A very short documentation on using OpenSSL keys to encrypt and decrypt files.

fileEncryption.md

Procedure

1. Create a random key.
2. Encrypt the random key via an SSH RSA public key
3. Send the encrypted file and encrypted key
4. Encrypt the key
5. Encrypt the file

Create key via

openssl genrsa -out rsa.private 4096
openssl rsa -in rsa.private -out rsa.public -pubout -outform PEM

Encrypt file

openssl rand -hex -out key.txt 64
openssl rsautl -encrypt -oaep -pubin -inkey rsa.public -in key.txt -out key.txt.enc
openssl enc -aes-256-cbc -pbkdf2 -salt -in secret.pdf -out secret.pdf.enc -pass file:./key.txt

Dencrypt file

openssl rsautl -decrypt -oaep -inkey rsa.private -in key.txt.enc -out key.txt
openssl enc -d -aes-256-cbc -pbkdf2 -in secret.pdf.enc -out secret.pdf -pass file:./key.txt