Ciphers ! What are they and how they work ??? (Part – 1)
Enigma Machine
Hi there everybody !
This time I’m back with yet another topic related to cryptography and ciphers. Today I’m gonna discuss various ways to encrypt your message… Or let me put it this way… I’ll be discussing various ciphers (Encryption Techniques) which are used to convert your plain text into cipher text.
The history of ciphers dates back to as old as 400 BC in Sparta (Greece). It all started in Sparta with the “scytale“, a device used for communication between military commanders, and ends with quantum cryptography. The scytale was a tapered baton around which was wrapped a spiral strip of parchment or leather containing the message. Words were then written lengthwise along the baton, one letter on each loop of the strip. When unwrapped, the letters of the message appeared scrambled and the parchment was sent on its way. The receiver wrapped the parchment around another baton of the same shape and the original message reappeared.
The next step in the history of ciphers was due to Julius Caesar, who allegedly used a simple letter-substitution method in his correspondence. The emperor replaced each letter in the message with the letter that followed it alphabetically by three places. Thus the letter A was replaced by D, the letter B by E, and so on. For example, the English word COLD after the Caesar substitution would appear as FROG. This method is still called the “Caesar cipher” (regardless of the size of the shift used for the substitution).
In all cipher systems one assumes that the message has been intercepted. The objective is then to make it impossible, or at any rate very difficult and time-consuming, for the interceptor to decrypt the message.
Substitution ciphers
Substitution ciphers (of which the Enigma is a sophisticated development) involve substituting one letter for another according to some rule.
The simplest substitution is Caesar’s cipher:
ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFG
….ABCDEFGHIJKLMNOPQRSTUVWXYZ
To encipher, the letter on the bottom row is written down as the substitution for the text letter on the top row. To decipher, the received cipher is looked up in the bottom row and the text letter read off from the top row above it.
In this case the message key, which the recipient needs to know, is just the displacement between the two alphabets. This is a simple example of a cipher system which shows an immediate flaw: there are only 26 possible message keys and so anyone can just try them out. (Example: crack FDHVDU)
A more sophisticated system uses a random series of characters for the lower alphabet.
ABCDEFGHIJKLMNOPQRSTUVWXYZ
IPHBOSFCQZJNTWGLMYRXDKEUVA
Now the recipient has to know the substitution alphabet, and this sequence of letters is in effect the message key. There are a huge numbers of possible substitutions (actually 403,291,461,126,605,635,584,000,000 for an alphabet of 26 letters.)
But such encipherments are still easily broken by using common-sense facts such as that E is the most common letter, THE the most common word, and so forth. It is very worthwhile noting that having a large number of possible keys does not in itself provide security. (This is really the same principle as allows you to solve crossword anagrams. There are vast numbers of possible permutations of the letters, but most of them can be eliminated because they lead to impossible words.)
In the nineteenth century various schemes for polyalphabetic systems were invented. In these, there is more than one substitution alphabet and they are used in rotation, or by some other rule. The message key then has to give the total system involving the alphabets used and the rule for using them. If the rule is simple then statistical methods can still easily break the cipher; and the problem about making such systems more complex is that the encipherment then requires a large handbook and hours of error-prone labour.
By the twentieth century it became possible to carry out substitutions by using electrical connections to mechanise the dreary and difficult work of looking up tables in a handbook. This is what led to the Enigma (Shown in the above Pic)… !!!
The basic Enigma was invented in 1918 by Arthur Scherbius in Berlin. It enciphers a message by performing a number of substitutions one after the other. Scherbius’s idea was to achieve these substitutions by electrical connections.
In this post, I have discussed about a brief history of ciphers and a very common way to do it… Substitution Cipers. In my next post, I’ll be going a lil’ more deep and discuss about the most recent version of ciphers.. “The Polymorphic Ciphes”.
Do keep watching….. Any comments / feedbacks / suggestions would be highly appreciated.
Enjoy !
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Cryptography | Ne0 | October 18, 2008
Nice one again!!! Caesar’s cipher is still used at many places for non-commercial use. Like when I was a child and if I wanted to note down name and address of any gal, I would note it down using Caesar’s cipher
(well that time I was not not aware of any encryption fundas) We all must have used encryption atleast once in our life , knowing or unknowingly.
Anyways looking forward for your next parts.
Thanks w0lf ! I have lined up a couple of more sub-topics under this. I’ll be discussing more about anigma and how it worked, in later posts. Thanks for always suggestive……