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February 24th, 2009, 06:58 AM  #1 
Member Joined: Jan 2009 Posts: 30 Thanks: 0  Affine transformation and RSA cipher
1. If the two most common letters in a long ciphertext, enciphered by a an affine transformation C is congruent aP + b (mod 26) are W and B, respectively, then what are the most likely values for a and b? 2. This message WEZBF TBBNJ THNBT ADZQE TGTYR BZAJN ANOOZ ATWGN ABOVG FNWZV A was enciphered using an affine transformation C is congruent to aP + b (mod 26): Suppose it is know that the most common letters in the plaintext message are A, E, N, and S. Use the frequency of letters to determine a and b. Then decrypt the message. 3. If the ciphertext message produced by the RSA cipher with key (e; n) = (13; 2747) is 2206 0755 0436 1165 1737 what is the plaintext message? 
February 25th, 2009, 06:47 PM  #2 
Member Joined: Jan 2009 Posts: 30 Thanks: 0  Re: Affine transformation and RSA cipher
can anybody help me out with this??

March 12th, 2009, 02:36 AM  #3 
Newbie Joined: Mar 2009 Posts: 4 Thanks: 0  Re: Affine transformation and RSA cipher
For the first cyphertext: plaintext= "this message was enciphered using an affine transformation" 
March 12th, 2009, 03:46 AM  #4 
Newbie Joined: Mar 2009 Posts: 4 Thanks: 0  Re: Affine transformation and RSA cipher
For the second cyphertext: 2747=41*67 phi(2747)=40*66=2640 and 13*2437=1 mod 2640 Decryption key is (2437,2747) Decryption: 2206^2437 mod 2747=617 0755^2437 mod 2747=404 0436^2437 mod 2747=1908 1165^2437 mod 2747=1306 1737^2437 mod 2747=1823 

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