Hello all!

I have a little question about Public/Private Keys.

For this question, lets talk about the keys concerning to ssh authentication.

My question is:

If I have my private key but I don't have the public key, if the the public key on the remote computer has been deleted can I restore it?

My question is if I can restore public key, from private key?

Thanks!

Hi there,

I am not an expert on the question of keys and security, but I believe you can restore your keys, or create new ones, with For the details on how to do so, you can search the web for example and more explanation.

Cheers

Your public and private keys are the by-product of a mathematical computation. Think of mathematical computation as division and the public key as the result. The private key is the remainder. If all you have is the remainder, there is no way to use it to compute the result unless you still have the original two numbers used in the computation.

Due to the fact that key generators use random number generators and entropy gatherers, there is no way to reproduce the exact mathematical sequence that generated your two keys. This is by design. If someone could use one key to derive the other key, it would open the door to a lot of attacks.

That being said, if you are using GPG or PGP, you should have key ring files that have stored copies of both your public and private keys. The reason you need to keep a copy of your public key is so that you can encrypt your messages to yourself to allow you to read them later. If you do not encrypt to yourself, only the recipient can read your message.

EDIT: Pardon me. I glossed over the part about this being restricted to ssh.

Dunno about this one. I've deleted my public key accidentally several times, but was able to rebuild a public key by using the private key. Note that this is for SSH key pairs, though, so in the case of PKI, it may be different (I thought the technology was very similar, though).

See man ssh-keygen for future reference.

OP clearly asked about ssh keys, why would you lead them on a wild goose chase with OpenSSL? If you don't know what you're talking about, just leave the question alone and let someone else answer it (which colucix did).

I will check the commands you gave me.

Your answers are great! I really appreciate it.

Thanks again!

First of all, thanks again.

BUT, I must to ask about David1357's answer...

Why it's matter talk I have asked the question about PPK of SSH? Why I can solve the problem with SSH PPK and other public/private keys pairs I can't?

Thanks in advance.

Dmor.

ssh-keygen clearly creates a file that contains both the public and private keys (e.g. id_rsa). When you delete the public key (e.g. id_rsa.pub) you can extract another copy using "ssh-keygen -y".

On the other hand, imagine if someone could take your public key and derive your private key: they could read your messages and forge messages from you.

Thanks David.

You want to tell me that id_dsa for example contains the public key??? (the contents of id_dsa.pub)?

I always thought of it has the DELTA between them...