Secure File transer

The program emulates the scp program, i.e. the program to copy files encrypted and encapsulated inside a ssh connection/tunnel, authentication is done using HMAC

Overview :

There is a server program
- forks
- child process : creates a tcp socket which binds to port no 9999 and recieves the encrypted payload
- parent process : first does HMAC validation, then
Client program
- forks
- child process : encrypts the plaintext, generates random IV using /dev/urandom , implements HMAC signature
- Parent process : connects to port 9999, sends to the server where payload is “HMAC signature || Cipher text || IV“
Used sockets API for TCP scokets generation.
Used EVP cbc encrypt and decrypt functions for ciphertext generation.
Used HMAC signing with message digest.
To check for tampering the signature : uncomment the code in server program from line 284-294, it shows the errors such as :
If everything works properly , we can see output like this:

Other smaple runs , where it is encrypted and decrypted properly , which might differ due to randomisation.

Due to randomly generated bytes by /dev/urandom for IV : the text is decrypted properly only sometimes as the randomised and encrypted string might have deliminator(”||”) which I used here. So the output might differ in some runs. But if we do repetitively for 2-3 times , it works fine.