Safety of encryption when knowing part of the content [migrated]

I want to encrypt a JSON file while exposing its interface (the name of the object fields) in clear text.

Since this exposes part of the content of the file, my guess is that an attacker could use this to hack the encryption key.

Are there encryption methods that can circumvent, or at least be safer for cases like this?

I am mostly convinced that knowing part of the content of an encrypted file can make attacks easier, but I do not know if there is a technical term for such conditions or how to evaluate if some algorithms are safer or not. So far I am specially interested if using aes-192-cbc or gpg would be OK.