init

README.md

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+# 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](utils/packet.go).
+```
+0        15   23
+┌─────────┬────┬──────────────┐
+│   len   │type│ ... data ... │
+└─────────┴────┴──────────────┘
+```
+
+### len
+The length of the packet without itself.
+### type
+Defined in [utils/packet.go](utils/packet.go).
+```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](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](https://github.com/fumiama/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](rsa_2048_private_x509.b14) and AES key is saved and passed by base16384 format.
+### The Usage of Raw RSA Encrypting Method
+In the file [utils/rsa.go](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.