vimwiki/tech/substitution.wiki

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2021-10-11 03:22:53 +00:00
= Substitution =
A Cipher where characters are replaced based on a mapping
== Monoalphabetic Subsititutions ==
Cipher where each occurrence of a plaintext symbol is replaced by a
corresponding ciphertext symbol
=== Afline ===
An affine cipher E(x) = (ax + b) MOD 26 is a monoalphabetic sub cipher, where a
and b are given constants
=== Columnar Transposition ===
Use letters to create columns, then fill all remaining columns with remaining
letters in alphabetic order
== Cryptoanalysis ==
=== Monoalphabetic Substitution ===
We make some assumptions
* Its english and has same stats as standard english
* word divisions are not preserved
* use frequency analysis to guess high frequency letters
- E E N O R I A S are 70% of letters in english
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* identify
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- vowels
- diagraphs (common combos of letters ie TH)
* Use cribs
* guess and rely on luck
== Also see ==
* [[gcd]]
[[index]]