There's no need for a big application when all you want is to securely share some files or other data. OpenSSL is ubiquitious, so we can rely on the command line tools.
The following examples encrypt/decrypt the secrets.txt file base64 encoded into a secrets.txt.enc file.
The password is entered interactively. For details see the man page of openssl enc.
openssl enc -aes-256-cbc -a -salt -in secrets.txt -out secrets.txt.enc
openssl enc -d -aes-256-cbc -a -salt -in secrets.txt.enc > secrets.txt