C# 中 AEAD_AES_256_GCM 加密实践
前言
网络安全威胁的日益增多，数据加密技术成为了保障信息安全的关键手段之一。
其中，AEAD_AES_256_GCM（Authenticated Encryption with Associated Data using Advanced Encryption Standard with a 256-bit key and Galois/Counter Mode）因其高效的数据加密能力和完整性验证功能而备受青睐。
本文将详细介绍 C# 中如何实现 AEAD_AES_256_GCM 加密算法，并探讨其在实际应用中的优势与挑战。
通过本篇文章将了解到这一加密技术的基本原理以及如何在 C# 开发环境中有效应用它，以增强应用程序的安全性。
C# 中的 AEAD_AES_256_GCM
注意：AEAD_AES_256_GCM Key的长度必须是32位，nonce的长度必须是12位，附加数据有可能为空值。AEAD_AES_128_GCM Key的长度必须是16位，nonce的长度必须是12位，附加数据有可能为空值。
使用中不管AEAD_AES_256_GCM还是AEAD_AES_128_GCM加密，是根据key的长度来决定的。size = key.Length * 8 256 = 32 * 8, AEAD_AES_256_GCM的key长度必须是 32 位。128 = 16 * 8, AEAD_AES_128_GCM的key长度必须是 16 位。
使用BouncyCastle类库实现
安装 Install-Package Portable.BouncyCastle -Version 1.8.9。
微信支付官方代码中同样使用了 BouncyCastle。
csharp
/// <summary>
/// 使用BouncyCastle进行AEAD_AES_256_GCM 解密
/// </summary>
/// <param name="key">key:32位字符</param>
/// <param name="nonce">随机串12位</param>
/// <param name="cipherData">密文(Base64字符)</param>
/// <param name="associatedData">附加数据可能null</param>
/// <returns></returns>
static string AesGcmDecryptByBouncyCastle(string key, string nonce, string cipherData, string associatedData)
{
var associatedBytes = associatedData == null ? null : Encoding.UTF8.GetBytes(associatedData);
var gcmBlockCipher = new GcmBlockCipher(new AesEngine());
var parameters = new AeadParameters(
new KeyParameter(Encoding.UTF8.GetBytes(key)),
128, //128 = 16 * 8 => (tag size * 8)
Encoding.UTF8.GetBytes(nonce),
associatedBytes);
gcmBlockCipher.Init(false, parameters);
var data = Convert.FromBase64String(cipherData);
var plaintext = new byte[gcmBlockCipher.GetOutputSize(data.Length)];
var length = gcmBlockCipher.ProcessBytes(data, 0, data.Length, plaintext, 0);
gcmBlockCipher.DoFinal(plaintext, length);
return Encoding.UTF8.GetString(plaintext);
}
/// <summary>
/// 使用BouncyCastle进行AEAD_AES_256_GCM 加密
/// </summary>
/// <param name="key">key32位字符</param>
/// <param name="nonce">随机串12位</param>
/// <param name="plainData">明文</param>
/// <param name="associatedData">附加数据可能null</param>
/// <returns></returns>
static string AesGcmEncryptByBouncyCastle(string key, string nonce, string plainData, string associatedData)
{
var associatedBytes = associatedData == null ? null : Encoding.UTF8.GetBytes(associatedData);
var gcmBlockCipher = new GcmBlockCipher(new AesEngine());
var parameters = new AeadParameters(
new KeyParameter(Encoding.UTF8.GetBytes(key)),
128, //128 = 16 * 8 => (tag size * 8)
Encoding.UTF8.GetBytes(nonce),
associatedBytes);
gcmBlockCipher.Init(true, parameters);
var data = Encoding.UTF8.GetBytes(plainData);
var cipherData = new byte[gcmBlockCipher.GetOutputSize(data.Length)];
var length = gcmBlockCipher.ProcessBytes(data, 0, data.Length, cipherData, 0);
gcmBlockCipher.DoFinal(cipherData, length);
return Convert.ToBase64String(cipherData);
}1
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使用官方AesGcm类
自aspnetcore3.0之后，System.Security.Cryptography支持 AES_GCM，不支持.net framework。
在加密时，请使用AesGcmEncryptToBase64_WithTag方法，这个方法的结果包含了tag (authentication tag)。
加密结果最后面的16位字符就是tag，但是官方的加密方法没有帮我们拼接上。
c#
/// <summary>
/// 使用 AesGcm 解密
/// </summary>
/// <param name="key">key32位字符</param>
/// <param name="nonce">随机串12位</param>
/// <param name="encryptedData">密文（Base64字符）</param>
/// <param name="associatedData">(可能null)</param>
/// <returns></returns>
static string AesGcmDecryptFromBase64(string key, string nonce, string encryptedData, string associatedData)
{
var keyBytes = Encoding.UTF8.GetBytes(key);
var nonceBytes = Encoding.UTF8.GetBytes(nonce);
var associatedBytes = associatedData == null ? null : Encoding.UTF8.GetBytes(associatedData);
var encryptedBytes = Convert.FromBase64String(encryptedData);
//tag size is 16
var cipherBytes = encryptedBytes[..^16];
var tag = encryptedBytes[^16..];
var decryptedData = new byte[cipherBytes.Length];
using var cipher = new AesGcm(keyBytes);
cipher.Decrypt(nonceBytes, cipherBytes, tag, decryptedData, associatedBytes);
return Encoding.UTF8.GetString(decryptedData);
}
/// <summary>
/// 使用 AesGcm AEAD_AES_256_GCM 加密，不要在正式环境中使用这个方法。因为在解密时不知道tag，除非额外返回tag。
/// </summary>
/// <param name="key">key32位字符</param>
/// <param name="nonce">随机串12位</param>
/// <param name="plainData">明文</param>
/// <param name="associatedData">附加数据(可能null)</param>
/// <returns>只返回加密数据不包含authentication tag</returns>
static string AesGcmEncryptToBase64(string key, string nonce, string plainData, string associatedData)
{
var keyBytes = Encoding.UTF8.GetBytes(key);
var nonceBytes = Encoding.UTF8.GetBytes(nonce);
var associatedBytes = associatedData == null ? null : Encoding.UTF8.GetBytes(associatedData);
var plainBytes = Encoding.UTF8.GetBytes(plainData);
var cipherBytes = new byte[plainBytes.Length];
using var cipher = new AesGcm(keyBytes);
//tag size must be is 16
var tag = new byte[16];
cipher.Encrypt(nonceBytes, plainBytes, cipherBytes, tag, associatedBytes);
return Convert.ToBase64String(cipherBytes);
}
/// <summary>
/// 使用 AesGcm进行AEAD_AES_256_GCM加密
/// </summary>
/// <param name="key">key32位字符</param>
/// <param name="nonce">随机串12位</param>
/// <param name="plainData">明文</param>
/// <param name="associatedData">附加数据(可能null)</param>
/// <returns>base64(加密后数据 + authentication tag)</returns>
static string AesGcmEncryptToBase64_WithTag(string key, string nonce, string plainData, string associatedData)
{
var keyBytes = Encoding.UTF8.GetBytes(key);
var nonceBytes = Encoding.UTF8.GetBytes(nonce);
var associatedBytes = associatedData == null ? null : Encoding.UTF8.GetBytes(associatedData);
var plainBytes = Encoding.UTF8.GetBytes(plainData);
var cipherBytes = new byte[plainBytes.Length];
//tag size is 16
var tag = new byte[16];
using var cipher = new AesGcm(keyBytes);
cipher.Encrypt(nonceBytes, plainBytes, cipherBytes, tag, associatedBytes);
var cipherWithTag = new byte[cipherBytes.Length + tag.Length];
Buffer.BlockCopy(cipherBytes, 0, cipherWithTag, 0, cipherBytes.Length);
Buffer.BlockCopy(tag, 0, cipherWithTag, cipherBytes.Length, tag.Length);
return Convert.ToBase64String(cipherWithTag);
}1
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测试代码
C#
var text = "{'A':123, count:'10', isOk:false, body:{'Text':'select * from table_A where name=@_p1', result:[{'id':1, 'age':23}]}}";
//KEY 必须是两个32位
var key = "1234567890_1234567890_1234567890";
var nonce = "77d0a5ff3937";//Guid.NewGuid().ToString("N").Substring(0, 12);
var associated = "6df132d42d0b4581"; //Guid.NewGuid().ToString("N").Substring(0, 16);
var pythonResult = "PrTO/594j0CYMi2CQF9IFIp7UNkiTtIiIUbmR+jv1c1iO8Ng/HDFHDjL2t0DYo7xo5Vr0O0fUg9hD3bfCoomP+taVaPrW2kJbPTiFXkohXk3T80lQIdWP5lrl21vJvZO3MbmvshyjU+Oxk7pSnjiE5mw/sPXBs4jzS5wtvLUgHvWGaNxzw==";
Console.WriteLine();
var cipherText = AesGcmEncryptToBase64(key, nonce, text, nonce);
Console.WriteLine($"原始密文Base64 ：\t{cipherText}");
//Console.WriteLine($"密文tag Base64：\t\t{AesGcmEncryptToBase64(keyBytes, nonceBytes, text, associatedBytes)}");
Console.WriteLine($"Python GCM密文 ：\t{pythonResult}");
var cryptText1 = AesGcmEncryptByBouncyCastle(key, nonce, text, associated);
Console.WriteLine($"BouncyCastle密文: \t{cryptText1} ");
var cryptText2 = AesGcmEncryptToBase64_WithTag(key, nonce, text, associated);
Console.WriteLine($"密文+Tag Base64 : \t{cryptText2} ");
Console.WriteLine();
Console.WriteLine();
var t30 = AesGcmDecryptByBouncyCastle(key, nonce, pythonResult, associated);
Console.WriteLine($"BouncyCastle 解密 Python :{t30} \tisOk:{text == t30}");
var t40 = AesGcmDecryptFromBase64(key, nonce, pythonResult, associated);
Console.WriteLine($"AesGcm 解密 Python :{t40} \tisOk:{text == t40}");
Console.WriteLine();
Console.WriteLine();
var t31 = AesGcmDecryptByBouncyCastle(key, nonce, cryptText1, associated);
Console.WriteLine($"BouncyCastle 解密 BouncyCastle:{t31} \tisOk:{text == t31}");
var t41 = AesGcmDecryptFromBase64(key, nonce, cryptText1, associated);
Console.WriteLine($"AesGcm 解密 BouncyCastle:{t41} \tisOk:{text == t41}");
Console.WriteLine();
Console.WriteLine();
var t32 = AesGcmDecryptByBouncyCastle(key, nonce, cryptText2, associated);
Console.WriteLine($"BouncyCastle 解密 密文+Tag :{t32} \tisOk:{text == t32}");
var t42 = AesGcmDecryptFromBase64(key, nonce, cryptText2, associated);
Console.WriteLine($"AesGcm 解密 密文+Tag :{t42} \tisOk:{text == t42}");1
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总结
本文通过详细的讲解和实例演示，探讨了 C# 中 AEAD_AES_256_GCM 加密算法的实现方法及其重要性。
我们了解到，AEAD_AES_256_GCM 不仅能够提供高强度的数据加密，还能确保数据传输过程中的完整性和认证性，从而有效抵御多种网络攻击。
通过本篇文章的学习可以掌握在 C# 应用程序中使用 AEAD_AES_256_GCM 的基本技能，并能够在实际开发中加以应用，进一步提升软件系统的安全性。