The sha1pure Home Page

sha1pure is a Tcl extension that computes an sha1 message digest or hmac. sha1pure uses only core Tcl commands and therefore requires no compilation.

How To Use

sha1pure can be loaded using package require sha1pure. Alternatively, it can be sourced or even inserted directly into another source file.

sha1 message digests are computed using the sha1pure::sha1 command. It takes a single argument and returns the message digest. For example:

      % sha1pure::sha1 "hello world"
      2aae6c35c94fcfb415dbe95f408b9ce91ee846ed
    

sha1 hmacs are computed using the sha1pure::hmac command. Its takes key and text arguments and returns the hmac. For example:

      % sha1pure::hmac "our little secret" "hello world"
      a7ed9d62819b9788e22171d9108a00c370104526
    

Performance

sha1pure was not written for efficiency and is inappropriate for large arguments. Applications requiring high-performance should use Andreas Kupries' trf extension. trf implements several other message digests and contains many other conversion functions.

sha1pure is appropriate for small arguments. Here are some timings. The numbers along the top of this chart indicate the message size (in bytes). So for example, to produce a digest of a 50-byte string on a Sparc 20 required 46ms (about 1/20 of a second). Question marks are placeholders timings Iexpect to get in the near future.

The careful reader will note that the times for 10 and 50 are very close. In fact, the sha1 algorithm pads all messages out to (roughly speaking) 64-byte boundaries so any difference in times is just system noise. The precise steps in the algorithm occur at 56 + 64n characters.

If you want to do your own timings, run: sha1pure::time

I have optimized the code but only modestly because the performance is already acceptable for my own purposes. If you want to send me additional speedups, fine. However, I would prefer not to destroy the readability of the code or otherwise perturb it too much. The current implementation parallels the pseudocode in FIPS 180-1 very closely - in fact, most of the comments are direct quotes from the FIPS. I'd hesitate to give that up.

Credits

The hmac-sha1 implementation was taken from hmac-md5 which was written by D. J. Hagberg.

Other Caveats

sha1 is defined over strings with length less than 2^64. This implementation limits string lengths to 2^32. This restriction could be removed, however there seems no point to it given the speed with which such strings could be handled in the first place.

sha1pure has not been tested on machines with 64-bit integers. It is possible that it may not work on all 64-bit machines, due to integer layout although I haven't checked any. (I would be interested to hear feedback about this.)

Testing

sha1pure includes a test suite. For simplicity, it is included in the sha1pure package itself. To run the tests, load the package and run: sha1pure::test

Source

Installation

There is no installation script since it is expected that most people will simply insert or include the sha1pure.tcl file into their applications directly. However, a pkgIndex.tcl file is available so that sha1pure can be installed as a package.

Generic Disclaimer

Although I can't promise anything in the way of support, I'd be interested to hear about your experiences using it (good or bad). I'm also interested in hearing bug reports and suggestions for improvement even though I can't promise to implement them.

If you send me a bug, fix, or question, include the version of sha1pure, version of Tcl, and name and version of the OS that you are using. Before sending mail, it may be helpful to verify that your problem still exists in the latest version. You can check on the current release and whether it addresses your problems by retrieving the latest HISTORY.

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Last edited: Wed May 30 16:28:44 EDT 2001 by Don Libes