1 files changed, 17 insertions, 9 deletions
diff --git a/crypto/src/bcpg/UserAttributeSubpacket.cs b/crypto/src/bcpg/UserAttributeSubpacket.cs
index 05f60ac17..246ac0759 100644
--- a/crypto/src/bcpg/UserAttributeSubpacket.cs
+++ b/crypto/src/bcpg/UserAttributeSubpacket.cs
@@ -1,6 +1,7 @@
 using System;
 using System.IO;
 
+using Org.BouncyCastle.Crypto.Utilities;
 using Org.BouncyCastle.Utilities;
 
 namespace Org.BouncyCastle.Bcpg
@@ -43,23 +44,30 @@ namespace Org.BouncyCastle.Bcpg
         {
             int bodyLen = data.Length + 1;
 
-            if (bodyLen < 192 && !longLength)
+            if (longLength || bodyLen > 8383)
             {
+#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+                Span<byte> buf = stackalloc byte[5];
+                buf[0] = 0xFF;
+                Pack.UInt32_To_BE((uint)bodyLen, buf, 1);
+                os.Write(buf);
+#else
+                os.WriteByte(0xff);
+                os.WriteByte((byte)(bodyLen >> 24));
+                os.WriteByte((byte)(bodyLen >> 16));
+                os.WriteByte((byte)(bodyLen >> 8));
                 os.WriteByte((byte)bodyLen);
+#endif
             }
-            else if (bodyLen <= 8383 && !longLength)
+            else if (bodyLen < 192)
             {
-                bodyLen -= 192;
-
-                os.WriteByte((byte)(((bodyLen >> 8) & 0xff) + 192));
                 os.WriteByte((byte)bodyLen);
             }
             else
             {
-                os.WriteByte(0xff);
-                os.WriteByte((byte)(bodyLen >> 24));
-                os.WriteByte((byte)(bodyLen >> 16));
-                os.WriteByte((byte)(bodyLen >> 8));
+                bodyLen -= 192;
+
+                os.WriteByte((byte)(((bodyLen >> 8) & 0xff) + 192));
                 os.WriteByte((byte)bodyLen);
             }