# Tag Info

5

I'll assume that the plaintext consists entirely of capital ASCII letters as in the example. This implies the high 3 bits of each byte of plaintext are 010. It is useful to visualize how 3 consecutive bytes of plaintext map to 4 consecutive Base64 characters. 1. Frequency analysis of the last character of 4-char blocks in ciphertext We see there is a ...

5

The feasibility depends a lot on the length of the corpus. The more statistics, the better guesses an attacker would be able to make. He'll try to use statistical attacks to fit the frequency curve of the tokens to the frequency curve of English words. This will allow him to guess the preimages of more frequent words with high confidence, but will he be ...

4

This sounds like a classic codebook or nomenclator. Even if we assume a perfect random oracle that generates a completely random codeword for each word of English text, I agree with otus that frequency attacks and N-grams would likely be able to decode the most-frequently-used words. Also, a known-plaintext attack (or worse, a chosen-plaintext attack) would ...

3

You can solve it at http://www.quipqiup.com/index.php in about 5 seconds. contrariwise continued tweedle dee if it was so it might be and if it were so it would be but as it isnt it aint thats logic It's an excerpt from Through the Looking-Glass by Lewis Carroll Information on how quipqiup works is available at http://www.quipqiup.com/howwork.php

2

The encryption is weak This encryption is more susceptible to frequency analysis than original "substitution ciphers" because the frequency tables should be much more Non-uniform. In my opinion, it should be less secure than substitution cipher although the key space is much much bigger (compare $64!$ to $26!$). Some evidences of the weakness If I assume ...

2

You should not just "pick the highest frequency character and assume it should be E" because it will probably fail most of the time, except if your ciphertext is really long. If your alphabet is small enough (usually either 26 or 255), it would be wiser to try all the possibilities for each group, and to check if the output looks like real english ...

2

There are different approaches to crack a substitution cipher. A human would use a different strategy than a computer. But as the word boundaries are not preserved it will be rather challenging for a human solving this cipher. The quipqiuq tool mentioned by John is using word lists, but there are other methods as well. Resources: ...

2

Provided the text was long enough and used an simple codebook substitution cipher, absolutely. English has common bigrams and trigrams as well as words that are typically positioned in certain places in sentences, like The. Also, if punctuation was tokenized in the codebook, it would be incredibly easy to guess or identify . and ,, because those will be ...

1

Such a scheme would have two effects against an attacker trying to analyze the frequency of words and word combinations: They would need more samples to differentiate between two tokens at the same level of confidence. For two different tokens with similar frequency they would no longer know that the words differ. The first means you are making the ...

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