Linux · Apache: TLS & Let's Encrypt

acme.sh's cron job auto-renews certificates — at what age does it renew, and how do you test the renewal without waiting?

Answer locked. Get the free KnowCard app to reveal it — plus spaced-repetition review so it actually sticks.

This is one card from the KnowCard library — thousands more across SAP, Linux, Python and more. In the app you get the answer, AI explanations, and cards that come back right before you would forget them. Free to start on iOS, Android or the web.

More in Apache: TLS & Let's Encrypt

A site serves data over plain HTTP and browsers flag it as insecure. What does switching to HTTPS actually add, and why is a CA-issued certificate still needed on top of that?

In TLS, which key encrypts and which decrypts, and how do client and server end up sharing one session key without ever transmitting a private key?

Online banking data is transmitted perfectly tap-proof but arrives at a fraudster's server instead of the bank. Which security property did the encryption fail to provide?

When juggling TLS files, what do the extensions .key, .csr, .pem, and .crt each hold?

What single command generates a private RSA server key with openssl, and what one permission mistake makes the whole certificate worthless?

Encrypting the server key with a passphrase sounds strictly safer. Why does Apache in practice get an unencrypted copy of the key instead?

Start learning today

Free to start — download the app or use it in your browser.