DemoBlockCipher Project

This project presents an educational example of a custom block cipher algorithm. The algorithm is entirely non-standard, not cryptographically analyzed, and does not adhere to established cryptographic standards. The purpose is to illustrate the complexity of designing a secure cipher and to demonstrate why adherence to standardized, proven algorithms is crucial.

Overview

• DemoBlockCipher Class:
  This class implements a fictional block cipher that uses:

  • A custom S-Box derived deterministically from the master key (not a standard, analyzed S-box).
  • A rudimentary mix_columns and shift_rows step.
  • A polialphabetic_shift mechanism based on the round key bits.

  While these operations mimic certain aspects of known ciphers, none of these steps are mathematically grounded or security-evaluated. This is not AES, DES, or any recognized cipher.

• Key and Encryption Process:
  The cipher requires a 256-bit (32-byte) master key. From this key, a series of round keys is derived. The algorithm applies 12 rounds of transformations to 16-byte blocks of data.

• Padding, Encryption, and Decryption Functions:
  encrypt_data and decrypt_data handle arbitrary-length input by applying PKCS#7-like padding and processing data block-by-block. However, since no authenticated or approved mode of operation (CBC, CTR, GCM, etc.) is used, this approach does not guarantee actual security.

Security Standards Evaluation

This algorithm is not compliant with any industry or NIST standard. Here are some reasons:

• Non-Standard S-Box:
  Unlike AES’s mathematically defined S-box, this cipher uses a S-box generated from the master key, with no known security proofs.

• Undefined Key Schedule:
  The key schedule is a simple XOR-based approach with pseudo-randomness, not an accepted design from standards.

• No Recognized Cipher Mode:
  The cipher operates directly on blocks without using a proven mode such as CBC, CTR, or GCM. Standards (e.g., NIST SP 800-38A) recommend always using approved modes.

• No Mathematical Security Assurance:
  The transformations (mix_columns, shift_rows, polialphabetic_shift) are not derived from known cryptographic constructs or analyzed for security.

In summary, this algorithm does not meet any recognized security standards or guidelines.

Testing

The included test files, run with pytest, demonstrate the algorithm’s lack of adherence to established cryptographic standards. Some tests compare the cipher's behavior to known AES test vectors, which it cannot match, thereby showing non-compliance. Other tests fail deliberately to highlight the absence of standard modes or recognized S-box usage.

Running the Tests

1. Install the required dependencies:

   pip install pytest
   

2. Run the tests:

   pytest test_security.py -v
   

3. You will see that certain tests fail. This is expected. These failures indicate that the algorithm does not comply with standard cryptographic practices.

Example Test Scenarios

Key Length Test: Verifies the key is at least 256 bits, which meets a basic length requirement but is insufficient by itself to ensure standard compliance.

Known Standard Mode Comparison: Attempts to match AES test vectors. The DemoBlockCipher fails these tests, proving it does not adhere to the AES standard.

No Standard Mode Usage: Tests confirm that no recommended NIST mode (e.g., CBC, CTR, GCM) is employed, resulting in a test failure that documents this non-compliance.

Random S-Box Check: The test ensures the custom S-box does not match any known standard. It fails the test, emphasizing the lack of standardized S-box usage.

Conclusion

The DemoBlockCipher serves as a learning tool, showcasing how easy it is to create a cipher-like structure that does not meet established security standards. The provided tests underscore the importance of using well-analyzed, standardized encryption methods (e.g., AES-256-GCM) for real-world applications. This project should never be used for securing sensitive data.