• Cryptography is the science of information security.• The word is derived from the Greek kryptos, meaning hidden.• Cryptography includes techniques such as microdots, merging words with images, and other ways to hide information in storage or transit.
• Confidentiality:- the information cannot be understood by anyone for whom it was unintended.• Integrity :-the information cannot be altered in storage or transit between sender and intended receiver without the alteration being detected.• Authentication :-the sender and receiver can confirm each others identity and the origin/destination of the information.
Overview of Cryptography & Its Applications• People wants and needs privacy and security while communicating.• In the past, cryptography is heavily used for military applications to keep sensitive information secret from enemies (adversaries).• Nowadays, with the technologic progress as our dependency on electronic systems has increased we need more sophisticated techniques.• Cryptography provides most of the methods and techniques for a secure communication
• Encryption – It is a process of changing or converting normal text or data information into gibberish text.• Decryption – It is a process of changing or converting gibberish text back to correct message or data by using encryption method.
TerminologyCryptology : All-inclusive term used for the study of securecommunication over non-secure channels.Cryptography : The process of designing systems to realizesecure communications over non-secure channels.Cryptoanalysis : The discipline of breaking the cryptographicsystems.Coding Theory : Deals with representing the informationusing codes. It covers compression, secrecy, anderror correction.
The Aspects of Cryptography• Modern cryptography heavily depends on mathematics and the usage of digital systems.• It is a inter-disciplinary study of basically three fields: Mathematics Computer Science Electrical Engineering• Without having a complete understanding of crypto analysis (or cryptoanalytic techniques) it is impossible to design good (secure, unbreakable) cryptographic systems.• It makes use of other disciplines such as error-correcting codes compression.
• A single common encryption key is used to encode and decode messages.• Both sender and receiver must know the common key.• The common key need to be exchanged before hand by some other secure method.• Symmetric encryption is simple and fast.• But - key management is impractical with large number of senders and receivers. 11
Asymmetric-key cryptography• Asymmetric system under, which two different keys are used to encrypt and decrypt the message or received data packet.• On public key is used to encrypt the data or message and the private key on receiving end is used to decrypt the message or data packet.• Each user has a Public key and a corresponding Private (secret) key 12
• Sender”sign” messages by means of his private secret key.• Recipient verify the senders signature by means of the senders public key.• The senders identity is certified by means of a”Certificate” which is digitally signed by a trusted third party.
• public-key cryptography Increased security and convenience.• public-key cryptography is best suited for an open multi-user environment.• Symmetric encryption is simple and fast.
• cryptography = physics + Information theory• Information is physical.• Information gain implies disturbances.