How to use OpenSSL to encrypt/decrypt files

Encrypt a file with OpenSSL:

$ openssl enc -aes-256-gcm -salt -pbkdf2 -iter 100000 -in my_file.jpg -out my_file.jpg.enc

Decrypt a file with OpenSSL:

$ openssl enc -d -aes-256-gcm -salt -pbkdf2 -iter 100000 -in my_file.jpg.enc -out my_file2.jpg

macOS

Unfortunately, on macOS LibreSSL is used instead of OpenSSL. You can see it by running the following command in your terminal:

$ openssl version
LibreSSL 2.8.3

Thus, the newer and more secure PBKDF2 algorithm is not available to turn your password into a secure encryption key.

Instead you can use the following command to encrypt your file:

$ openssl enc -aes-256-gcm -salt -md sha512 -in my_file.jpg -out my_file.jpg.enc

And this one to decrypt the encrypted file:

$ openssl enc -d -aes-256-gcm -salt -md sha512 -in my_file.jpg.enc -out my_file2.jpg