1. What is Cryptography?
Cryptography derived its name from a
Greek word called “Kryptos” which means
“Hidden Secrets”.
Cryptography is the practice and study of
hiding information. It is the Art or Science
of converting a plain intelligible data into
an unintelligible data and again
retransforming that message into its
original form.
It provides Confidentiality, Integrity,
Authentication.
2. There are three eras in the history of Cryptography:
The Manual era
The Mechanical era
The Modern era
Manual era refers to Pen and Paper Cryptography and dates back to 2000 B.C.eg :
Scytale, Atbash , Caesar, Vigenere.
Mechanical era refers to the invention of cipher machines. E.g.: Japanese Red and
Purple Machines , German Enigma.
The modern era of cryptography refers to computers.
There are infinite permutations of cryptography available using computers. E.g.: Lucifer,
Rijndael , RSA , ElGamal.
2
3. What is Encryption / Decryption
Encryption –
The process of converting plain text into an unintelligible format (cipher text)
is called Encryption.
Decryption –
The process of converting cipher text into a plain text is called Decryption.
5. Symmetric
o Even if an attacker captures the data, the attacker
will not be able to manipulate it in any meaningful
way.
o Symmetric algorithms use a single key shared by
two communicating parties.
o The same key is used for both encryption and
decryption.
6. Classic or Symmetric Cryptography
•have two basic components of
classical ciphers: substitution and
transposition
•in substitution ciphers letters
are replaced by other letters
•in transposition ciphers the
letters are arranged in a different
order.
9. PUBLIC KEY or Assymmatric CRYPTOGRAPHY
A form of cryptography in which the key used to encrypt a
message differs from the key used to decrypt it.
In public key cryptography, a user has a pair of cryptographic
keys—a public key and a private key. The private key is kept
secret, while the public key may be widely distributed.
The two main branches of public key cryptography are:
1. Public key encryption
2. Digital signatures
Editor's Notes
The history of cryptography begins where many stories of history do…. in ancient Egypt with hieroglyphics.
Scytale – Spartan method involved wrapping a belt around a rod of a given diameter and length
Atbash – Hewbrew cipher which mirrored the normal alphabet (shown in The DaVinci Code)
Caesar – Shift all letters by a given number of letters in the alphabet
Vignère – Use of a key and multiple alphabets to hide repeated characters in an encrypted message