Protecting a file using asymmetric cryptography

Question

I know how asymmetric cryptography works. I know there are two keys (one private and one public).

When someone wants to communicate they exchange their public keys encrypt messages with those public keys AND then the respective message could be decrypted ONLY by the user that has the private key.

Now, I'm using Node.js and I need to do something like this...

I need an application that EACH hour reads a database, extracts data and saves it to a file that I need to send to another server.
My problem is that I DON'T WANT that file will be visible to other, I do the transfer using SSH so there is no problem BUT I must encrypt that file because I'm not the admin of that server SO maybe someone could read it. Unfortunately the admin is the same for both servers. So my idea is to encrypt the file with a public key, and then only he who has the private key(me) could decrypt it.

I think it is pointless using something like:

var key = 'blablabla'

If I use a public key, there is no problem, all can read it..... it is public indeed. But with this public key, nobody can decrypt the message, so it is something like one-way encryption.

Now, could someone tell me if I need a signer/verifier to do this job, OR maybe I have to generate two keys (public/private) with openssl and pass those keys to a cipher/dechiper?

I'm looking at crypto modules, but there are no examples....

Answer 1

In general, your idea is right - you encrypt using public key and decrypt using private key of yours. However, practically the procedure is more complex. Random symmetric key is generated and the data is encrypted using that key. Then the public key is used to encrypt the random key. Encrypted key is sent to recipient together with encrypted data. On the other side encrypted key is decrypted using a private key, then the data is decrypted.

You can use OpenPGP keys or X.509 certificates to do the job.

In case of OpenPGP the standard offers encryption and decryption as atomic procedures (on the user level). In case of X.509 certificates you need to use PKCS#7 / CMS.

OpenSSL library offers operations with PKCS#7 / CMS, however when I look at nodeJS API for OpenSSL, that API is very limited and doesn't expose those functions. Maybe you can write your own nodeJS module which will interface with OpenSSL and provide missing functions.

Another alternative is to use OpenPGP keys and node-gpg module. That module uses gnupg to do the actual job, so gnupg must be installed.

Unfortunately I don't see any other suitable libraries in the 3rd-party module list provided in nodeJS wiki.