Old Cryptography
The next series of blogs on cryptography are aimed at those who do not have extensive knowledge of cryptography and are interested in the subject. -
To begin we must define what is cryptography that according to the Royal Spanish Academy is the art of writing with a secret key or enigmatically. The word cryptography comes from the Greek krypto (hidden), and graphos (write), which literally be hidden writing, with this definition we can say it is art rather than old. -
We can say that cryptography was used by the Babylonians around 2,500 BC in a kind of tablet on which are terms to which they took their first consonant or likewise use a few common characteristics in order to hide formulas for creating clay, or the case of Hebrew scholars who took monoalphabetic substitution ciphers (encryption Atbash) dating from 600 BC or so.
But the first encryption system described was used by the Spartans during the Peloponnesian War, where the Athenians fought between the year 431 BC and 404 BC the method described by Plutarch is the first transposition cipher system known scitala Spartan in this method took two pieces of wood are exactly alike in their thickness (which we call key) To write a secret message is rolled fabric on the rod and the message was written on top of that fabric. When unrolled, the text was not legible, thus leaving the encrypted message. -
“Transposition method encrypts the plain text by changing the order of the letters.”
This was followed in 150 BC an encryption called Polybius (203-120 BC) the famous Greek historian, this system consists of a table as shown below. -
as shown the letters i, j are together to give a total of 25 positions, with this system a method of substitution. -
do a test, suppose we want to encrypt the word mkit
plaintext: mkit
take the “M” and look for his cell and see that the row numbers and column form, 32 thus to “M” found 32. -
ENCRYPTION: 32252444
decoding must be separated into groups of 2 digits and place the letters knowing that the first number are the rows and second columns. -
Although the cryptographic method known and most studied of antiquity is the Code Cesar, which was created in about AD 50 and widely used by the Roman Emperor Gaius Julius Caesar (100-44 BC). This encryption method is displacement, its operation is very simple and allows the study of modular arithmetic. -
Its operation is very simple since it is the movement and the key is to move as the alphabet, we see an example
Original alphabet: ABCDEFGHIJKLMNÑOPQRSTUVWXYZ Coded alphabet: XYZABCDEFGHIJKLMNÑOPQRSTUVW
In this case the displacement is 24 spaces to the right and this action can change the encryption key. -
Once you have established your key to encrypt, so let’s use the word again mkit. -
plaintext: mkit
to encrypt the task is to find each letter in the original script and play the corresponding alphabet in the encoding and decoding is the reverse. -
Clear text mkit Cipher Text JHFQ
The vulnerability in this method is given for a frequency analysis, because without knowing the amount of displacement of the alphabet but if having a table of frequency of use of the letters (see picture), one can deduce the content of the message. -
“The frequency analysis is the study of the frequency of letters or groups of letters in a ciphertext. this being a method for breaking classical ciphers “
Cristian Amicelli Rivero
