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May 26th, 2012, 12:08 PM   #1
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a multiplicative cipher

[Moderator note: question was deleted by user; see the now-restored third post.]
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May 26th, 2012, 03:10 PM   #2
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Re: a multiplicative cipher

Lots isn't clear here. Since you are using z26, I assume you are associating every letter of the alphabet with a number between 0 and 25 inclusive. Is that correct? If so, do you start with 0 or 1 (or some other number, for that matter)? It'll make a difference. If w=23, it looks like the answers to my questions are yes and 1. If so and 'multiplicative' means you multiply the numerical values of the letters together, then 'when' = 23*8*5*14 mod 26 and I'm getting 16. I'm too tired to recheck my arithmetic.

If this is the way this is supposed to work, this an odd cipher, since many different numbers can multiply out to the same number, especially in modular arithmetic, and decrypting even if you know the key is therefore not just difficult but impossible, as information is irretrievably lost.
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May 27th, 2012, 01:51 PM   #3
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Re: a multiplicative cipher

A multiplicative cipher is defined on Z26 by the rule
M5(m) = 5×26 m.
Messages in English are coded numerically using the correspondence
below.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
(i) Encipher the message ‘Who’ using M5 (that is, find the
ciphertext for this message).

i just need to get a little start off with the w.. i got w=15 when i worked this out as i got my multiplicatice inverse of 5 in z26 to be 21 is this correct
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May 27th, 2012, 05:11 PM   #4
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Re: a multiplicative cipher

Quote:
Originally Posted by milly2012
A multiplicative cipher is defined on Z26 by the rule
M5(m) = 5×26 m.
Messages in English are coded numerically using the correspondence
below.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
(i) Encipher the message ‘Who’ using M5 (that is, find the
ciphertext for this message).

i just need to get a little start off with the w.. i got w=15 when i worked this out as i got my multiplicatice inverse of 5 in z26 to be 21 is this correct
21 = -5 mod 26
5*-5 = -25 = 1 mod 26
Yes, 21 is the multiplicative inverse of 5 mod 26

w = 23 in this system. 23 = -3 and -3*-5 = 15 mod 26

So, if you are taking the numbers initially assigned value and multiplying it by the multiplicative inverse of 5 mod 26, you are right.
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May 28th, 2012, 12:07 AM   #5
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Re: a multiplicative cipher

Thanks johnr
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May 28th, 2012, 02:54 AM   #6
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Re: a multiplicative cipher

So does this mean that H = 8 = 17 (mod26) ?
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May 28th, 2012, 03:36 AM   #7
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Re: a multiplicative cipher

The account for milly2012 has been deactivated.
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May 28th, 2012, 04:17 AM   #8
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Re: a multiplicative cipher

Hmmm. No that's not right. Certainly.
Could you clear up how to go about this, please.

You don't necessarily have to use the letters above, but a swift run through any of them would set me at rest.
Thank you.
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