AES-128 with Multi-Block Support

Instruction for USE

• Clone the repository
• Run the aes_server.py file first and then run the aes_client.py file
• The Client will ask for the message and the key
• NEW: You can now enter messages of ANY LENGTH! The system will automatically handle padding and multi-block encryption.
• Key Handling: Enter the same key on both client and server sides. If the key is not exactly 16 characters, it will be automatically adjusted:
  • Keys shorter than 16 characters are padded with zeros
  • Keys longer than 16 characters are truncated to 16 characters
• Messages are now processed using PKCS#7 padding and ECB (Electronic Codebook) mode

Features Added

• Variable Length Messages: No longer limited to 16 characters
• PKCS#7 Padding: Automatically pads messages to block boundaries
• Multi-Block Processing: Encrypts/decrypts messages in 16-byte blocks
• Error Handling: Better error handling for padding and decryption
• Automatic Key Adjustment: Keys are padded or truncated to 16 characters

Examples

Key Examples:

• "Two nine" (8 chars) → "Two nine00000000" (16 chars)
• "mypassword" (10 chars) → "mypassword000000" (16 chars)
• "thisisaverylongpassword" (22 chars) → "thisisaverylongp" (16 chars)

Message Examples:

• Short message: "Hello"
• Medium message: "This is a longer message that spans multiple blocks"
• Long message: "This is a very long message that demonstrates the capability of handling arbitrary length inputs in our AES implementation..."

Important Notes

• BOTH client and server must use the SAME key for successful encryption/decryption
• The key adjustment happens automatically on both sides, so enter the same original key on both client and server
• Example: If you enter "Two nine" on client, enter "Two nine" (not "Two nine00000000") on server