A MINI PROJECT ON
Submitted By :
L Ramalingam ,Sr. Lecturer
Department of Computer Science Engineering
Cryptography is the science of writing messages in secret codes .
Cryptography, a word with Greek origins ,means SECRET WRITING.
Cryptography components :
Plaintext : It is original message ,before being transformed .The data are not encrypted.
Ciphertext : After the message is transformed . The data are encrypted.
Alice : Alice is the person who needs to send secure data.
Bob : Bob is the recipient of the data.
Eve : Eve is the person who somehow disturbs the communication between Alice and Bob.
Information is often stored and transmitted in a file.
Encryption algorithm transforms the plain text into cipher text.
A plain text file uses a common encoding format such as ASCII or UNICODE to represent the character of file.
Encryption is a translation of a file into a format that hides the content from EVE ;secret code;ciphertext.
After sending the information by ALICE , BOB receive the information and decrypt the data.
A decryption algorithm transforms the ciphertext back into plaintext.
For decrypting the data receiver uses three types of key :
Two categories :
Symmetric key cryptography
Asymmetric key cryptography
In symmetric key cryptography,the same key is used by the sender(for Encryption) and the receiver(for Decryption) .
In case of symmetric key,the key is shared.
In asymmetric key cryptography,two types of key is used :
DES: DATA ENCRYPTION STANDARDS
DES encrypts and decrypts at the bit level.
The plaintext are broken into segments of 64 bits.
Each section is encrypted using a 56-bit key. (Fig. 16.3)
Every bit of ciphertext depends on every bit of plaintext and the key.
It is very difficult to guess the bits of plaintext from the bits of ciphertext.
Uses of Encryption & Decryption :
Privacy & Secruty : E-mail message,Wireless network
Confidentiality :Personal records,Transaction records .
Authentication : Digital signatures,Login.
Intellectual Property : Copy protection
Advantage & Disadvantage
Individuals can post their public key on their Web site.
The number of the keys is only twice of the number of user.
The complexity of the algorithm: calculating the ciphertext from plaintext using the long keys takes a lot of time