AES Decryptor gives wrong result in .NET6 compared to .NET Framework

[onefreddy]

Description

The same code works differently on two platforms and unfortunately not in favor of .NET6. Which is why I am getting the wrong result.

Reproduction Steps

Execute the code (which I will provide below) and encrypt something and you will see how .NET6 is mistaken.

Expected behavior

The code
Console.WriteLine(Enc.Decrypt(Enc.Encrypt("server=.;database=DB_MyTest;password=MyPassword;user id=sa;")));
should return

server=.;database=DB_MyTest;password=MyPassword;user id=sa;

Actual behavior

The code
Console.WriteLine(Enc.Decrypt(Enc.Encrypt("server=.;database=DB_MyTest;password=MyPassword;user id=sa;")));
returns

server=.;database=DB_MyTest;password=MyPassword;

Regression?

No response

Known Workarounds

No response

Configuration

Windows 10, x64
Visual Studio 2022 RC2
.NET6 RC2
.NET Framework 4.8

Other information

Decryption/Encryption Code:

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace EncTest
{
    public static class Enc
    {
        private static string passPhrase = "@y88MP*Qv";
        private static string saltValue = "?5b#9DbtS";
        private static string hashAlgorithm = "SHA256";
        private static int passwordIterations = 2;
        private static string initVector = "BSY_DJT7hu#6$sRQ";
        private static int keySize = 128;

        public static string Encrypt(string plainText)
        {
            byte[] rgbSalt = Encoding.UTF8.GetBytes(saltValue);
            byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);
            byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);
            PasswordDeriveBytes password = new PasswordDeriveBytes(passPhrase, rgbSalt, hashAlgorithm, passwordIterations);
            byte[] keyBytes = password.GetBytes(keySize / 8);
            RijndaelManaged symmetricKey = new RijndaelManaged();
            symmetricKey.Mode = CipherMode.CBC;
            symmetricKey.Padding = PaddingMode.PKCS7;
            ICryptoTransform encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes);
            MemoryStream memoryStream = new MemoryStream();
            CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
            cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
            cryptoStream.FlushFinalBlock();
            byte[] cipherTextBytes = memoryStream.ToArray();
            memoryStream.Close();
            cryptoStream.Close();
            string cipherText = Convert.ToBase64String(cipherTextBytes);
            return cipherText;
        }

        public static string Decrypt(string cipherText)
        {
            byte[] rgbSalt = Encoding.UTF8.GetBytes(saltValue);
            byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);
            byte[] cipherTextBytes = Convert.FromBase64String(cipherText);
            PasswordDeriveBytes password = new PasswordDeriveBytes(passPhrase, rgbSalt, hashAlgorithm, passwordIterations);
            byte[] keyBytes = password.GetBytes(keySize / 8);
            RijndaelManaged symmetricKey = new RijndaelManaged();
            symmetricKey.Mode = CipherMode.CBC;
            symmetricKey.Padding = PaddingMode.PKCS7;
            ICryptoTransform decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes);
            MemoryStream memoryStream = new MemoryStream(cipherTextBytes);
            CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);
            byte[] plainTextBytes = new byte[cipherTextBytes.Length];
            int decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
            memoryStream.Close();
            cryptoStream.Close();
            string plainText = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
            return plainText;
        }
    }
}

Tagging subscribers to this area: @bartonjs, @vcsjones, @krwq, @GrabYourPitchforks
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Issue Details

---

Description

The same code works differently on two platforms and unfortunately not in favor of .NET6. Which is why I am getting the wrong result.

Reproduction Steps

Execute the code (which I will provide below) and encrypt something and you will see how .NET6 is mistaken.

Expected behavior

The code
Console.WriteLine(Enc.Decrypt(Enc.Encrypt("server=.;database=DB_MyTest;password=MyPassword;user id=sa;")));
should return

server=.;database=DB_MyTest;password=MyPassword;user id=sa;

Actual behavior

The code
Console.WriteLine(Enc.Decrypt(Enc.Encrypt("server=.;database=DB_MyTest;password=MyPassword;user id=sa;")));
returns

server=.;database=DB_MyTest;password=MyPassword;

Regression?

No response

Known Workarounds

No response

Configuration

Windows 10, x64
Visual Studio 2022 RC2
.NET6 RC2
.NET Framework 4.8

Other information

Decryption/Encryption Code:

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace EncTest
{
    public static class Enc
    {
        private static string passPhrase = "@y88MP*Qv";
        private static string saltValue = "?5b#9DbtS";
        private static string hashAlgorithm = "SHA256";
        private static int passwordIterations = 2;
        private static string initVector = "BSY_DJT7hu#6$sRQ";
        private static int keySize = 128;

        public static string Encrypt(string plainText)
        {
            byte[] rgbSalt = Encoding.UTF8.GetBytes(saltValue);
            byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);
            byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);
            PasswordDeriveBytes password = new PasswordDeriveBytes(passPhrase, rgbSalt, hashAlgorithm, passwordIterations);
            byte[] keyBytes = password.GetBytes(keySize / 8);
            RijndaelManaged symmetricKey = new RijndaelManaged();
            symmetricKey.Mode = CipherMode.CBC;
            symmetricKey.Padding = PaddingMode.PKCS7;
            ICryptoTransform encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes);
            MemoryStream memoryStream = new MemoryStream();
            CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
            cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
            cryptoStream.FlushFinalBlock();
            byte[] cipherTextBytes = memoryStream.ToArray();
            memoryStream.Close();
            cryptoStream.Close();
            string cipherText = Convert.ToBase64String(cipherTextBytes);
            return cipherText;
        }

        public static string Decrypt(string cipherText)
        {
            byte[] rgbSalt = Encoding.UTF8.GetBytes(saltValue);
            byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);
            byte[] cipherTextBytes = Convert.FromBase64String(cipherText);
            PasswordDeriveBytes password = new PasswordDeriveBytes(passPhrase, rgbSalt, hashAlgorithm, passwordIterations);
            byte[] keyBytes = password.GetBytes(keySize / 8);
            RijndaelManaged symmetricKey = new RijndaelManaged();
            symmetricKey.Mode = CipherMode.CBC;
            symmetricKey.Padding = PaddingMode.PKCS7;
            ICryptoTransform decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes);
            MemoryStream memoryStream = new MemoryStream(cipherTextBytes);
            CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);
            byte[] plainTextBytes = new byte[cipherTextBytes.Length];
            int decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);
            memoryStream.Close();
            cryptoStream.Close();
            string plainText = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
            return plainText;
        }
    }
}

Author:	onefreddy
Assignees:	-
Labels:	area-System.Security, untriaged
Milestone:	-

[filipnavara]

You are assuming that Read on a Stream always reads the number of bytes you ask for. That's not part of the contract. You should check the return value and handle it accordingly.

[vcsjones]

This is a duplicate of #55527. The CryptoStream needs to be read to completion as outlined in https://docs.microsoft.com/en-us/dotnet/core/compatibility/core-libraries/6.0/partial-byte-reads-in-streams.

Changing the decrypt to read to completion addresses the issue:

public static string Decrypt(string cipherText)
{
    byte[] rgbSalt = Encoding.UTF8.GetBytes(saltValue);
    byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);
    byte[] cipherTextBytes = Convert.FromBase64String(cipherText);
    PasswordDeriveBytes password = new PasswordDeriveBytes(passPhrase, rgbSalt, hashAlgorithm, passwordIterations);
    byte[] keyBytes = password.GetBytes(keySize / 8);
    RijndaelManaged symmetricKey = new RijndaelManaged();
    symmetricKey.Mode = CipherMode.CBC;
    symmetricKey.Padding = PaddingMode.PKCS7;
    ICryptoTransform decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes);
    MemoryStream memoryStream = new MemoryStream(cipherTextBytes);
    CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);
    byte[] plainTextBytes = new byte[cipherTextBytes.Length];

    int decryptedByteCount = 0;
    int read;
    while ((read = cryptoStream.Read(plainTextBytes, decryptedByteCount, plainTextBytes.Length - decryptedByteCount)) > 0)
    {
        decryptedByteCount += read;
    }
    memoryStream.Close();
    cryptoStream.Close();
    string plainText = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);
    return plainText;
}

Note: In .NET 6 you can simplify your code considerably, for example:

public static string Decrypt(string cipherText)
{
    byte[] rgbSalt = Encoding.UTF8.GetBytes(saltValue);
    byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);
    byte[] cipherTextBytes = Convert.FromBase64String(cipherText);
    PasswordDeriveBytes password = new PasswordDeriveBytes(passPhrase, rgbSalt, hashAlgorithm, passwordIterations);
    byte[] keyBytes = password.GetBytes(keySize / 8);

    using (Aes symmetricKey = Aes.Create())
    {
        symmetricKey.Key = keyBytes;
        byte[] plainTextBytes = symmetricKey.DecryptCbc(cipherTextBytes, initVectorBytes);
        return Encoding.UTF8.GetString(plainTextBytes);
    }
}

[onefreddy]

@filipnavara @vcsjones Oh, I got it. There were changes in Stream.Read https://docs.microsoft.com/en-us/dotnet/core/compatibility/core-libraries/6.0/partial-byte-reads-in-streams after replacing it with a loop reading, I checked it and it works! @vcsjones thanks also for this modern example, beautiful!