This outlines the gronsfeld cipher, which is a modification of the vigenere cipher. I like and find this cipher interesting because of it using numbers instead of letters, and I like cryptography which uses numbers.
Interesting. Gronsfeld ciphers then form a subset of Vigenere ciphers. That is, there's a one-to-one correspondence between Gronsfeld ciphers and Vigenere ciphers where keywords are formed from the letters A through J.
An in-depth description of Julius Caesar's shift cipher and how it works. Also shows how to use frequency analysis and chi-square values to quickly break the cipher.
Clues left in the clumsily encrypted notes of a Mafia don have helped Italian investigators to track his associates and ultimately contributed to his capture after years on the run. The recently busted Bernardo Provenzano, reputed to be the "boss of bosses" of the Sicilian Mafia, used a modified form of the Caesar cipher to obscure "sensitive information" in notes left to either his family or underlings.
I found this article and liked it because it gave me a lot of information about the Beale Cipher and treasure, even more information than Singh. I especially was interested in the reasons describing the possibility of it being real or a hoax.
This website gives a good description about the Vigenère cipher and techniques for cracking it. It also shows another way we could more easily crack one of these ciphers using Microsoft Excel. Lastly, on the menu on the left side of the page is a link that lets you contact Simon Singh.
This is a website introducing codes and ciphers in WW II by Tony Sale. Given this specific war context, is there really a guideline of what an action is ethical and what is not in terms of cryptoanalysis? Would an action be ethical whenever the majority's well-being is satisfied, or there's a line that should not be crossed?
A useful document detailing the different substitution ciphers (including the Caesar Shift) and the application of Modular Arithmetic in modern day Cryptography.
For longer ciphers, Kasiski analysis is useful for determining possible keywords using a modified frequency analysis and repetition analysis. This is an online tool to find repeat sequences in a ciphertext, and can be used to quickly decrypt a Vigenere ciphertext.