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S-boxes in Blowfish
Hey there, Im just working on a project for a crypto class and I decided to implement blowfish on VHDL(Hardware Description Language) to run on a hardware piece. Anyways, the real question is that the blowfish algorithm initializes its famous 4 S-boxes and a P array with the hex values of the decimal part of pi. I have found some programs which calculate pi with enough accuracy to get enough values for initialization of these S-boxes (they are 4 each with 256 32 bit entries). Problem is I dont know how to change this number later to hex or even binary. Any help here would be greatly appreciated.
I know I haven't given much information on the algorithm but it is not really necessary to understand what I need.
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hey sounds like a cool project, are you gonna have two cpld or fpga's? one encrypting and on decrypting?
I found this page,
http://www.ee.ualberta.ca/~elliott/e...sh_encryption/
http://personal.sip.fi/~lm/c2txt2c/blowfish.txt <---hehehe :)
http://www.packetstormsecurity.org/crypt/blowfish/
dunno whether there any help...
i2c
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Hi
An excellent list of the initialisation numbers for the 18x32bit P and the 4 256x32bit S-boxes
can be obtained here[1], in a useful format.
How is this computed?
The starting point chosen by Bruce is the number: Pi - 3 = 0.14159265...
How can this number be assembled in hex-base? As follows:
First digit: 1/16 = 0.0625
Q: How often does that fit into this number 0.14159...?
A: 2 times.
Code:
0.14159265 - 2* 1/16 = 0.01659265...
Note: This number 0.01659265... is smaller than 1/16, and thus has to
be "approximated" using the next smaller possibility: 1/(16^2)
Second digit: 1/(16^2) = 0.00390625
Q: How often does that fit into the rest-term 0.01659265...
A: 4 times
Code:
0.14159265 - 2* 1/16 - 4*1/(16^2) = 0.0009676535...
Third digit: 1/(16^3) = 0.00024414...
Q: How often does that fit into the rest-term 0.000967653...
A: 3 times
and the fourth digit: 15 times. 15 in hexadezimal notation is F.
Thus: 24 3F ...
etcetc
The initialisation starts with P, then S0, S1, S2 and finally S3.
Cheers.
[1] http://www.sstorie.com/school/cs4821...owfishSPInit.h
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Thanks a lot guys, definitely going to help. Oh and i2c, ill be using fpga's .
