[Cryptography] Rubber-hose resistance?

[Ray Dillinger]

On 12/19/2017 10:15 AM, Howard Chu wrote:

> I do this too. But just out of curiosity, what do you use for ssh
> credentials when traveling?

You really want unguessable credentials you can hold in your head?  You
can do it; it just takes some effort.

You can easily memorize a nonsense phrase that talks about, eg, the
fictitious exports of a fictitious city near a fictitious landmark,
inhabited by fictitious animals, where the fictitious ethnicity
inhabitants eat fictitious food.... Or about something from an entirely
different category that involves a similar number of fictitious nouns or
verbs or adjectives....  and make up a good original pseudo-word for
each of these things and arrange the whole so it rhymes. Or maybe so it
scans like a surreal passage from your favorite cyberpunk author or a
conspiracy theorist on an acid trip.  Or so it's funny. Or something,
anyway, that makes it easy for you to remember.

Got something over a hundred characters that you can say in eight
seconds or less?  That's easy for your audio loop memory to hold as a
single chunk.  That's probably good.

You know a dozen different desktop ciphers that have popular methods
for constructing keys from words, just because you've read books on
the history of crypto.  You can use seven-or-so of the made-up words in
the phrase as keywords.

Now come up with a mnemonic that links at least one of the desktop
ciphers and at least one of the words with each of the places you have
to log in.  If your mnemonic doesn't guarantee uniqueness, you should
also prepend the name of the place to each keyword when constructing
your cipher keys.

Now encrypt your phrase according to the derived instructions, do it
again to make sure you get the same ciphertext on the second try, do a
test decryption to make sure you get the original phrase as plaintext,
and when you're sure, change your password or key to the ciphertext.

Then you'll want to throw the paper you worked it out on into a blender
with a quart of water and puree it (or whatever; office shredders don't
secure anything any more).

That gives you enough underlying (and shared) structure to keep it
entirely in your head if you want to have the credentials not recorded
on anything.  But the structure (and sharing of structure) is made
sufficiently obscure that password guessing programs are never going to
find it.  And when you do work out those credentials, you are entering
them into your password manager or keyring only.  You never have to
communicate them to another human being, which drastically reduces the
odds that anybody is going to crack your desktop ciphers and figure out
what you're doing.

It's hard enough to do that you'll want to keep the times you have to
actually re-derive the passwords rare, because it'll take a half-hour
per password.  But if you really want to go "clean" for border
crossings, you can do it with good solid keys/passwords stored
completely inside your head.

				Bear

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