1 files changed, 39 insertions, 35 deletions

diff --git a/crypto/src/asn1/misc/CAST5CBCParameters.cs b/crypto/src/asn1/misc/CAST5CBCParameters.cs
index 3adafe05f..1dc3dbe39 100644
--- a/crypto/src/asn1/misc/CAST5CBCParameters.cs
+++ b/crypto/src/asn1/misc/CAST5CBCParameters.cs
@@ -1,6 +1,5 @@
 using System;
 
-using Org.BouncyCastle.Asn1;
 using Org.BouncyCastle.Utilities;
 
 namespace Org.BouncyCastle.Asn1.Misc
@@ -8,51 +7,48 @@ namespace Org.BouncyCastle.Asn1.Misc
     public class Cast5CbcParameters
         : Asn1Encodable
     {
-        private readonly DerInteger keyLength;
-        private readonly Asn1OctetString iv;
-
-		public static Cast5CbcParameters GetInstance(
-            object o)
+        public static Cast5CbcParameters GetInstance(object o)
         {
-            if (o is Cast5CbcParameters)
-            {
-                return (Cast5CbcParameters) o;
-            }
-
-			if (o is Asn1Sequence)
-            {
-                return new Cast5CbcParameters((Asn1Sequence) o);
-            }
-
-			throw new ArgumentException("unknown object in Cast5CbcParameters factory");
+            if (o == null)
+                return null;
+            if (o is Cast5CbcParameters cast5CbcParameters)
+                return cast5CbcParameters;
+            return new Cast5CbcParameters(Asn1Sequence.GetInstance(o));
         }
 
-		public Cast5CbcParameters(
-            byte[]	iv,
-            int		keyLength)
+        public static Cast5CbcParameters GetInstance(Asn1TaggedObject taggedObject, bool declaredExplicit)
         {
-            this.iv = new DerOctetString(iv);
-            this.keyLength = new DerInteger(keyLength);
+            return new Cast5CbcParameters(Asn1Sequence.GetInstance(taggedObject, declaredExplicit));
         }
 
-		private Cast5CbcParameters(
-            Asn1Sequence seq)
+        private readonly Asn1OctetString m_iv;
+        private readonly DerInteger m_keyLength;
+
+        private Cast5CbcParameters(Asn1Sequence seq)
         {
-			if (seq.Count != 2)
-				throw new ArgumentException("Wrong number of elements in sequence", "seq");
+            int count = seq.Count, pos = 0;
+            if (count < 1 || count > 2)
+                throw new ArgumentException("Bad sequence size: " + count, nameof(seq));
+
+            m_iv = Asn1Utilities.ReadOptional(seq, ref pos, Asn1OctetString.GetOptional)
+                ?? new DerOctetString(new byte[8]);
+            m_keyLength = DerInteger.GetInstance(seq[pos++]);
 
-			iv = (Asn1OctetString) seq[0];
-            keyLength = (DerInteger) seq[1];
+            if (pos != count)
+                throw new ArgumentException("Unexpected elements in sequence", nameof(seq));
         }
 
-        public Asn1OctetString IV => iv;
+        public Cast5CbcParameters(byte[] iv, int keyLength)
+        {
+            m_iv = new DerOctetString(iv ?? new byte[8]);
+            m_keyLength = new DerInteger(keyLength);
+        }
+
+        public Asn1OctetString IV => m_iv;
 
-        public byte[] GetIV() => Arrays.Clone(iv.GetOctets());
+        public byte[] GetIV() => Arrays.Clone(m_iv.GetOctets());
 
-		public int KeyLength
-		{
-            get { return keyLength.IntValueExact; }
-		}
+        public int KeyLength => m_keyLength.IntValueExact;
 
 		/**
          * Produce an object suitable for an Asn1OutputStream.
@@ -67,7 +63,15 @@ namespace Org.BouncyCastle.Asn1.Misc
          */
         public override Asn1Object ToAsn1Object()
         {
-			return new DerSequence(iv, keyLength);
+            return IsDefaultIV(m_iv)
+                ?  new DerSequence(m_keyLength)
+                :  new DerSequence(m_iv, m_keyLength);
+        }
+
+        private static bool IsDefaultIV(Asn1OctetString iv)
+        {
+            return iv.GetOctetsLength() == 8
+                && Arrays.AreAllZeroes(iv.GetOctets(), 0, 8);
         }
     }
 }