Abstract
In this dissertation a PicPass algorithm is proposed for the solution of Key Exchange problem using Symmetric and Asymmetric key cryptography. Diffie and Hellman proposed an algorithm for key exchange. But this algorithm suffers from Man-in middle attack. So to overcome this problem Seo proposed another algorithm that uses text password for the agreement between two parties. But again the password suffers from offline dictionary attack. In this, a PicPass Protocol i.e. picture is used as a password to make an agreement between two parties. The protocol contains two function i.e. picture function as well as distortion function is used to make picture in a compact size and then it is sent to receiver. Firstly the sender encrypts the Plain Text using Secret Picture and creates the Cipher Text using Symmetric key cryptography.Then the Secret Picture will be encrypted by covered picture resulting into Encrypted Picture.Now the Cipher Text and Encrypted Picture will be placed into digital envolpe and then the envelope will be send to the receiver. The receiver will receive the digital envelope, open it and then decrypt the Encrypted Picture using his Key Picture. This will result the receiver to get the Secret Picture. Now the receiver will open the Cipher Text using the Secret Picture and get the Plain Text. In between if any person wants to predict the Encrypted Picture then he cannot guess as the picture will only be decrypted using the Secret Key which will be only with the receiver. So in this dissertation, a picture is used as a password to authenticate key exchange is that gives practical solution against offline dictionary attacks only by using both private and public key cryptography.
Highlights
Basics of Cryptography and The Problem Of Key Agreement.1.1 Basics of CryptographyCryptography is the science of information security
Since the sender and the receiver will use the same key to lock and unlock, this is called as symmetric key cryptography
Based upon symmetric key algorithm Diffie-Hellman Key Exchange/Agreement Devised by Whitefield Diffie and Martin Hellman in 1976.Two parties can agree on a symmetric key using this technique i.e. the same key can be used for encryption as well as decryption.Key can be used only for key agreement,but not for encryption & decryption of messages.Once the parties are agree on key the key can be used for encryption as well as decryption
Summary
Cryptography is the science of information security. The word is derived from the Greek kryptos, meaning hidden. Cryptography is closely related to the disciplines of cryptology and cryptanalysis. Cryptography includes techniques such as microdots, merging words with images, and other ways to hide information in storage or transit. In today's computer-centric world, cryptography is most often associated with scrambling plaintext(ordinary text, sometimes referred to as cleartext) into ciphertext (a process called encryption), back again (known as decryption). Individuals who practice this field are known as cryptographers. Many algorithms are publicly known and are not the secret part ofthe encryption process. The key is made up of random valueswithin the keyspace range
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