C/S demo with RSA and AES Algorithm

This program is my homework for the IoT course, demonstrating the use of symmetric encryption AES and asymmetric encryption RSA.

Communication Process

Server

1. Create a socket and listen for TCP connections.
2. Upon receiving a connection, perform corresponding operations based on the client's request:
   • utils.PacketTypeInit: Encrypt its own RSA public key with the pre-shared AES key and send it to the client.
   • utils.PacketTypeComm: Decrypt and print the message sent by the client using RSA-OAEP with the private key, then encrypt its replyment with a self-made signature algorithm using the RSA private key and send it.
3. When the client actively disconnects, one processing ends.

Client

1. Establish a TCP connection to the server address.
2. Send a utils.PacketTypeInit packet to the server to request the RSA key.
3. Continuously send Hello to the server using EncryptOAEP while decrypting and printing the message sent by server with its public key using the self-made signature algorithm.
4. When the user manually terminates, close the connection to the server.

Packet Protocol

The overall encapsulation is defined in utils/packet.go.

0        15   23
┌─────────┬────┬──────────────┐
│   len   │type│ ... data ... │
└─────────┴────┴──────────────┘

len

The length of the packet without itself.

type

Defined in utils/packet.go.

const (
	PacketTypeInit PacketType = iota // PacketTypeInit pass RSA pubkey by AES pre-shared key
	PacketTypeComm                   // PacketTypeComm normal communication
	PacketTypeTop                    // PacketTypeTop for valid checking
)

data

The payload, whose type is described by the type field.

PacketTypeInit

Defined in utils/packet_init.go.

0    7       23                87
┌────┬────────┬─────────────────┬──────────────────────┐
│type│ length │  pub key crc64  │     x509rsapubkey    │
└────┴────────┴─────────────────┴──────────────────────┘

• type: PacketInitTypeReq or PacketInitTypeAck
• length: length of x509rsapubkey

PacketTypeComm

The whole data field is encrypted by RSA and can fill in with any data, which is plain text in this demo.

Interesting Points

The Implementation of Base16384

Base16384 is a base64-like algorithm designed by me. It can encode binary file to printable utf16be, and vice versa.

In this demo, the RSA Private Key and AES key is saved and passed by base16384 format.

The Usage of Raw RSA Encrypting Method

In the file utils/rsa.go, I use go:linkname to hook the private function of crypto/rsa library and realized a self-made signature algorithm that can get the decoding result but not just verify whether it is valid (unlike the official method rsa.VerifyPKCS1v15).

Demo

See the video below.

https://github.com/fumiama/aes-rsa-tcp-demo/assets/41315874/e4f6522b-e147-4a2f-add3-3a2abb90e96b