Cryptography

Secret Writing

Types of Secret Writing

Secret writing

Steganography Cryptography

Overview of Cryptography Terminology

• Cryptographic/Cipher System - A method of disguising a message so only authorized users may read it.

• Cryptology - The study of cryptography.• Encryption - The process of converting plaintext into

ciphertext.• Decryption - The process of converting ciphertext

back to its original plaintext.• Cryptographic Algorithm - The computational

procedure used to encrypt and decrypt messages. • Cryptanalysis - The process of finding a weakness in,

or actual breaking of, a cryptographic system.

• Cryptography is the science of information security.

• The word is derived from the Greek kryptos, meaning hidden.

• Cryptography includes techniques such as 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 militaryapplications to keep sensitive information secret from enemies (adversaries).

• Nowadays, with the technologic progress as our dependency on electronic systems has increased we needmore sophisticated techniques.

• Cryptography provides most of the methods and techniquesfor a secure communication

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Cryptography components

• 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.

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Categories of cryptography

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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.

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Symmetric-key cryptography

Currently Available Crypto Algorithms (private key)

– DES (Data Encryption Standard) and derivatives: double DES and triple DES

– IDEA (International Data Encryption Standard)

– Blowfish– RC5 (Rivest Cipher #5)– AES (Advance Encryption Standard)

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• 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

Asymmetric-key cryptography

Asymmetric-key cryptography

– RSA (Rivest, Shamir, Adleman)– DH (Diffie-Hellman Key Agreement

Algorithm)– ECDH (Elliptic Curve Diffie-Hellman Key

Agreement Algorithm) – RPK (Raike Public Key)

Currently Available Crypto Algorithms (public key)

Keys used in cryptography

• 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.

Steganography

• Steganography – covered writing – is an art of hiding information

• Popular contemporary steganographic technologies hide information in images

Hiding information in pictures

Image in which to hide Text

Image to hide within the other image

Digital Watermarks