Vigenere Cipher question - 未名空间MITBBS历史存档

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Vigenere Cipher question

Vigenere Cipher question# CS - 计算机科学

q*z2004-05-13 07:05

1 楼

Hi there anyone is doing cryptology?
I have one question about vigenere cipher.
I know I can break the code if I have long enough
cipher text, but I am not sure what the probability to
correctly find out the key if some letters of the cipher text
are modified? Any math equations for that?
Thanks a lot

a*i2004-05-13 07:05

2 楼

ah, meet somebody in crypto at last...
I don't know the answer, only some rough idea for reference:
if the modification doesn't change the frequency of the letters much, it won't
change the probability to find out the key much.
But what's probability when there's no modification? It depends on whether the
frequency of the letters matches the statistic frequency based on which the
cracking algorithm is designed. I guess it's possible to deduce a math
equations for it, but not sure how much time.

【在 q***z 的大作中提到】

: Hi there anyone is doing cryptology?
: I have one question about vigenere cipher.
: I know I can break the code if I have long enough
: cipher text, but I am not sure what the probability to
: correctly find out the key if some letters of the cipher text
: are modified? Any math equations for that?
: Thanks a lot

q*z2004-05-13 07:05

3 楼

I am not studying crypt
actually I study EE
but I am using vigenere cipher, now I need more theory
for my question. I really wanna get some math expression
for that.
Do you have any ideas about the variation of Vigenere cipher?

【在 a****i 的大作中提到】

: ah, meet somebody in crypto at last...
: I don't know the answer, only some rough idea for reference:
: if the modification doesn't change the frequency of the letters much, it won't
: change the probability to find out the key much.
: But what's probability when there's no modification? It depends on whether the
: frequency of the letters matches the statistic frequency based on which the
: cracking algorithm is designed. I guess it's possible to deduce a math
: equations for it, but not sure how much time.