• My name: Haoyu Jin
• My email: jin511@purdue.edu

0. Environment

• Ubuntu 20.04 x86_64 GNU/Linux
• gcc (Ubuntu 9.4.0-1ubuntu1~20.04.2) 9.4.0
• GNU Make 4.2.1
• libgcrypt20

1. Compile

# working dir: SCP/
make

1.1 Clear (the binary)

# working dir: SCP/
make clean

2. Run

2.1 Sender

purenc <input file> [-d <output IP-addr:port>] [-l]

2.2 Receiver

purdec [port] [-l <input file>]

2.3 example for local run

# 127.0.0.1
cp data data.cpy
purenc data.cpy -l
rm data.cpy
purdec -l data.cpy.pur
diff data data.cpy

2.4 example for remote run

2.4.1 Sender side

purenc data -d 192.168.3.5:7777

2.4.2 Receiver side

purdec 7777

3. Auto Local Test

• This script along with files under data directory helps you check the correctness and functionality for the local run
• And you can directly run this script right after you download this repo to your machine and cd into it, instead of compiling first (running make).
• one parameter is needed, which is the file name (choose one from data/)
  • need_pad is a file with 1027 bytes, which is helpful for checking the padding
  • an_executable is a historical verision of a binary (purenc/purdec)
  • random is a file of random byte sequence, and with size around 10M, which aims to show the robustness of the program
  • All the above files are also passed for the remote tests, using two remote machines

3.1 Usage example

bash ./autotest_local.sh random

4. Sorce files

• see directory src/, along with Makefile

5. Overview of work accomplished

• I build the TCP socket for the network programming
• I build the key from password
• I encrypt the data, and then add a hash suffix before sending it to the network
  • on the receiver side, symmetrical actions are taken.
• I support the multithreading version of receiver, and more public-key based certification process on another branch real. (not required in this assignment)

6. Description of code and code layout

• Here I only explain the main content about each source file, please check the comment in source files to get the detail of each function

1. dec.c: main routine of receiver
2. enc.c: main routine of sender
3. network.c: my wrapper for building and using the socket
4. crypto.c: functions used for crypto purpose, building on <gcrypt.h>
5. util.c: extension for dec.c and enc.c

7. General comments and design decisions made

• see the source codes for comments
• Design Decision:
  • for both local and remote mode, the enc should encrypt and append a hash before sending msg chunk, the dec should checking the hash and decrypt after receiving msg chunk.

8. Answer to the question

• I need a salt string
• It's used to protect the key, since directly mapping password to key may suffer a type of attack which uses brute force to sampling the mapping function.
  • The salt is like a user-specific characteristic.
• In this project, the salt just stays constant through both sides, for the simplicity.

9. Number of hours spent on the project and level of effort required

• 3 days, be stopped by a misfortune (delete the source code unconciously) for 1 day and more..
• workload is similar to lab2 (MiniVPN)

-1. What's more?

• see branch real to see my progress on developing this project into more real-world-like senario.