QueryContextAttributesW

        //<sspi.h>
        //<schannel.h>
        private enum ContextAttribute : uint {
            Sizes               = 0x00,
            Names               = 0x01,
            Lifespan            = 0x02,
            DceInfo             = 0x03,
            StreamSizes         = 0x04,
            //KeyInfo             = 0x05, must not be used, see ConnectionInfo instead
            Authority           = 0x06,
            ProtoInfo           = 7,
            PasswordExpiry      = 8,
            SessionKey          = 9,
            PackageInfo         = 0x0A,
            UserFlags           = 11,
            NegotiationInfo     = 0x0C,
            NativeNames         = 13,
            Flags               = 14,
            UseValidated        = 15,
            CredentialName      = 16,
            TargetInformation   = 17,
            AccessToken         = 18,
            Target              = 19,
            AuthenticationId    = 20,
            UniqueBindings      = 0x19,
            EndpointBindings    = 0x1A,
            ClientSpecifiedSpn  = 0x1B,      // SECPKG_ATTR_CLIENT_SPECIFIED_TARGET = 27
            RemoteCertificate   = 0x53,
            LocalCertificate    = 0x54,
            RootStore           = 0x55,
            IssuerListInfoEx    = 0x59,
            ConnectionInfo      = 0x5A,
            EAPKeyBlock         = 0x5b,      // returns SecPkgContext_EapKeyBlock
            MappedCredAttr      = 0x5c,      // returns SecPkgContext_MappedCredAttr
            SessionInfo         = 0x5d,      // returns SecPkgContext_SessionInfo
            AppData             = 0x5e,      // sets/returns SecPkgContext_SessionAppData
            RemoteCertificates  = 0x5F,      // returns SecPkgContext_Certificates
            ClientCertPolicy    = 0x60,      // sets    SecPkgCred_ClientCertCtlPolicy
            CCPolicyResult      = 0x61,      // returns SecPkgContext_ClientCertPolicyResult
            UseNcrypt           = 0x62,      // Sets the CRED_FLAG_USE_NCRYPT_PROVIDER FLAG on cred group
            LocalCertInfo       = 0x63,      // returns SecPkgContext_CertInfo
            CipherInfo          = 0x64,      // returns new CNG SecPkgContext_CipherInfo
            EAPPrfInfo          = 0x65,      // sets    SecPkgContext_EapPrfInfo
            SupportedSignatures = 0x66,      // returns SecPkgContext_SupportedSignatures
            RemoteCertChain     = 0x67,      // returns PCCERT_CONTEXT
            UiInfo              = 0x68,      // sets SEcPkgContext_UiInfo
        }

        private enum ALG_ID : uint
        {
            CALG_3DES                   = 0x00006603,   //Triple DES encryption algorithm.
            CALG_3DES_112               = 0x00006609,   //Two-key triple DES encryption with effective key length equal to 112 bits.
            CALG_AES                    = 0x00006611,   //Advanced Encryption Standard (AES).
                                                        //This algorithm is supported by the Microsoft AES Cryptographic Provider.
            CALG_AES_128                = 0x0000660e,   //128 bit AES. This algorithm is supported by the Microsoft AES Cryptographic
                                                        //Provider.
            CALG_AES_192                = 0x0000660f,   //192 bit AES. This algorithm is supported by the Microsoft AES Cryptographic
                                                        //Provider.
            CALG_AES_256                = 0x00006610,   //256 bit AES. This algorithm is supported by the Microsoft AES Cryptographic
                                                        //Provider.
            CALG_AGREEDKEY_ANY          = 0x0000aa03,   //Temporary algorithm identifier for handles of Diffie-Hellman–agreed keys.
            CALG_CYLINK_MEK             = 0x0000660c,   //An algorithm to create a 40-bit DES key that has parity bits and zeroed
                                                        //key bits to make its key length 64 bits.
                                                        //This algorithm is supported by the Microsoft
                                                        //Base Cryptographic Provider.
            CALG_DES                    = 0x00006601,   //DES encryption algorithm.
            CALG_DESX                   = 0x00006604,   //DESX encryption algorithm.
            CALG_DH_EPHEM               = 0x0000aa02,   //Diffie-Hellman ephemeral key exchange algorithm.
            CALG_DH_SF                  = 0x0000aa01,   //Diffie-Hellman store and forward key exchange algorithm.
            CALG_DSS_SIGN               = 0x00002200,   //DSA public key signature algorithm.
            CALG_ECDH                   = 0x0000aa05,   //Elliptic curve Diffie-Hellman key exchange algorithm.
                                                        //Note This algorithm is supported only through Cryptography API:
                                                        //Next Generation. Windows Server 2003
                                                        //and Windows XP:  This algorithm is not supported.
            CALG_ECDH_EPHEM             = 0x0000ae06,   //Ephemeral elliptic curve Diffie-Hellman key exchange algorithm.
                                                        //Note  This algorithm is supported only through Cryptography API:
                                                        //Next Generation Windows Server 2003 and Windows XP:
                                                        //This algorithm is not supported.
            CALG_ECDSA                  = 0x00002203,   //Elliptic curve digital signature algorithm. Note  This algorithm is
                                                        //supported only through Cryptography API: Next Generation.
                                                        //Windows Server 2003 and Windows XP:  This algorithm is not supported.
            CALG_ECMQV                  = 0x0000a001,   //Elliptic curve Menezes, Qu, and Vanstone (MQV) key exchange algorithm.
                                                        //This algorithm is not supported.
            CALG_HASH_REPLACE_OWF       = 0x0000800b,   //One way function hashing algorithm.
            CALG_HUGHES_MD5             = 0x0000a003,   //Hughes MD5 hashing algorithm.
            CALG_HMAC                   = 0x00008009,   //HMAC keyed hash algorithm. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_KEA_KEYX               = 0x0000aa04,   //KEA key exchange algorithm (FORTEZZA). This algorithm is not supported.
            CALG_MAC                    = 0x00008005,   //MAC keyed hash algorithm. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_MD2                    = 0x00008001,   //MD2 hashing algorithm. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_MD4                    = 0x00008002,   //MD4 hashing algorithm.
            CALG_MD5                    = 0x00008003,   //MD5 hashing algorithm. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_NO_SIGN                = 0x00002000,   //No signature algorithm.
            CALG_OID_INFO_CNG_ONLY      = 0xffffffff,   //The algorithm is only implemented in CNG.
                                                        //The macro, IS_SPECIAL_OID_INFO_ALGID, can be used to determine whether
                                                        //a cryptography algorithm is only supported by using the CNG functions.
            CALG_OID_INFO_PARAMETERS    = 0xfffffffe,   //The algorithm is defined in the encoded parameters. The algorithm is only
                                                        //supported by using CNG. The macro, IS_SPECIAL_OID_INFO_ALGID, can be used
                                                        //to determine whether a cryptography algorithm is only supported by
                                                        //using the CNG functions.
            CALG_PCT1_MASTER            = 0x00004c04,   //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
            CALG_RC2                    = 0x00006602,   //RC2 block encryption algorithm. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_RC4                    = 0x00006801,   //RC4 stream encryption algorithm.
                                                        //This algorithm is supported by the Microsoft Base Cryptographic Provider.
            CALG_RC5                    = 0x0000660d,   //RC5 block encryption algorithm.
            CALG_RSA_KEYX               = 0x0000a400,   //RSA public key exchange algorithm. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_RSA_SIGN               = 0x00002400,   //RSA public key signature algorithm. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_SCHANNEL_ENC_KEY       = 0x00004c07,   //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
            CALG_SCHANNEL_MAC_KEY       = 0x00004c03,   //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
            CALG_SCHANNEL_MASTER_HASH   = 0x00004c02,   //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
            CALG_SEAL                   = 0x00006802,   //SEAL encryption algorithm. This algorithm is not supported.
            CALG_SHA                    = 0x00008004,   //SHA hashing algorithm. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_SHA1                   = 0x00008004,   //Same as CALG_SHA. This algorithm is supported by the
                                                        //Microsoft Base Cryptographic Provider.
            CALG_SHA_256                = 0x0000800c,   //256 bit SHA hashing algorithm. This algorithm is supported by
                                                        //Microsoft Enhanced RSA and AES Cryptographic Provider.
                                                        //Windows XP with SP3: This algorithm is supported by the Microsoft
                                                        //Enhanced RSA and AES Cryptographic Provider (Prototype).
                                                        //Windows XP with SP2, Windows XP with SP1 and Windows XP:
                                                        // This algorithm is not supported.
            CALG_SHA_384                = 0x0000800d,   //384 bit SHA hashing algorithm. This algorithm is supported by
                                                        //Microsoft Enhanced RSA and AES Cryptographic Provider. Windows XP with SP3:
                                                        //This algorithm is supported by the Microsoft Enhanced RSA and AES
                                                        //Cryptographic Provider (Prototype). Windows XP with SP2,
                                                        //Windows XP with SP1 and Windows XP: This algorithm is not supported.
            CALG_SHA_512                = 0x0000800e,   //512 bit SHA hashing algorithm. This algorithm is supported by
                                                        //Microsoft Enhanced RSA and AES Cryptographic Provider. Windows XP with SP3:
                                                        //This algorithm is supported by the Microsoft Enhanced RSA and AES
                                                        //Cryptographic Provider (Prototype). Windows XP with SP2,
                                                        //Windows XP with SP1 and Windows XP: This algorithm is not supported.
            CALG_SKIPJACK               = 0x0000660a,   //Skipjack block encryption algorithm (FORTEZZA).
                                                        //This algorithm is not supported.
            CALG_SSL2_MASTER            = 0x00004c05,   //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
            CALG_SSL3_MASTER            = 0x00004c01,   //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
            CALG_SSL3_SHAMD5            = 0x00008008,   //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
            CALG_TEK                    = 0x0000660b,   //TEK (FORTEZZA). This algorithm is not supported.
            CALG_TLS1_MASTER            = 0x00004c06,   //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
            CALG_TLS1PRF                = 0x0000800a    //Used by the Schannel.dll operations system.
                                                        //This ALG_ID should not be used by applications.
        }

        private enum SchProtocols {
            Zero                = 0,
            PctClient           = 0x00000002,
            PctServer           = 0x00000001,
            Pct                 = (PctClient | PctServer),
            Ssl2Client          = 0x00000008,
            Ssl2Server          = 0x00000004,
            Ssl2                = (Ssl2Client | Ssl2Server),
            Ssl3Client          = 0x00000020,
            Ssl3Server          = 0x00000010,
            Ssl3                = (Ssl3Client | Ssl3Server),
            Tls10Client         = 0x00000080,
            Tls10Server         = 0x00000040,
            Tls10               = (Tls10Client | Tls10Server),
            Tls11Client         = 0x00000200,
            Tls11Server         = 0x00000100,
            Tls11               = (Tls11Client | Tls11Server),
            Tls12Client         = 0x00000800,
            Tls12Server         = 0x00000400,
            Tls12               = (Tls12Client | Tls12Server),
            Ssl3Tls             = (Ssl3 | Tls10),
            UniClient           = unchecked((int)0x80000000),
            UniServer           = 0x40000000,
            Unified             = (UniClient | UniServer),
            ClientMask          = (PctClient | Ssl2Client | Ssl3Client | Tls10Client | Tls11Client | Tls12Client | UniClient),
            ServerMask          = (PctServer | Ssl2Server | Ssl3Server | Tls10Server | Tls11Server | Tls12Server | UniServer)
        };

        private enum SchProtocolsSimple : int
        {
            SP_PROT_TLS1_CLIENT = 0x80,       //Transport Layer Security 1.0 client-side.
            SP_PROT_TLS1_SERVER = 0x40,       //Transport Layer Security 1.0 server-side.
            SP_PROT_SSL3_CLIENT = 0x20,       //Secure Sockets Layer 3.0 client-side.
            SP_PROT_SSL3_SERVER = 0x10,       //Secure Sockets Layer 3.0 server-side.
            SP_PROT_TLS1_1_CLIENT = 0x200,    //Transport Layer Security 1.1 client-side.
            SP_PROT_TLS1_1_SERVER = 0x100,    //Transport Layer Security 1.1 server-side.
            SP_PROT_TLS1_2_CLIENT = 0x800,    //Transport Layer Security 1.2 client-side.
            SP_PROT_TLS1_2_SERVER = 0x400,    //Transport Layer Security 1.2 server-side.
            SP_PROT_PCT1_CLIENT = 0x2,        //Private Communications Technology 1.0 client-side. Obsolete.
            SP_PROT_PCT1_SERVER = 0x1,        //Private Communications Technology 1.0 server-side. Obsolete.
            SP_PROT_SSL2_CLIENT = 0x8,        //Secure Sockets Layer 2.0 client-side. Superseded by SP_PROT_TLS1_CLIENT.
            SP_PROT_SSL2_SERVER = 0x4,        //Secure Sockets Layer 2.0 server-side. Superseded by SP_PROT_TLS1_SERVER.
        }


        public const int SEC_E_OK = 0;

        [DllImport("secur32.dll", CharSet = CharSet.Auto, ExactSpelling=true, SetLastError=false)]
        private static extern int QueryContextAttributesW(SSPIHandle contextHandle,
                                                          [In] ContextAttribute attribute,
                                                          [In] [Out] ref SecPkgContext_ConnectionInfo ConnectionInfo);

        [StructLayout(LayoutKind.Sequential, Pack=1)]
        private struct SSPIHandle {
            private IntPtr HandleHi;
            private IntPtr HandleLo;

            public bool IsZero {
                get {return HandleHi == IntPtr.Zero && HandleLo == IntPtr.Zero;}
            }

            internal void SetToInvalid() {
                HandleHi = IntPtr.Zero;
                HandleLo = IntPtr.Zero;
            }

            public override string ToString() {
                { return HandleHi.ToString("x") + ":" + HandleLo.ToString("x");}
            }
        }

        //[SuppressUnmanagedCodeSecurity]
        private struct SecPkgContext_ConnectionInfo
        {
            public SchProtocols dwProtocol;
            public ALG_ID aiCipher;
            public int dwCipherStrength;
            public ALG_ID aiHash;
            public int dwHashStrength;
            public ALG_ID aiExch;
            public int dwExchStrength;
        }


====================================================================================

       SSPIHandle ContextHandle = new SSPIHandle();
       ContextHandle = [m_Worker.Context.m_SecurityContext._handle]

       SecPkgContext_ConnectionInfo SecConnectionInfo = new SecPkgContext_ConnectionInfo();

       if (QueryContextAttributesW(ContextHandle, ContextAttribute.ConnectionInfo, ref SecConnectionInfo) == SEC_E_OK)
       {
           SslProtocols SslProtocol = (SslProtocols)SecConnectionInfo.dwProtocol;
       }