How to encrypt a string with my SSH pubkey?

Question

If I only have an SSH pubkey, how can I encrypt an ex.: IP address (so a short string), only using the ssh pubkey?

For decryption, the other party would have the pair of the pubkey, so the private key, with which it can decrypt the string.

Solution

Here is one way to do that:

First of all you should install the latest versions of OpenSSL and OpenSSH.

Before we can encrypt the plaintext with our public key, we must export our public key into a PEM format suitable for OpenSSL's consumption

openssl rsa -in ~/.ssh/id_rsa -pubout ~/.ssh/id_rsa.pub.pem

then you can encrypt:

cat plain.txt | openssl rsautl -encrypt -pubin -inkey ~/.ssh/id_rsa.pub.pem > cipher.txt

• rsautl: RSA Utility
• -encrypt: key indicates we are encrypting from plaintext to cipher text
• -pubin: flag indicates we are loading a public key from -inkey [public key file].

and for decrypt:

cat cipher.txt | openssl rsautl -decrypt -inkey ~/.ssh/id_rsa

Comments

[pepite]

although it sometimes request for ssh password many times.. any ide for that?

[Wissam Roujoulah]

@ccpizza take a look here stackoverflow.com/questions/30056762/…

[Bolwerk]

In my case, I didn't actually stream to cipher.txt. I actually piped to base64, and used that hash to store my password in my PERL script. Decryption is with a command like $pass=echo "$password_hash" | base64 -d | openssl rsautl -decrypt -inkey /home/myhomedirectory/.ssh/id_rsa