Encrypt and decrypt a string with a pass phrase.

CryptoService.cs

using System.Security.Cryptography;
using System.Text;


/// <summary>
/// Encrypt and decrypt a string with a pass phrase.
/// // https://stackoverflow.com/questions/10168240/encrypting-decrypting-a-string-in-c-sharp
/// </summary>
public class CryptoService : ICryptoService
{
    public const string DefaultPassPhrase = "WXk1CNr4m8B9JEUKI0ry355WMCwH4VUMZmuWuy8G1ieG1G7xRzjdb0Ty0YjM718n";

    private const int BlockSizeBits = 128;

    // This constant is used to determine the key size of the encryption algorithm in bytes.
    private const int KeySizeBytes = BlockSizeBits / 8; // 16 bytes

    // This constant determines the number of iterations for the password bytes generation function.
    private const int DerivationIterations = 100;

    public string Encrypt(string text, string passPhrase = DefaultPassPhrase)
    {
        // Salt and IV is randomly generated each time, but is prepended to encrypted cipher text
        // so that the same Salt and IV values can be used when decrypting.
        var saltStringBytes = RandomNumberGenerator.GetBytes(KeySizeBytes);
        var ivStringBytes = RandomNumberGenerator.GetBytes(KeySizeBytes);
        var plainTextBytes = Encoding.UTF8.GetBytes(text);

        using var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations);
        var keyBytes = password.GetBytes(KeySizeBytes);

        using var symmetricKey =  Aes.Create();
        symmetricKey.BlockSize = BlockSizeBits;
        symmetricKey.Mode = CipherMode.CBC;
        symmetricKey.Padding = PaddingMode.PKCS7;

        using var encryptor = symmetricKey.CreateEncryptor(keyBytes, ivStringBytes);
        using var memoryStream = new MemoryStream();
        using var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);

        cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
        cryptoStream.FlushFinalBlock();

        var encryptedTextBytes = saltStringBytes.Concat(ivStringBytes)
                                                .Concat(memoryStream.ToArray())
                                                .ToArray();
        memoryStream.Close();
        cryptoStream.Close();
        return Convert.ToBase64String(encryptedTextBytes);
    }

    public string Decrypt(string encryptedText, string passPhrase = DefaultPassPhrase)
    {
        // Get the complete stream of bytes that represent:
        // [32 bytes of Salt] + [32 bytes of IV] + [n bytes of CipherText]
        var encryptedTextBytesWithSaltAndIv = Convert.FromBase64String(encryptedText);

        // Get the salt bytes by extracting the first 32 bytes from the supplied cipherText bytes.
        var saltStringBytes = encryptedTextBytesWithSaltAndIv.Take(KeySizeBytes).ToArray();

        // Get the IV bytes by extracting the next 32 bytes from the supplied cipherText bytes.
        var ivStringBytes = encryptedTextBytesWithSaltAndIv.Skip(KeySizeBytes).Take(KeySizeBytes).ToArray();

        // Get the actual cipher text bytes by removing the first 64 bytes from the cipherText string.
        var encryptedTextBytes = encryptedTextBytesWithSaltAndIv.Skip(KeySizeBytes * 2).ToArray();

        using var password = new Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations);
        var keyBytes = password.GetBytes(KeySizeBytes);

        using var symmetricKey =  Aes.Create();
        symmetricKey.BlockSize = BlockSizeBits;
        symmetricKey.Mode = CipherMode.CBC;
        symmetricKey.Padding = PaddingMode.PKCS7;

        using var decryptor = symmetricKey.CreateDecryptor(keyBytes, ivStringBytes);
        using var memoryStream = new MemoryStream(encryptedTextBytes);
        using var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);

        var plainTextBytes = new byte[encryptedTextBytes.Length];
        var decryptedByteCount = 0;
        int readBytes;

        do
        {
            readBytes = cryptoStream.Read(plainTextBytes, decryptedByteCount, plainTextBytes.Length - decryptedByteCount);
            decryptedByteCount += readBytes;
        } while (readBytes > 0);

        // var decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
        memoryStream.Close();
        cryptoStream.Close();
        return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
    }
}

public interface ICryptoService
{
    string Encrypt(string text, string passPhrase = CryptoService.DefaultPassPhrase);
    string Decrypt(string encryptedText, string passPhrase = CryptoService.DefaultPassPhrase);
}