SSH public RSA key errors

Seen these before when trying to login via SSH with your new RSA public key?

Nov 2 12:09:17 hostname sshd[12712]: error: buffer_get_ret: trying to get more bytes 257 than in buffer 73
Nov 2 12:09:17 hostname sshd[12712]: error: buffer_get_string_ret: buffer_get failed
Nov 2 12:09:17 hostname sshd[12712]: error: buffer_get_bignum2_ret: invalid bignum
Nov 2 12:09:17 hostname sshd[12712]: error: key_from_blob: can't read rsa key
Nov 2 12:09:17 hostname sshd[12712]: error: key_read: key_from_blob AAAAB3N[...] failed

In my case these were the result of copying a public key from e-mail, which tends to mangle long text lines. I usually don’t have this problem because I use the ssh-copy-id script to copy my keys to a remote host before attempting to log in.

User-friendly PKI: not yet

Public-key infrastructure is great. When it works, you can be quite sure that you are communicating with whom you want to communicate, and you can even communicate securely if you wish. Alice and Clare can send each other mail, and Bob won’t be able to sneak in there and read it.

It’s supremely easy for Alice to create a private key, and publish her public key to a keyserver. “That’s it?” she thinks, with a leap of her heart. “Wow! It’s so easy!”

Let’s fast-forward a bit.

For a while, Alice and Clare have fun sending encrypted messages back and forth. They find a plug-in to send encrypted mail through their GMail accounts (FireGPG), and that’s useful for a while, although oops, the developer discontinues GMail support. But they can still use other clients, and they do so.

Things are hunky-dory for a while.

Then one day Alice upgrades her computer, and she forgets to migrate her private key over to the new box. She doesn’t have her passphrase at hand, of course, because she had her e-mail client save it for her; she had it on a sticky note so she only had to look it up once in a while.

“Oh, well,” thinks Alice. “I’ll just create a new public key.”

Oops. Is this user-friendly?

Now Alice has a PGP key sitting out there on a keyserver. She can’t use it because she doesn’t have the equivalent private key. She can’t revoke it because she didn’t think it was that important to create a revocation certificate at the time and save it. Someone told her to do that once. “Don’t save it in the cloud, but on a disk that would never lose its data and could never be compromised. Then lock it away in a safe in your basement. You did make sure your basement was a Faraday cage, didn’t you?”

PKI is such a useful, powerful tool. But… it’s still very easy to screw up and cause lasting damage, though. I guess it’s like a “Hole Hawg,” an apt comparison to other powerful technologies, as noted by Neal Stephenson.

There IS an option for Alice. She can create a new key, with a user ID like: “only use this key. That other one is bad,” and then get all her friends to sign the new key. There are other techniques, but that’s pretty much as close as she’s going to get.

Questions like this in security-related topics interest me: If it’s easier to use, will more people use it? And if it’s more widely used, will that increase its relevance?


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