My Math Forum Multiplicative cipher - part 2
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 May 28th, 2012, 05:23 AM #1 Newbie     Joined: May 2012 From: Surrey, UK Posts: 6 Thanks: 0 Multiplicative cipher - part 2 In a previous post an ex member asked about multiplicative inverses & ciphers I am now curious as to how this works. A multiplicative cipher is defined on Z26 by the rule M5(m) = 5×26 m. Messages are in English are coded numerically where the alphabet is mapped to a number. A = 1 B = 2. . . . . . z = 26 Could you encipher any letter or word using M5 (that is, find the ciphertext for this message) as I'm curious now. Thank you
May 28th, 2012, 07:30 AM   #2
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Re: Multiplicative cipher - part 2

Quote:
 Originally Posted by purecotton In a previous post an ex member asked about multiplicative inverses & ciphers I am now curious as to how this works. A multiplicative cipher is defined on Z26 by the rule M5(m) = 5×26 m. Messages are in English are coded numerically where the alphabet is mapped to a number. A = 1 B = 2. . . . . . z = 26 Could you encipher any letter or word using M5 (that is, find the ciphertext for this message) as I'm curious now. Thank you
It took me awhile to figure out even approximately what the former member wanted to do and I'm still not sure, as the value for w they wanted confirmation for was correct if you multiply w's initial value, ie 23, not by 5, as 23*5 = 11 mod 26, but by the multiplicative inverse of 5 mod 26, ie 21. But in any vent, yes, you can define a simply code by assigning each letter in the alphabet a value mod 26 and then multiplying those values by any number coprime with 26. So don't use an even number or 13, but anything else would work.

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