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## PowerPoint Slideshow about 'Cryptology' - ryo

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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.

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

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.

- 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.

- 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.

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

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

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.

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