# Math Help - Affine Cipher Encryption

1. ## 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

2. 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

3. 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

4. i think that link is only useful for the simple version of the affine cipher.... thanks anyway

any other ideas anyone?

5. Is $\pi$ supposed to be a number or a variable?

6. $\pi$ represents the letter that is to be ciphered or deciphered

7. 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.

8. i tried the others for myself and got UT~GG and HS~SX.... sound right?