using System;

using System.Security.Cryptography;

using System.IO;

using System.Text;

public class Program

{

    public static void Main()

    {

        //For DSV

        string serviceUrl = "https://api-gateway.walmart.com/v3/items?limit=200&nextCursor=*&shipNode=64103";

        string clientId ="b606771d-ced6-4553-9356-a8a920827d03";

        string clientSecret ="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";        

        DateTime UtcNow = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);

        long timeStampVal = (long)(DateTime.UtcNow - UtcNow).TotalMilliseconds;

​

                StringBuilder sbStringToSign = new StringBuilder();

                sbStringToSign.Append(clientId);//Consumer ID

                sbStringToSign.Append("\n");

                sbStringToSign.Append(serviceUrl);

                sbStringToSign.Append("\n");

                sbStringToSign.Append("GET");

                sbStringToSign.Append("\n");

                sbStringToSign.Append(timeStampVal);

                sbStringToSign.Append("\n");

​

         String signature = GenerateSignature(sbStringToSign.ToString(), clientSecret);

        Console.WriteLine("Signature : "+ signature);

        Console.WriteLine("timestamp : "+ timeStampVal);

    }

    public static string GenerateSignature(

            string stringToBeSigned,

            string encodedPrivateKey

        )

        {

            string signatureString = null;

            try

            {

                byte[] privateKey = Convert.FromBase64String(encodedPrivateKey);

                RSACryptoServiceProvider rsa = DecodePrivateKeyInfo(privateKey);

                if (rsa != null)

                {

                    byte[] CO = Encoding.UTF8.GetBytes(stringToBeSigned);

​

                    byte[] SignedBytes = rsa.SignData(CO, CryptoConfig.MapNameToOID("SHA256"));

​

                    signatureString = Convert.ToBase64String(SignedBytes);

                }

            }

            catch

            {

                return null;

            }

            return signatureString;

        }

      public static RSACryptoServiceProvider DecodePrivateKeyInfo(

            byte[] pkcs8

        )

        {

            // encoded OID sequence for  PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"

            // this byte[] includes the sequence byte and terminal encoded null 

            byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };

            byte[] seq;

            // ---------  Set up stream to read the asn.1 encoded SubjectPublicKeyInfo blob  ------

            MemoryStream mem = new MemoryStream(pkcs8);

            int lenstream = (int)mem.Length;

            BinaryReader binr = new BinaryReader(mem);    //wrap Memory Stream with BinaryReader for easy reading

            byte bt = 0;

            ushort twobytes = 0;

​

            try

            {

                twobytes = binr.ReadUInt16();

                if (twobytes == 0x8130) //data read as little endian order (actual data order for Sequence is 30 81)

                {

                    binr.ReadByte();    //advance 1 byte

                }

                else if (twobytes == 0x8230)

                {

                    binr.ReadInt16();   //advance 2 bytes

                }

                else

                {

                    return null;

                }

​

                bt = binr.ReadByte();

                if (bt != 0x02)

                {

                    return null;

                }

​

                twobytes = binr.ReadUInt16();

​

                if (twobytes != 0x0001)

                {

                    return null;

                }

​

                seq = binr.ReadBytes(15);       //read the Sequence OID

                if (!CompareBytearrays(seq, SeqOID))    //make sure Sequence for OID is correct

                {

                    return null;

                }

​

                bt = binr.ReadByte();

                if (bt != 0x04) //expect an Octet string 

                {

                    return null;

                }

​

                bt = binr.ReadByte();       //read next byte, or next 2 bytes is  0x81 or 0x82; otherwise bt is the byte count

                if (bt == 0x81)

                {

                    binr.ReadByte();

                }

                else if (bt == 0x82)

                {

                    binr.ReadUInt16();

                }

                //------ at this stage, the remaining sequence should be the RSA private key

​

                byte[] rsaprivkey = binr.ReadBytes((int)(lenstream - mem.Position));

                RSACryptoServiceProvider rsacsp = DecodeRSAPrivateKey(rsaprivkey);

                return rsacsp;

            }

            catch

            {

                return null;

            }

            finally

            {

                binr.Close();

            }

        }

            private static bool CompareBytearrays(

            byte[] a,

            byte[] b

        )

        {

            if (a.Length != b.Length)

            {

                return false;

            }

            int i = 0;

            foreach (byte c in a)

            {

                if (c != b[i])

                {

                    return false;

                }

                i++;

            }

            return true;

        }

      public static RSACryptoServiceProvider DecodeRSAPrivateKey(

            byte[] privkey

        )

        {

            byte[] MODULUS, E, D, P, Q, DP, DQ, IQ;

​

            // ---------  Set up stream to decode the asn.1 encoded RSA private key  ------

            MemoryStream mem = new MemoryStream(privkey);

            BinaryReader binr = new BinaryReader(mem);    //wrap Memory Stream with BinaryReader for easy reading

            byte bt = 0;

            ushort twobytes = 0;

            int elems = 0;

            try

            {

                twobytes = binr.ReadUInt16();

                if (twobytes == 0x8130) //data read as little endian order (actual data order for Sequence is 30 81)

                {

                    binr.ReadByte();    //advance 1 byte

                }

                else if (twobytes == 0x8230)

                {

                    binr.ReadInt16();   //advance 2 bytes

                }

                else

                {

                    return null;

                }

​

                twobytes = binr.ReadUInt16();

                if (twobytes != 0x0102) //version number

                {

                    return null;

                }

                bt = binr.ReadByte();

                if (bt != 0x00)

                {

                    return null;

                }

​

                //------  all private key components are Integer sequences ----

                elems = GetIntegerSize(binr);

                MODULUS = binr.ReadBytes(elems);

​

                elems = GetIntegerSize(binr);

                E = binr.ReadBytes(elems);

​

                elems = GetIntegerSize(binr);

                D = binr.ReadBytes(elems);

​

                elems = GetIntegerSize(binr);

                P = binr.ReadBytes(elems);

​

                elems = GetIntegerSize(binr);

                Q = binr.ReadBytes(elems);

​

                elems = GetIntegerSize(binr);

                DP = binr.ReadBytes(elems);

​

                elems = GetIntegerSize(binr);

                DQ = binr.ReadBytes(elems);

​

                elems = GetIntegerSize(binr);

                IQ = binr.ReadBytes(elems);

​

                // ------- create RSACryptoServiceProvider instance and initialize with public key -----

                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();

                RSAParameters RSAparams = new RSAParameters();

                RSAparams.Modulus = MODULUS;

                RSAparams.Exponent = E;

                RSAparams.D = D;

                RSAparams.P = P;

                RSAparams.Q = Q;

                RSAparams.DP = DP;

                RSAparams.DQ = DQ;

                RSAparams.InverseQ = IQ;

                RSA.ImportParameters(RSAparams);

                return RSA;

            }

            catch

            {

                return null;

            }

            finally

            {

                binr.Close();

            }

        }

      private static int GetIntegerSize(

            BinaryReader binr

        )

        {

            byte bt = 0;

            byte lowbyte = 0x00;

            byte highbyte = 0x00;

            int count = 0;

            bt = binr.ReadByte();

            if (bt != 0x02)     //expect integer

            {

                return 0;

            }

            bt = binr.ReadByte();

​

            if (bt == 0x81)

            {

                count = binr.ReadByte();    // data size in next byte

            }

            else if (bt == 0x82)

            {

                highbyte = binr.ReadByte(); // data size in next 2 bytes

                lowbyte = binr.ReadByte();

                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };

                count = BitConverter.ToInt32(modint, 0);

            }

            else

            {

                count = bt;     // we already have the data size

            }

            while (binr.ReadByte() == 0x00)

            {   //remove high order zeros in data

                count -= 1;

            }

            binr.BaseStream.Seek(-1, SeekOrigin.Current);       //last ReadByte wasn't a removed zero, so back up a byte

            return count;

        }

}