using the ChaCha20 algorithm.

• Supports encryption and decryption.
• Reads and writes to files.
• Takes command-line arguments to specify the operation mode, input file, and output file.

1. Encrypt a file:

   cargo run -e <input_file> <output_file>
   

2. Decrypt a file:

   cargo run -d <input_file> <output_file>
   

• -e for encryption.
• -d for decryption.
• <input_file> is the file to be encrypted/decrypted.
• <output_file> is the result file to store the encrypted/decrypted data.

• The key and nonce are hardcoded as zero arrays for simplicity.
• The input and output files are binary, so make sure to handle them accordingly.

cargo run -e plaintext.txt encrypted.bin
cargo run -d encrypted.bin decrypted.txt