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Thread: Help finding the decryptor

  1. #1
    Oct 2009

    Help finding the decryptor

    If Z(w) is equivalent to 21w+12 and this is an encryptor, then how would I find the decryptor?

    I know the decryption law is w=A^(-1) * (Z-B) (mod N) where A^(-1) is the multiplicative inverse.

    The encryption law is E(w) is equivalent to Aw + B (mod N)
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  2. #2
    MHF Contributor chisigma's Avatar
    Mar 2009
    near Piacenza (Italy)
    Under the hypothesis that $\displaystyle N=26$ , if $\displaystyle A=21$ then $\displaystyle 21 \cdot 5= 105 = 1 \mod 26 \rightarrow A^{-1}=5$, so that the decription law will be...

    $\displaystyle w= 5 \cdot (Z-12) \mod 26$ (1)

    Kind regards

    $\displaystyle \chi$ $\displaystyle \sigma$
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