256 bit AES Encryption doesn't work

[mattosaurus]

256 bit AES encryption doesn't work, an error message of "System.ArgumentException: 'Specified initialization vector (IV) does not match the block size for this algorithm.'" is generated on line 87 of ZipAESTransform.cs during the creation of the encryptor. 128 bit AES encryption works as expected.

_encryptor = rm.CreateEncryptor(byteKey1, byteKey2);

Steps to reproduce

Try and encrypt file with 256bit AES encryption

class Program
{
    static void Main(string[] args)
    {
        ZipFile(@"C:\TEMP\test\test.txt", @"C:\TEMP\test\test.zip", "password");
    }

    public static void ZipFile(string srcPath, string outPath, string password)
    {
        using (ZipOutputStream zipStream = new ZipOutputStream(File.Create(outPath)))
        {
            zipStream.SetLevel(9); // 0-9, 9 being the highest level of compression

            // optional. Null is the same as not setting. Required if using AES.
            zipStream.Password = password; 

            ZipEntry zipEntry = new ZipEntry(Path.GetFileName(srcPath));

            // Specifying the AESKeySize triggers AES encryption. 
            // Allowable values are 0 (off), 128 or 256. 
            // A password on the ZipOutputStream is required if using AES.
            zipEntry.AESKeySize = 256; 
            zipEntry.DateTime = DateTime.Now;

            zipStream.PutNextEntry(zipEntry);

            byte[] buffer = new byte[4096]; // Zip the file in buffered chunks

            using (FileStream fileStream = File.OpenRead(sourceFilePath))
            {
                // Using a fixed size buffer here makes no noticeable difference
                // for output but keeps a lid on memory usage.
                int sourceBytes = fileStream.Read(buffer, 0, buffer.Length);

                while (sourceBytes > 0)
                {
                    zipStream.Write(buffer, 0, sourceBytes);
                    sourceBytes = fileStream.Read(buffer, 0, buffer.Length);
                }
            }
        }
    }
}

Expected behavior

Password protected zip file should be created.

Actual behavior

Fails to encrypt zip file.

Version of SharpZipLib

0.86.0.518

Obtained from (place an x between the brackets for all that apply)

• Compiled from source
• branch: master
• commit: be53259

[fabien367]

Hello, for me it's the same.
I tried to change => public ZipAESTransform (string key, byte[] saltBytes, int blockSize, bool writeMode)
into byte[] byteKey2 = pdb.GetBytes(_blockSize/2);

It work but I can't open the zip with the password because password is incorrect....

[konark]

@mattosaurus @fabien367 - I ran into a similar issue. Were you able to get around this?

[mattosaurus]

Hi @konark, I got round this using 7zip and calling the executable directly, not the tidiest solution but it worked for me.

public static void SevenZipFile(string srcPath, string outPath, string password, string execPath)
{
	System.Diagnostics.Process process = new System.Diagnostics.Process();
	var startInfo = new System.Diagnostics.ProcessStartInfo();
	startInfo.FileName = "\"" + execPath + "\"";
	startInfo.Arguments = "a " + "\"" + outPath + "\"" + " -p" + "\"" + password 
            + "\" -mem=AES256 \"" + srcPath + "\"";
	process.StartInfo = startInfo;
	process.Start();
	process.WaitForExit();
}

[harrisonmeister]

Don't know if this will help at all, but experimenting with this library I found I received the exception when trying to zip a zero length (empty file). Specifically the part where you copy bytes into the zipentry stream. It's simple enough to resolve by checking the length of the file. If it's 0, don't do any copying. I have a sample snippet of code if anyone would find it useful

[alexhiggins732]

I don't receive an exception using 256. It creates the file but when attempting to open it says wrong password.

[FastJack2]

The Problem is in ZipAESTransform.cs functino ZipAESTransform()

if you alter it this way, it should work:

public ZipAESTransform(string key, byte[] saltBytes, int blockSize, bool writeMode)
{

    if (blockSize != 16 && blockSize != 32) // 24 valid for AES but not supported by Winzip
        throw new Exception("Invalid blocksize " + blockSize + ". Must be 16 or 32.");
    if (saltBytes.Length != blockSize / 2)
        throw new Exception("Invalid salt len. Must be " + blockSize / 2 + " for blocksize " + blockSize);
    // initialise the encryption buffer and buffer pos
    _blockSize = blockSize;
    _encryptBuffer = new byte[_blockSize];
    _encrPos = ENCRYPT_BLOCK;

    // Performs the equivalent of derive_key in Dr Brian Gladman's pwd2key.c
    var pdb = new Rfc2898DeriveBytes(key, saltBytes, KEY_ROUNDS);
    var rm = new AesManaged();//Aes.Create();
    rm.Mode = CipherMode.ECB;           // No feedback from cipher for CTR mode
    _counterNonce = new byte[_blockSize];
    byte[] byteKey1 = pdb.GetBytes(_blockSize);
    byte[] byteIV = pdb.GetBytes(_blockSize);
    if (byteIV.Length > 16)
    {
        byte[] byteInit = new byte[16];
        Buffer.BlockCopy(byteIV, 0, byteInit, 0, 16);
        byteIV = byteInit;
    }
    _encryptor = rm.CreateEncryptor(byteKey1, byteIV);
    _pwdVerifier = pdb.GetBytes(PWD_VER_LENGTH);
    //
    _hmacsha1 = IncrementalHash.CreateHMAC(HashAlgorithmName.SHA1, byteIV);
    _writeMode = writeMode;
}

problem seems to be that aes always needs 16 byte IV, even in 256bit mode, so just use the lower 16...

[piksel]

This looks like the solution. Want to make a PR?

…

________________________________ From: FastJack2 <notifications@github.com> Sent: Friday, August 10, 2018 07:25 To: icsharpcode/SharpZipLib Cc: Subscribed Subject: Re: [icsharpcode/SharpZipLib] 256 bit AES Encryption doesn't work (#181) The Problem is in ZipAESTransform.cs functino ZipAESTransform() if you alter it this way, it should work: `public ZipAESTransform(string key, byte[] saltBytes, int blockSize, bool writeMode) { if (blockSize != 16 && blockSize != 32) // 24 valid for AES but not supported by Winzip throw new Exception("Invalid blocksize " + blockSize + ". Must be 16 or 32."); if (saltBytes.Length != blockSize / 2) throw new Exception("Invalid salt len. Must be " + blockSize / 2 + " for blocksize " + blockSize); // initialise the encryption buffer and buffer pos _blockSize = blockSize; _encryptBuffer = new byte[_blockSize]; _encrPos = ENCRYPT_BLOCK; // Performs the equivalent of derive_key in Dr Brian Gladman's pwd2key.c var pdb = new Rfc2898DeriveBytes(key, saltBytes, KEY_ROUNDS); var rm = new AesManaged();//Aes.Create(); rm.Mode = CipherMode.ECB; // No feedback from cipher for CTR mode _counterNonce = new byte[_blockSize]; byte[] byteKey1 = pdb.GetBytes(_blockSize); byte[] byteIV = pdb.GetBytes(_blockSize); if (byteIV.Length > 16) { byte[] byteInit = new byte[16]; Buffer.BlockCopy(byteIV, 0, byteInit, 0, 16); byteIV = byteInit; } _encryptor = rm.CreateEncryptor(byteKey1, byteIV); _pwdVerifier = pdb.GetBytes(PWD_VER_LENGTH); // _hmacsha1 = IncrementalHash.CreateHMAC(HashAlgorithmName.SHA1, byteIV); _writeMode = writeMode; }` problem seems to be that aes always needs 16 byte IV, even in 256bit mode, so just use the lower 16... — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or mute the thread.

[harrisonmeister]

@piksel - I can raise one if you want. Which branch should I target?

[FastJack2]

@piksel sure.. working on it ;)

[FastJack2]

Pull reuqest created:
#260

[piksel]

@harrisonmeister This seems like a different issue. Could you make a separate issue with repro?