How Do I Find the Decryption Function for C = (7M + 9) mod 26?

Thread starter stunner5000pt
Start date Apr 20, 2004
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Linear

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To find the decryption function for C = (7M + 9) mod 26, the key is to determine the multiplicative inverse of 7 in the group U(26). The multiplicative inverse is a number that, when multiplied by 7, yields 1 modulo 26. In this case, the inverse is 15, which can be verified through calculations. Once the inverse is established, it can be applied to rearrange the equation to solve for M. Understanding these steps is crucial for successfully decrypting the message.

Apr 20, 2004

stunner5000pt

another little bit of help and this is NOT a homework assignment this is for an exam i need to understand it

the qustion is find the decryption function for C = (7M + 9 ) mod 26

how do i fin the decryption function using the inverse?

that is 15 in this case

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Apr 21, 2004

matt grime

Science Advisor

Homework Helper

the same way you do it for any other equation:
you've just got to find what the multiplicative inverse of 7 is in U(26)
I don't see where 15 comes from.

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