Warning on storing encryption keys on a YubiKey People wishing to move their private encryption keys to such a security token should be very careful as there are special precautions to take for disaster recovery. I am toying with the idea of writing an article specifically about disaster recovery for secrets and backups, dealing specifically with cases of death or disabilities.

Autocrypt changes One nice change is the impact on Autocrypt headers, which are considerably shorter. Before, the header didn't even fit on a single line in an email, it overflowed to five lines:

Autocrypt: addr=anarcat@torproject.org; prefer-encrypt=nopreference;
 keydata=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
 JSe3WSHsB0IAQZAQgAHRYhBHsWQgTQlnI7AZY1qz6h3d2yYdl7BQJZngt6AAoJED6h3d2yYdl7CowH/Rp7GHEoPZTSUK8Ss7crwRmuAIDGBbSPkZbGmm4bOTaNs/gealc2tsVYpoMx7aYgqUW+t+84XciKHT+bjRv8uBnHescKZgDaomDuDKc2JVyx6samGFYuYPcGFReRcdmH0FOoPCn7bMW5mTPztV/wIA80LZD9kPKIXanfUyI3HLP0BPwZG4WTpKzJaalR1BNwu2oF6kEK0ymH3LfDiJ5Sr6emI2jrm4gH+/19ux/x+ST4tvm2PmH3BSQOPzgiqDiFd7RZoAIhmwr3FW4epsK9LtSxsi9gZ2vATBKO1oKtb6olW/keQT6uQCjqPSGojwzGRT2thEANH+5t6Vh0oDPZhrKUXRAAxHMBNHEaoo/M0sjZo+5OF3Ig1rMnI6XbKskLv6hu13cCymW0w/5E4XuYnyQ1cNC3pLvqDQbDx5mAPfBVHuqxJdRLQ3yDM/D2QIsxnkzQwi0FsJuni4vuJzWK/NHHDCvxMCh0YmSgbptUtgW8/niatd2Y6MbfRGxUHoctKtzqzivC8hKMTFrj4AbZhg/e9QVCsh5zSXtpWP0qFDJsxRMx0/432n9d4XUiy4U672r9Q09SsynB3QN6nTaCTWCIxGxjIb+8kJrRqTGwy/PElHX6kF0vQUWZNf2ITV1sd6LK/s/7sH+x4rzgUEHrsKr/qPvY3rUY/dQLd+owXesY83ANOu6oMWhSJnPMksbNa4tIKKbjmw3CFIOfoYHOWf3FtnydHNXoXfj4nBX8oSnkfhLILTJgf6JDFXfw6mTsv/jMzIfDs7PO1LK2oMK0+prSvSoM8bP9dmVEGIurzsTGjhTOBcb0zgyCmYVD3S48vZlTgHszAes1zwaCyt3/tOwrzU5JsRJVns+B/TUYaR/u3oIDMDygvE5ObWxXaFVnCC59r+zl0FazZ0ouyk2AYIR
 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

After the change, the entire key fits on a single line, neat!

Autocrypt: addr=anarcat@torproject.org; prefer-encrypt=nopreference;
 keydata=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

Note that I have implemented my own kind of ridiculous Autocrypt support for the Notmuch Emacs email client I use, see this elisp code. To import keys, I pipe the message into this script which is basically just:

sq autocrypt decode   gpg --import

... thanks to Sequoia best-of-class Autocrypt support.

Note on OpenPGP usage While some have claimed OpenPGP's death, I believe those are overstated. Maybe it's just me, but I still use OpenPGP for my password management, to authenticate users and messages, and it's the interface to my YubiKey for authenticating with SSH servers. I understand people feel that OpenPGP is possibly insecure, counter-intuitive and full of problems, but I think most of those problems should instead be attributed to its current flagship implementation, GnuPG. I have tried to work with GnuPG for years, and it keeps surprising me with evilness and oddities. I have high hopes that the Sequoia project can bring some sanity into this space, and I also hope that RFC4880bis can eventually get somewhere so we have a more solid specification with more robust crypto. It's kind of a shame that this has dragged on for so long, but Update: there's a separate draft called openpgp-crypto-refresh that might actually be adopted as the "OpenPGP RFC" soon! And it doesn't keep real work from happening in Sequoia and other implementations. Thunderbird rewrote their OpenPGP implementation with RNP (which was, granted, a bumpy road because it lost compatibility with GnuPG) and Sequoia now has a certificate store with trust management (but still no secret storage), preliminary OpenPGP card support and even a basic GnuPG compatibility layer. I'm also curious to try out the OpenPGP CA capabilities. So maybe it's just because I'm becoming an old fart that doesn't want to change tools, but so far I haven't seen a good incentive in switching away from OpenPGP, and haven't found a good set of tools that completely replace it. Maybe OpenSSH's keys and CA can eventually replace it, but I suspect they will end up rebuilding most of OpenPGP anyway, just more slowly. If they do, let's hope they avoid the mistakes our community has done in the past at least...

1. Review the entire codebase for simple mistakes.
2. Review the entire codebase for license issues.
3. Review the entire codebase for files without source, and track down (and include source for) any sourceless files (such as pickle files, etc).
4. Get to know the upstream, get to know open bugs, write something using the lib, in case I need to debug later.
5. Install the package.
6. Test the package.
7. Work out any Debian package issues (this is easy).

1. Review the changes between the last uploaded version (in diff format, if it's sane, otherwise get the VCS and review), ensure all the above are still OK.
2. Review for Debian-local issues (such as how it will upgrade, using piuparts, and adequate, etc).
3. Check to make sure it won't break any reverse dependencies.
4. Review for bugfixes that I might need to bring back to the stable release.
5. Figure out if I should (or even can) backport the package, if API is stable.
6. Review for bugs (upstream or in Debian) that I need to mention in the debian/changelog.

• Use pip without sudo always. Don't tell people to use sudo.
• Use apt or dpkg when deploying system-wide.
• Understand people are going to package, and they will be more concerned about software using your library then keeping your library up to date.
• Understand Debian Developers and package maintainers have to do a lot of work when updating or sponsoring an upload.
• Understand upstream developers can't be bothered to fix every issue with every release (release early, release often) with some snapshot you introduced into unstable.
• Use pip and virtualenv in development setups, so we can upgrade your app when we upgrade the lib.

-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v1.4.10 (GNU/Linux)
Comment: A revocation certificate should follow
iHIEIBEIADIFAkyaOZwrHQJBIGNvbXB1dGVyIGNvbnRhaW5pbmcgdGhpcyBrZXkg
d2FzIHN0b2xlbgAKCRDYDvNai7UnrzWAAKC34eF76JQjxrZqSjNwcC0dU/5VbACg
gMIMmYg91Sl3y8KsZXdGj/rV7UE=
=rdlT
-----END PGP PUBLIC KEY BLOCK-----

$ OLDKEY=xyHywJuHD3nsfLh03G1TqUEBKSj6NlzMfB1T759haoAQ
$ for host in $(cat .ssh/known_hosts   cut -f 1 -d \  cut -f 1 -d ,  
                sort   uniq); do 
    echo == $host
    ssh-copy-id -i .ssh/id_rsa.new.pub $host && 
    ssh $host "perl -n -i -e 'next if /$OLDKEY/;print' .ssh/authorized_keys"
done

• .ssh/known_hosts' lines start with the server's name (or names, if more than one, comma-separated), followed by the key algorithm and the key fingerprint (space-separated). That's the reason for the double cut It could probably be better using a regex-enabled thingy understanding /[, ]/, but... I didn't think of that. Besides, the savings would be just for academic purposes ;-)
• I thought about not having the ssh line conditionally depend on ssh-copy-id. But OTOH, this makes sure I only try to remove the old key from the servers it is present on, and that I don't start sending my new key everywhere just for the sake of it.
• my $OLDKEY (declared in Shell, and only literally interpolated in the Perl one-liner below) contains the final bits of my old key. It is long enough for me not to think I'm risking collision with any other key. Why did I choose that particular length? Oh, it was a mouse motion.
• perl -n -i -e is one of my favorite ways to invoke perl. -i means in-line editing, it allows me to modify a file on the fly. This line just skips (removes) any keys containing $OLDKEY; -n tells it to loop all the lines over the provided program (and very similarly, -p would add a print at the end Which in this particular ocassion, I prefer not to have). It is a sed lookalike, if you wish, but with a full Perl behind.

• This assumes you have set HashKnownHosts: no in your .ssh/config. It is a tradeoff, after all I use a lot tab-expansion (via bash_completion) for hostnames, so I do have the fully parseable list of hosts I have used on each of my computers.
• I have always requested my account names to be gwolf. If you use more than one username... well, you will have to probably do more than one run of it connecting to foo@$host instead.
• Although most multiuser servers stick to the usual port 22, many people change the ports (me included) either because they perceive concealing them gives extra security, or (as in my case) because they are fed up with random connection attempts. Those hosts are stored as [hostname]:port (i.e. [foo.gwolf.org]:22000). Of course, a little refinement takes care of it all.,/li>
• Oh, I am not storing results... I should, so for successive runs I won't try to connect to a system I already did, or that already denied me access. Why would I want to? Because some computers are not currently turned on. So I'll run this script at least a couple of times.