runtime: Crash on WindowsCryptographicException on net60 GA

Hi @vcsjones, I’ve not observed the issue anymore! Nice to hear it uncovered another issue nevertheless! Thanks!

The code is approximately this:

var files = new []{ "path to file", ... }; //list of files
await Task.WhenAll(files.Select(async f => await DoSomethingWithFile(f, Sha256.ComputeHash(await File.ReadAllBytesAsync(f)))));

It looks like you are using an instance of SHA256 concurrently. You have a property, field, or local instance named Sha256 that is concurrently (Task.WhenAll) computing the file hashes.

If you are targeting net5.0 or higher, you can change it to this:

var files = new []{ "path to file", ... }; //list of files
await Task.WhenAll(files.Select(async f => await DoSomethingWithFile(f, SHA256.HashData(await File.ReadAllBytesAsync(f)))));

HashData was introduced in .NET 5. It is a static method and it is thread safe.

To round things out here:

1. The issue reported by @theolivenbaum and @jaylagorio was due to misusing an instance between threads. @theolivenbaum did switching to the static one-shot alleviate your exceptions?
2. The issue reported by @alanmcgovern was fixed, and has been backported to .NET 6. I believe the fix will be in the 6.0.2 release.

@vcsjones I have a repro case for a similar, if not identical, issue:

This breaks:

var buffer = new byte[1024];
var hasher = SHA1.Create ();
hasher.TransformBlock (buffer, 0, buffer.Length, buffer, 0);
//hasher.TransformFinalBlock (Array.Empty<byte> (), 0, 0);
hasher.Initialize ();
hasher.TransformBlock (buffer, 0, buffer.Length, buffer, 0);
hasher.TransformFinalBlock (Array.Empty<byte> (), 0, 0);
GC.KeepAlive (hasher.Hash);
hasher.Initialize ();
hasher.TransformBlock (buffer, 0, buffer.Length, buffer, 0);

If you want things to break in .NET6 just leave the 4th line commented. If you want it to not break, uncomment line 4.

If you re-initialize a hasher after calling TransformBlock and before calling TransformFinalBlock, you corrupt the hasher and it fails.

EDIT: Thanks to @EvgeniyZ-ru for bringing this issue to my attention, and working with me to provide the information I needed to distill a testcase 😃

A few guesses, since I don’t have a lot to go on.

1. Assuming it is this project: https://github.com/JKorf/Kraken.Net/
2. And it’s throwing at this line: https://github.com/JKorf/Kraken.Net/blob/0802f64af669bd77209218517063303750aadc79/Kraken.Net/KrakenAuthenticationProvider.cs#L59

I suspect it is might be because the HMACSHA512 encryptor field is being accessed from multiple threads. Instances of HMACSHA512 are not thread safe.

I can reproduce this exception by using an HMACSHA512 instance between threads:

using System;
using System.Threading;
using System.Security.Cryptography;

using HMACSHA512 hmac = new HMACSHA512();
Thread thread1 = new Thread(static obj => {
    while (true)
    {
        ((HMACSHA512)obj).ComputeHash(new byte[1]);
    }
});
Thread thread2 = new Thread(static obj => {
    while (true)
    {
        ((HMACSHA512)obj).ComputeHash(new byte[1]);
    }
});

thread1.Start(hmac);
thread2.Start(hmac);
thread1.Join();
thread2.Join();

That will quickly give me the same issue as described in the original post.

At this point I can only suggest that you confirm with the library author that no instance of a hash or HMAC algorithm is being used by two or more threads, concurrently.

If that is indeed the case, I would recommend creating a new instance of the hash / HMAC algorithm per-thread, or just always as-needed. Alternatively, using the HMACXYZ.HashData one-shot static methods that were introduced in .NET 5 for digests, and .NET 6 for HMACs.