用 .NET 加解密已是老生常談，.NET 內建 MD5、SHA1、RSA、AES、DES... 等雜湊及加密演算法，寫來易如反掌，網路上的文章也很多。但沒有自己整理過一次，每回要用都要爬文找半天。有些基本功不能省就是不能省，所以，我的 RSA 私房筆記來了。
程式範例 1 包含：產生隨機 RSA 金鑰、匯出公私鑰、對一小段文字加密、產生數位簽章。第二階段則包含匯入私鑰、解密加密內容、驗證數位簽章，並試著偷改內容驗證簽章是否因此失效。
staticvoid RSAEncDec()
{//建立RSA公私鑰 var rsaEnc = new RSACryptoServiceProvider();//Key長度384-16384, Win8.1+最小512//預設1024，可new RSACryptoServiceProvider(2048)指定不同大小 Console.WriteLine($"KeySize={rsaEnc.KeySize}");//匯出公鑰(用於解密，檢驗簽章)，XML格式 var pubKey = rsaEnc.ToXmlString(false); Console.WriteLine($"PubKey={pubKey}");//匯出公私鑰 var rsaKeys = rsaEnc.ToXmlString(true); Console.WriteLine($"RSAKeys={rsaKeys}");//加密小段文字(用公鑰) var rawText = ".NET Rocks!";var rawData = Encoding.UTF8.GetBytes(rawText);
//第二個參數指定是否使用OAEP提高安全性 var encData = rsaEnc.Encrypt(rawData, true);//產生數位簽章 var stream = new MemoryStream(rawData);var signature = rsaEnc.SignData(stream,
new SHA1CryptoServiceProvider());//** 解密 ** 需要公私鑰 var rsaDec = new RSACryptoServiceProvider();//從XML還原公私鑰rsaDec.FromXmlString(rsaKeys);
//使用私鑰解密 var decData = rsaDec.Decrypt(encData, true);var test = Encoding.UTF8.GetString(decData);
Console.WriteLine($"解密結果: {test}");//** 驗章 ** 只需公鑰 var rsa4Sign = new RSACryptoServiceProvider();rsa4Sign.FromXmlString(pubKey);
//檢驗數位簽章var valid = rsa4Sign.VerifyData(decData,
new SHA1CryptoServiceProvider(), signature);Console.WriteLine($"數位簽章: {(valid?"PASS":"FAILED")}");
//測試修改一個Byte讓簽章無效decData[0]++;
valid = rsa4Sign.VerifyData(decData,
new SHA1CryptoServiceProvider(), signature);Console.WriteLine($"篡改版數位簽章: {(valid ? "PASS" : "FAILED")}");
}
執行結果：
KeySize=1024
PubKey=<RSAKeyValue><Modulus>q+SlvTWJ...+4BW7j0=</Modulus>
<Exponent>AQAB</Exponent></RSAKeyValue>
RSAKeys=<RSAKeyValue><Modulus>q+SlvTWJ...+4BW7j0=</Modulus>
<Exponent>AQAB</Exponent><P>ztDGDTc...d3ST3ow==</P>
<Q>1MW/8rq...ZrA3+Kxgnw==</Q>
<DP>cE4mfh6WruasI...IKsn/UiQ==</DP>
<DQ>dY81OPWZH...qtGoZ0MXQ==</DQ>
<InverseQ>cPTkfCrpSy...XmOH5qiu982pw==</InverseQ>
<D>IOtWDmld...+V3VeU=</D></RSAKeyValue>
解密結果: .NET Rocks!
數位簽章: PASS
篡改版數位簽章: FAILED
RSA 加解密只適用小段資料內容，資料長度不能超過其金鑰長度減去 Header、Padding 長度，以 2048 位元 RSA 只能加密 256 - 11 = 245 Bytes(參考: RFC2313 The length of the data D shall not be more than k-11 octets, which is positive since the length k of the modulus is at least 12 octets.) 實務上加密大量內容還是得靠對稱式加密(例如: DES、3DES、AES)，RSA 則用來加密對稱式加密的金鑰。
程式範例 2 展示使用 RSA + AES 聯手處理 488MB 的 zip 檔的加解密以及數位簽章：
staticvoid RsaEncDecFile()
{//建立RSA公私鑰 var rsaEnc = new RSACryptoServiceProvider(2048);//匯出金鑰 var pubKey = rsaEnc.ToXmlString(false); var rsaKeys = rsaEnc.ToXmlString(true);//建立AES Managed時產生隨機Key及IV，不用另行指定 var aes = new AesManaged();var encAesKeyIV = aes.Key.Concat(aes.IV).ToArray();
var aesKeyEncrypted = rsaEnc.Encrypt(encAesKeyIV, true);byte[] signature; Stopwatch sw = new Stopwatch();sw.Start();
//準備加密Streamusing (var encFile = new FileStream("D:\\Encrypted.bin", FileMode.Create))
{using (var outStream = new
CryptoStream(
encFile, aes.CreateEncryptor(), CryptoStreamMode.Write))
{//讀取約500MB檔案寫入加密Streamusing (var fs = new FileStream("D:\\Source.zip",
FileMode.Open))
{//REF: Buffer Size 64K CPU clock 較少 //https://goo.gl/UAuPytvar buff = newbyte[65536];
int bytesRead = 0;while ((bytesRead = fs.Read(buff, 0, buff.Length)) > 0) {outStream.Write(buff, 0, bytesRead);
}
}
}
}
sw.Stop();
Console.WriteLine($"加密耗時: {sw.ElapsedMilliseconds}ms");byte[] srcHash = SHA1.Create().ComputeHash(new FileStream("D:\\Source.zip", FileMode.Open));
signature = rsaEnc.SignHash(srcHash, CryptoConfig.MapNameToOID("SHA1")); var rsaDec = new RSACryptoServiceProvider();//從XML還原公私鑰rsaDec.FromXmlString(rsaKeys);
//解密出AES Key var aesKeyIV = rsaDec.Decrypt(aesKeyEncrypted, true); aes = new AesManaged() {KeySize = 256,
Key = aesKeyIV.Take(32).ToArray(),
IV = aesKeyIV.Skip(32).Take(16).ToArray(),
BlockSize = 128
};
sw.Restart();
//準備解密Streamusing (var decFile = new FileStream("D:\\Decrypted.zip", FileMode.Create))
{using (var encFile = new FileStream("D:\\Encrypted.bin", FileMode.Open))
{using (var decStream = new CryptoStream(encFile,
aes.CreateDecryptor(), CryptoStreamMode.Read))
{var buff = newbyte[65536];
int bytesRead = 0;while ((bytesRead = decStream.Read(buff, 0, buff.Length)) > 0) {decFile.Write(buff, 0, bytesRead);
}
}
}
}
sw.Stop();
Console.WriteLine($"解密耗時: {sw.ElapsedMilliseconds}ms");//印出解密檔案Hash與原始檔比對是否相同byte[] decHash = SHA1.Create().ComputeHash(new FileStream("D:\\Decrypted.zip", FileMode.Open));
Console.WriteLine($"Source SHA1={BitConverter.ToString(srcHash)}"); Console.WriteLine($"Decrypted SHA1={BitConverter.ToString(decHash)}");//檢驗數位簽章var valid =
rsaDec.VerifyHash(decHash, CryptoConfig.MapNameToOID("SHA1"), signature);Console.WriteLine($"數位簽章: {(valid ? "PASS" : "FAILED")}");
}
實測 AES 加密 488MB 檔案需 12.3 秒，解密需 13.5 秒，速度蠻快的。
加密耗時: 12251ms
解密耗時: 13522ms
Source SHA1=34-F4-75-C1-81-7E-F4-25-4F-97-28-43-0C-7A-9D-5F-10-BD-2F-11
Decrypted SHA1=34-F4-75-C1-81-7E-F4-25-4F-97-28-43-0C-7A-9D-5F-10-BD-2F-11
數位簽章: PASS
另外，實務上不建議讓金鑰以文字檔形式曝露在外，多半會用金鑰容器保存 RSA 金鑰，詳情可參考官方文件，以下是簡單筆記：
staticvoid RsaKeyContainer()
{//在個人RSA容器區建立金鑰容器並存入RSA金鑰//一個KeyContainerName對應一把金鑰 var csp1 = new CspParameters(); csp1.KeyContainerName = "RSALab"; var rsa1 = new RSACryptoServiceProvider(csp1);//如果要從外部匯入金鑰，先建立RSA再FromXmlString() var csp2 = new CspParameters() { KeyContainerName = "RSALab"};
var rsa2 = new RSACryptoServiceProvider(csp2); rsa2.PersistKeyInCsp = true; rsa2.FromXmlString("...");//若同名金鑰容器已存在，自動取回上次存入的金鑰 var csp3 = new CspParameters() { KeyContainerName = "RSALab"};
var rsa3 = new RSACryptoServiceProvider(csp3);//要刪除金鑰，先取消PersistKeyInCsp再Clear()//金鑰容器也會一併被刪除 var csp4 = new CspParameters() { KeyContainerName = "RSALab"};
var rsa4 = new RSACryptoServiceProvider(csp4); rsa4.PersistKeyInCsp = false;rsa4.Clear();
}
