1 files changed, 37 insertions, 17 deletions

diff --git a/crypto/src/asn1/x500/DirectoryString.cs b/crypto/src/asn1/x500/DirectoryString.cs
index a04ed0056..c622113d4 100644
--- a/crypto/src/asn1/x500/DirectoryString.cs
+++ b/crypto/src/asn1/x500/DirectoryString.cs
@@ -11,30 +11,50 @@ namespace Org.BouncyCastle.Asn1.X500
 
 		public static DirectoryString GetInstance(object obj)
 		{
-			if (obj == null || obj is DirectoryString)
-				return (DirectoryString) obj;
-
-            if (obj is DerStringBase)
-			{
-				if (obj is DerT61String
-					|| obj is DerPrintableString
-					|| obj is DerUniversalString
-					|| obj is DerUtf8String
-					|| obj is DerBmpString)
-				{
-					return new DirectoryString((DerStringBase) obj);
-				}
-			}
-
-            throw new ArgumentException("unknown object in factory: " + Platform.GetTypeName(obj), "obj");
-		}
+            if (obj == null)
+                return null;
+
+            if (obj is Asn1Encodable element)
+            {
+                var result = GetOptional(element);
+                if (result != null)
+                    return result;
+            }
+
+            throw new ArgumentException("Invalid object: " + Platform.GetTypeName(obj), nameof(obj));
+        }
 
         public static DirectoryString GetInstance(Asn1TaggedObject obj, bool isExplicit) =>
             Asn1Utilities.GetInstanceChoice(obj, isExplicit, GetInstance);
 
+        public static DirectoryString GetOptional(Asn1Encodable element)
+        {
+            if (element == null)
+                throw new ArgumentNullException(nameof(element));
+
+            if (element is DirectoryString directoryString)
+                return directoryString;
+
+			var innerObject = GetOptionalInnerObject(element);
+			if (innerObject != null)
+				return new DirectoryString(innerObject);
+
+			return null;
+        }
+
         public static DirectoryString GetTagged(Asn1TaggedObject taggedObject, bool declaredExplicit) =>
             Asn1Utilities.GetTaggedChoice(taggedObject, declaredExplicit, GetInstance);
 
+		private static DerStringBase GetOptionalInnerObject(Asn1Encodable element)
+		{
+            return DerT61String.GetOptional(element)
+                ?? DerPrintableString.GetOptional(element)
+                ?? DerUniversalString.GetOptional(element)
+                ?? DerUtf8String.GetOptional(element)
+                ?? DerBmpString.GetOptional(element)
+				?? (DerStringBase)null;
+        }
+
         private DirectoryString(
 			DerStringBase str)
 		{