Question

while encrypting and descripting the string with rsa provider I am getting this error.

RSA Data decryption error.The data to be decrypted exceeds the maximum for this modulus of 64 bytes.

Can any one have idea how to slove this error?

    internal sealed class RSAProvider
    {
        #region key store class

        [Serializable]
            private struct rsaKey
        {
            public rsaKey(RSAParameters rsaKeyInfo)
            {
                D = rsaKeyInfo.D;
                DP = rsaKeyInfo.DP;
                DQ = rsaKeyInfo.DQ;
                Exponent = rsaKeyInfo.Exponent;
                InverseQ = rsaKeyInfo.InverseQ;
                Modulus = rsaKeyInfo.Modulus;
                P = rsaKeyInfo.P;
                Q = rsaKeyInfo.Q;
            }

            public RSAParameters CreateRSAKey()
            {
                RSAParameters rsaKeyInfo = new RSAParameters();

                rsaKeyInfo.D = D;
                rsaKeyInfo.DP = DP;
                rsaKeyInfo.DQ = DQ;
                rsaKeyInfo.Exponent = Exponent;
                rsaKeyInfo.InverseQ = InverseQ;
                rsaKeyInfo.Modulus = Modulus;
                rsaKeyInfo.P = P;
                rsaKeyInfo.Q = Q;

                return rsaKeyInfo;
            }

            public byte[] D;
            public byte[] DP;
            public byte[] DQ;
            public byte[] Exponent;
            public byte[] InverseQ;
            public byte[] Modulus;
            public byte[] P;
            public byte[] Q;
        }

        #endregion

        private static RSAParameters rsaKeyParameters;

        static RSAProvider()
        {
            string rsaKeyString = System.Configuration.ConfigurationSettings.AppSettings["RSAKey"];
            if(rsaKeyString != null)
            {
                rsaKeyParameters = GetKeyByString(rsaKeyString);
            }
        }

        private RSAProvider()
        {
        }

        private static RSAParameters RSAKeyInfo
        {
            get
            {
                return rsaKeyParameters;
            }
        }

        private static bool DoOAEPPadding
        {
            get
            {
                return false;
            }
        }

        public static string GenerateKey(int keySize)
        {
            //Create a new instance of RSACryptoServiceProvider to generate
            //public and private key data.
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(keySize);

            RSAParameters rsaKeyInfo = RSA.ExportParameters(true);

            return GetKeyString(rsaKeyInfo);
        }


        #region Encrypt

        public static byte[] Encrypt(byte[] dataToEncrypt, string rsaKeyString)
        {
            RSAParameters rsaKeyInfo = GetKeyByString(rsaKeyString);

            return Encrypt(dataToEncrypt, rsaKeyInfo);
        }

        public static byte[] Encrypt(byte[] dataToEncrypt, RSAParameters rsaKeyInfo)
        {
            try
            {   
                //Create a new instance of RSACryptoServiceProvider.
               // Common.Identity.ImpersonateValidUser("prana", "eetplpvt", "Avdhoota1985");
                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();

                //Import the RSA Key information. This only needs
                //toinclude the public key information.
                RSA.ImportParameters(rsaKeyInfo);

                //Encrypt the passed byte array and specify OAEP padding.  
                //OAEP padding is only available on Microsoft Windows XP or
                //later.  
                //return RSA.Encrypt(dataToEncrypt, DoOAEPPadding);
                byte[] data = RSA.Encrypt(dataToEncrypt, DoOAEPPadding);
                RSA.Clear();
                //Common.Identity.UndoImpersonation();
                return data;
            }
                //Catch and display a CryptographicException  
                //to the console.
            catch(CryptographicException e)
            {
                // Updated By Divya Bhalodia on 27th June 2008 for Localization task
                //throw new Exception("Data encryption error.", e);
                Common.EnumLocalization.EnumLocalization loc = new Common.EnumLocalization.EnumLocalization(ASP.BL.ApplicationUsers.ApplicationUserController.CurrentUserCulture.Code, ASP.BL.Applications.ApplicationController.CurrentApplicationInfo.ItemId);
                throw new Exception(loc.LocalizeString("RSA Data encryption error.") + e.Message, e);
                // end Updated - Divya
            }
        }

        public static byte[] Encrypt(byte[] dataToEncrypt)
        {
            return Encrypt(dataToEncrypt, RSAKeyInfo);
        }

        #endregion

        #region Decrypt

        public static byte[] Decrypt(byte[] dataToDecrypt, string rsaKeyString, bool doOAEPPadding)
        {
            RSAParameters rsaKeyInfo = GetKeyByString(rsaKeyString);
            return Decrypt(dataToDecrypt, rsaKeyInfo, doOAEPPadding);
        }

        public static byte[] Decrypt(byte[] dataToDecrypt, RSAParameters rsaKeyInfo, bool doOAEPPadding)
        {
            try
            {
                //Create a new instance of RSACryptoServiceProvider.
                Common.Identity.ImpersonateValidUser();
                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();

                //Import the RSA Key information. This needs
                //to include the private key information.
                RSA.ImportParameters(rsaKeyInfo);

                //Decrypt the passed byte array and specify OAEP padding.  
                //OAEP padding is only available on Microsoft Windows XP or
                //later.  
                //return RSA.Decrypt(dataToDecrypt, doOAEPPadding);
                byte[] data = RSA.Decrypt(dataToDecrypt, doOAEPPadding);
                RSA.Clear();
                Common.Identity.UndoImpersonation();
                return data;
            }
                //Catch and display a CryptographicException  
                //to the console.
            catch(CryptographicException e)
            {

                // Updated By Divya Bhalodia on 27th June 2008 for Localization task
                //throw new Exception("Data decryption error.", e);
                Common.EnumLocalization.EnumLocalization loc = new Common.EnumLocalization.EnumLocalization(ASP.BL.ApplicationUsers.ApplicationUserController.CurrentUserCulture.Code, ASP.BL.Applications.ApplicationController.CurrentApplicationInfo.ItemId);
                throw new Exception(loc.LocalizeString("RSA Data decryption error.") + e.Message, e);
                // end Updated - Divya
            }
        }

        public static byte[] Decrypt(byte[] dataToDecrypt)
        {
            return Decrypt(dataToDecrypt, RSAKeyInfo, DoOAEPPadding);
        }
        #endregion

        #region Additional functions

        private static string GetKeyString(RSAParameters rsaKeyInfo)
        {
            byte[] tmp;
            rsaKey k = new rsaKey(rsaKeyInfo);
            BinaryFormatter formater = new BinaryFormatter();

            using(MemoryStream stream = new MemoryStream())
            {
                formater.Serialize(stream, k);
                tmp = stream.ToArray();
            }

            Code(tmp);

            return Convert.ToBase64String(tmp);
        }


        private static RSAParameters GetKeyByString(string rsaKeyString)
        {
            rsaKey k;

            byte[] tmp = Convert.FromBase64String(rsaKeyString);
            Code(tmp);

            BinaryFormatter formater = new BinaryFormatter();

            using(MemoryStream stream = new MemoryStream(tmp))
            {
                k = (rsaKey)formater.Deserialize(stream);
            }
            return k.CreateRSAKey();
        }


        private static void Code(byte[] tmp)
        {
            byte mask1 = 0x55;
            byte mask3 = 0xB9;
            byte mask4 = 0xCF;

            for(int i = 0; i 

Answer 1

I’ve encoutered similar problems but you can do two things to help yourself overcome them.

1. You need to ensure that hte data you are encrypting is shorter than the key that you are using. so if your key is 1024 bits then make sure that you are only bassing in say 1000 bits. To do this you need to get chunk your byte array into smaller chunks, encrypt each chunk and then store the encrypeted value in an array or a string. So instead of encrypting 1 string you encrypt say 5 strings.

When storing this information as a string make sure that all numbers are the same length, so if the formatter returns 15 you store the string with 015 so that you just divide by 3 later to get the byte to then put into the array.

To decrypt your data you need to simply read the length of the string and determine how many chunks to decrypt. Decrupt these one by one and then you can recreate the object with the decrupted byte array.

if you would like actual code please contact me personally and I’ll be able to help you better with some script that can do this for you.