Cryptology

1. Cryptology By Greg Buss Pat Shields Barry Burke

2. What is Cryptology? • Cryptology is the study of “secret writing.” Modern cryptology combines the studies of computer science and mathematics for the purpose of encoding information to ensure that data is secure.

3. Key terms Cryptography – from the Greek words kryptos, meaning “hidden”, and graphein, meaning “to write”. Literally secret writing. Cryptanalysis – also referred to as code breaking, the process of undoing Cryptography Encryption – converts “plaintext” into an encoded text or a “ciphertext” Decryption – the reverse of Encryption Cipher – algorithms used to encrypt and decrypt text Key – an unknown parameter needed to operate a particular cipher’s algorithms

4. The History • Devices used throughout history: • Scytale (fr. Gr. skytale). Spartan message in (transposition) cipher. Originally it described a rod or baton carried as a badge of office. It is still used by military officers today. Used as an early enciphering device, a parchment was wrapped spirally around it, and the text was written-in lengthwise. A similar rod at the receiving end permitted correct decipherment. The word scytale is now used for the message as well as the media.

5. cipher disk: an enciphering and deciphering tool developed in the 15th century by Leon Battista Alberti. Rather than constructing a table with the regular and cipher alphabets on it, he created two circular scales, one smaller and on a disk that he mounted concentric to the larger circle. This enabled him to move the two alphabet scales relative to each other.

6. Enigma: a portable cipher machine used to encrypt and decrypt secret messages. • The German military model, the Wehrmacht Enigma, is the version most commonly discussed. The machine has gained notoriety because Allied cryptologists were able to decrypt a large number of messages that had been enciphered on the machine. • Although the Enigma cipher has cryptographic weaknesses, it was, in practice, only their combination with other significant factors which allowed code breakers to read messages: mistakes by operators, procedural flaws, and the occasional captured machine or codebook.

7. Basic Letter Substitution Program

8. Modern Applications

9. Symmetric-Key Cryptology Also known as single-key, private-key, one-key and secret-key Method of encoding where both the sender and receiver of a message hold the same key which is needed to decode the message, and involving the use of block ciphers and stream ciphers. Encoding through Block Ciphers – Uses a fixed-length groups of bits, known as a block. Will take a plaintext as an input and using a secret key encode the text, and output ciphertext of the same bit size as the input Encoding through Stream Ciphers - plaintext digits are encrypted one at a time, with the transformation of successive digits varying during the encryption

10. Public-key Cryptology Uses a widely distributed public key used for encoding the message, and a different key, related mathematically to the former, used for decoding which is kept secret More secure than Symmetric-Key Cryptology because the receivers private decoding key is never made known reducing the chance that it may be copied in transit

11. The Future of Cryptology • Quantum mechanics has now provided the foundation to a new approach to cryptology – quantum cryptology. It has been claimed that quantum cryptology, with the use of quantum computers, can solve many problems that are impossible from the perspective of conventional cryptology. • A quantum computer can instantaneously decipher any code written by today’s standards. However, with the introduction of a working quantum computer, the enciphered codes will also become impossible to decode without a key, even by another quantum computer.