Kurt Seifried, [email protected], Copyright Kurt Seifried 2001


Basic cryptography book - by Kurt Seifried

This book is intended as a basic primer for people that do not know a lot (or anything as the case may be) about cryptography but are interested or concerned about it (in an actual "should I be using it, and if yes, what should I use, and how?"). The book starts with a brief set of explanations of why you might want to use cryptographic software, and how cryptography works. This is followed by chapters on the various tasks or problems you wish to solve using cryptography and which packages might be useful. The bulk of the book is practical explanations of how to install, configure and use various software packages for various situations (such as encrypting email in Windows).

Storing credit card numbers securely

This question came up recently on a mailing list and at first glance I thought "no problem" but upon further reflection it turned out to be a lot harder then expected. The first assumption to be made is that the Database you are storing the numbers in will not be 100% secure, outside attacker, inside attacker, data entry people jotting down numbers, and so forth. The obvious solution is to encrypt the data, use a strong one way hash like SHA1 and be done with it. This problem is very difficult especially if you plan to store the data for a long time and use it to run statistical programs to help predict fraud rates and so on since you must be sure that whatever encrypted string of data that represents the card is the same in all cases (meaning you cannot use random salt values to help hash it).

Breaking trust in certificates

For a while now I've been writing articles about SSL, outlining various problems, and why SSL in general is a poor solution that should be improved (before we start doing things like online voting, yikes). The whole premise of certificates is that multiple parties trust a central certificate authority (CA), so when Alice wants to talk to Bob they can verify each others certificates through the CA, in theory proving that they are actually taking to the person that they claim to be. This CA has a very important job, especially so with the use of X.509 certificates (currently the most common for SSL, smartcards and so on). Unlike PGP or GnuPG for example where you can have multiple entities sign a certificate (such as your mother, your boss, the post office, etc.) with X.509 you are limited to one only. Because X.509 certificates can only be signed by one entity you ultimately have to place all your trust in the entity that signed it.

End of SSL and SSH?

Today [Yesterday if this is posted on the 18th] dsniff 2.3 was released, why is this important you ask? dsniff 2.3 allows you to exploit several fundamental flaws in two extremely popular encryption protocols, SSL and SSH. SSL and SSH are used to protect a large amount of network traffic, from financial transactions with online banks and stock trading sites to network administrator access to secured hosts holding extremely sensitive data. Both SSH and SSL use "public key encryption", wherein their vulnerabilities lay. They also rely heavily on the user to make the right decisions when faced with an attack, and most users are not educated enough to know what exactly they are dealing with and usually make the wrong decision (how many times have we told users not to open up executables emailed to them?).

End of SSL and SSH - Follow-up.

Well, I certainly managed to kick over a hornet's next with my article "The End of SSL and SSH?". There were quite a few points I did not cover in the article, many I did not think of, and some I trimmed. This article will cover the reaction to SSL and SSH being "dead", as well as numerous implementation issues I did not cover. The real issue is that technology cannot solve problems completely. Anytime you put a new solution in you breed new problems. This of course assumes you installed and are maintaining the new solution correctly in the first place. Vendors ships SSL and SSH, you turn it on, it works. Unfortunately most people feel that they are then done and move on to other problems, this is far from the truth. Both SSL and SSH have numerous avenues an attacker can take, many of these rely on the end user to make the right decision or have a secure system, meaning a user can shoot themselves in the foot with incredible ease. Pretty much any cryptographic "solution" requires a degree of maintenance and continued attention.

Encryption keys

A variety of encryption keys, from vendors to professionals and other interesting people.

Why Random Numbers Are Important For Security

January 26, 2000 - Modern computer security requires some level of encryption to be applied to various kinds of data, for example secure web transactions, or SSH. But something that often goes ignored is the fact that all good crypto relies on some degree of randomness, which if not fulfilled properly can lead to a significant loss in the strength of encryption.

GnuPG and freedom

Well last week caused a bit of a stir, which is good. Hopefully this week will really get people thinking. As you may or may not have heard, GnuPG 1.0 has been released. If you haven't heard, GnuPG is a GPL'ed cryptographic program that uses no patented algorithms, and happens to be perfectly compatible with PGP. I interviewed Werner Koch (via email), the heart and soul of the GnuPG project. 

Advanced Encryption Standard released today

About 25 years ago the US NBS (National Board of Standards, renamed to NIST) put out a call for an encryption algorithm, unfortunately back then there wasn't a whole lot of public cryptography going on (they mostly worked for the NSA). Another call was put out in the federal register to which IBM responded with a algorithm called "Lucifer". This is where things get interesting. Originally Lucifer used a 128 bit key, however after the NSA got involved the key length was reduced to 56 bits, making it 4,722,366,482,869,645,213,696 times easier to brute force the key (2^72). This is rather interesting because it made it possible for the EFF to design and build a custom chip that had one purpose, to brute force DES keys. For less then $250,000 they engineered, and manufactured a machine that could run through the entire 56 bit key space in a matter of days (less then 5 days on average). This was accomplished by a small public effort and completed in January of 1999. This is especially interesting since the NSA is many years ahead of public cryptographic efforts (the NSA is the worlds largest employer of mathematicians). People realized that DES on it's own was secure against casual attackers, but not against a reasonably determined attacker, so 3DES was created, basically 2 56 bit keys are used to encrypt the data, first the A key, then the B key, then the A key again. This makes the resulting effort required to brute force it exponentially higher, unless there is some fundamental flaw in DES it probably isn't possible to brute force it. This of course creates a new problem, the resulting encryption and decryption is extremely slow and computationally expensive. NIST responded to this several years ago by calling for a replacement for DES, the AES (Advanced Encryption Standard), which has now been chosen and announced.



Last updated 4/10/2001

Copyright Kurt Seifried 2001