using System;
using System.Security.Cryptography;
    /// <summary>
    /// 
    /// </summary>
    /// 
    /// the cipher key is  a pair of values thet determined the encription strength
    /// by set the encryption key lengt and block size.
    /// thare are 3 possible pair according to the desired encryption strength.
    /// eache pair have index-0 for weak,1 medium strength, encryption and 2 for the strong encryption
    struct CipherKey
    { 
        // the const for the pair inedex;
        private const int  LowLevelEnc=0;
        private const int  MedLevelEnc=1;
        private const int  HigLevelEnc=2;
        //const for key length
        private const int  LowKeyLen=16;
        private const int  MedKeyLen=24;
        private const int  HigKeyLen=32;
        //const for block size
        private const int  LowKeySiz=128;
        private const int  MedKeySiz=192;
        private const int  HigKeySiz=256;
        public int Len;
        public int Size;
        //function gets the cipher pair index and return the pair -blocj size ,key length
        public static   CipherKey getCipherKey(int EncLevel)
        {   
            CipherKey Key;
            switch (EncLevel)
            {
                case LowLevelEnc:
                { 
                    Key.Len=LowKeyLen;
                    Key.Size=LowKeySiz;
                    return Key;
                }
                case MedLevelEnc:
                {
                    Key.Len=MedKeyLen;
                    Key.Size=MedKeySiz;
                    return Key;
                }
                case HigLevelEnc:
                {
                    Key.Len=HigKeyLen;
                    Key.Size=HigKeySiz;
                    return Key;
                }
            }
            throw new Exception("Invalid cipher Level- allow 0..2 -get: "+EncLevel.ToString());
        }

    }
    
    
    public class EncDec
    {    
        //the encription cipher mode 
        private static   System.Security.Cryptography.CipherMode sCipherMode=CipherMode.CBC;
        //the padding mode-
        //available values:
        //PaddingMode.None,PaddingMode.PKCS7,PaddingMode.Zeros ;
        private static   System.Security.Cryptography.PaddingMode sPaddingMode=PaddingMode.PKCS7;                                                        
        public static string  encrypt(string text, //the text to be encrypt
            string password,// the encryption key
            int cipherindex//The strength of the encryption
            )
        {
            try
            {                
                //get the cipher strength--from cipherindex
                CipherKey Key=CipherKey.getCipherKey(cipherindex);
                //build and init the Encryptor
                RijndaelManaged rijndaelCipher = new RijndaelManaged();
                rijndaelCipher.Mode = sCipherMode;
                rijndaelCipher.Padding = sPaddingMode;
                rijndaelCipher.KeySize = Key.Size;
                rijndaelCipher.BlockSize =Key.Size;
                byte[] pwdBytes = System.Text.Encoding.UTF8.GetBytes(password);
                byte[] keyBytes = new byte[Key.Len];    
                int len= pwdBytes.Length;
                if (len > keyBytes.Length) len= keyBytes.Length;
                System.Array.Copy(pwdBytes,keyBytes,len);
                rijndaelCipher.Key = keyBytes;
                rijndaelCipher.IV = keyBytes;
                ICryptoTransform transform = rijndaelCipher.CreateEncryptor();
            
                byte [] plainText = System.Text.Encoding.UTF8.GetBytes(text);
                byte[] cipherBytes = transform.TransformFinalBlock(plainText, 0, plainText.Length);
                return Convert.ToBase64String(cipherBytes);
            }
            catch (Exception)
            {
                throw  ;
            }


        }
        public static string  decrypt(string text, //the text to be decrypt
            string password,//the original encription key
            int cipherindex// the strength of the original encryption
            )
        {
            try
            {      //get the cipher strength--from cipherindex            
                CipherKey Key=CipherKey.getCipherKey(cipherindex);
                //build and init the Decryptor
                RijndaelManaged  rijndaelCipher = new RijndaelManaged();
                rijndaelCipher.Mode = sCipherMode;
                rijndaelCipher.Padding = sPaddingMode;
                rijndaelCipher.KeySize = Key.Size;
                rijndaelCipher.BlockSize =Key.Size;            
                byte[] encryptedData = Convert.FromBase64String(text);
                byte[] pwdBytes = System.Text.Encoding.UTF8.GetBytes(password);
                byte[] keyBytes = new byte[Key.Len];
                int len= pwdBytes.Length;
                if (len > keyBytes.Length) len= keyBytes.Length;
                System.Array.Copy(pwdBytes,keyBytes,len);
                rijndaelCipher.Key = keyBytes;
                rijndaelCipher.IV = keyBytes;
                ICryptoTransform transform = rijndaelCipher.CreateDecryptor();
                byte[] plainText = transform.TransformFinalBlock(encryptedData, 0, encryptedData.Length);
                return System.Text.Encoding.UTF8.GetString(plainText);
            }
            catch (Exception)
            {
                throw  ;
            }

        }
    }