Fix a bug in the encrypt sample, that was causing the decrypt to fail

[IEvangelist]

Summary

• Upgrade encrypt / decrypt snippets to .NET 5
• Use top-level statements
• Use target-type new expressions
• Use explicitly scoped using to avoid encryption errors

Fixes #23814

Internal preview

✔️ Encrypting data
✔️ Decrypting data

[tdykstra]

LGTM but I added a request for @bartonjs to review.

[bartonjs]

The title says that it's fixing a bug in the sample, but there are so many aesthetic changes that I can't see what may have actually needed to be changed.

I strongly recommend using braced usings for cryptographic/security code (and, honestly, for all code, but less strongly). But they already weren't, so ::shrug::.

I'm not sure that the target-typed new enhances readability here. (Personally, I only use it for long lines or multiple-argument generics)

The calls to CreateEncryptor and CreateDecryptor produce IDisposable values that never get disposed (CryptoStream doesn't dispose them). If we're trying for perfection with our IDisposable-usings these'll get pulled out.

And, finally, the snippets lifted into the concept documents no longer match what the samples have. If we want to hand wave and say that they're only highlighting the functional aspects of the code (which is why they're not showing the using statements), that's fine, but the encryption document shows a call to CreateEncryptor(key, iv) when the sample has changed to CreateEncryptor().

No major blockers, but these are my aesthetic observations. It does look like the decrypt and encrypt samples are matched pairs.

[IEvangelist]

Thanks for the review, @bartonjs and @tdykstra.

Yes, that was actually the bug that was being addressed here. I am following your advice now on the explicit scoping of the disposable implementations, part of the issue was not properly scoping these - careless of me really.

I still need someone's approval to merge this one.

[tdykstra]

This looks better 😄

[aynur-safin]

You have done a great job ). Thank you.

I was late for the party, but maybe it will come in handy.
Encryption uses
encryptWriter.WriteLine("Hello World!");
but when decrypting
await decryptReader.ReadToEndAsync();
the resulting line contains a line break
"Hello World!\r\n"

When decrypting, a single asynchronous call is used
await decryptReader.ReadToEndAsync();
Can be used synchronous to keep everything in the same style, or alternatively make other calls asynchronous
await encryptWriter.WriteLineAsync("Hello World!");
etc.