# Chapter 1: An Overview of the Subject

## Index:

### 1.1: Converting Strings of Digits to Vectors

This converts a string of digits to a vector of one-character digits

Usage:

To convert a string of digits to a vector: Enter a string of digits and press enter.

Ex:
1298310981580123009123

To convert a vector to a string of digits: Enter a vector of one-character digits, separated by spaces, and press enter.

Ex:
1 7 4 1 0 2 4 3 4 6 9 0 2 5 4 3 4 1 4 7 9 7 4 6 0 8 2 0 1 7 4 2 3 5 4 3

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### 1.2: Converting Upper-Case Text to/from Integers

This converts a string of upper-case text to its integer representation in the range [0,25], where A=0...Z=25, and vice-versa.

Usage:

To convert Upper-Case text to integer representation: Enter a string of Upper-Case letters and press enter.

Ex:
THEQUICKBROWNFOXJUMPSOVERTHELAZYDOG

To convert integers to Upper-Case text: Enter a sequence of integers in the range [0,25], separated by spaces, and press enter.

Ex:
19 7 4 16 20 8 2 10 1 17 14 22 13 5 14 23 9 20 12 15 18 14 21 4 17 19 7 4 11 0 25 24 3 14 6

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### 1.3: Converting Lower-Case Text to/from Integers

This converts a string of lower-case text to its integer representation in the range [0,25], where a=0...z=25., and vice-versa.

Usage:

To convert Lower-Case text to integer representation: Enter a string of Lower-Case letters and press enter.

Ex:
thelazybrownfoxjumpsoverthequickdog

To convert integers to Lower-Case text: Enter a sequence of integers in the range [0,25], separated by spaces, and press enter.

Ex:
19 7 4 11 0 25 24 1 17 14 22 13 5 14 23 9 20 12 15 18 14 21 4 17 19 7 4 16 20 8 2 10 3 14 6

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### 1.4: Shift Cipher

Given 2 of a plaintext, key, or ciphertext, this uses a shift cipher to determine the third.

Usage:

To encipher a plaintext string with a given key: Select the ciphertext button. Enter the plaintext as a lowercase string with no spaces, and an integer k>0 as the key, and press enter.

Ex:
packmyboxwithfivedozenliquorjugs
3

To decipher a ciphertext string with a given key: Select the plaintext button. Enter the ciphertext as an uppercase string with no spaces, and an integer k>0 as the key, and press enter.

Ex:
3
SDFNPBERAZLWKILYHGRCHQOLTXRUMXJV

To determine a key given a ciphertext and a plaintext: Select the key button. Enter the plaintext as a lowercase string with no spaces, the ciphertext as an uppercase string with no spaces, and press enter.

Ex:
packmyboxwithfivedozenliquorjugs
SDFNPBERAZLWKILYHGRCHQOLTXRUMXJV

### 1.5: Vigenere Cipher

Given 2 of a plaintext, key, or ciphertext, this uses the Vignere cipher to determine the third.

Usage:

To encipher a plaintext string with a given key: Select the ciphertext button. Enter the plaintext as a lowercase string with no spaces, a keyword as a lowercase string with no spaces, and press enter.

Ex:
theeaglesoarsatmidnight
diner

To decipher a ciphertext string with a given key: Select the plaintext button. Enter the ciphertext as an uppercase string with no spaces, a keyword as a lowercase string with no spaces, and press enter.

Ex:
diner
WPRIRJTRWFDZFEKPQQRZJPG

To determine a key given a ciphertext and a plaintext: Select the key button. Enter the plaintext as a lowercase string with no spaces, the ciphertext as an uppercase string with no spaces, and press enter.

Ex:
theeaglesoarsatmidnight
WPRIRJTRWFDZFEKPQQRZJPG

### 1.6: Random Integer Generator

Given a lower bound, n, upper bound, m, and vector length, k, this produces k integers in the range [n,m) = the set of integers greater than or equal to n, but less than m.

Usage:

To generate a vector of k integers in the range [n,m), enter a non-negative integer n as the lower bound, a non-negative integer m>n as the upper bound, a vector length k, and press enter.

Ex:
14
235
5
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