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AES+HMAC

Xenophobic Xenomorph answered on March 14, 2024 Popularity 1/10 Helpfulness 1/10

answer AES+HMAC

AES+HMAC

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

public class AESEncryptionWithHMAC
{
    // Key sizes for AES
    private const int KeySize = 256;
    private const int BlockSize = 128;

    // Generate random key and IV
    private static byte[] GenerateRandomBytes(int size)
    {
        using (var rng = new RNGCryptoServiceProvider())
        {
            byte[] randomBytes = new byte[size];
            rng.GetBytes(randomBytes);
            return randomBytes;
        }
    }

    // Encrypt data using AES with CBC mode and HMAC for authentication
    public static byte[] EncryptAESWithHMAC(string plainText, byte[] encryptionKey, byte[] hmacKey)
    {
        using (Aes aesAlg = Aes.Create())
        {
            aesAlg.Key = encryptionKey;
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.BlockSize = BlockSize;
            aesAlg.Padding = PaddingMode.PKCS7;

            aesAlg.IV = GenerateRandomBytes(aesAlg.BlockSize / 8);

            using (MemoryStream ms = new MemoryStream())
            {
                using (CryptoStream csEncrypt = new CryptoStream(ms, aesAlg.CreateEncryptor(), CryptoStreamMode.Write))
                {
                    byte[] plainBytes = Encoding.UTF8.GetBytes(plainText);
                    csEncrypt.Write(plainBytes, 0, plainBytes.Length);
                    csEncrypt.FlushFinalBlock();

                    byte[] cipherText = ms.ToArray();

                    // Calculate HMAC
                    using (HMACSHA256 hmac = new HMACSHA256(hmacKey))
                    {
                        byte[] hmacValue = hmac.ComputeHash(cipherText);
                        byte[] result = new byte[cipherText.Length + hmacValue.Length];
                        Buffer.BlockCopy(cipherText, 0, result, 0, cipherText.Length);
                        Buffer.BlockCopy(hmacValue, 0, result, cipherText.Length, hmacValue.Length);
                        return result;
                    }
                }
            }
        }
    }

    // Decrypt data using AES with CBC mode and HMAC for authentication
    public static string DecryptAESWithHMAC(byte[] cipherTextWithHMAC, byte[] encryptionKey, byte[] hmacKey)
    {
        using (Aes aesAlg = Aes.Create())
        {
            aesAlg.Key = encryptionKey;
            aesAlg.Mode = CipherMode.CBC;
            aesAlg.BlockSize = BlockSize;
            aesAlg.Padding = PaddingMode.PKCS7;

            // Extract HMAC from end of cipherTextWithHMAC
            int hmacLength = 32; // HMACSHA256 produces 32-byte hash
            byte[] hmacValue = new byte[hmacLength];
            Buffer.BlockCopy(cipherTextWithHMAC, cipherTextWithHMAC.Length - hmacLength, hmacValue, 0, hmacLength);

            byte[] cipherText = new byte[cipherTextWithHMAC.Length - hmacLength];
            Buffer.BlockCopy(cipherTextWithHMAC, 0, cipherText, 0, cipherText.Length);

            // Validate HMAC
            using (HMACSHA256 hmac = new HMACSHA256(hmacKey))
            {
                byte[] computedHMAC = hmac.ComputeHash(cipherText);
                for (int i = 0; i < hmacLength; i++)
                {
                    if (computedHMAC[i] != hmacValue[i])
                        throw new CryptographicException("HMAC validation failed.");
                }
            }

            // Decrypt AES
            using (MemoryStream ms = new MemoryStream(cipherText))
            {
                using (CryptoStream csDecrypt = new CryptoStream(ms, aesAlg.CreateDecryptor(), CryptoStreamMode.Read))
                {
                    using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                    {
                        return srDecrypt.ReadToEnd();
                    }
                }
            }
        }
    }

    public static void Main(string[] args)
    {
        string plainText = "Hello, AES with HMAC!";
        byte[] encryptionKey = GenerateRandomBytes(KeySize / 8);
        byte[] hmacKey = GenerateRandomBytes(KeySize / 8);

        byte[] cipherTextWithHMAC = EncryptAESWithHMAC(plainText, encryptionKey, hmacKey);
        Console.WriteLine("Encrypted Text with HMAC: " + Convert.ToBase64String(cipherTextWithHMAC));

        string decryptedText = DecryptAESWithHMAC(cipherTextWithHMAC, encryptionKey, hmacKey);
        Console.WriteLine("Decrypted Text: " + decryptedText);
    }
}

Popularity 1/10 Helpfulness 1/10 Language csharp

Source: chat.openai.com

Tags: c#

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Contributed on Mar 14 2024

Xenophobic Xenomorph

0 Answers Avg Quality 2/10

AES+HMAC

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