Cryptology
By
Greg Buss
Pat Shields
Barry Burke
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.
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
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.
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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.
Basic Letter
Substitution Program
Modern Applications
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
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
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.
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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.