You need to pay attention to this points while crypting anything:
● Confidentiality
● Integrity
● Authenticity
● Non-repudiation
● Access control
● Difficulty compromise
Taking this as the base you shoud choose the method wich helps you the most. (Being an Asymetric cypher a great way of accommplish a lot of the above.[Use a private and a public key..])
Also Here's the GPG QuickStart Guide.
In the symetric ways there is AES(128, 192, 256 bits) and DES(64 bit per block)
Check this part of this OpenSSL Manual
As someone says above using GPG is a great Idea beacuse of the use of Assymetric Keys which is always safer than just Passwords in any access...
To get a list of Cipher methos you can use:
openssl list-cipher-commands
So for example an AES Cipher:
openssl enc -aes-256-cbc -salt -in file.txt -out file.enc
And to decrypt
openssl enc -d -aes-256-cbc -a -in file.enc
Still, you may have occasion to want to encrypt a file without having to build or use a key/certificate structure.
In the link there is the How do I base64-encode something? part and the How do I simply encrypt a file? part. Hope this can help you
For more info Dive onto Asymmetric key techniques and Symmetric-key
Here's the RFC for Determining Strengths For Public Keys Used For Exchanging Symmetric Keys
Hope this helps. Remember Always to read the manual of what you use.
Best Answer
OpenPGP is a protocol not implemented by OpenSSL, including a derivated mode of symmetric encryption. While you could use OpenSSL for the actual cryptographic algorithms, for implementing OpenPGP with OpenSSL commands, you'd have to:
Don't write your own crypto code (this is not an actually small project here), rely on available libraries instead. There's GnuPG which can be interfaced with GPGME, and a bunch of GPGME interfaces and native libraries for pretty much all (more or less) important programming language.