![]() What is the difference between them in general. But I'm wondering if a block cipher is always substitution cipher. So my understanding so far is that substitution cipher can be considered as a block cipher. I feel this description is talking about the problem of ECB mode in block cipher. Symbols by analyzing the frequency distribution of the Provided the message is of reasonable length (see below), theĬryptanalyst can deduce the probable meaning of the most common (1 letter is 1 block)Īlthough the number of possible keys is very large ($26! \approx 2^$, orĪbout 88 bits), this cipher is not very strong, and is easily broken. What I thought here is that this is also a block cipher. And given $k$, one of the bijection(substitution) functions is (uniformly)selected and used to substitute a letter. I started from Caesar Cipher which can be considered as a kind of substitution cipher (if my understanding is right).Īnd an ideal substitution cipher (in 26 alphabets) is the two functions $E(x,k)$ and $D(x,k)$ where $0 \leq k < 26!$. I'm studying(and clearing my head) about block cipher.
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