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Math Help - Affine Cipher Encryption

  1. #1
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    Affine Cipher Encryption

    Hi!

    Anyone any good with codebreaking?....

    Let plaintext be written in the alphabet a, b, . . . , y, z and let ciphertext be
    written in the alphabet A, B, . . . , Y, Z. Both alphabets have N = 26 letters.
    Consider the affine cipher on digraphs with encryption

    E( \pi) = 9 \pi + 43mod676:

    Encipher the plaintext TRUTHS.

    In this question I want to use standard numbering, so A=0, B=1..... Z=25
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  2. #2
    Newbie kira's Avatar
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    i would have helped u if encryption is of the form (ax+b)modc

    but here inclusion of 9 \pi makes it helpless for me
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  3. #3
    Newbie kira's Avatar
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    i can may be help u if u tell me whats use of 9 \pi here

    between , see this for some help: http://www.math.cornell.edu/~kozdron...uts/affine.pdf
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  4. #4
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    i think that link is only useful for the simple version of the affine cipher.... thanks anyway

    any other ideas anyone?
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  5. #5
    Senior Member roninpro's Avatar
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    Is \pi supposed to be a number or a variable?
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  6. #6
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    \pi represents the letter that is to be ciphered or deciphered
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  7. #7
    Senior Member roninpro's Avatar
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    This is somewhat unusual notation. I've seen people use a letter to denote this, say, P.

    In any case, you need to represent your digraphs numerically. To do this, you first convert each letter to a number. For the digraph TR, we have T\mapsto 19 and R\mapsto 17. Then, we write this as a number base 26: TR\mapsto 19\times 26+17=511. Then pass it through E: E(511)=586. Then, 586=22\times 26+14\mapsto WO.

    In summary, the plaintext TR is encrypted into WO. Try the rest for yourself.
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  8. #8
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    i tried the others for myself and got UT~GG and HS~SX.... sound right?
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