当文本少于 15 个字符时，将 CryptoStream 转换为使用声明会使内存流为空

Question

我在使用 C# 加密文本时遇到一个奇怪的问题。 ReSharper（我同意）建议替换此代码中的 using 块：

public object GetEncryptedOrDefault(object value, ICryptoTransform encryptor)
{
    if (encryptor is null)
    {
        throw new ArgumentNullException(nameof(encryptor));
    }
    var isEncryptionNeeded = value != null;
    if (isEncryptionNeeded)
    {
        using var memoryStream = new MemoryStream();
        using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
        {
            using var writer = new StreamWriter(cryptoStream);
            var valueAsText = value.ToString();
            writer.Write(valueAsText);
        }

        var encryptedData = memoryStream.ToArray();
        var encryptedText = Convert.ToBase64String(encryptedData);
        return encryptedText;
    }

    return default;
}

到这个简化的（注意使用声明而不是块）：

public object GetEncryptedOrDefault(object value, ICryptoTransform encryptor)
{
    if (encryptor is null)
    {
        throw new ArgumentNullException(nameof(encryptor));
    }
    var isEncryptionNeeded = value != null;
    if (isEncryptionNeeded)
    {
        using var memoryStream = new MemoryStream();
        using var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
        using var writer = new StreamWriter(cryptoStream);
        var valueAsText = value.ToString();
        writer.Write(valueAsText);

        var encryptedData = memoryStream.ToArray();
        var encryptedText = Convert.ToBase64String(encryptedData);
        return encryptedText;
    }

    return default;
}

嗯.. 第一个效果很好，它能够加密文本。但是第二个不起作用！ encryptedData 是空的，因此它产生一个空的 encryptedText.

我看不出问题所在。为什么？

更新 1 多亏了 Emanuel 的回答，我才能够使它仅在要加密的文本大于 15 个字符时才起作用。 这真奇怪。少于 15 个字符，只有带有 "old fashioned" using 块的代码才能工作，而不是使用 using 声明的代码。

我重现了问题in this sample repo at Github。

即使这个问题与 AesManaged（我不知道）有关，为什么第一个方法成功而第二个方法失败 对于任何 15 或更少的文本字符数？

这是代码：

class Program
{
    static void Main(string[] args)
    {
        var encryptor = GetEncryptor();
        var text = "Under 15 characters this text causes problems";
        while (text.Length >= 0)
        {
            text = text.Substring(0, text.Length - 1);
            Console.WriteLine($"Result Method A with {text.Length} characters: {GetWorkingEncrypted(text, encryptor)}");
            Console.WriteLine($"Result Method B with {text.Length} characters: {GetNonWorkingEncrypted(text, encryptor)}");
        }
    }

    private static string GetWorkingEncrypted(string text, ICryptoTransform encryptor)
    {
        using var memoryStream = new MemoryStream();
        using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
        {
            using var writer = new StreamWriter(cryptoStream);
            writer.Write(text);
            writer.Flush();
        }

        var encryptedData = memoryStream.ToArray();
        if (encryptedData.Length == 0)
        {
            throw new Exception($"Encrypted data is 0 for text {text}");
        }
        var encryptedText = Convert.ToBase64String(encryptedData);
        return encryptedText;
    }

    private static string GetNonWorkingEncrypted(string text, ICryptoTransform encryptor)
    {
        using var memoryStream = new MemoryStream();
        using var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
        using var writer = new StreamWriter(cryptoStream);
        writer.Write(text);
        writer.Flush();

        var encryptedData = memoryStream.ToArray();
        if (encryptedData.Length == 0)
        {
            throw new Exception($"Encrypted data is 0 for text \"{text}\" with length {text.Length}");
        }
        var encryptedText = Convert.ToBase64String(encryptedData);
        return encryptedText;
    }

    private static ICryptoTransform GetEncryptor()
    {
        var aesManaged =
            new AesManaged
            {
                Padding = PaddingMode.PKCS7
            };

        return aesManaged.CreateEncryptor();
    }
}

这是执行的结果：

Result Method A with 44 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3937Peo255iHRylA9DF0lf4K+
Result Method B with 44 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 43 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934Pwaqyce+T6SG3WaqnzNRt
Result Method B with 43 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 42 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3936tIT0560Lky1gz3FXKHU3Y
Result Method B with 42 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 41 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934xr6AiKuSxRet/e8iWhLEV
Result Method B with 41 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 40 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3937gCR2Lf9zQClOlCFw51dVo
Result Method B with 40 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 39 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3936OjZ4HEtzkcIjVMUJcDzum
Result Method B with 39 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 38 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3936ti1b7pskEFKb2zJrRkVaD
Result Method B with 38 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 37 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3937rKO73A+OiHd1aAMqOd3Df
Result Method B with 37 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 36 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934/BNp0BiYZPRMUUiODp/kb
Result Method B with 36 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 35 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3935sjuGp/uE4fVOn26J1ESzH
Result Method B with 35 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 34 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+39360AAj7hDLcnbMZH7aknpDl
Result Method B with 34 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 33 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3935EfO82m/jR81he3Jt4z1h+
Result Method B with 33 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 32 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934zeVj3CoE5YIFK8/g07QmH
Result Method B with 32 characters: /ppBS775B1KRShB+QKTLZJH/fCQbNFhCvzfbFP+3934=
Result Method A with 31 characters: /ppBS775B1KRShB+QKTLZCRCNZXU9Ndp7uKLJkUXFsw=
Result Method B with 31 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 30 characters: /ppBS775B1KRShB+QKTLZJ1WbVjggwJM3uOTZ2dHx5c=
Result Method B with 30 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 29 characters: /ppBS775B1KRShB+QKTLZDiI785bQRbNeZX2aNFQvZo=
Result Method B with 29 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 28 characters: /ppBS775B1KRShB+QKTLZMmLT/ycIHWz0sjPsdfg/ys=
Result Method B with 28 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 27 characters: /ppBS775B1KRShB+QKTLZJDekWQLgx9tTUE/59ldSqs=
Result Method B with 27 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 26 characters: /ppBS775B1KRShB+QKTLZKIkr5xwCc8SS9eSnw715vk=
Result Method B with 26 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 25 characters: /ppBS775B1KRShB+QKTLZFAtZM8oTV/uTBb6OccqErc=
Result Method B with 25 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 24 characters: /ppBS775B1KRShB+QKTLZD5BAXR9qZav1rG5NnaLEQQ=
Result Method B with 24 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 23 characters: /ppBS775B1KRShB+QKTLZFof3ATUQWJqiZ2wZ6Gj4Vc=
Result Method B with 23 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 22 characters: /ppBS775B1KRShB+QKTLZNWhgIhTYyERb74rKEl8bos=
Result Method B with 22 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 21 characters: /ppBS775B1KRShB+QKTLZIsgSoHGJT3XysDLqmV9Bi0=
Result Method B with 21 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 20 characters: /ppBS775B1KRShB+QKTLZO0ZdC9DzISByS5T1Rx4hQ4=
Result Method B with 20 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 19 characters: /ppBS775B1KRShB+QKTLZBFfUwWYJ5ECKF2JexKf8Xk=
Result Method B with 19 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 18 characters: /ppBS775B1KRShB+QKTLZNkZyUqqwkELWI4JN14M2RE=
Result Method B with 18 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 17 characters: /ppBS775B1KRShB+QKTLZOKdO3s345tAlCrN+q3QV68=
Result Method B with 17 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 16 characters: /ppBS775B1KRShB+QKTLZE6HtWd1ZLwZMvy3E9Bm5CI=
Result Method B with 16 characters: /ppBS775B1KRShB+QKTLZA==
Result Method A with 15 characters: OMMFxti/svtQ/Z5fqaLaEg==
Unhandled exception. System.Exception: Encrypted data is 0 for text "Under 15 charac" with length 15
   at IssueEncryptionStreamEmpty.Program.GetNonWorkingEncrypted(String text, ICryptoTransform encryptor) in /media/sasw/Data/src/issue-encryption-stream-empty/Program.cs:line 53
   at IssueEncryptionStreamEmpty.Program.Main(String[] args) in /media/sasw/Data/src/issue-encryption-stream-empty/Program.cs:line 17

Process finished with exit code 134.

Answer 1

因为你的 writer 不再局限于 cryptoStream 的 using 块，它现在在你的函数返回之前被处理掉（而不是在 cryptoStream 时被处理掉）范围结束）。但它没有将其内容刷新到流中，因为您没有在其上调用 Flush，并且其 AutoFlush 属性默认为 false.

public object GetEncryptedOrDefault(object value, ICryptoTransform encryptor)
{
    if (encryptor is null)
    {
        throw new ArgumentNullException(nameof(encryptor));
    }
    var isEncryptionNeeded = value != null;
    if (isEncryptionNeeded)
    {
        using var memoryStream = new MemoryStream();
        using var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
        using var writer = new StreamWriter(cryptoStream);
        var valueAsText = value.ToString();
        writer.Write(valueAsText);
        writer.Flush();

        var encryptedData = memoryStream.ToArray();
        var encryptedText = Convert.ToBase64String(encryptedData);
        return encryptedText;
    }

    return default;
}

在您的第一个示例中，writer 在用完它写入的流之前被释放（因此刷新其缓冲区），因此在尝试访问它时流不是空的。

更新： 在查看 CryptoStream.Dispose 的源代码时，我注意到对 FlushFinalBlock 的调用，这就是输出不匹配的原因。

关于输入长度问题，encryptor.InputBlockSize等于16，这就是为什么写15个或更少字符的文本而不调用FlushFinalBlock的原因（注意CryptoStream.Flush是无操作）导致空流。

因此，再次工作的代码变为：

private static string GetWorkingEncrypted(string text, ICryptoTransform encryptor)
{
    using var memoryStream = new MemoryStream();
    using var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
    using var writer = new StreamWriter(cryptoStream);
    writer.Write(text);
    writer.Flush();
    cryptoStream.FlushFinalBlock();

    var encryptedData = memoryStream.ToArray();
    var encryptedText = Convert.ToBase64String(encryptedData);
    return encryptedText;
}

当文本少于 15 个字符时，将 CryptoStream 转换为使用声明会使内存流为空

Converting a CryptoStream to using declaration makes memory stream empty when text less than 15 chars

c#

encryption

memorystream

aes

cryptostream