[Lecotti]

Hello everybody, hopefully somebody can help me with this . Recently i have been reading an article from 'The New Turing Omnibus'(public key cryptography) and i cannot get my head around this bit, its on p.g 254 for any of you who have the book.

B'x = 3522 x (901)^-1 mod 1234
= 3522 x 1171 mod 1234 how did he get 1171 from the previous expression???
= 234

Therefore B'x = 234

So far, I havn't found the rest of the book that bad but i just can't seem to figure this bit out! Any help would be greatly appreciated!

This post has been edited by Lecotti: 26 March 2010 - 10:47 AM

[Galois]

I'd assume that the author explains modular division. If that's not the case then look online for more information. Basically, a division by a number "a" mod "x" can be replaced by a multiplication by a number "b" if "ab" is equivalent to 1 mod "x". And so in this case the division by 901 was replaced by a multiplication by 1171 precisely because the number "901 * 1171" is equivalent to 1 mod 1234.

[Lecotti]

Thanks alot, you explained this much better than the author did!