doc: improve CCM example

[tniessen]

Applications should never attempt to use the deciphered message if authentication fails. In reality, this is usually not a problem since OpenSSL does not disclose the plaintext in this case, but it is still a design mistake and can lead to critical security problems in other cipher modes and implementations.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

[nodejs-github-bot]

Lite-CI: https://ci.nodejs.org/job/node-test-pull-request-lite-pipeline/3357

[bnoordhuis]

I agree the example can be improved but doing too much work inside the try block isn't something we should promote in our docs. I would have written it like this:

let ex;
try {
  deciper.final();
} catch (err) {
  ex = err;
}

if (ex)
  console.error('Authentication failed.');
else
  console.log(receivedPlaintext);

Or:

let ok = false;
try {
  decipher.final();
  ok = true;
} catch (err) {
  console.error('Authentication failed.');
}

if (ok) console.log(receivedPlaintext);

[tniessen]

@bnoordhuis I agree that doing it in the try block is not the best way to do it. However, I believe there is a slightly simpler way. How about using process.exit or return? Or setting receivedPlaintext to undefined on error?

[bnoordhuis]

How about using process.exit or return? Or setting receivedPlaintext to undefined on error?

Sounds good.

[tniessen]

Landed in 153c101, thanks for reviewing!