Cryptography PowerPoint PDF

CRYPTOGRAPHY By: Donna Garcia CRYPTOGRAPHY Cryptography is the study of secure communications techniques that allow only the sender and intended recipient of a message to view its contents. The term is derived from the Greek word kryptos, which means hidden. ...

CRYPTOGRAPHY By: Donna Garcia CRYPTOGRAPHY Cryptography is the study of secure communications techniques that allow only the sender and intended recipient of a message to view its contents. The term is derived from the Greek word kryptos, which means hidden.  3 CRYPTOGRAPHY FOCUSES ON FOUR DIFFERENT OBJECTIVES: Confidentiality: Confidentiality ensures that only the intended recipient can decrypt the message and read its contents. Non-repudiation: Non-repudiation means the sender of the message cannot backtrack in the future and deny their reasons for sending or creating the message. Integrity: Integrity focuses on the ability to be certain that the information contained within the message cannot be modified while in storage or transit. Authenticity: Authenticity ensures the sender and recipient can verify each other’s identities and the destination of the message. These objectives help ensure a secure and authentic transfer of information. ENCRYPTION AND DECRYPTION ENCRYPTION - process by which a readable message is converted to an unreadable form to prevent unauthorized parties from reading it. DECRYPTION - process of converting an encrypted message back to its original (readable) format. The original message is called the plaintext message. The encrypted message is called the ciphertext message. Digital encryption algorithms work by manipulating the digital content of a plaintext message mathematically, using an encryption algorithm and a digital key to produce a ciphertext version of the message. The sender and recipient can communicate securely if the sender and recipient are the only ones who know the key.  8 SHARED KEY ENCRYPTION Shared key encryption uses one key to encrypt and decrypt messages. For shared key cryptography to work, the sender and the recipient of a message must both have the same key, which they must keep secret from everybody else. The sender uses the shared key to encrypt a message, shown in the following figure, and then sends the ciphertext message to the recipient.  9 SENDER USES KEY TO ENCRYPT PLAINTEXT TO CIPHERTEXT  10 RECIPIENT USES KEY TO DECRYPT CIPHERTEXT TO PLAINTEXT 11  12 PUBLIC KEY ENCRYPTION Public key encryption uses a pair of complementary keys (a public key and a private key) to encrypt and decrypt messages. The two keys are mathematically related such that a message encoded with one key can only be decoded with the other key. Although a user's public and private keys are mathematically related, knowledge of a public key does not make it possible to calculate the corresponding private key.  13 Public Key: This is like a lock that anyone can use to secure (or "lock up") information they send to you. It’s shared openly, so anyone who wants to send you a secure message can use it. Private Key: This is like the key that only you have, which can unlock the information encrypted with your public key. It must be kept secret, as it’s what lets you access and read the messages meant only for you.  16 MONOALPHABETIC CIPHER A monoalphabetic cipher is any cipher in which the letters of the plain text are mapped to cipher text letters based on a single alphabetic key. Examples of monoalphabetic ciphers would include the Caesar-shift cipher, where each letter is shifted based on a numeric key, and the atbash cipher, where each letter is mapped to the letter symmetric to it about the center of the alphabet.  17 POLYALPHABETIC CIPHER A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. The Vigenère cipher is probably the best-known example of a polyalphabetic cipher, though it is a simplified special case. Vigenere Cipher 18 VIGENÈRE CIPHER Vigenere Cipher is a method of encrypting alphabetic text. It uses a simple form of polyalphabetic substitution. A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. The encryption of the original text is done using the Vigenère square or Vigenère table. Vigenere Square/Table 19 PLAIN TEXT K E Y 20 Vigenere Cipher 21 VIGENÈRE CIPHER Encryption The plaintext(P) and key(K) are added modulo 26. Ei = (Pi + Ki) mod 26 Decryption Di = (Ei - Ki + 26) mod 26  22 Hill Cipher Hill cipher is a polygraphic substitution cipher based on linear algebra. Each letter is represented by a number modulo 26. To encrypt a message, each block of n letters (considered as an n-component vector) is multiplied by an invertible n × n matrix, against modulus 26. To decrypt the message, each block is multiplied by the inverse of the matrix used for encryption. The matrix used for encryption is the cipher key, and it should be chosen randomly from the set of invertible n × n matrices (modulo 26). Developed by Lester Hill in 1929.  23 Formula 24 25 26 27 THANK YOU