Using the command-line interface

The command-line interface (CLI) provides a quick way to test all three encryption algorithms at once. This guide covers how to use main.py for encryption operations.

Running the CLI

Activate the environment

First, activate the Pipenv virtual environment:

pipenv shell

Run the main script

Execute the CLI application:

python main.py

Enter your message

When prompted, type your message:

Ingrese el mensaje a operar: HOLA MUNDO

The program will automatically encrypt and decrypt your message using all three algorithms.

Understanding the output

The CLI processes your message through all three algorithms sequentially:

Example session

$ python main.py
Ingrese el mensaje a operar: HOLA MUNDO
Mensaje original: HOLA MUNDO

# Sustitución (César)
Mensaje cifrado: OWSITCULW
Mensaje descifrado: HOLAMUNDO

# Transposición
Mensaje cifrado: HUONLDAOM*
Mensaje descifrado: HOLAMUNDO

# RSA
Mensaje cifrado: [210781516, 270112935, 1336237868, 270112935, 1025793116, 270112935, 1508442393, 1508442393, 1025793116]
Mensaje descifrado: HOLA MUNDO

Algorithm processing flow

The CLI follows this execution order defined in main.py:6-25:

Sustitución (César)

Parameters:

Shift position: 8

Process:

Converts message to numbers
Shifts each number by 8 positions
Converts back to letters
Displays encrypted and decrypted results

Code:

pos = 8
susti_des = sustitucion_cifrar(mensaje, pos)
sustitucion_descifrar(susti_des, pos)

Transposición

Parameters:

Key (columns): 5

Process:

Arranges message in a matrix with 5 columns
Reads by columns to create ciphertext
Reverses the process to decrypt
Displays encrypted and decrypted results

Code:

clave = 5
transp_descifrar = transposicion_cifrar(mensaje, clave)
transposicion_descifrar(transp_descifrar, clave)

RSA

Parameters:

Key size: 32 bits

Process:

Generates RSA key pair (e, d, n)
Encrypts message using public key (e, n)
Decrypts using private key (d, n)
Displays keys, encrypted list, and decrypted message

Code:

bits = 32
e, d, n = RSA.gen_keys(bits)
mensaje_cifrado = RSA_cifrar(mensaje, e, n)
RSA_descifrar(mensaje_cifrado, d, n)

Detailed algorithm usage

Sustitución
Transposición
RSA

The Caesar cipher implementation shifts letters in the Spanish alphabet (including Ñ).

How it works

# Encrypt
def sustitucion_cifrar(mensaje, pos):
    cifrado = sustitucion.convertiraNumero(mensaje)
    cifrado = sustitucion.cifrar(cifrado, pos)
    mensajecifrado = sustitucion.convertiraLetra(cifrado)
    util.printResultado("cifrado", mensajecifrado)
    return mensajecifrado

# Decrypt
def sustitucion_descifrar(mensaje_cifrado, pos):
    mensaje_cifrado = sustitucion.convertiraNumero(mensaje_cifrado)
    descifrado = sustitucion.descifrar(mensaje_cifrado, pos)
    mensajedescifrado = sustitucion.convertiraLetra(descifrado)
    util.printResultado("descifrado", mensajedescifrado)
    return mensajedescifrado

Key features

Supports Spanish alphabet with Ñ
Default shift: 8 positions
Removes spaces from output
Case-insensitive processing

Example transformations

Input	Shift	Output
HOLA	8	OWSI
ABC	8	IJK
XYZ	8	FGH

The transposition cipher rearranges characters in a columnar fashion.

How it works

# Encrypt
def transposicion_cifrar(mensaje, clave):
    cifrado = transposicion.cifrar(mensaje, clave)
    util.printResultado("cifrado", cifrado)
    return cifrado

# Decrypt
def transposicion_descifrar(mensaje, clave):
    descifrado = transposicion.descifrar(mensaje, clave)
    util.printResultado("descifrado", descifrado)

Key features

Default key: 5 columns
Adds * padding when needed
Preserves character positions relatively

Example with key=5

Input: HOLA MUNDO (10 characters)Matrix arrangement:

H O L A   
M U N D O

Read by columns: HUONLDAOM*

The key determines how many columns the matrix has. A larger key means more columns and a different transposition pattern.

RSA encryption uses public-key cryptography with automatically generated keys.

How it works

# Generate keys
bits = 32
e, d, n = RSA.gen_keys(bits)

# Encrypt
def RSA_cifrar(mensaje, e, n):
    mensaje_cifrado = RSA.encrypt(mensaje, e, n)
    print(f"Mensaje cifrado: {mensaje_cifrado}")
    return mensaje_cifrado

# Decrypt
def RSA_descifrar(mensaje_cifrado, d, n):
    mensaje_descifrado = RSA.decrypt(mensaje_cifrado, d, n)
    if mensaje_descifrado is not None:
        print(f"Mensaje descifrado: {mensaje_descifrado}")
    else:
        print("Error al descifrar el mensaje.")

Key components

e (public exponent): Used for encryption
d (private exponent): Used for decryption
n (modulus): Product of two prime numbers
bits: Key size (default: 32 for demo purposes)

Output format

RSA outputs a list of encrypted integers:

[210781516, 270112935, 1336237868, 270112935, 1025793116]

Each number represents an encrypted character from the original message.

32-bit keys are extremely weak and only suitable for educational purposes. Real-world RSA uses 2048-bit or 4096-bit keys.

Customizing parameters

You can modify the algorithm parameters by editing main.py:

# Change from shift=8 to shift=13 (ROT13)
pos = 13  # Line 11
susti_des = sustitucion_cifrar(mensaje, pos)
sustitucion_descifrar(susti_des, pos)

Using individual algorithms

If you want to use only one algorithm instead of running all three, you can import and use the functions directly:

import sustitucion
import util

mensaje = "HOLA MUNDO"
pos = 8

# Encrypt
cifrado = sustitucion.convertiraNumero(mensaje)
cifrado = sustitucion.cifrar(cifrado, pos)
mensajecifrado = sustitucion.convertiraLetra(cifrado)
print(f"Cifrado: {mensajecifrado}")

# Decrypt
numeros = sustitucion.convertiraNumero(mensajecifrado)
descifrado = sustitucion.descifrar(numeros, pos)
mensajedescifrado = sustitucion.convertiraLetra(descifrado)
print(f"Descifrado: {mensajedescifrado}")

Command output formatting

The CLI uses utility functions from util.py to format output consistently:

util.printResultado("cifrado", mensajecifrado)
util.printResultado("descifrado", mensajedescifrado)

This ensures all algorithm outputs follow the same format for easy comparison.

Error handling

The CLI includes basic error handling:

RSA decryption errors: Returns None and prints error message
Invalid input: Handled by individual algorithm modules
Empty messages: Processed but may produce unexpected results

The CLI is designed for quick testing and demonstration. For production use, implement more robust error handling and input validation.

Get Started

Algorithms

Usage Guides

Additional

Running the CLI

Understanding the output

Example session

Algorithm processing flow

Detailed algorithm usage

How it works

Key features

Example transformations

How it works

Key features

Example with key=5

How it works

Key components

Output format

Customizing parameters

Using individual algorithms

Command output formatting

Error handling

Build docs developers (and LLMs) love

Get Started

Algorithms

Usage Guides

Additional

​Running the CLI

​Understanding the output

​Example session

​Algorithm processing flow

​Detailed algorithm usage

​How it works

​Key features

​Example transformations

​How it works

​Key features

​Example with key=5

​How it works

​Key components

​Output format

​Customizing parameters

​Using individual algorithms

​Command output formatting

​Error handling

Build docs developers (and LLMs) love

Running the CLI

Understanding the output

Example session

Algorithm processing flow

Detailed algorithm usage

How it works

Key features

Example transformations

How it works

Key features

Example with key=5

How it works

Key components

Output format

Customizing parameters

Using individual algorithms

Command output formatting

Error handling