There has been a lot of discussion about how the crypto doesn't work. I have some quibbles about the Go. Don't put a mutex in your io.Reader. It is assumed t

There has been a lot of discussion about how the crypto doesn't work. I have some quibbles about the Go. Don't put a mutex in your io.Reader. It is assumed that, unless mentioned in the documentation, it is not safe to use anything in Go from multiple goroutines. If someone wants to make the reader synchronous for use among multiple goroutines, they can do so themselves. But it's so rare that it's unlikely anyone would want this. read/write mutexes typically perform worse than a plain mutex. You pay a performance cost to prevent readers and writers from starving each other; if you don't care (and this code doesn't), use a Mutex. https://zephyrtronium.github.io/articles/rwmutex.html https://zephyrtronium.github.io/articles/rwmutex.html Finally, it's fine to embed the mutex value directly in your struct if your methods take pointer receivers. &MyThing{Mutex: new(sync.Mutex)} is pretty weird to see. If the mutex were included as its value, then the zero value of MyThing is ready to use; &MyThing{} has a new mutex in it. (You can't copy the value of &MyThing either way; a correct copy requires holding the mutex. The reason to embed a *sync.Mutex instead of a sync.Mutex is so that you can copy the containing type, but that is actually unsafe. You grab a pointer to the wrong Mutex in your copy, and you also copy data protected by the mutex without holding it. So your methods MUST have a pointer receiver either way, and thus the indirection to *sync.Mutex is unnecessary.)