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Mar
2
awarded  Critic
Mar
2
comment Vigenere ciphers : Need help for math analysis
@EkoJunaidiSalam in math you don't use 'looping'. This is done with recursion. If you take a close look at my formula for $M_i$, you see that its second case ($i\ge|K|$) is recursive: if you want to apply it, you'll first need to compute $M_{i-|K|}$. If $i-|K| < |K|$ you can apply the first rule, otherwise you'll first have to compute $M_{i-|K|-|K|}$, et cetera... The formula for decryption relies on itself.
Mar
2
comment Vigenere ciphers : Need help for math analysis
@EkoJunaidiSalam please clarify. $i$ is a number, not a character. About which formula are you talking exactly?
Mar
2
comment Vigenere ciphers : Need help for math analysis
@EkoJunaidiSalam why do you think so? For $i<|K|$ we have $M_i=C_i-K_i=M_i+K_i-K_i=M_i$ and for $i\ge|K|$ we have $M_i=C_i-M_{i-|K|} = M_i + M_{i-|K|} - M_{i-|K|} = M_i$.
Mar
2
awarded  Commentator
Mar
2
comment Vigenere ciphers : Need help for math analysis
@EkoJunaidiSalam you're right, I had forgotten your question a bit. $C_i$ should've been $M_i$ in two places; I edited the answer.
Mar
2
revised Vigenere ciphers : Need help for math analysis
deleted 136 characters in body
Mar
2
awarded  Editor
Mar
2
revised Vigenere ciphers : Need help for math analysis
added 802 characters in body
Mar
1
comment How does $g$ being a generator imply Diffie-Hellman's correctness?
@fgrieu absolutely. I did not answer the question the OP asked, only addressed the problem he turned out to have.
Mar
1
awarded  Teacher
Mar
1
answered How does $g$ being a generator imply Diffie-Hellman's correctness?
Feb
26
comment Vigenere ciphers : Need help for math analysis
Then your question is unclear. Try editing it to make the problem clear.
Feb
26
answered Vigenere ciphers : Need help for math analysis
Feb
17
comment What prime lengths are used for RSA?
Good luck implementing RSA with $p =1$...
Feb
8
comment Simple multiplication as an encryption method
@Melab your numbers will be too big for small texts already, is my point. Breaking into smaller blocks will make a difference, this will allow frequency analysis.
Feb
8
comment Simple multiplication as an encryption method
@Melab ah, you're not dividing the plaintext in blocks at all? Then, you would have extremely large numbers. Suppose I have a document of 10kB. Do you have an idea of how large a number that would be? To prevent brute force attacks, you would need a large key as well, making this scheme impossible to handle.
Feb
8
answered Simple multiplication as an encryption method
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