Re: Paper & pencil password algorithm

You may be right, but....

I can't consider it all to be a real problem. Actually, only one of
the pages I use change the URL. It was done in a way I can probably
remember forever (domain .com -> .eu). In the same time the password
changed several times.

Maybe James would go for a memory-only system. I'd rather set up a
publicly accessible page with all the data I don't need to keep
secret. I'd also use a small javascript on the page for the
preprocessing of the URL before hashing and for the postprocessing of
the hash. There's no security problem involved as I need to enter both
the URL and the hash in the computer. Only the key and the computation
are to be kept off it.

If you can remember something like that for every site -- incuding
ones you rarely access -- you can remember a unique password for
each site.

I don't think so. Any time I see "google.co.uk" or "google.com" or
"www.google.com" I say "It's google, isn't it?". So I use "google".
How much memory do I need for this as compared to my favorite password
"j7hjg//hT;5FJJ45"? Maybe the amouts of memory are of the same order
of magnitude when measured in bits, but the first thing is impossible
to forget, the second impossible to remember.

However, this is not a security problem. I think, if Jason wants to do
it this way, it's his problem. If there's a problem, no desaster
occurs, he'll need to find his written down original URL.

I'd much more appreciate hints concerning the security of paper and
pencil algorithms. It'd be really bad to spend so much time while
hashing, if somebody could find out the key.

I'm curious to know what kind of problem it is.
When you compute backward, there's no influence over a distance at
all. That's surely bad and it can be done better. I more think about
the use of the algorithm for encryption, and I'm afraid that the
problem could lead to easy cracking of the password.

Actually, my biggest problem with your suggested method is that
multiplication modulo 11 proved to be too difficult...
I think it's not difficult at all, but sometimes it happens I start
explaining from the wrong side and than nobody understands. After a
while, I try again and it's obvious. However, currently I wouldn't use
multiplication modulo 11 anymore.

I would switch completelly to modulo 11 arithmetic, but use only
addition. This is very easy to explain: simply consider 10 to be a
digit, reduce anything greater by subtracting 11.

I'll tell you more when I get more time.
.