Cryptography - The Science of Secrecy

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Ankit Jain

Introduction

“A secret is precious
 and
a lost secret is priceless”

Make any enquiry about computer security, and you will almost immediately fall over the terms cryptography and encryption (and also decryption), but what exactly is meant by this?

Cryptography is the science of writing in secret code and is an ancient art; Some experts argue that cryptography appeared spontaneously sometime after writing was invented. It is no surprise that new forms of cryptography came soon after the widespread development of computer communications. In data and telecommunications, cryptography is necessary when communicating over any untrusted medium, which includes just about any network, particularly the Internet.

Understanding ‘crypto’

The word “cryptography” is derived from the Greek ‘kryptos’ (hidden) and ‘graphia’ (writing). The dictionary, defines cryptography as hidden writing. The Ancient Egyptians, the Arabs and the Romans developed their own systems. The definitions of some technical words are as follows:

Cryptology:      The study of secure communications, which involves both cryptography & cryptanalysis.

Cryptography:  It’s an art and science of using mathematics to secure information and create a high degree of trust in the electronic realm.

Cryptanalysis:   The branch of cryptology dealing with breaking of cipher to recover information, or forging encrypted information that will be accepted as authentic.

The verb encrypt means ‘to convert’ (as information) from one system of
communication into another; especially: to convert (a message) into code. It’s a process of
scrambling or transforming text into an unintelligible form to hide the true meaning of data.

The conversion of plaintext or data into unintelligent form by means of a reversible translation, based on a translation table or algorithm is called “Encryption”.

Reversing the process of encryption is called decryption.

The translation of encrypted text or data (called cipher text) into original text or data (called plaintext) is called “Decryption”.

Plaintext:        The input to an encryption function or the output of a decryption function is known as plaintext. It is the secret data which is encrypted.

Cipher text:    It is the encrypted data.

Cipher:          It is an encryption-decryption algorithm.

Today's cryptography is more than encryption and decryption. Authentication is as fundamentally a part of our lives as privacy. We use authentication throughout our everyday lives.

The Chronology of Cryptography

Some experts argue that cryptography appeared spontaneously sometime after writing was invented. The first documented use of encryption was in 1900 BC. And after that, developments are started and this field is growing more, more and more… The Time-Line of developments is mentioned as follows.

1900 BC -- A scribe in Egypt creates an inscription using non-standard hieroglyphs.  This may have been the first implementation of an encryption algorithm. 

1500 BC -- Assyrian merchants, fearing misrepresentation in the marketplace, institute a primitive form of identification.  They began using intaglio.  This was a flat stone with engravings on it unique to a specific trader.  In this manner, people could be guaranteed of whom they were actually dealing with in business transactions.  This is the ancient history equivalent to the modern day ‘digital signature’ used for transacting business on the Internet. 

500-600 BC -- The book of Jeremiah is written by Hebrew scribes using the ATBASH cipher.  The ATBASH cipher will be explained later.

487 BC -- “Skytale” encryption method is created by the Greeks.  This method used a belt, a staff, and a writing utensil.  The belt was wrapped around the staff, the message was written, and the belt would then be worn as usual. Once at the destination, the belt would be re-wrapped around an identical sized staff, and the message could be decoded.

100-44 BC -- Alphabetical substitution is implemented by Julius Caesar for sending government communications.

1379 -- Gabrieli di Lavinde created a combination substitution alphabet and small code. His encryption method was used, largely by diplomats, for about 450 years.  While stronger methods were developed, this one held favor due to simplicity.

1466 -- Leon Battista Alberti invented and published the first polyalphabetic cipher. He also created a cipher disk. A tool used to simplify the process of encoding and decoding messages. This later became known to Americans as the Captain Midnight Decoder Badge. This class of cipher was not broken until the 1800’s.

1518 -- Johannes Trithemius wrote the first printed book on cryptology. He invented a steganographic cipher in which each letter was represented as a word taken from a succession of columns. The resulting series of words would be a legitimate prayer. He also described polyalphabetic ciphers in the now-standard form of rectangular substitution tables. He introduced the notion of changing alphabets with each letter.

1563 -- Giovanni Battista Porta wrote a text on ciphers, introducing the digraphic cipher. He classified ciphers as transposition, substitution and symbol substitution (use of a strange alphabet). He suggested use of synonyms and misspellings to confuse the cryptanalyst. He apparently introduced the notion of a mixed alphabet in a polyalphabetic tableau.

1585 -- Blaise de Vigenère documented the first auto key system for plain- and cipher-text.

1623 -- Sir Francis Bacon described a 5-bit binary encoding that he later advanced in to a steganographic device.

1790 -- With the help of Dr. Robert Patterson, Thomas Jefferson invented the wheel cipher. This was reincarnated and used in WW-II by the US Navy as the Strip Cipher, M-138-A.

1917 -- William Frederick Friedman began work as a cryptanalyst for the U.S. government.  He later started the first military school for cryptanalysis.

1933-1945 -- The Enigma machine is implemented as the premier cryptographic device for Germany.