Cryptography finds its origin in military organizations where the encryption of messages was of vital importance to safeguard the secret military strategies and ammunition details and various other sensitive decisions from the enemy.
"Cryptography" This word is coined from Greek words
"Krypo" means "Hidden" and
"Graphen" means "to write"
It is the science of secret communication. It is a methodology for altering the representation or appearance of the message keeping its information content intact.
The original or input message is called "Plain Text" and the transformed or output message is called "Cipher text".
A crypto algorithm is used to transform the plain text to cipher text. It specifies the mathematical transformation that is performed on data to encrypt or decrypt it. The mathematical transformation comprises of a function which is parameterized by a key.
Key is a secret value that is used as parameter to a function implementing a complex mathematical algorithm to encrypt or decrypt messages.
The original message is encrypted using the secret key and can be decrypted only using the secret key.
But distribution of key in symmetric key cryptography (using single key) posed the vulnerability threat. As it is often said, "The strength of the chain is measured by its weakest link"! The key distribution made the cryptosystems still vulnerable.
Thus, asymmetric key cryptography was evolved to overcome the short coming of single key cryptography system.
Asymmetric key cryptography, also called Public key cryptography (PKI) uses a key pair (public key and private key).
This system is commonly used on internet to transfer data in a secured manner.
PKC has two keys(Key pair) - First, "Public key", which is made publicly widely available and second "Private key", which is possessed by the individual and maintained secretly.
The public key is used to encrypt the message and only the private key corresponding to that public key can decrypt the message.
i.e. If 'A' intends to send a message to 'B'. He encrypts the message using B's public key and sends the message over internet.
The message can be decrypted only by B's private key which is possessed exclusively by B. Hence, even if the message is snooped by any other person, it is of no use to him as he is unable to extract the original message due to unavailability of corresponding private key.
 The main area of concern in Public key cryptography is to have a strong cryptosystem i.e. one in which the following requirements of keys are met:
i) Decryption function should be able to provide the original message intact
ii) It is very difficult to deduce Decryption key(private key) from Encryption key(public key)
iii) The cipher text should not make the encryption logic obvious easily i.e. the encryption logic should not be easy to crack.
Last update : 04-08-2007 13:31
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