Intro to Cryptography

Introduction to Cryptography

CSEC 630
Lab Assignment #1

Caesar Encrypt

Caesar Entrophy

Caesar Floating Frequency

Caesar Histogram

Caesar N-Gram

Caesar Autocorrelation

Caesar Periodicity


ROT-13 Entrophy

ROT-13 Floating Frequency

ROT-13 Histogram

ROT-13 N-Gram

ROT-13 Autocorrelation

ROT-13 Periodicity

Q1: The tool that is most effective for a cryptanalyst to use to decipher a text encrypted with the Caesar cipher is the Histogram because this tool displays the relative frequency of each character in the document, which would increase the chances of the cryptanalyst’s ability to decipher a text.   The Histogram compares the usage of different letters which can reveal the context of the message; this applies especially to monoalphabetic substitution ciphers like the Caesar cipher.   The character with the largest frequency is the letter H followed by W.


Vigenere Entrophy

Vigenere Floating Frequency

Vigenere Histogram

Vigenere N-Gram


Vigenere Autocorrelation

Vigenere Periodicity

Q2: The histogram results when text is encrypted with Vigenere cipher in comparison to the results of the Caesar cipher show the Vigenere has more letters with high frequency than the Caesar cipher.   In essence with the Vigenere cipher, it is extremely difficult to tell which letter is the most frequently used because many of the letters appear about the same number of times.   The reason why many letters have a high frequency rate is because the Vigenere is no longer just shifting the letters in the alphabet.


Q3: The correct ciphertext includes the fourth to the last letter to be an “O” and not a “C”.
Q4: The following data are the results of the entropy tests on the three different ciphers:
Caesar = 4.17
Vigenere = 4.65
Playfair = 4.42
The maximum possible entropy is 4.70; based on the entropy data results, the Vigenere cipher has the highest...