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SSL-Client-Server

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A simple Java SSL/TSL socket client and server demo.

// repository documentation

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#### Simple Java SSL/TSL Socket Server

##### 1. What is the role of public key and private key

* Public key is used to encrypt information. 
* Private key is used to decrypt information.

##### 2. What is the difference between digital signature and encryption

* When encrypting, you(client) use their public key to write message, and they(server) use their private key to decrypt to read it. 
* When signing, you(client) use your own private key to write message’s signature, and they(server) use your public key to verify if the message is yours.

##### 3. What is the difference between keystore and truststore

* A keystore has certs and keys in it and defines what is going to be presented to the other end of a connection.
* A truststore has just certs in it and defines what certs that the other end will send are to be trusted.

##### 4. The standard handshake for SSL/TSL

he standard SSL Handshake

1. Client Hello (Information that the server needs to communicate with the client using SSL.)  
   * SSL version Number 
   * Cipher setting (Compression Method) 
   * Session-specific Data 
2. Server Hello  
   * Server picks a cipher and compression that both client and server support and tells the client about its choice, as well as some other things like a session id. 
   * Server presents its certificate ( This is what client needs to validate as being signed by a trusted CA.) 
   * Server presents a list of certificate authority DNs that client certs may be signed by. 
3. Client response 
   * Client continues the key exchange protocol necessary to set up a TLS session. 
   * Cclient presents a certificate that was signed by one of the CAs and encrypts with the server’s public key.  
   * Send the pre-master (based on cipher) encrypted by Server’s public key to server. 
4. Server accepts the cert presented by client. 
   * Server uses its private key to decrypt the pre-master secret. Both client and server perform steps to generate the master secret with the agreed cipher. 
5. Encryption with Session Key.  
   * Both client and server exchange messages to inform that future messages will be encrypted.

##### 5.In this simple demo, it demonstrates how to start a very simple SSL/TSL Client & server.

* Step 1. Create a private key and public certificate for client & server by openssl tool.

```bash
openssl req -newkey rsa:2048 -nodes -keyout client-key.pem -x509 -days 365 -out client-certificate.pem
```

```bash
openssl req -newkey rsa:2048 -nodes -keyout server-key.pem -x509 -days 365 -out server-certificate.pem
```

* Step 2. Combine the private key and public certificate into `PCKS12(P12)` format for client and server respectively.

```bash
openssl pkcs12 -inkey client-key.pem -in client-certificate.pem -export -out client-certificate.p12
```

```bash
openssl pkcs12 -inkey server-key.pem -in server-certificate.pem -export -out server-certificate.p12
```

* Step 3. Place `client-certificate.p12` and `server-certificate.p12` into `keystore` and `trustStore` location.

![client-server](https://raw.githubusercontent.com/AlphaGarden/SSL-Client-Server/master/img/client-server.jpg)

##### 6. If everything went well, you will see this:

![result](https://raw.githubusercontent.com/AlphaGarden/SSL-Client-Server/master/img/result.jpg)

SSL-Client-Server

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