C# Signature:

[DllImport("secur32.dll", SetLastError=true)]
static extern int InitializeSecurityContext(ref SECURITY_HANDLE phCredential,//PCredHandle
    IntPtr phContext, //PCtxtHandle
    string pszTargetName,
    int fContextReq,
    int Reserved1,
    int TargetDataRep,
    IntPtr pInput, //PSecBufferDesc SecBufferDesc
    int Reserved2,
    out SECURITY_HANDLE phNewContext, //PCtxtHandle
    out SecBufferDesc pOutput, //PSecBufferDesc SecBufferDesc
    out uint pfContextAttr, //managed ulong == 64 bits!!!
    out SECURITY_INTEGER ptsExpiry); //PTimeStamp

VB Signature:

Declare Function InitializeSecurityContext Lib "secur32.dll" (TODO) As TODO

User-Defined Types:

None.

Notes:

Check out complete program below....

Contributed by http://dotnetjunkies.com/weblog/dotnetruminator

Tips & Tricks:

Please add some!

Sample Code:

#region Using directives

using System;
using System.Text;

#endregion

using System.Collections;
using System.Security.Principal;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Net.Sockets;
using TestMe;

using HANDLE = System.IntPtr;

public enum SecBufferType
{
    SECBUFFER_VERSION = 0,
    SECBUFFER_EMPTY = 0,
    SECBUFFER_DATA = 1,
    SECBUFFER_TOKEN = 2
}

[StructLayout(LayoutKind.Sequential)]
public struct SecHandle //=PCtxtHandle
{
    uint dwLower;
    uint dwUpper;
}

[StructLayout(LayoutKind.Sequential)]
public struct SecBuffer :  IDisposable
{
    public int cbBuffer;
    public int BufferType;
    public IntPtr pvBuffer;


    public SecBuffer(int bufferSize)
    {
    cbBuffer = bufferSize;
    BufferType = (int)SecBufferType.SECBUFFER_TOKEN;
    pvBuffer = Marshal.AllocHGlobal(bufferSize);
    }

    public SecBuffer(byte[] secBufferBytes)
    {
        cbBuffer = secBufferBytes.Length;
        BufferType = (int)SecBufferType.SECBUFFER_TOKEN;
        pvBuffer = Marshal.AllocHGlobal(cbBuffer);
        Marshal.Copy(secBufferBytes,0,pvBuffer,cbBuffer);
    }

    public SecBuffer(byte[] secBufferBytes,SecBufferType bufferType)
    {
        cbBuffer = secBufferBytes.Length;
        BufferType = (int)bufferType;
        pvBuffer = Marshal.AllocHGlobal(cbBuffer);
        Marshal.Copy(secBufferBytes,0,pvBuffer,cbBuffer);
    }

    public void Dispose()
    {
        if(pvBuffer != IntPtr.Zero)
        {
            Marshal.FreeHGlobal(pvBuffer);
            pvBuffer = IntPtr.Zero;
        }
    }
}

public struct MultipleSecBufferHelper
{
    public byte[] Buffer;
    public SecBufferType BufferType;

    public MultipleSecBufferHelper(byte[] buffer,SecBufferType bufferType)
    {
        if(buffer == null || buffer.Length == 0)
        {
            throw new ArgumentException("buffer cannot be null or 0 length");
        }

        Buffer = buffer;
        BufferType = bufferType;
    }
};

[StructLayout(LayoutKind.Sequential)]
public struct SecBufferDesc : IDisposable
{

    public int ulVersion;
    public int cBuffers;
    public IntPtr pBuffers; //Point to SecBuffer

    public SecBufferDesc(int bufferSize)
    {
    ulVersion = (int)SecBufferType.SECBUFFER_VERSION;
    cBuffers = 1;
        SecBuffer ThisSecBuffer = new SecBuffer(bufferSize);
    pBuffers = Marshal.AllocHGlobal(Marshal.SizeOf(ThisSecBuffer));
    Marshal.StructureToPtr(ThisSecBuffer,pBuffers,false);
    }

    public SecBufferDesc(byte[] secBufferBytes)
    {
        ulVersion = (int)SecBufferType.SECBUFFER_VERSION;
        cBuffers = 1;
        SecBuffer ThisSecBuffer = new SecBuffer(secBufferBytes);
        pBuffers = Marshal.AllocHGlobal(Marshal.SizeOf(ThisSecBuffer));
        Marshal.StructureToPtr(ThisSecBuffer,pBuffers,false);
    }

    public SecBufferDesc(MultipleSecBufferHelper[] secBufferBytesArray)
    {
        if(secBufferBytesArray == null || secBufferBytesArray.Length == 0)
        {
            throw new ArgumentException("secBufferBytesArray cannot be null or 0 length");
        }

        ulVersion = (int)SecBufferType.SECBUFFER_VERSION;
        cBuffers = secBufferBytesArray.Length;

        //Allocate memory for SecBuffer Array....
        pBuffers = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(SecBuffer)) * cBuffers);

        for(int Index = 0;Index < secBufferBytesArray.Length;Index++)
        {
            //Super hack: Now allocate memory for the individual SecBuffers
            //and just copy the bit values to the SecBuffer array!!!
            SecBuffer ThisSecBuffer = new SecBuffer(secBufferBytesArray[Index].Buffer,secBufferBytesArray[Index].BufferType);

            //We will write out bits in the following order:
            //int cbBuffer;
            //int BufferType;
            //pvBuffer;
            //Note that we won't be releasing the memory allocated by ThisSecBuffer until we
            //are disposed...
            int CurrentOffset = Index*Marshal.SizeOf(typeof(SecBuffer));
            Marshal.WriteInt32(pBuffers,CurrentOffset,ThisSecBuffer.cbBuffer);    
            Marshal.WriteInt32(pBuffers,CurrentOffset + Marshal.SizeOf(ThisSecBuffer.cbBuffer),ThisSecBuffer.BufferType);
            Marshal.WriteIntPtr(pBuffers,CurrentOffset + Marshal.SizeOf(ThisSecBuffer.cbBuffer)+Marshal.SizeOf(ThisSecBuffer.BufferType),ThisSecBuffer.pvBuffer);
        }
    }

    public void Dispose()
    {
        if(pBuffers != IntPtr.Zero)
        {
            if(cBuffers == 1)
            {
                SecBuffer ThisSecBuffer = (SecBuffer)Marshal.PtrToStructure(pBuffers,typeof(SecBuffer));
                ThisSecBuffer.Dispose();
            }
            else
            {
                for(int Index = 0;Index < cBuffers;Index++)
                {
                    //The bits were written out the following order:
                    //int cbBuffer;
                    //int BufferType;
                    //pvBuffer;
                    //What we need to do here is to grab a hold of the pvBuffer allocate by the individual
                    //SecBuffer and release it...
                    int CurrentOffset = Index*Marshal.SizeOf(typeof(SecBuffer));
                    IntPtr SecBufferpvBuffer = Marshal.ReadIntPtr(pBuffers,CurrentOffset + Marshal.SizeOf(typeof(int))+Marshal.SizeOf(typeof(int)));
                    Marshal.FreeHGlobal(SecBufferpvBuffer);
                }
            }

            Marshal.FreeHGlobal(pBuffers);
            pBuffers = IntPtr.Zero;
        }
    }

    public byte[] GetSecBufferByteArray()
    {
        byte[] Buffer = null;

        if(pBuffers == IntPtr.Zero)
        {
            throw new InvalidOperationException("Object has already been disposed!!!");
        }

        if(cBuffers == 1)
        {
            SecBuffer ThisSecBuffer = (SecBuffer)Marshal.PtrToStructure(pBuffers,typeof(SecBuffer));

            if(ThisSecBuffer.cbBuffer > 0)
            {
                Buffer = new byte[ThisSecBuffer.cbBuffer];
                Marshal.Copy(ThisSecBuffer.pvBuffer,Buffer,0,ThisSecBuffer.cbBuffer);
            }
        }
        else
        {
            int BytesToAllocate = 0;

            for(int Index = 0;Index < cBuffers;Index++)
            {
                //The bits were written out the following order:
                //int cbBuffer;
                //int BufferType;
                //pvBuffer;
                //What we need to do here calculate the total number of bytes we need to copy...
                int CurrentOffset = Index*Marshal.SizeOf(typeof(SecBuffer));
                BytesToAllocate += Marshal.ReadInt32(pBuffers,CurrentOffset);    
            }

            Buffer = new byte[BytesToAllocate];

            for(int Index = 0,BufferIndex = 0;Index < cBuffers;Index++)
            {
                //The bits were written out the following order:
                //int cbBuffer;
                //int BufferType;
                //pvBuffer;
                //Now iterate over the individual buffers and put them together into a
                //byte array...
                int CurrentOffset = Index*Marshal.SizeOf(typeof(SecBuffer));
                int BytesToCopy = Marshal.ReadInt32(pBuffers,CurrentOffset);    
                IntPtr SecBufferpvBuffer = Marshal.ReadIntPtr(pBuffers,CurrentOffset + Marshal.SizeOf(typeof(int))+Marshal.SizeOf(typeof(int)));
                Marshal.Copy(SecBufferpvBuffer,Buffer,BufferIndex,BytesToCopy);
                BufferIndex += BytesToCopy;
            }
        }

        return(Buffer);
    }

    /*public SecBuffer GetSecBuffer()
    {
        if(pBuffers == IntPtr.Zero)
        {
            throw new InvalidOperationException("Object has already been disposed!!!");
        }

        return((SecBuffer)Marshal.PtrToStructure(pBuffers,typeof(SecBuffer)));
    }*/
}


[StructLayout(LayoutKind.Sequential)]
public struct SECURITY_INTEGER
{
    public uint LowPart;
    public int HighPart;
    public SECURITY_INTEGER(int dummy)
    {
    LowPart = 0;
    HighPart = 0;
    }
};

[StructLayout(LayoutKind.Sequential)]
public struct SECURITY_HANDLE
{
    public uint LowPart;
    public uint HighPart;
    public SECURITY_HANDLE(int dummy)
    {
    LowPart = HighPart = 0;
    }
};

[StructLayout(LayoutKind.Sequential)]
public struct SecPkgContext_Sizes
{
    public uint cbMaxToken;
    public uint cbMaxSignature;
    public uint cbBlockSize;
    public uint cbSecurityTrailer;
};


namespace SSPITest
{
    public class SSPIHelper
    {
    public const int TOKEN_QUERY = 0x00008;
    public const int SEC_E_OK = 0;
        public const int SEC_I_CONTINUE_NEEDED = 0x90312;
        const int SECPKG_CRED_OUTBOUND = 2;
        const int SECURITY_NATIVE_DREP = 0x10;
        const int SECPKG_CRED_INBOUND = 1;
        const int MAX_TOKEN_SIZE = 12288;
    //For AcquireCredentialsHandle in 3er Parameter "fCredentialUse"

        SECURITY_HANDLE _hInboundCred = new SECURITY_HANDLE(0);
        public SECURITY_HANDLE _hServerContext = new SECURITY_HANDLE(0);

        SECURITY_HANDLE _hOutboundCred = new SECURITY_HANDLE(0);
        public SECURITY_HANDLE _hClientContext = new SECURITY_HANDLE(0);

        public const int ISC_REQ_DELEGATE      =     0x00000001;
        public const int ISC_REQ_MUTUAL_AUTH       =     0x00000002;
        public const int ISC_REQ_REPLAY_DETECT     =     0x00000004;
        public const int ISC_REQ_SEQUENCE_DETECT   =     0x00000008;
        public const int ISC_REQ_CONFIDENTIALITY   =     0x00000010;
        public const int ISC_REQ_USE_SESSION_KEY   =     0x00000020;
        public const int ISC_REQ_PROMPT_FOR_CREDS   =    0x00000040;
        public const int ISC_REQ_USE_SUPPLIED_CREDS =    0x00000080;
        public const int ISC_REQ_ALLOCATE_MEMORY    =    0x00000100;
        public const int ISC_REQ_USE_DCE_STYLE      =    0x00000200;
        public const int ISC_REQ_DATAGRAM       =    0x00000400;
        public const int ISC_REQ_CONNECTION     =    0x00000800;
        public const int ISC_REQ_CALL_LEVEL     =    0x00001000;
        public const int ISC_REQ_FRAGMENT_SUPPLIED  =    0x00002000;
        public const int ISC_REQ_EXTENDED_ERROR     =    0x00004000;
        public const int ISC_REQ_STREAM         =    0x00008000;
        public const int ISC_REQ_INTEGRITY      =    0x00010000;
        public const int ISC_REQ_IDENTIFY       =    0x00020000;
        public const int ISC_REQ_NULL_SESSION       =    0x00040000;
        public const int ISC_REQ_MANUAL_CRED_VALIDATION = 0x00080000;
        public const int ISC_REQ_RESERVED1      =    0x00100000;
        public const int ISC_REQ_FRAGMENT_TO_FIT    =    0x00200000;

        public const int SECPKG_ATTR_SIZES       =     0;

        public const int STANDARD_CONTEXT_ATTRIBUTES = ISC_REQ_CONFIDENTIALITY | ISC_REQ_REPLAY_DETECT | ISC_REQ_SEQUENCE_DETECT | ISC_REQ_CONNECTION;

        bool _bGotClientCredentials = false;
        bool _bGotServerCredentials = false;
        bool _bGotServerContext = false;

    [DllImport("secur32", CharSet = CharSet.Auto)]
    static extern int AcquireCredentialsHandle(
    string pszPrincipal, //SEC_CHAR*
    string pszPackage, //SEC_CHAR* //"Kerberos","NTLM","Negotiative"
    int fCredentialUse,
    IntPtr PAuthenticationID,//_LUID AuthenticationID,//pvLogonID, //PLUID
    IntPtr pAuthData,//PVOID
    int pGetKeyFn, //SEC_GET_KEY_FN
    IntPtr pvGetKeyArgument, //PVOID
    ref SECURITY_HANDLE phCredential, //SecHandle //PCtxtHandle ref
    ref SECURITY_INTEGER ptsExpiry); //PTimeStamp //TimeStamp ref

    [DllImport("secur32", CharSet = CharSet.Auto, SetLastError = true)]
    static extern int InitializeSecurityContext(ref SECURITY_HANDLE phCredential,//PCredHandle
    IntPtr phContext, //PCtxtHandle
    string pszTargetName,
    int fContextReq,
    int Reserved1,
    int TargetDataRep,
    IntPtr pInput, //PSecBufferDesc SecBufferDesc
    int Reserved2,
    out SECURITY_HANDLE phNewContext, //PCtxtHandle
    out SecBufferDesc pOutput, //PSecBufferDesc SecBufferDesc
    out uint pfContextAttr, //managed ulong == 64 bits!!!
    out SECURITY_INTEGER ptsExpiry); //PTimeStamp

        [DllImport("secur32", CharSet = CharSet.Auto, SetLastError = true)]
        static extern int InitializeSecurityContext(ref SECURITY_HANDLE phCredential,//PCredHandle
            ref SECURITY_HANDLE phContext, //PCtxtHandle
            string pszTargetName,
            int fContextReq,
            int Reserved1,
            int TargetDataRep,
            ref SecBufferDesc SecBufferDesc, //PSecBufferDesc SecBufferDesc
            int Reserved2,
            out SECURITY_HANDLE phNewContext, //PCtxtHandle
            out SecBufferDesc pOutput, //PSecBufferDesc SecBufferDesc
            out uint pfContextAttr, //managed ulong == 64 bits!!!
            out SECURITY_INTEGER ptsExpiry); //PTimeStamp

        [DllImport("secur32.Dll", CharSet = CharSet.Auto, SetLastError = false)]
        static extern int AcceptSecurityContext(ref SECURITY_HANDLE phCredential,
                                                IntPtr phContext,
                                                ref SecBufferDesc pInput,
                                                uint fContextReq,
                                                uint TargetDataRep,
                                                out SECURITY_HANDLE phNewContext,
                                                out SecBufferDesc pOutput,
                                                out uint pfContextAttr,    //managed ulong == 64 bits!!!
                                                out SECURITY_INTEGER ptsTimeStamp);

        [DllImport("secur32.Dll", CharSet = CharSet.Auto, SetLastError = false)]
        static extern int AcceptSecurityContext(ref SECURITY_HANDLE phCredential,
                                                ref SECURITY_HANDLE phContext,
                                                ref SecBufferDesc pInput,
                                                uint fContextReq,
                                                uint TargetDataRep,
                                                out SECURITY_HANDLE phNewContext,
                                                out SecBufferDesc pOutput,
                                                out uint pfContextAttr,    //managed ulong == 64 bits!!!
                                                out SECURITY_INTEGER ptsTimeStamp);

        [DllImport("secur32.Dll", CharSet = CharSet.Auto, SetLastError = false)]
        public static extern int ImpersonateSecurityContext(ref SECURITY_HANDLE phContext);

        [DllImport("secur32.Dll", CharSet = CharSet.Auto, SetLastError = false)]
        public static extern int QueryContextAttributes(ref SECURITY_HANDLE phContext,
                                                        uint ulAttribute,
                                                        out SecPkgContext_Sizes pContextAttributes);

        [DllImport("secur32.Dll", CharSet = CharSet.Auto, SetLastError = false)]
        public static extern int EncryptMessage(ref SECURITY_HANDLE phContext,
                                                uint fQOP,        //managed ulong == 64 bits!!!
                                                ref SecBufferDesc pMessage,
                                                uint MessageSeqNo);    //managed ulong == 64 bits!!!

        [DllImport("secur32.Dll", CharSet = CharSet.Auto, SetLastError = false)]
        public static extern int DecryptMessage(ref SECURITY_HANDLE phContext,
                                                 ref SecBufferDesc pMessage,
                                                 uint MessageSeqNo,
                                                 out uint pfQOP);

        [DllImport("secur32.Dll", CharSet = CharSet.Auto, SetLastError = false)]
        public static extern int MakeSignature(ref SECURITY_HANDLE phContext,          // Context to use
                                                uint fQOP,         // Quality of Protection
                                                ref SecBufferDesc pMessage,        // Message to sign
                                                uint MessageSeqNo);      // Message Sequence Num.

        [DllImport("secur32.Dll", CharSet = CharSet.Auto, SetLastError = false)]
        public static extern int VerifySignature(ref SECURITY_HANDLE phContext,          // Context to use
                                                ref SecBufferDesc pMessage,        // Message to sign
                                                uint MessageSeqNo,            // Message Sequence Num.
                                                out uint pfQOP);      // Quality of Protection

    string _sAccountName =  WindowsIdentity.GetCurrent().Name;

        public SSPIHelper()
        {

        }

        public SSPIHelper(string sRemotePrincipal)
        {
            _sAccountName = sRemotePrincipal;                
        }

        public void InitializeClient(out byte[] clientToken,byte[] serverToken,
                                     out bool bContinueProcessing)
        {
            clientToken = null;
            bContinueProcessing = true;

            SECURITY_INTEGER ClientLifeTime = new SECURITY_INTEGER(0);            

            if(!_bGotClientCredentials)
            {
                if(AcquireCredentialsHandle(_sAccountName,"Kerberos",SECPKG_CRED_OUTBOUND,
                                            IntPtr.Zero,IntPtr.Zero,0,IntPtr.Zero,
                                            ref _hOutboundCred,ref ClientLifeTime) != SEC_E_OK)
                {
                    throw new Exception("Couldn't acquire client credentials");
                }

                _bGotClientCredentials = true;
            }

            int ss = -1;

            SecBufferDesc ClientToken = new SecBufferDesc(MAX_TOKEN_SIZE);

            try
            {
                uint ContextAttributes = 0;

                if(serverToken == null)
                {
                    ss = InitializeSecurityContext(ref _hOutboundCred,
                        IntPtr.Zero,
                        _sAccountName,// null string pszTargetName,
                        STANDARD_CONTEXT_ATTRIBUTES,
                        0,//int Reserved1,
                        SECURITY_NATIVE_DREP,//int TargetDataRep
                        IntPtr.Zero,    //Always zero first time around...
                        0, //int Reserved2,
                        out _hClientContext, //pHandle CtxtHandle = SecHandle
                        out ClientToken,//ref SecBufferDesc pOutput, //PSecBufferDesc
                        out ContextAttributes,//ref int pfContextAttr,
                        out ClientLifeTime); //ref IntPtr ptsExpiry ); //PTimeStamp

                }
                else
                {
                    SecBufferDesc ServerToken = new SecBufferDesc(serverToken);

                    try
                    {
                        ss = InitializeSecurityContext(ref _hOutboundCred,
                            ref _hClientContext,
                            _sAccountName,// null string pszTargetName,
                            STANDARD_CONTEXT_ATTRIBUTES,
                            0,//int Reserved1,
                            SECURITY_NATIVE_DREP,//int TargetDataRep
                            ref ServerToken,    //Always zero first time around...
                            0, //int Reserved2,
                            out _hClientContext, //pHandle CtxtHandle = SecHandle
                            out ClientToken,//ref SecBufferDesc pOutput, //PSecBufferDesc
                            out ContextAttributes,//ref int pfContextAttr,
                            out ClientLifeTime); //ref IntPtr ptsExpiry ); //PTimeStamp
                    }
                    finally
                    {
                        ServerToken.Dispose();    
                    }
                }

                if(ss != SEC_E_OK && ss != SEC_I_CONTINUE_NEEDED)
                {
                    throw new Exception("InitializeSecurityContext() failed!!!");                
                }

                clientToken = ClientToken.GetSecBufferByteArray();
            }
            finally
            {
                ClientToken.Dispose();
            }

            bContinueProcessing = ss != SEC_E_OK;            
        }

        public void InitializeServer(byte[] clientToken,out byte[] serverToken,
                                     out bool bContinueProcessing)
        {
            serverToken = null;
            bContinueProcessing = true;
            SECURITY_INTEGER NewLifeTime = new SECURITY_INTEGER(0);

            if(!_bGotServerCredentials)
            {
                if(AcquireCredentialsHandle(_sAccountName,"Kerberos",SECPKG_CRED_INBOUND,
                                            IntPtr.Zero,IntPtr.Zero,0,IntPtr.Zero,
                                            ref _hInboundCred,ref NewLifeTime) != SEC_E_OK)
                {
                    throw new Exception("Couldn't acquire server credentials handle!!!");
                }

                _bGotServerCredentials = true;
            }

            SecBufferDesc ServerToken = new SecBufferDesc(MAX_TOKEN_SIZE);
            SecBufferDesc ClientToken = new SecBufferDesc(clientToken);

            try
            {    
                int ss = -1;
                uint uNewContextAttr = 0;

                if(!_bGotServerContext)
                {
                    ss = AcceptSecurityContext(ref _hInboundCred,        // [in] handle to the credentials
                        IntPtr.Zero,                // [in/out] handle of partially formed context.  Always NULL the first time through
                        ref ClientToken,            // [in] pointer to the input buffers
                        STANDARD_CONTEXT_ATTRIBUTES,                        // [in] required context attributes
                        SECURITY_NATIVE_DREP,    // [in] data representation on the target
                        out _hServerContext,    // [in/out] receives the new context handle    
                        out ServerToken,        // [in/out] pointer to the output buffers
                        out uNewContextAttr,    // [out] receives the context attributes        
                        out NewLifeTime);        // [out] receives the life span of the security context
                }
                else
                {
                    ss = AcceptSecurityContext(ref _hInboundCred,        // [in] handle to the credentials
                        ref _hServerContext,                // [in/out] handle of partially formed context.  Always NULL the first time through
                        ref ClientToken,            // [in] pointer to the input buffers
                        STANDARD_CONTEXT_ATTRIBUTES,                        // [in] required context attributes
                        SECURITY_NATIVE_DREP,    // [in] data representation on the target
                        out _hServerContext,    // [in/out] receives the new context handle    
                        out ServerToken,        // [in/out] pointer to the output buffers
                        out uNewContextAttr,    // [out] receives the context attributes        
                        out NewLifeTime);        // [out] receives the life span of the security context
                }

                if(ss != SEC_E_OK && ss != SEC_I_CONTINUE_NEEDED)
                {
                    throw new Exception("AcceptSecurityContext() failed!!!");                
                }

                if(!_bGotServerContext)
                {
                    _bGotServerContext = true;
                }

                serverToken = ServerToken.GetSecBufferByteArray();

                bContinueProcessing = ss != SEC_E_OK;        
            }        
            finally
            {
                ClientToken.Dispose();
                ServerToken.Dispose();    
            }
        }                            

        public void EncryptMessage(byte[] message,bool bUseClientContext,out byte[] encryptedBuffer)
        {
            encryptedBuffer = null;

            SECURITY_HANDLE EncryptionContext = _hServerContext;

            if(bUseClientContext)
            {
                EncryptionContext = _hClientContext;    
            }

            SecPkgContext_Sizes ContextSizes = new SecPkgContext_Sizes();

            if(QueryContextAttributes(ref EncryptionContext,SECPKG_ATTR_SIZES,out ContextSizes) != SEC_E_OK)
            {
                throw new Exception("QueryContextAttribute() failed!!!");                    
            }

            MultipleSecBufferHelper[] ThisSecHelper = new MultipleSecBufferHelper[2];
            ThisSecHelper[0] = new MultipleSecBufferHelper(message,SecBufferType.SECBUFFER_DATA);
            ThisSecHelper[1] = new MultipleSecBufferHelper(new byte[ContextSizes.cbSecurityTrailer],SecBufferType.SECBUFFER_TOKEN);

            SecBufferDesc DescBuffer = new SecBufferDesc(ThisSecHelper);

            try
            {
                if(EncryptMessage(ref EncryptionContext,0,ref DescBuffer,0) != SEC_E_OK)
                {
                    throw new Exception("EncryptMessage() failed!!!");                    
                }

                encryptedBuffer = DescBuffer.GetSecBufferByteArray();    
            }
            finally
            {
                DescBuffer.Dispose();
            }
        }

        public void DecryptMessage(int messageLength,byte[] encryptedBuffer,bool bUseClientContext,
                                    out byte[] decryptedBuffer)
        {
            decryptedBuffer = null;

            SECURITY_HANDLE DecryptionContext = _hServerContext;

            if(bUseClientContext)
            {
                DecryptionContext = _hClientContext;    
            }

            byte[] EncryptedMessage = new byte[messageLength];
            Array.Copy(encryptedBuffer,0,EncryptedMessage,0,messageLength);

            int SecurityTrailerLength = encryptedBuffer.Length - messageLength;

            byte[] SecurityTrailer = new byte[SecurityTrailerLength];
            Array.Copy(encryptedBuffer,messageLength,SecurityTrailer,0,SecurityTrailerLength);

            MultipleSecBufferHelper[] ThisSecHelper = new MultipleSecBufferHelper[2];
            ThisSecHelper[0] = new MultipleSecBufferHelper(EncryptedMessage,SecBufferType.SECBUFFER_DATA);
            ThisSecHelper[1] = new MultipleSecBufferHelper(SecurityTrailer,SecBufferType.SECBUFFER_TOKEN);
            SecBufferDesc DescBuffer = new SecBufferDesc(ThisSecHelper);                            
            try
            {
                uint EncryptionQuality = 0;

                if(DecryptMessage(ref DecryptionContext,ref DescBuffer,0,out EncryptionQuality) != SEC_E_OK)
                {
                    throw new Exception("DecryptMessage() failed!!!");                    
                }

                decryptedBuffer = new byte[messageLength];
                Array.Copy(DescBuffer.GetSecBufferByteArray(),0,decryptedBuffer,0,messageLength);
            }
            finally
            {
                DescBuffer.Dispose();
            }
        }

        public void SignMessage(byte[] message,bool bUseClientContext,out byte[] signedBuffer,
                                ref SECURITY_HANDLE hServerContext)
        {
            signedBuffer = null;

            SECURITY_HANDLE EncryptionContext = _hServerContext;

            if(bUseClientContext)
            {
                EncryptionContext = _hClientContext;    
            }

            SecPkgContext_Sizes ContextSizes = new SecPkgContext_Sizes();

            if(QueryContextAttributes(ref EncryptionContext,SECPKG_ATTR_SIZES,out ContextSizes) != SEC_E_OK)
            {
                throw new Exception("QueryContextAttribute() failed!!!");                    
            }

            MultipleSecBufferHelper[] ThisSecHelper = new MultipleSecBufferHelper[2];
            ThisSecHelper[0] = new MultipleSecBufferHelper(message,SecBufferType.SECBUFFER_DATA);
            ThisSecHelper[1] = new MultipleSecBufferHelper(new byte[ContextSizes.cbMaxSignature],SecBufferType.SECBUFFER_TOKEN);

            SecBufferDesc DescBuffer = new SecBufferDesc(ThisSecHelper);

            try
            {
                if(MakeSignature(ref EncryptionContext,0,ref DescBuffer,0) != SEC_E_OK)
                {
                    throw new Exception("MakeSignature() failed!!!");                    
                }

                //SSPIHelper.SignAndVerify(ref _hClientContext,ref hServerContext,ref DescBuffer);
                uint EncryptionQuality = 0;
                VerifySignature(ref this._hServerContext,ref DescBuffer,0,out EncryptionQuality);

                signedBuffer = DescBuffer.GetSecBufferByteArray();    
            }
            finally
            {
                DescBuffer.Dispose();
            }        
        }

        public void VerifyMessage(int messageLength,byte[] signedBuffer,bool bUseClientContext,
                                    out byte[] verifiedBuffer)
        {
            verifiedBuffer = null;

            SECURITY_HANDLE DecryptionContext = _hServerContext;

            if(bUseClientContext)
            {
                DecryptionContext = _hClientContext;    
            }

            byte[] SignedMessage = new byte[messageLength];
            Array.Copy(signedBuffer,0,SignedMessage,0,messageLength);

            int SignatureLength = signedBuffer.Length - messageLength;

            byte[] Signature = new byte[SignatureLength];
            Array.Copy(signedBuffer,messageLength,Signature,0,SignatureLength);

            MultipleSecBufferHelper[] ThisSecHelper = new MultipleSecBufferHelper[2];
            ThisSecHelper[0] = new MultipleSecBufferHelper(SignedMessage,SecBufferType.SECBUFFER_DATA);
            ThisSecHelper[1] = new MultipleSecBufferHelper(Signature,SecBufferType.SECBUFFER_TOKEN);
            SecBufferDesc DescBuffer = new SecBufferDesc(ThisSecHelper);                            
            try
            {
                uint EncryptionQuality = 0;

                int Return = VerifySignature(ref DecryptionContext,ref DescBuffer,0,out EncryptionQuality);

                if(Return != SEC_E_OK)
                {
                    throw new Exception("VerifySignature() failed!!!");                    
                }

                verifiedBuffer = new byte[messageLength];
                Array.Copy(DescBuffer.GetSecBufferByteArray(),0,verifiedBuffer,0,messageLength);
            }
            finally
            {
                DescBuffer.Dispose();
            }
        }
    }

    class TestMe
    {
        static void Main(string[] args)
        {
            try
            {

                SSPIHelper MyHelper = new SSPIHelper();
                SSPIHelper MyServerHelper = new SSPIHelper();

                byte[] ClientToken = null;
                byte[] ServerToken = null;
                bool bContinueClient = true, bContinueServer = true;
                while(bContinueClient || bContinueServer)
                {
                    MyHelper.InitializeClient(out ClientToken,ServerToken,out bContinueClient);
                    MyServerHelper.InitializeServer(ClientToken,out ServerToken,out bContinueServer);
                }
                byte[] Message = System.Text.Encoding.ASCII.GetBytes("hi there");
                byte[] EncryptedBuffer = null;

                MyHelper.EncryptMessage(Message,true,out EncryptedBuffer);

                byte[] DecryptedBuffer;
                MyServerHelper.DecryptMessage(Message.Length,EncryptedBuffer,false,out DecryptedBuffer);
                Console.WriteLine(System.Text.Encoding.ASCII.GetString(DecryptedBuffer));
            }
            catch(Exception Ex)
            {
                Console.WriteLine(Marshal.GetLastWin32Error());
            }
        }
    }
    }

Alternative Managed API:

Whidbey makes it trivial to Kerberize your application using NegotiateStream. Check the Beta documentation for details...

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