Sending Encrypted Data Through Socket And Decrypting Doesn't Work

Question

I am creating a simple encryption software. The problem I currently have is that sending encrypted aes file data through a socket doesn\'t work. At the receiving end, the fi

Answer 1

The code is too non-minimal so here's a minimal example of downloading an unencrypted file. Also, TCP is a streaming protocol and using sleeps to separate your data is incorrect. Define a protocol for the byte stream instead. This is the protocol of my example:

1. Open the connection.
2. Send the UTF-8-encoded filename followed by a newline.
3. Send the encoded file size in decimal followed by a newline.
4. Send the file bytes.
5. Close the connection.

Note Python 3 code. Python 2 is dead to me. Support ends next year for it so upgrade!

server.py

from socket import *
import os

CHUNKSIZE = 1_000_000

# Make a directory for the received files.
os.makedirs('Downloads',exist_ok=True)

sock = socket()
sock.bind(('',5000))
sock.listen(1)

with sock:
    while True:
        client,addr = sock.accept()

        # Use a socket.makefile() object to treat the socket as a file.
        # Then, readline() can be used to read the newline-terminated metadata.
        with client, client.makefile('rb') as clientfile:
            filename = clientfile.readline().strip().decode()
            length = int(clientfile.readline())
            print(f'Downloading {filename}:{length}...')
            path = os.path.join('Downloads',filename)

            # Read the data in chunks so it can handle large files.
            with open(path,'wb') as f:
                while length:
                    chunk = min(length,CHUNKSIZE)
                    data = clientfile.read(chunk)
                    if not data: break # socket closed
                    f.write(data)
                    length -= len(data)

            if length != 0:
                print('Invalid download.')
            else:
                print('Done.')

client.py

from socket import *
import os

CHUNKSIZE = 1_000_000

filename = input('File to upload: ')

sock = socket()
sock.connect(('localhost',5000))
with sock,open(filename,'rb') as f:
    sock.sendall(filename.encode() + b'\n')
    sock.sendall(f'{os.path.getsize(filename)}'.encode() + b'\n')

    # Send the file in chunks so large files can be handled.
    while True:
        data = f.read(CHUNKSIZE)
        if not data: break
        sock.sendall(data)