Feature: AES-CTR

[balladyna]

The branch is named AES-CTR as it focuses on implementing AES encryption in Counter (CTR) mode, a widely used and efficient encryption mode that enables parallel processing of data. It does so by turning a block cipher into a stream cipher: it encrypts successive values of a counter and XORs the result with the plaintext. While this implementation currently targets AES256Randomized (256-bit key size), the architecture is designed to be extensible, allowing future support for other AES key lengths (e.g., 128-bit, 192-bit) and additional cipher modes such as (e.g., CBC or GCM). This branch introduces reimplementation of the AES-CTR encryption algorithm using principles and components inspired by the encrypt and pointycastle packages. The goal was to provide a modular, testable, and extensible AES infrastructure, enabling secure encryption and decryption of sensitive data in compliance with cryptographic standards.

List of changes:

• created aes_ctr.dart, aes256_randomized.dart, and aes_engine.dart to implement AES encryption logic and coordinate the encryption process
• created cipher_text.dart to represent the result of an encryption algorithm and encapsulate the encrypted data
• created aes_iv.dart to represent the initialization vector (IV), enabling unique encryption sessions
• created aes_key.dart to store AES key used in encryption
• created i_cipher_key.dart, a_block_cipher.dart, i_cipher_padding.dart, to define the base abstraction to block, padding and cipher key
• created cipher_key_with_iv.dart to encapsulate both AES key and IV for cipher initialization
• created ctr_stream_cipher.dart to implement CTR (Counter) mode to stream cipher using a block cipher
• created padded_block_cipher.dart and ctr_block_cipher.dart to enable AES block cipher processing with support for padding and arbitrary-length input
• created pkcs7_padding.dart to implement the PKCS7 padding scheme used for aligning plaintext blocks before encryption
• unrelated with domain: changed the Ubuntu Actions runner image to the latest general availability version 24.04, due to the deprecation of the version 20.04