要检查您使用的密码是否正确，您可以使用以下代码
Dim decryptedByteCount As Integer
Try
decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length)
Catch exp As System.Exception
Return "Password Not Correct"
End Try
本质上，检查解密过程中是否生成错误消息。
我在下面报告了所有解码代码
Public Shared Function Decrypt(ByVal cipherText As String) As String
If System.Web.HttpContext.Current.Session("Crypto") = "" Then
HttpContext.Current.Response.Redirect("http://yoursite.com")
Else
If cipherText <> "" Then
'Setto la password per criptare il testo
Dim passPhrase As String = System.Web.HttpContext.Current.Session("Crypto")
'Ottieni lo stream completo di byte che rappresentano: [32 byte di Salt] + [32 byte di IV] + [n byte di testo cifrato]
Dim cipherTextBytesWithSaltAndIv = Convert.FromBase64String(cipherText)
'Ottieni i Salt bytes estraendo i primi 32 byte dai byte di testo cifrato forniti
Dim saltStringBytes = cipherTextBytesWithSaltAndIv.Take((Keysize)).ToArray
'Ottieni i IV byte estraendo i successivi 32 byte dai byte testo cifrato forniti.
Dim ivStringBytes = cipherTextBytesWithSaltAndIv.Skip((Keysize)).Take((Keysize)).ToArray
'Ottieni i byte del testo cifrato effettivo rimuovendo i primi 64 byte dal testo cifrato.
Dim cipherTextBytes = cipherTextBytesWithSaltAndIv.Skip(((Keysize) * 2)).Take((cipherTextBytesWithSaltAndIv.Length - ((Keysize) * 2))).ToArray
Dim password = New Rfc2898DeriveBytes(passPhrase, saltStringBytes, DerivationIterations)
Dim keyBytes = password.GetBytes((Keysize))
Dim symmetricKey = New RijndaelManaged
symmetricKey.BlockSize = 256
symmetricKey.Mode = CipherMode.CBC
symmetricKey.Padding = PaddingMode.PKCS7
Dim decryptor = symmetricKey.CreateDecryptor(keyBytes, ivStringBytes)
Dim memoryStream = New MemoryStream(cipherTextBytes)
Dim cryptoStream = New CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read)
Dim plainTextBytes = New Byte((cipherTextBytes.Length) - 1) {}
Dim decryptedByteCount As Integer
Try
decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length)
Catch exp As System.Exception
Return "La password di Cryptazione non è corretta"
End Try
memoryStream.Close()
cryptoStream.Close()
Return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount)
Else
Decrypt = ""
End If
End If
End Function
虽然我在 Teoman Soygul 的帖子中对 CRC/哈希有些同意，但有一件非常重要的事情需要注意。永远不要加密哈希，因为这可能会使寻找结果密钥更容易。即使没有加密哈希，您仍然为他们提供了一种轻松的方法来测试他们是否成功获得了正确的密码；然而，让我们假设这已经是可能的。由于我知道您加密的数据类型，无论是文本、序列化对象还是其他类型，我都可以编写代码来识别它。
话虽如此，我曾使用以下代码的变形来加密 / 解密数据：
static void Main()
{
byte[] test = Encrypt(Encoding.UTF8.GetBytes("Hello World!"), "My Product Name and/or whatever constant", "password");
Console.WriteLine(Convert.ToBase64String(test));
string plain = Encoding.UTF8.GetString(Decrypt(test, "My Product Name and/or whatever constant", "passwords"));
Console.WriteLine(plain);
}
public static byte[] Encrypt(byte[] data, string iv, string password)
{
using (RijndaelManaged m = new RijndaelManaged())
using (SHA256Managed h = new SHA256Managed())
{
m.KeySize = 256;
m.BlockSize = 256;
byte[] hash = h.ComputeHash(data);
byte[] salt = new byte[32];
new RNGCryptoServiceProvider().GetBytes(salt);
m.IV = h.ComputeHash(Encoding.UTF8.GetBytes(iv));
m.Key = new Rfc2898DeriveBytes(password, salt) { IterationCount = 10000 }.GetBytes(32);
using (MemoryStream ms = new MemoryStream())
{
ms.Write(hash, 0, hash.Length);
ms.Write(salt, 0, salt.Length);
using (CryptoStream cs = new CryptoStream(ms, m.CreateEncryptor(), CryptoStreamMode.Write))
{
cs.Write(data, 0, data.Length);
cs.FlushFinalBlock();
return ms.ToArray();
}
}
}
}
public static byte[] Decrypt(byte[] data, string iv, string password)
{
using (MemoryStream ms = new MemoryStream(data, false))
using (RijndaelManaged m = new RijndaelManaged())
using (SHA256Managed h = new SHA256Managed())
{
try
{
m.KeySize = 256;
m.BlockSize = 256;
byte[] hash = new byte[32];
ms.Read(hash, 0, 32);
byte[] salt = new byte[32];
ms.Read(salt, 0, 32);
m.IV = h.ComputeHash(Encoding.UTF8.GetBytes(iv));
m.Key = new Rfc2898DeriveBytes(password, salt) { IterationCount = 10000 }.GetBytes(32);
using (MemoryStream result = new MemoryStream())
{
using (CryptoStream cs = new CryptoStream(ms, m.CreateDecryptor(), CryptoStreamMode.Read))
{
byte[] buffer = new byte[1024];
int len;
while ((len = cs.Read(buffer, 0, buffer.Length)) > 0)
result.Write(buffer, 0, len);
}
byte[] final = result.ToArray();
if (Convert.ToBase64String(hash) != Convert.ToBase64String(h.ComputeHash(final)))
throw new UnauthorizedAccessException();
return final;
}
}
catch
{
//never leak the exception type...
throw new UnauthorizedAccessException();
}
}
}
我喜欢Can Gencer的回答; 你不能真正验证没有HMAC的解密。
但是，如果你有一个非常大的明文，那么解密可能会非常昂贵。你可能需要做很多工作才能发现密码无效。能够快速拒绝错误密码而不必经历所有这些工作将是很好的。有一种方法可以使用PKCS#5 PBKDF2。(在RFC2898中标准化，可通过Rfc2898DeriveBytes在您的C#程序中访问)。
通常，数据协议要求使用PBKDF2从密码和盐生成密钥，进行1000个周期或某个指定的数字。然后，也可以（可选地）通过同一算法的继续来初始化向量。附言：你写道：
我能想到的最简单的方法是在加密时在消息开头放置一个“魔数”，并在解密后检查它是否仍然存在。
避免将明文放入加密文本中。这只会暴露另一个攻击向量，使攻击者更容易消除错误的方向。我上面提到的密码验证是一个不同的问题，不会暴露这种风险。
Public Sub decryptFile(ByVal input As String, ByVal output As String)
inputFile = New FileStream(input, FileMode.Open, FileAccess.Read)
outputFile = New FileStream(output, FileMode.OpenOrCreate, FileAccess.Write)
outputFile.SetLength(0)
Dim buffer(4096) As Byte
Dim bytesProcessed As Long = 0
Dim fileLength As Long = inputFile.Length
Dim bytesInCurrentBlock As Integer
Dim rijandael As New RijndaelManaged
Dim cryptoStream As CryptoStream = New CryptoStream(outputFile, rijandael.CreateDecryptor(encryptionKey, encryptionIV), CryptoStreamMode.Write)
While bytesProcessed < fileLength
bytesInCurrentBlock = inputFile.Read(buffer, 0, 4096)
cryptoStream.Write(buffer, 0, bytesInCurrentBlock)
bytesProcessed = bytesProcessed + CLng(bytesInCurrentBlock)
End While
Try
cryptoStream.Close() 'this will raise error if wrong password used
inputFile.Close()
outputFile.Close()
File.Delete(input)
success += 1
Catch ex As Exception
fail += 1
inputFile.Close()
outputFile.Close()
outputFile = Nothing
File.Delete(output)
End Try
我使用这段代码来解密任何文件。当使用错误的密码解密文件时，会在cryptostream.close()处检测到错误。当发生错误时，只需关闭输出流并释放它（将outputFile设置为Nothing），然后删除输出文件即可。这对我很有效。