src.ch04.practice package

Submodules

src.ch04.practice.p1_hack_lincoln module

Hack route cipher sent by Abraham Lincoln.

src.ch04.practice.p1_hack_lincoln.decode_route(keys: list, cipherlist: list) → list

Decode route cipher.

Decode cipherlist encoded with a route cipher using keys.

Parameters

• keys (list) – List of signed, integer keys.

• cipherlist (list) – List of strings representing encoded message.

Returns

List of strings representing plaintext message.

Note

Assumes vertical encoding route.

src.ch04.practice.p1_hack_lincoln.get_factors(integer: int) → list

Get factors of integer.

Calculate factors of a given integer.

Parameters

integer (int) – Number to get factors of.

Returns

List of integer factors of integer.

src.ch04.practice.p1_hack_lincoln.hack_route(ciphertext: str) → None

Hack route cipher.

Hack route cipher by using get_factors() to find all possible key lengths. Then use keygen() to generate all possible keys and pass each one through decode_route().

Parameters

ciphertext (str) – Message encoded with route cipher.

Returns

None. Prints all possible decoded messages.

src.ch04.practice.p1_hack_lincoln.keygen(length: int) → list

Generate all possible route cipher keys.

Generates a list of all possible route cipher keys of length.

Parameters

length (int) – Length of route cipher key.

Returns

List of lists of integers representing all possible route cipher keys of length.

Example

>>> from src.ch04.practice.p1_hack_lincoln import keygen
>>> keygen(2)
[[-1, -2], [-1, 2], [1, -2], [1, 2]]

src.ch04.practice.p1_hack_lincoln.main()

Demonstrate hack of Lincoln’s route cipher.

src.ch04.practice.p2_identify_cipher module

Identify letter transposition or substitution cipher.

src.ch04.practice.p2_identify_cipher.identify_cipher(ciphertext: str, threshold: float) → bool

Identify letter transposition or substitution cipher.

Compare most frequent letters in ciphertext with the most frequent letters in the English alphabet. If above threshold, it is a letter transposition cipher. If not, it is a letter substitution cipher.

Parameters

• ciphertext (str) – Encrypted message to identify.

• threshold (float) – Percent match in decimal form.

Returns

True if the ciphertext is a letter transposition cipher. False otherwise.

src.ch04.practice.p2_identify_cipher.is_substitution(ciphertext: str) → bool

Identify letter substitution cipher.

Wrapper for identify_cipher(). threshold defaults to 0.45.

Parameters

ciphertext (str) – Encrypted message to identify.

Returns

True if the ciphertext is a letter substitution cipher. False otherwise.

src.ch04.practice.p2_identify_cipher.is_transposition(ciphertext: str) → bool

Identify letter transposition cipher.

Wrapper for identify_cipher(). threshold defaults to 0.75.

Parameters

ciphertext (str) – Encrypted message to identify.

Returns

True if the ciphertext is a letter transposition cipher. False otherwise.

src.ch04.practice.p2_identify_cipher.main(ciphertext: str = None) → None

Demonstrate the cipher identifier.

This is only supposed to be a demo, but coverage necessitates excessiveness.

Parameters

ciphertext (str) – Encrypted letter transposition or letter substitution cipher to demonstrate.

Returns

None. Identifies ciphertext’s cipher.

src.ch04.practice.p2_identify_cipher_deco module

Identify letter transposition or substitution cipher using decorator.

Note

Not part of the book, I was just curious about decorators and decided to tinker with them a bit.

src.ch04.practice.p2_identify_cipher_deco.identify(threshold: float = 0.5)

Make decorator for identify_cipher.

Decorator factory to replace a decorated function with identify_cipher(). A bit like going around the world to reach the teleporter across the street, but at import time instead of runtime, so it doesn’t matter.

Luciano Ramalho’s book Fluent Python appropriately calls decorators “syntactic sugar” when they aren’t used in classes. It also references the wrapt module’s blog on GitHub for a deeper explanation of decorators.

Not sure what a decorator factory would be called…syntactic caramel?

Parameters

threshold (float) – Percent match in decimal form.

Returns

Whatever the output of identify_cipher() would be given the decorated function’s input.

src.ch04.practice.p2_identify_cipher_deco.is_substitution(ciphertext: str) → bool

Identify letter substitution cipher.

Empty function to wrap with identify_cipher() using identify(). threshold defaults to 0.45.

Parameters

ciphertext (str) – Encrypted message to identify.

Returns

True if the ciphertext is a letter substitution cipher. False otherwise.

src.ch04.practice.p2_identify_cipher_deco.is_transposition(ciphertext: str) → bool

Identify letter transposition cipher.

Empty function to wrap with identify_cipher() using identify(). threshold defaults to 0.75.

Parameters

ciphertext (str) – Encrypted message to identify.

Returns

True if the ciphertext is a letter transposition cipher. False otherwise.

src.ch04.practice.p3_get_keys module

Get route cipher key from user and store as dictionary.

Note

Assumes vertical cipher routes.

src.ch04.practice.p3_get_keys.get_keys() → list

Get route cipher keys from user.

User only has to enter positive/negative integers. Each gets added to a list and returned when the user has no other keys to add.

Returns

List of integers as column numbers and positive/negative values as route direction.

src.ch04.practice.p3_get_keys.key_to_dict(keys: list) → dict

Convert route cipher key to dictionary.

Take a route cipher key in list format where integers are column numbers and positive/negative is the route direction and convert to a dictionary where the column numbers are keys and the route direction as up/down are the values.

Parameters

keys (list) – List of integers with direction as positive/negative.

Returns

Integers keys and up/down as values.

src.ch04.practice.p3_get_keys.main()

Demonstrate getting route cipher keys from the user.

src.ch04.practice.p4_generate_keys module

Generate route cipher keys for brute-forcing a route cipher.

Already implemented with keygen(), but this version will return a list of tuples.

src.ch04.practice.p4_generate_keys.generate_keys(length: int) → list

Generate all possible route cipher keys.

Generates a list of all possible route cipher keys of length.

Parameters

length (int) – Length of route cipher key.

Returns

List of tuples of integers representing all possible route cipher keys of length.

src.ch04.practice.p4_generate_keys.main()

Demonstrate the key generator.

src.ch04.practice.p5_hack_route module

Another way to hack a route cipher.

Already implemented in p1_hack_lincoln, but this version will use the building blocks made in p2_identify_cipher, p3_get_keys, and p4_generate_keys.

src.ch04.practice.p5_hack_route.decode_route(keys: dict, cipherlist: list) → list

Decode route cipher.

Decode cipherlist encoded with a route cipher using keys.

Parameters

• keys (dict) – up/down dictionary with column numbers as keys.

• cipherlist (list) – List of strings representing encoded message.

Returns

List of strings representing plaintext message.

Note

Assumes vertical encoding route.

src.ch04.practice.p5_hack_route.hack_route(ciphertext: str, columns: int) → None

Hack route cipher using brute-force attack.

Determine if ciphertext is a transposition cipher. If so, use columns to generate all possible keys. Convert each key to an up/down dictionary for each route to take, then print the result of each key.

Parameters

• ciphertext (str) – Route cipher encoded string to hack.

• columns (int) – Number route cipher columns.

Returns

None. Prints all possible decoded messages.

src.ch04.practice.p5_hack_route.main()

Demonstrate the route cipher hacker.

Module contents

Chapter 4 Practice Projects.