AES String Encryption (CBC) Example Code for C#

aes_example.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace aes_example
{
    using System;
    using System.IO;
    using System.Security.Cryptography;

    class Program
    {
        public static void Main()
        {
            try
            {

                string original = "Here is some data to encrypt!";

                // Create a new instance of the Aes 
                // class.  This generates a new key and initialization  
                // vector (IV). 
                using (var random = new RNGCryptoServiceProvider())
                {
                    var key = new byte[16];
                    random.GetBytes(key);

                    // Encrypt the string to an array of bytes. 
                    byte[] encrypted = EncryptStringToBytes_Aes(original, key);

                    // Decrypt the bytes to a string. 
                    string roundtrip = DecryptStringFromBytes_Aes(encrypted, key);

                    //Display the original data and the decrypted data.
                    Console.WriteLine("Original:   {0}", original);
                    Console.WriteLine("Encrypted (b64-encode): {0}", Convert.ToBase64String(encrypted));
                    Console.WriteLine("Round Trip: {0}", roundtrip);
                    Console.ReadKey();
                }

            }
            catch (Exception e)
            {
                Console.WriteLine("Error: {0}", e.Message);
            }
        }
        
        static byte[] EncryptStringToBytes_Aes(string plainText, byte[] Key)
        {
            byte[] encrypted;
            byte[] IV;

            using (Aes aesAlg = Aes.Create())
            {
                aesAlg.Key = Key;

                aesAlg.GenerateIV();
                IV = aesAlg.IV;

                aesAlg.Mode = CipherMode.CBC;

                var encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);

                // Create the streams used for encryption. 
                using (var msEncrypt = new MemoryStream())
                {
                    using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                    {
                        using (var swEncrypt = new StreamWriter(csEncrypt))
                        {
                            //Write all data to the stream.
                            swEncrypt.Write(plainText);
                        }
                        encrypted = msEncrypt.ToArray();
                    }
                }
            }

            var combinedIvCt = new byte[IV.Length + encrypted.Length];
            Array.Copy(IV, 0, combinedIvCt, 0, IV.Length);
            Array.Copy(encrypted, 0, combinedIvCt, IV.Length, encrypted.Length);

            // Return the encrypted bytes from the memory stream. 
            return combinedIvCt;

        }

        static string DecryptStringFromBytes_Aes(byte[] cipherTextCombined, byte[] Key)
        {
            
            // Declare the string used to hold 
            // the decrypted text. 
            string plaintext = null;

            // Create an Aes object 
            // with the specified key and IV. 
            using (Aes aesAlg = Aes.Create())
            {
                aesAlg.Key = Key;

                byte[] IV = new byte[aesAlg.BlockSize/8];
                byte[] cipherText = new byte[cipherTextCombined.Length - IV.Length];
                
                Array.Copy(cipherTextCombined, IV, IV.Length);
                Array.Copy(cipherTextCombined, IV.Length, cipherText, 0, cipherText.Length);

                aesAlg.IV = IV;

                aesAlg.Mode = CipherMode.CBC;

                // Create a decrytor to perform the stream transform.
                ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);

                // Create the streams used for decryption. 
                using (var msDecrypt = new MemoryStream(cipherText))
                {
                    using (var csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                    {
                        using (var srDecrypt = new StreamReader(csDecrypt))
                        {

                            // Read the decrypted bytes from the decrypting stream
                            // and place them in a string.
                            plaintext = srDecrypt.ReadToEnd();
                        }
                    }
                }

            }

            return plaintext;

        }
    }
}

hello....thats some good code

thank you very much for your code

MSDN article for AES system.security.cryptography.aes https://msdn.microsoft.com/en-us/library/system.security.cryptography.aes(v=vs.110).aspx

i used your code, thank you.

Is this aes-128-cbc? thanks
Nice code though

I have a file encrypted by AES 256

SaltIterationCount = 20000;
SaltLength = 16;
Salt[NfmsPackager::kSaltLength] = {0xd3, 0x31, 0x29, 0x4a, 0xae, 0x3d, 0xe5, 0xc5, 0xdf, 0x64, 0xd0, 0xf2, 0xa4, 0x97, 0xa2, 0x15};
InitializationVectorLength = 16; //128 bits long key
Password = "helloword";
Algorithm : PKCS5_PBKDF2_HMAC_SHA1

how can i decrypt

@jipsonsds, In this example, the text is encrypted and not the file

Are you the original writer of this code?
https://docs.microsoft.com/en-us/dotnet/api/system.security.cryptography.aes?view=netframework-4.8

@kelalaka-153 No, I did not write this code. The fine folks at Microsoft did, but I’m guessing that you may already know that since you pasted a link to their site in your original comment. 😄

I copied this code into a snippet to make it easier for me to find and reference without having to search for it again.

No, I don't know. Usually, I put a link on top of the class, function.

Thanks man, awesome code!