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The web interface provides an intuitive way to encrypt and decrypt messages using all three supported algorithms. This guide will walk you through using the Flask application.

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Starting the web server

1

Activate the environment

First, activate the Pipenv virtual environment:
pipenv shell
2

Launch the Flask application

Start the web server:
python app.py
The application will start on http://localhost:5000 by default.
3

Open in browser

Navigate to http://localhost:5000 in your web browser to access the interface.

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Interface overview

The web interface consists of a single-page application with the following elements:
  • Message input: A textarea where you enter the text to encrypt or decrypt
  • Operation selector: Choose between “Cifrar” (Encrypt) or “Descifrar” (Decrypt)
  • Algorithm selector: Select from Sustitución (César), Transposición, or RSA
  • Process button: Submit the form to perform the operation
  • Result display: Shows the encrypted/decrypted output
  • Additional info: For RSA, displays generated keys and instructions

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Using different algorithms

The Caesar cipher shifts letters by a fixed position (default: 8 positions).

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Encrypting a message

  1. Enter your plaintext message in the “Mensaje” field
  2. Select ”🔒 Cifrar” from the Operation dropdown
  3. Select ”🔄 Sustitución (César)” from the Type dropdown
  4. Click “Procesar ✨”
Example:
  • Input: HOLA MUNDO
  • Output: OWSITCULW

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Decrypting a message

  1. Enter the encrypted text in the “Mensaje” field
  2. Select ”🔓 Descifrar” from the Operation dropdown
  3. Select ”🔄 Sustitución (César)” from the Type dropdown
  4. Click “Procesar ✨”
Example:
  • Input: OWSITCULW
  • Output: HOLAMUNDO
The shift position is fixed at 8 in the web interface. Spaces are removed from the output.

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Understanding the workflow

The web application uses Flask sessions to manage RSA keys and processes requests through the following flow: 
app.py:10-38
  1. Form submission: User submits message, operation, and algorithm type
  2. Algorithm routing: Based on tipo_cifrado, the appropriate function is called
  3. Session management: For RSA, keys are stored in Flask session
  4. Result rendering: Output is displayed in the result container

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Common issues and solutions

Problem: You’re trying to decrypt without first encrypting a message.Solution: Encrypt a message first to generate keys, then copy the encrypted list to decrypt.
Problem: The encrypted message wasn’t pasted in the correct format.Solution: Ensure you’re pasting the complete list with brackets: [123, 456, 789]
Problem: The algorithms may add padding (*) or remove spaces.Solution: This is expected behavior. Spaces are removed in substitution cipher, and * is used for padding in transposition.

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Technical details

The web interface is implemented in app.py with the following key features:
  • Secret key: Uses Flask sessions with a secret key (line 8)
  • Fixed parameters: Substitution uses shift=8, Transposition uses key=5
  • RSA key size: Generates 32-bit keys (suitable for educational purposes only)
  • Session storage: RSA keys (e, d, n) are stored in Flask session for reuse
This implementation is for educational purposes only. The 32-bit RSA keys and simple Caesar/transposition ciphers are not secure for real-world use.

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