AesUtil.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace Meadow.Cli
{
    static class AesUtil
    {
        const int ITERATIONS = 50000;
        static readonly HashAlgorithmName HASH_ALGO = HashAlgorithmName.SHA512;

        public static string EncryptString(string text, string password)
        {
            var passwordBytes = new UTF8Encoding(false, false).GetBytes(password);

            using (Aes aesAlg = Aes.Create())
            {
                aesAlg.GenerateIV();
                byte[] iv = aesAlg.IV;

                // The Salt will be the first 8 bytes of the IV.
                byte[] theSalt = new byte[8];
                Array.Copy(iv, theSalt, 8);

                // A key for AES is generated by expanding the password using the following method.
                Rfc2898DeriveBytes keyGen = new Rfc2898DeriveBytes(passwordBytes, theSalt, ITERATIONS, HASH_ALGO);
                byte[] aesKey = keyGen.GetBytes(aesAlg.KeySize / 8);
                aesAlg.Key = aesKey;
                aesAlg.Mode = CipherMode.CBC;
                aesAlg.Padding = PaddingMode.PKCS7;

                // Create a decrytor to perform the stream transform.
                using (ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, iv))
                using (MemoryStream msEncrypt = new MemoryStream())
                {
                    // You can write the IV here and not need to do it later.
                    msEncrypt.Write(iv, 0, iv.Length);

                    using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                    using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                    {
                        // Write all data to the stream.
                        swEncrypt.Write(text);
                    }
                    
                    return Convert.ToBase64String(msEncrypt.ToArray());
                }
            }

        }

        public static string DecryptString(string cipherText, string password)
        {
            var passwordBytes = new UTF8Encoding(false, false).GetBytes(password);

            var fullCipher = Convert.FromBase64String(cipherText);

            using (Aes aesAlg = Aes.Create())
            {
                aesAlg.Mode = CipherMode.CBC;
                aesAlg.Padding = PaddingMode.PKCS7;

                // Grab IV from ciphertext
                byte[] iv = new byte[16];
                Array.Copy(fullCipher, 0, iv, 0, 16);

                // Use the IV for the Salt
                byte[] theSalt = new byte[8];
                Array.Copy(iv, theSalt, 8);

                Rfc2898DeriveBytes keyGen = new Rfc2898DeriveBytes(passwordBytes, theSalt, ITERATIONS, HASH_ALGO);

                byte[] aesKey = keyGen.GetBytes(aesAlg.KeySize / 8);
                aesAlg.Key = aesKey;

                // Create a decrytor to perform the stream transform.
                using (ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, iv))
                using (MemoryStream msDecrypt = new MemoryStream(fullCipher))
                {
                    msDecrypt.Position += 16;
                    using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read)) //Notice this is Read mode not Write mode.
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                    {
                        //Decrypt the ciphertext
                        return srDecrypt.ReadToEnd();
                    }
                }
            }
        }

    }
}