Is it bad to tell someone what encryption algorithm your system uses?
No, it's not bad to tell this info. In fact, it's suspicious when someone doesn't reveal the design of the system. Kerckhoffs's principle states that a system must remain secure so long as an attacker knows everything except a designated secret &quot;key&quot;.
For symmetric encryption, &quot;key&quot; means secret keys. For asymmetric cryptography (signatures and key exchange) that means private keys. For password storage, that means the passwords themselves (and possibly a &quot;pepper&quot; value, if used).
I'd personally assume that anyone who isn't familiar with this is hiding a backdoor in their system. If the cryptography isn't auditable, it's safer to assume it's insecure and use an auditable (open-source or at least source-available) implementation whenever possible.