diff --git a/MatterDotNet/Security/AesCtr.cs b/MatterDotNet/Security/AesCtr.cs
new file mode 100644
index 0000000..d134a2b
--- /dev/null
+++ b/MatterDotNet/Security/AesCtr.cs
@@ -0,0 +1,83 @@
+// MatterDotNet Copyright (C) 2024 
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or any later version.
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY, without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU Affero General Public License for more details.
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using System.Security.Cryptography;
+
+namespace MatterDotNet.Security
+{
+    internal class AesCtr : IDisposable
+    {
+        private const int BLOCK_SIZE = 16;
+        private readonly byte[] counter = new byte[BLOCK_SIZE];
+
+        private readonly ICryptoTransform counterEncryptor;
+        private bool isDisposed;
+
+        public AesCtr(byte[] key, byte[] initialCounter)
+        {
+            this.isDisposed = false;
+
+            SymmetricAlgorithm aes = Aes.Create();
+            aes.Mode = CipherMode.ECB;
+            aes.Padding = PaddingMode.None;
+
+            Buffer.BlockCopy(initialCounter, 0, this.counter, 0, BLOCK_SIZE);
+
+            var zeroIv = new byte[BLOCK_SIZE];
+            this.counterEncryptor = aes.CreateEncryptor(key, zeroIv);
+        }
+
+        public Span<byte> EncryptDecrypt(Span<byte> input)
+        {
+            if (isDisposed)
+                throw new ObjectDisposedException("AES CTR disposed");
+
+            Span<byte> output = new byte[input.Length];
+            int offset = 0, numBytes = input.Length;
+            byte[] block = new byte[BLOCK_SIZE];
+
+            while (numBytes > 0)
+            {
+                this.counterEncryptor.TransformBlock(counter, 0, BLOCK_SIZE, block, 0);
+
+                for (int i = 0; i < BLOCK_SIZE; i++)
+                {
+                    if (++counter[i] != 0)
+                        break;
+                }
+
+                if (numBytes <= BLOCK_SIZE)
+                {
+                    for (int i = 0; i < numBytes; i++)
+                        output[i + offset] = (byte)(input[i + offset] ^ block[i]);
+                    return output;
+                }
+
+                for (int i = 0; i < BLOCK_SIZE; i++)
+                    output[i + offset] = (byte)(input[i + offset] ^ block[i]);
+
+                numBytes -= BLOCK_SIZE;
+                offset += BLOCK_SIZE;
+            }
+            return output;
+        }
+
+        public void Dispose()
+        {
+            if (!isDisposed)
+                this.counterEncryptor?.Dispose();
+
+            isDisposed = true;
+            GC.SuppressFinalize(this);
+        }
+    }
+}
diff --git a/MatterDotNet/Security/Crypto.cs b/MatterDotNet/Security/Crypto.cs
index 3475c5f..04757c3 100644
--- a/MatterDotNet/Security/Crypto.cs
+++ b/MatterDotNet/Security/Crypto.cs
@@ -11,6 +11,7 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 
+using System.Buffers.Binary;
 using System.Security.Cryptography;
 
 namespace MatterDotNet.Security
@@ -56,10 +57,93 @@ public static bool Crypto_AEAD_DecryptVerify(byte[] key, Span<byte> payload, Rea
             }
         }
 
-        public static ReadOnlySpan<byte> Crypto_Privacy_Encrypt(byte[] key, Span<byte> message, byte[] nonce)
+        /// <summary>
+        /// Performs the decryption of message using the key and a nonce; the output is the decryption of message
+        /// </summary>
+        /// <param name="key"></param>
+        /// <param name="message"></param>
+        /// <param name="nonce"></param>
+        /// <returns></returns>
+        public static Span<byte> Crypto_Privacy_Decrypt(byte[] key, Span<byte> message, byte[] nonce)
         {
-            // TODO
-            throw new NotImplementedException();
+            AesCtr ctr = new AesCtr(key, nonce);
+            return ctr.EncryptDecrypt(message);
+        }
+
+        /// <summary>
+        /// Performs the Encryption of message using the key and a nonce; the output is the decryption of message
+        /// </summary>
+        /// <param name="key"></param>
+        /// <param name="message"></param>
+        /// <param name="nonce"></param>
+        /// <returns></returns>
+        public static Span<byte> Crypto_Privacy_Encrypt(byte[] key, Span<byte> message, byte[] nonce)
+        {
+            AesCtr ctr = new AesCtr(key, nonce);
+            return ctr.EncryptDecrypt(message);
+        }
+
+        /// <summary>
+        /// Returns the key of len bits derived from inputKey using the salt and the info; len SHALL be a multiple of 8.
+        /// </summary>
+        /// <param name="inputKey"></param>
+        /// <param name="salt"></param>
+        /// <param name="info"></param>
+        /// <param name="len"></param>
+        /// <returns></returns>
+        public static Span<byte> Crypto_KDF(byte[] inputKey, byte[] salt, byte[] info, int len)
+        {
+            if (len > 256)
+                throw new ArgumentException("This wasn't designed for multiple blocks");
+            int L = len / 8;
+            const int HashLen = 32;
+            byte N = (byte)Math.Ceiling((double)(L / HashLen));
+            byte[] PRK = HKDF_Extract(salt, inputKey);
+            return HMAC_Hash(N, PRK, info);
+        }
+
+        private static byte[] HMAC_Hash(byte T, byte[] PRK, byte[] info)
+        {
+            if (T == 0)
+                return [];
+            byte[] bytes = SpanUtil.Combine(HMAC_Hash((byte)(T - 1), PRK, info), info, [T]);
+            return HMACSHA256.HashData(PRK, bytes);
+        }
+
+        public static byte[] HKDF_Extract(byte[] salt, byte[] IKM)
+        {
+            return HMACSHA256.HashData(salt, IKM);
+        }
+
+        /// <summary>
+        /// Password-based key derivation function to compute a derived key from a cryptographically weak password
+        /// </summary>
+        /// <param name="input"></param>
+        /// <param name="salt"></param>
+        /// <param name="iterations"></param>
+        /// <param name="len">Length in bits</param>
+        /// <returns></returns>
+        /// <exception cref="ArgumentOutOfRangeException"></exception>
+        public static byte[] Crypto_PBKDF(byte[] input, byte[] salt, int iterations, int len)
+        {
+            if (iterations < 1000 || iterations > 100000)
+                throw new ArgumentOutOfRangeException(nameof(iterations));
+            int numBlocks = (int)Math.Ceiling((double)(len / 256));
+            byte[] ret = new byte[len / 8];
+            for (int i = 0; i < numBlocks; i++)
+            {
+                byte[] IntI = new byte[4];
+                BinaryPrimitives.WriteUInt32BigEndian(IntI, (uint)i);
+                Span<byte> T = new byte[32];
+                byte[] U = SpanUtil.Combine(salt, IntI);
+                for (int j = 1; j < iterations; j++)
+                {
+                    U = HMACSHA256.HashData(input, U);
+                    T = SpanUtil.XOR(T, U);
+                }
+                T.CopyTo(ret.AsSpan(i * 32, 32));
+            }
+            return ret;
         }
     }
 }
diff --git a/MatterDotNet/Security/MemoryUtil.cs b/MatterDotNet/Security/SpanUtil.cs
similarity index 70%
rename from MatterDotNet/Security/MemoryUtil.cs
rename to MatterDotNet/Security/SpanUtil.cs
index 058bfc8..4274b4d 100644
--- a/MatterDotNet/Security/MemoryUtil.cs
+++ b/MatterDotNet/Security/SpanUtil.cs
@@ -15,8 +15,20 @@
 
 namespace MatterDotNet.Security
 {
-    internal static class MemoryUtil
+    internal static class SpanUtil
     {
+        public static byte[] Combine(params byte[][] arrays)
+        {
+            byte[] rv = new byte[arrays.Sum(a => a.Length)];
+            int offset = 0;
+            foreach (byte[] array in arrays)
+            {
+                System.Buffer.BlockCopy(array, 0, rv, offset, array.Length);
+                offset += array.Length;
+            }
+            return rv;
+        }
+
         public static Memory<byte> Fill(byte val, int count)
         {
             Memory<byte> ret = new byte[count];
@@ -25,38 +37,38 @@ public static Memory<byte> Fill(byte val, int count)
             return ret;
         }
 
-        public static Memory<byte> PadZeros(Memory<byte> val, int count)
+        public static Span<byte> PadZeros(Span<byte> val, int count)
         {
             if (count <= 0)
                 return val;
             Memory<byte> ret = new byte[val.Length + count];
             if (val.Length > 0)
-                val.CopyTo(ret);
-            return ret;
+                val.CopyTo(ret.Span);
+            return ret.Span;
         }
 
-        public static Memory<byte> LeftShift1(Memory<byte> array)
+        public static Span<byte> LeftShift1(Span<byte> array)
         {
             Memory<byte> ret = new byte[array.Length];
             for (int i = 0; i < ret.Length - 1; i++)
-                ret.Span[i] = (byte)(array.Span[i] << 1 | (array.Span[i + 1] >> 7));
-            ret.Span[ret.Length - 1] = (byte)(array.Span[array.Length - 1] << 1);
-            return ret;
+                ret.Span[i] = (byte)(array[i] << 1 | (array[i + 1] >> 7));
+            ret.Span[ret.Length - 1] = (byte)(array[array.Length - 1] << 1);
+            return ret.Span;
         }
 
-        public static Memory<byte> XOR(Memory<byte> a, Memory<byte> b)
+        public static Span<byte> XOR(Span<byte> a, Span<byte> b)
         {
             if (a.Length != b.Length)
                 throw new ArgumentException("Invalid Byte Array Sizes");
             Memory<byte> ret = new byte[a.Length];
             for (int i = 0; i < a.Length; i++)
-                ret.Span[i] = (byte)(a.Span[i] ^ b.Span[i]);
-            return ret;
+                ret.Span[i] = (byte)(a[i] ^ b[i]);
+            return ret.Span;
         }
 
-        public static byte XOR(Memory<byte> a, byte start)
+        public static byte XOR(Span<byte> a, byte start)
         {
-            foreach (byte b in a.Span)
+            foreach (byte b in a)
                 start ^= b;
             return start;
         }
@@ -71,11 +83,6 @@ public static void Increment(Span<byte> mem)
             }
         }
 
-        public static string Print(Memory<byte> mem)
-        {
-            return Print(mem.Span);
-        }
-
         public static string Print(ReadOnlySpan<byte> span)
         {
             StringBuilder ret = new StringBuilder(span.Length * 3);
@@ -88,7 +95,7 @@ public static string Print(ReadOnlySpan<byte> span)
             return ret.ToString();
         }
 
-        public static Memory<byte> From(string hexString)
+        public static Span<byte> From(string hexString)
         {
             if (hexString.Length % 2 != 0)
                 throw new ArgumentException("Not a hex string");
@@ -97,7 +104,7 @@ public static Memory<byte> From(string hexString)
             for (int index = 0; index < data.Length; index++)
                 data.Span[index] = byte.Parse(hexString.AsSpan(index * 2, 2), NumberStyles.HexNumber, CultureInfo.InvariantCulture);
 
-            return data;
+            return data.Span;
         }
     }
 }
diff --git a/README.md b/README.md
index df960a5..fe2ccf5 100644
--- a/README.md
+++ b/README.md
@@ -1,8 +1,9 @@
+[![Build](https://github.com/SmartHomeOS/MatterDotNet/actions/workflows/dotnet.yml/badge.svg)](https://github.com/SmartHomeOS/MatterDotNet/actions/workflows/dotnet.yml)
 # MatterDotNet
 **Coming Soon** - New implementation in progress
 
 #### What's Working
-* Nothing Yet
+* Some Crypto functions, message framing and QR/PIN parsing
 
 #### Coming Soon
 * Matter 1.3 Standard Implementation