Added support for querying the context's user name and authority. Still working my way up to EncryptMessage.

Contexts/Context.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
+using System.Runtime.InteropServices;
 
 namespace NSspi
 {
@@ -27,6 +28,22 @@ namespace NSspi
 
         public long ContextHandle { get; protected set; }
 
+        public string AuthorityName
+        {
+            get
+            {
+                return QueryContextString( ContextQueryAttrib.Authority );
+            }
+        }
+
+        public string ContextUserName
+        {
+            get
+            {
+                return QueryContextString( ContextQueryAttrib.Names );
+            }
+        }
+
         public void Dispose()
         {
             Dispose( true );
@@ -50,8 +67,79 @@ namespace NSspi
             this.disposed = true;
         }
 
+        /// <summary>
+        /// Encrypts the byte array using the context's session key. The encrypted data is stored in a new
+        /// byte array, which is formatted such that the first four bytes are the original message length 
+        /// as an unsigned integer and the remaining bytes are the encrypted bytes of the original message.
+        /// </summary>
+        /// <param name="input"></param>
+        /// <returns></returns>
         public byte[] Encrypt( byte[] input )
         {
+            // The message is encrypted in place in the buffer we provide to Win32 EncryptMessage
+            return null;
         }
+
+        internal SecPkgContext_Sizes QueryBufferSizes()
+        {
+            SecPkgContext_Sizes sizes = new SecPkgContext_Sizes();
+            long contextHandle = this.ContextHandle;
+            SecurityStatus status;
+
+            status = ContextNativeMethods.QueryContextAttributes_Sizes(
+                ref contextHandle,
+                ContextQueryAttrib.Sizes,
+                ref sizes 
+            );
+
+            if( status != SecurityStatus.OK )
+            {
+                throw new SSPIException( "Failed to query context buffer size attributes", status );
+            }
+
+            return sizes;
+        }
+
+        internal string QueryContextString(ContextQueryAttrib attrib)
+        {
+            SecPkgContext_String stringAttrib;
+            long contextHandle;
+            SecurityStatus status;
+            string result;
+
+            if( attrib != ContextQueryAttrib.Names && attrib != ContextQueryAttrib.Authority )
+            {
+                throw new InvalidOperationException( "QueryContextString can only be used to query context Name and Authority attributes" );
+            }
+
+            stringAttrib = new SecPkgContext_String();
+
+            contextHandle = this.ContextHandle;
+
+            status = ContextNativeMethods.QueryContextAttributes_String(
+                ref contextHandle,
+                attrib,
+                ref stringAttrib
+            );
+
+            
+            if( status == SecurityStatus.Unsupported )
+            {
+                return null;
+            }
+            else if( status == SecurityStatus.OK )
+            {
+                // TODO handle this safely.
+                result = Marshal.PtrToStringUni( stringAttrib.StringResult );
+                ContextNativeMethods.FreeContextBuffer( stringAttrib.StringResult );
+            }
+            else
+            {
+                throw new SSPIException( "Failed to query the context's associated user name", status );
+            }
+
+            return result;
+        }
+        
     }
 }