10/7/2019 Created by Omeed Mustafa 1 st Semester M.Sc (Computer Science department) Cyber-Security

Cryptography is associated with the process of converting ordinary plain text into unintelligible text and vice-versa. It is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it. Cryptography not only protects data from theft or alteration, but can also be used for user authentication.

 Messages: 1.Plaintext 2.Ciphertext  Ingredients: 1.Algorithm(s) 2.Key(s)  Players: 1.Cryptographer: invents clever algorithms 2.Cryptanalyst: breaks clever algorithms

1. Symmetric-key Cryptography: Both the sender and receiver share a single key. The sender uses this key to encrypt plaintext and send the cipher text to the receiver. On the other side the receiver applies the same key to decrypt the message and recover the plain text. 2. Public-Key Cryptography: This is the most revolutionary concept,In Public-Key Cryptography two related keys (public and private key) are used. Public key may be freely distributed, while its paired private key, remains a secret. The public key is used for encryption and for decryption private key is used. 3. Hash Functions: No key is used in this algorithm. A fixed-length hash value is computed as per the plain text that makes it impossible for the contents of the plain text to be recovered. Hash functions are also used by many operating systems to encrypt passwords.

Cryptographic algorithms are used for important tasks such as data encryption, authentication, and digital signatures, but one problem has to be solved to enable these algorithms: binding cryptographic keys to machine or user identities. Public key infrastructure (PKI) systems are built to bridge useful identities ( addresses, Domain Name System addresses, etc.)

Caesar Cipher in Cryptography Caesar Cipher is one of the simplest technique, It’s simply a type of substitution cipher that each letter of a given text is replaced by a letter some fixed number of positions down the alphabet, For example with a shift of 1, A would be replaced by B, B would become C, and so on.. Mathematical formula

To pass an encrypted message from one person to another, it is first necessary that both parties have the 'key' for the cipher, so that the sender may encrypt it and the receiver may decrypt it. For the caesar cipher, the key is the number of characters to shift the cipher alphabet Here the sender encrypt a particular massage with (Key=5) Plain text = suryadatta so each alphabet shifted 5 times Key = 5 Ciphertext = xzwdfifyyf The receiver must use of (Key=5) to decrypt the massage from sender.

 Nowadays we have 5 Common Encryption Algorithms the Unbreakable of the Future 1. Triple DES 2. RSA 3. Blowfish 4. Twofish 5. AES

Cryptography is the practice, study of technique, to secure communication and writing in secret code to encrypt and decrypt data so that no other person except the intended recipient could read The Main Goals of cryptography: * Data confidentiality * Data Authenticity * Data integrity