Minifycode 2023-02-14 Viewed 1.3K times C#

AES/CBC/PKCS5Padding Encryption/Decryption in C#


In this article you will learn, If you want to encrypt data in AES with mode CBC ( Cipher Block Chaining ) and in Padding > PKCS5, I use below code just for PKCS7, it is working as you need. 

You need to encrypt a string using DESede pkcs5 padding. However C# only provides PKCS7 padding. So how can I achieve this?

 

protected RijndaelManaged myRijndael;
        public string EncryptText(string plainText, string encryptionKey) 
        {
            string iv= GenerateKeyAndIV();
            using (myRijndael = new RijndaelManaged()) 
            {
                myRijndael.Key = HexStringToByte(encryptionKey); 
                myRijndael.IV = HexStringToByte(iv); 
                myRijndael.Mode = CipherMode.CBC; 
                myRijndael.Padding = PaddingMode.PKCS7; 
                byte[] encrypted = EncryptStringToBytes(plainText, myRijndael.Key, myRijndael.IV);
                byte[] data = myRijndael.IV.Concat(encrypted).ToArray();
                string encString = Convert.ToBase64String(data);
                return encString; 
            } 
        }
        protected byte[] EncryptStringToBytes(string plainText, byte[] Key, byte[] IV) 
        {     
            // Check arguments.
 
            if (plainText == null || plainText.Length <= 0)
         
                throw new ArgumentNullException("plainText");
     
            if (Key == null || Key.Length <= 0)
         
                throw new ArgumentNullException("Key");
     
            if (IV == null || IV.Length <= 0)
         
                throw new ArgumentNullException("Key");
     
            byte[] encrypted;     
            // Create an RijndaelManaged object 
            // with the specified key and IV. 
            using (RijndaelManaged rijAlg = new RijndaelManaged())         
            {         
                rijAlg.Key = Key;         
                rijAlg.IV = IV; 
                // Create a decrytor to perform the stream transform. 
                ICryptoTransform encryptor = rijAlg.CreateEncryptor(rijAlg.Key, rijAlg.IV);
                // Create the streams used for encryption. 
                using (MemoryStream msEncrypt = new MemoryStream())             
                {             
                    using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))                 
                    {                 
                        using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))                     
                        {
                            //Write all data to the stream. 
                            swEncrypt.Write(plainText);                     
                        }                 
                        encrypted = msEncrypt.ToArray();                 
                    }             
                }         
            }
            // Return the encrypted bytes from the memory stream.
            return encrypted;
        }

        public string DecryptText(string encryptedString,string encryptionKey)
        {
            
            using (myRijndael = new RijndaelManaged())

            {
                myRijndael.Key = HexStringToByte(encryptionKey);
                myRijndael.Mode = CipherMode.CBC;
                myRijndael.Padding = PaddingMode.PKCS7;
                Byte[] ourEnc = Convert.FromBase64String(encryptedString);
                byte[] enc = Convert.FromBase64String(encryptedString);
                myRijndael.IV = enc.Take(16).ToArray();
                enc = enc.Skip(16).ToArray();
                string ourDec = DecryptStringFromBytes(enc, myRijndael.Key, myRijndael.IV);
                return ourDec;
            }
        }
        protected string DecryptStringFromBytes(byte[] cipherText, byte[] Key, byte[] IV)
        {
            if (cipherText == null || cipherText.Length <= 0)

                throw new ArgumentNullException("cipherText");

            if (Key == null || Key.Length <= 0)

                throw new ArgumentNullException("Key");

            if (IV == null || IV.Length <= 0)

                throw new ArgumentNullException("Key");
            string plaintext = null;
            using (RijndaelManaged rijAlg = new RijndaelManaged())
            {
                rijAlg.Key = Key;

                rijAlg.IV = IV;
                // Create a decrytor to perform the stream transform.

                ICryptoTransform decryptor = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV);
                // Create the streams used for decryption.

                using (MemoryStream msDecrypt = new MemoryStream(cipherText))

                {

                    using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))

                    {

                        using (StreamReader srDecrypt = new StreamReader(csDecrypt))

                        {
                            plaintext = srDecrypt.ReadToEnd();

                        }

                    }

                }
            }
            return plaintext;
        }
        public  string GenerateKeyAndIV()
        {    
            // This code is only here for an example
            RijndaelManaged myRijndaelManaged = new RijndaelManaged();    
            myRijndaelManaged.Mode = CipherMode.CBC;    
            myRijndaelManaged.Padding = PaddingMode.PKCS7;
            myRijndaelManaged.GenerateIV();    
            myRijndaelManaged.GenerateKey();
            string newinitVector = ByteArrayToHexString(myRijndaelManaged.IV);
            return newinitVector;
        }
        protected static byte[] HexStringToByte(string hexString) 
        {
            try 
            {         
                int bytesCount = (hexString.Length) / 2;         
                byte[] bytes = new byte[bytesCount];         
                for (int x = 0; x < bytesCount; ++x)             
                {             
                    bytes[x] = Convert.ToByte(hexString.Substring(x * 2, 2), 16);             
                }         
                return bytes;         
            }     
            catch 
            {         
                throw;         
            }     
        }
        public static string ByteArrayToHexString(byte[] ba) 
        {         
            StringBuilder hex = new StringBuilder(ba.Length * 2);         
            foreach (byte b in ba)             
                hex.AppendFormat("{0:x2}", b);         
            return hex.ToString();         
        }

 

AES/CBC/PKCS5Padding Encryption/Decryption in C#
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