I want to generate an RSA key in GPG and use it in SSH login. Is this even possible? If so, how?
edit: see @wwerner's answer, I didn't try it but it seems to be the current solution (as of 2018)
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I know this is an old post, but for people like me stumbling over this:
It is now (since gpg 2.1) possible to simply extract ssh keys directly using gpg:
gpg --export-ssh-key <key id>!.
The ! mark is optional, it makes the primary key exportable and omits checking whether the key is authentication-capable ([CA]).
Details:
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Can you go the other way around? Convert an existing ssh key to a GPG key? – B T May 18 '20 at 19:31
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I noticed that if you have more than one authentication subkey, the (!) is actually required if you want to choose between the subkeys. Without exclamation point it always exports the first one on the list, and maybe really confusing. – Ciantic Jan 24 at 19:39
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According to the linked release notes, this only exports public keys. Is it possible to export the private key into an SSH
id_rsafile? – nh2 Feb 28 at 17:26
I'm doing some research about this topic and I can give you some hints, but I've not found a way to make it work yet.
Monkeysphere
Monkeysphere seems a very interesting project, but I've not been able to compile it under Mac OS X without clogging my little free disk space with MacPorts.
Using gpgkey2ssh
The first way I suggest you to try is to generate a compatible authorized_keys entry from your key id (e.g., BFB2E5E3) with
gpgkey2ssh BFB2E5E3 | tee -a ~/.ssh/authorized_keys
Here I added it to my localhost since I ran an ssh server for testing purposes, but of course you should add this to the target host ~/.ssh/authorized_keys.
Next you need to tell SSH to use the private portion of this key during authentication, but simply exporting an ASCII armored version of the keypair doesn't work:
gpg --armor --export-secret-key BFB2E5E3! |tee ~/.ssh/id_rsa
gpg --armor --export BFB2E5E3! | tee ~/.ssh/id_rsa.pub
chmod 400 ~/.ssh/id_rsa
ssh localhost
Using gpg-agent
gpg-agent has the option --enable-ssh-support that allows it to use it as a drop-in replacement for the well known ssh-agent.
I've read of some people trying to add via ssh-add their GPG key after launching gpg-agent this way:
gpg-agent --enable-ssh-support --daemon
gpg --armor --export-secret-key BFB2E5E3! | tee ~/.gnupg/exported-keys/BFB2E5E3_sec.asc
ssh-add ~/.gnupg/exported-keys/BFB2E5E3_sec.asc
But I don't think this will ever work. The gpg-agent manpage says:
SSH Keys, which are to be used through the agent, need to be added to the gpg-agent initially through the ssh-add utility. When a key is added, ssh-add will ask for the password of the provided key file and send the unprotected key material to the agent; this causes the gpg-agent to ask for a passphrase, which is to be used for encrypting the newly received key and storing it in a gpg-agent specific directory.
So it seems that gpg-agent should be used as an additional measure to protect your SSH keys with a GPG encryption.
Converting a GPG key to OpenSSH
Jérôme Pouiller in his blog writes that the Gpgsm utility can export keys and certificates in PCSC12; they can then be used by OpenSSH:
gpgsm -o secret-gpg-key.p12 --export-secret-key-p12 0xXXXXXXXX
openssl pkcs12 -in secret-gpg-key.p12 -nocerts -out gpg-key.pem
chmod 600 gpg-key.pem
cp gpg-key.pem ~/.ssh/id_rsa
ssh-keygen -y -f gpg-key.pem > ~/.ssh/id_rsa.pub
But I haven't found a way to make gpgsm accept my gpg keypairs.
Other things you can try
SSH has a -I option to specify the PKCS#11 shared library ssh should use to communicate with a PKCS#11 token providing the user's private RSA key.
ssh-keygen can use RFC4716/SSH2 public or private key, PEM PKCS8 public keys, and PEM public keys to generate an OpenSSH compatible private (or public) key using the -i and -m options.
Still I can't find a way to put it all together.
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6Note that
gpgkey2sshhas been replaced by--export-ssh-keyas of version 2.1.11 (2016-01-26). It took me a while to realize this. Usage isgpg --export-ssh-key BFB2E5E3. – MayeulC May 17 '17 at 19:29 -
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No, they are not interchangeable. Yes, it is possible to use GPG keys for authentication – the Monkeysphere package has tools to extract the raw RSA keypair from your GPG certificate.
Your GPG certificate will need a subkey with the "authentication" capability flag. To create such a subkey, run once:
monkeysphere gNow add your authentication subkeys to ssh-agent:
monkeysphere s
Somewhat relevant: this gnupg-users thread.
With the information from the answers on this question and the help of the gnupg-users mailinglist I was able to figure out how to use my GPG key for SSH authentication. As already mentioned by Claudio Floreani in his answer, there are a few possible methods to do this.
I have written a blogpost about some possible solutions: http://budts.be/weblog/2012/08/ssh-authentication-with-your-pgp-key
To summarize: Either you use GnuPG 2.1, which is currently in beta. When using this version, you can simply start gpg-agent with the --enable-ssh-support option and add the keygrip for you GPG key (or subkey) into ~/.gnupg/sshcontrol.
When you are using the current stable GnuPG version (2.0.x) you can use monkeysphere to add your key to gpg-agent (again, after starting gpg-agent with the --enable-ssh-support option).
It is also possible to use GNOME keyring (or even the regular ssh-agent) with the help of monkeysphere. The only problem in this case is that you will have to re-add your key when logging on again (into Gnome or XFCE). To solve this you can manually export your key and convert it.
