In 18.04 I encrypt files like so:
$ openssl enc -aes-256-cbc -in somefile.tar.gz -out somefile.tar.gz.enc
I then decrypt using:
$ openssl enc -aes-256-cbc -d -in somefile.tar.gz.enc -out somefile.tar.gz
I just upgraded one of machines to 18.10. When I decrypt a file in 18.10 that was encrypted in 18.04 (using the above method), I now get the following warning:
$ openssl enc -aes-256-cbc -d -in somefile.tar.gz.enc -out somefile.tar.gz enter aes-256-cbc decryption password: *** WARNING : deprecated key derivation used. Using -iter or -pbkdf2 would be better.
I'm planning on using both 18.04 and 18.10, and will be transferring encrypted files between the two regularly. I know the above is only a warning, I'd just like to know what it means, and if it's possible to either suppress it or get rid of it completely (perhaps by encrypting differently on 18.04, or decrypting on 18.10 using some flags/params).