fill(IV, 0x00);
             }
 
 			Reset();
 
-            // if null it's an IV changed only.
+            // if null it's an IV changed only (key is to be reused).
             if (parameters != null)
             {
                 cipher.Init(encrypting, parameters);
diff --git a/crypto/src/crypto/parameters/ParametersWithIV.cs b/crypto/src/crypto/parameters/ParametersWithIV.cs
index c5f04aab1..d33b18c37 100644
--- a/crypto/src/crypto/parameters/ParametersWithIV.cs
+++ b/crypto/src/crypto/parameters/ParametersWithIV.cs
@@ -72,6 +72,14 @@ namespace Org.BouncyCastle.Crypto.Parameters
             m_iv = new byte[ivLength];
         }
 
+        public void CopyIVTo(byte[] buf, int off, int len)
+        {
+            if (m_iv.Length != len)
+                throw new ArgumentOutOfRangeException(nameof(len));
+
+            Array.Copy(m_iv, 0, buf, off, len);
+        }
+
         public byte[] GetIV()
         {
             return (byte[])m_iv.Clone();
-- 
cgit 1.4.1