Why is My String Decryption Cut Off After Upgrading from .NET 5 to .NET 6?

Decrypt Issue When Upgrading to .NET 6: String Encryption Class

In a .NET 5 project, a string encryption class similar to the one provided as a solution worked well. However, upon upgrading to .NET 6, the decrypted string was cut off at a specific point.

Problem Analysis

The fundamental cause lies in a breaking change between .NET 5 and .NET 6. Specifically, the behavior of DeflateStream, GZipStream, and CryptoStream has diverged from that of other Stream types.

Resolution

This change affects the Decrypt method in the encryption class. Previously, when calling cryptoStream.Read, it was expected that the operation would complete only when the buffer was filled or the stream reached its end. However, in .NET 6, cryptoStream.Read now completes even if only one byte has been read or the underlying stream returns 0, indicating no more data is available.

Therefore, the Decrypt method needs to be updated to properly handle this behavior. One solution is to check how many bytes cryptoStream.Read actually reads and ensure that all data is read:

var plainTextBytes = new byte[cipherTextBytes.Length];
var decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

Alternatively, CopyTo or StreamReader can be employed for more efficient and concise code:

using (var plainTextStream = new MemoryStream())
{
    cryptoStream.CopyTo(plainTextStream);
    var plainTextBytes = plainTextStream.ToArray();
    return Encoding.UTF8.GetString(plainTextBytes, 0, plainTextBytes.Length);
}

using (var plainTextReader = new StreamReader(cryptoStream))
{
    return plainTextReader.ReadToEnd();
}

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