Fortuna prng
Fortuna is a cryptographically secure pseudo random number generator (PRNG) developed by Bruce Schneier and Niels Ferguson. It is described in their book 'Practical Cryptography'.
I have developed a C++ implementation of Fortuna. The design and the source code are available here, free for commercial or non commercial use.
The main goals of my implementation of Fortuna are the following:
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Designed for use on web servers running Windows/XP or Windows/2000 |
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Difficult to attack |
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Follow the design of Ferguson and Schneier as closely as possible |
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Use information from Windows as data sources for the 'entropy' pools |
My implementation differs from the original design in the following ways:
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The seed file in the original design appears to only save the state of the generator (Section 10.6.1, page 178). My seed file contains the state of each of the entropy pools. The seed file is encrypted using password based encryption with a user supplied password. |
Design Highlights
For more detailed information on the design of Fortuna, go here.
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Highly multithreaded. Each of the 32 entropy pools runs on it's own thread and each of the source pools runs on it's own thread. |
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There are 32 source threads which generate random data using the high performance counter timing the WaitForSingleObject function. I've done a little study to investigate using the high performance counter and found that a number of the bits in the counter difference pass the Diehard randomness tests. |
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The high performance timer and changes in the process monitoring (page faults, I/O counts etc) provide most of the entropy |
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The Windows registry is used as a large data repository to populate the entropy pools with a data source with no entropy. There are four threads which walk the registry, extracting data and adding it to the pools. While this is certainly not random data, it makes an attackers job more difficult due to the size of the registry and the way that the data is distributed among the pools. |
Entropy Sources
For more detailed information on entropy sources, go here.
Seed File
For more detailed information on the seed file, go here.
Credits
I used the SHA-1 and AES implementation from Dr. Brian Gladman.
I used the C++ Multithreading library from the book "Win32 Multithreaded Programming" by Cohen and Woodring. This is an excellent book and if you are new to multithreading I highly recommend it.
The MFC monitor app uses the compression library from www.zlib.net.
