diff --git a/src/Renci.SshNet/Common/AsyncResult.cs b/src/Renci.SshNet/Common/AsyncResult.cs
index cb8adb0a..c5c643af 100644
--- a/src/Renci.SshNet/Common/AsyncResult.cs
+++ b/src/Renci.SshNet/Common/AsyncResult.cs
@@ -166,7 +166,7 @@ namespace Renci.SshNet.Common
         /// </summary>
         /// <param name="asyncCallback">The async callback.</param>
         /// <param name="state">The state.</param>
-        public AsyncResult(AsyncCallback asyncCallback, Object state)
+        protected AsyncResult(AsyncCallback asyncCallback, Object state)
             : base(asyncCallback, state)
         {
         }
diff --git a/src/Renci.SshNet/Security/Cryptography/CipherDigitalSignature.cs b/src/Renci.SshNet/Security/Cryptography/CipherDigitalSignature.cs
index 921b12ee..88f6ddad 100644
--- a/src/Renci.SshNet/Security/Cryptography/CipherDigitalSignature.cs
+++ b/src/Renci.SshNet/Security/Cryptography/CipherDigitalSignature.cs
@@ -10,7 +10,6 @@ namespace Renci.SshNet.Security.Cryptography
     public abstract class CipherDigitalSignature : DigitalSignature
     {
         private readonly AsymmetricCipher _cipher;
-
         private readonly ObjectIdentifier _oid;
 
         /// <summary>
@@ -18,13 +17,13 @@ namespace Renci.SshNet.Security.Cryptography
         /// </summary>
         /// <param name="oid">The object identifier.</param>
         /// <param name="cipher">The cipher.</param>
-        public CipherDigitalSignature(ObjectIdentifier oid, AsymmetricCipher cipher)
+        protected CipherDigitalSignature(ObjectIdentifier oid, AsymmetricCipher cipher)
         {
             if (cipher == null)
                 throw new ArgumentNullException("cipher");
 
-            this._cipher = cipher;
-            this._oid = oid;
+            _cipher = cipher;
+            _oid = oid;
         }
 
         /// <summary>
@@ -37,8 +36,8 @@ namespace Renci.SshNet.Security.Cryptography
         /// </returns>
         public override bool Verify(byte[] input, byte[] signature)
         {
-            var encryptedSignature = this._cipher.Decrypt(signature);
-            var hashData = this.Hash(input);
+            var encryptedSignature = _cipher.Decrypt(signature);
+            var hashData = Hash(input);
             var expected = DerEncode(hashData);
             return expected.SequenceEqual(encryptedSignature);
         }
@@ -53,12 +52,12 @@ namespace Renci.SshNet.Security.Cryptography
         public override byte[] Sign(byte[] input)
         {
             //  Calculate hash value
-            var hashData = this.Hash(input);
+            var hashData = Hash(input);
 
             //  Calculate DER string
             var derEncodedHash = DerEncode(hashData);
 
-            return this._cipher.Encrypt(derEncodedHash).TrimLeadingZero().ToArray();
+            return _cipher.Encrypt(derEncodedHash).TrimLeadingZero().ToArray();
         }
 
         /// <summary>
@@ -75,15 +74,13 @@ namespace Renci.SshNet.Security.Cryptography
         /// <returns>DER Encoded byte array</returns>
         protected byte[] DerEncode(byte[] hashData)
         {
-            var data = new DerData();
-
             var alg = new DerData();
-            alg.Write(this._oid);
+            alg.Write(_oid);
             alg.WriteNull();
 
+            var data = new DerData();
             data.Write(alg);
             data.Write(hashData);
-
             return data.Encode();
         }
     }
diff --git a/src/Renci.SshNet/Security/Cryptography/Key.cs b/src/Renci.SshNet/Security/Cryptography/Key.cs
index c13ede0e..5cf42187 100644
--- a/src/Renci.SshNet/Security/Cryptography/Key.cs
+++ b/src/Renci.SshNet/Security/Cryptography/Key.cs
@@ -40,7 +40,7 @@ namespace Renci.SshNet.Security
         /// Initializes a new instance of the <see cref="Key"/> class.
         /// </summary>
         /// <param name="data">DER encoded private key data.</param>
-        public Key(byte[] data)
+        protected Key(byte[] data)
         {
             if (data == null)
                 throw new ArgumentNullException("data");
@@ -54,13 +54,13 @@ namespace Renci.SshNet.Security
                 keys.Add(der.ReadBigInteger());
             }
 
-            this._privateKey = keys.ToArray();
+            _privateKey = keys.ToArray();
         }
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Key"/> class.
         /// </summary>
-        public Key()
+        protected Key()
         {
         }
 
@@ -73,7 +73,7 @@ namespace Renci.SshNet.Security
         /// </returns>
         public byte[] Sign(byte[] data)
         {
-            return this.DigitalSignature.Sign(data);
+            return DigitalSignature.Sign(data);
         }
 
         /// <summary>
@@ -84,7 +84,7 @@ namespace Renci.SshNet.Security
         /// <returns><c>True</c> is signature was successfully verifies; otherwise <c>false</c>.</returns>
         public bool VerifySignature(byte[] data, byte[] signature)
         {
-            return this.DigitalSignature.Verify(data, signature);
+            return DigitalSignature.Verify(data, signature);
         }
     }
 }