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The Crypto Gardening Guide and Planting Tips

Posted by michael on from the nous-devons-cultiver-nos-jardins dept.

ncostigan writes "Peter Gutmann of cryptlib fame has written a very readable paper on real-world constraints for cryptographers, and points out problems that their designs will run into when attempts are made to deploy them. Also included is a motivational list of extremely uncool problems that implementors have been building ad-hoc solutions for since no formal ones exist."

6 of 91 comments (clear)

  1. The Real Question by The+Subliminal+Kid · · Score: 5, Interesting

    The problem I face every day has bugger all to do with the vague under the hood stuff that I see everyday about the inside or crypto engines but the problem of getting my clients to understand that the extra clicks when they send an email, the remebering a pass phrase, and the extra clicks to read incoming email is not only advisable but absolutly necessary. everyday I see lawyers send priviliged material over the internet and getting them to see both that it is going on a electronic post card and there is a solution is a task that has proved beyond me.

    Suggestions from the floor?

    1. Re:The Real Question by plcurechax · · Score: 3, Interesting

      You are right, the human factor is often ignored in building secure systems, though Schneier's Secrets and Lies and Anderson's Security Engineering (Chapter 3 I believe) deals with building entire systems that are secure including making them usable to the human users.

  2. why isn't an implementation standard? by PissedOffGuy · · Score: 3, Interesting

    the article says:

    Crypto designs are often described as mathematical abstractions that, while easy to work with mathematically, require a significant amount of work to translate into an actual implementation.

    i'm surprised by this, why can't the crypto whizzes put together a few lines of math.h and networking code to be a proof of concept? crypto is very much an applied field, so the theorists should include example source in their papers.

    1. Re:why isn't an implementation standard? by chialea · · Score: 5, Interesting

      >crypto is very much an applied field, so the theorists should include example source in their papers.

      Er.. security is an applied field. Crypto is applied non-applied mathematics, basically. I don't /do/ code, generally, and very rarely C or C++, which you seem to be implying should be used. The people who are interested in one are not always interested in the other. Coming from the math side of it, I'm sometimes tempted to say "learn some math and read the proofs before you implement". Not always practical, sure, but just as valid as expecting me to know about networking this'n'that.

      There's also not generally room in a paper for source. Rigorous proofs and definitions can take up a LOT of room. (Everyone who's read the 5x page HILL paper, or one of Dan Boneh's 3x page papers, raise your hand if you want to see source at the end of it.)

      Lea

    2. Re:why isn't an implementation standard? by dracken · · Score: 3, Interesting

      i'm surprised by this, why can't the crypto whizzes put together a few lines of math.h and networking code to be a proof of concept? crypto is very much an applied field, so the theorists should include example source in their papers.

      Well, There is nothing to be surprised about. Many theoretically secure encryption schemes have been broken in practice because the implementation is very difficult. One common pitfall: in theory, often, we assume the existance of a perfect source of random bits. Practically it is very very very difficult to ensure this (remember that part from cryptonomicon - where the encryption is broken because the keys were not perfectly random and there was a slight statistical anomaly ?).

      Also in theory, some schemes are secure only if the keys have some mathematical property. In practice, someone who does not understand this subtle point might make a horrendous implementation. (I dont want to go into the gory details about the field from which the keys should be chosen in the diffie-hellman scheme).

      Even with a perfect implementation, the user is also a very weak link in the chain.There is this famous incident of the more secure german naval enigma getting broken because some ship tranmitted using the new enigma scheme and the same message using the old enigma scheme (which was already broken).

  3. Re:What about the other side? by chialea · · Score: 3, Interesting

    >But I wonder if some of those suggestions decrease the strength of encryption?

    Most modern cryptography is based on a variety of problems which are believed -- NOT known -- to be hard in certain contexts. Factoring, RSA, CDH, DDH, bilinear maps over CDH/DDH gap groups, braid factoring, CVP, etc. There are people who believe that factoring (and thus RSA) may be poly-time solvable, and thus cryptosystems based on it may be insecure. Cryptosystems based on different hard problems are important for that reason. It's a hedge bet.

    There are also interesting things which come "for free" with certain types of hard problems, which may be very expensive to add on to more common cryptosystems. These properties, for example committment, are used in protocols like Deniable Ring Authentication. This sort of thing follows your suggestion of "a variety of rules", but it's really not possible to list every single cryptosystem in existance and how well it fits in. The authors simply say "(E,D) is a cryptosystem with the following properties", and leave anyone who wants to use it to find the best such cryptosystem, as it may change over time. (They usually do provide a trivial example or a reference, though)

    Of course, if one-way functions don't exist, we'll all be back to information-theoretically secure stuff, and some of these problems will go away :P

    Lea