Cryptanalysis “is the study of ciphers, ciphertext, or cryptosystems with a view to finding weaknesses in them that will permit retrieval of the plaintext from the ciphertext, without necessarily knowing the key or the algorithm”.
- Cryptanalysis of the Affine Cipher
- Cryptanalysis of the Bifid Cipher
- Cryptanalysis of the Caesar Cipher
- Cryptanalysis of the Hill Cipher
- Cryptanalysis of the Nihilist Substitution Cipher
- Cryptanalysis of the Playfair Cipher
There are a couple of methods of quantifying how close to English text is.
|
Method |
Depends on property | ||
| Frequency | Type | Order | |
| Index of Coincidence | True | False | False |
| Chi-Squared Statistic | True | True | False |
| N-Grams Probability | True | True | True |
Frequency – The individual counts regardless of letter
Type – The letter that the count is attributed to.
Order – The letters that proceed and follow this letter.
The best method is normal using N-Grams Probability as it takes into account all three properties, however this is not always possible when quantifying how ‘English’ a piece of text is.