readme: init

README.md

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+# SaiTLS
+
+`[no-std]` Client & Server side TLS implementation on top of smoltcp, using allocator.
+
+## Features
+This crate supports these algorithms:
+- Cipher suites:
+  - TLS_AES_128_GCM_SHA256
+  - TLS_AES_256_GCM_SHA384
+  - TLS_CHACHA20_POLY1305_SHA256
+  - TLS_AES_128_CCM_SHA256
+- Ecliptic curves:
+  - X25519
+  - secp256r1 (NIST P-256)
+- Digital signature algorithms:
+  - ecdsa_secp256r1_sha256
+  - ed25519
+  - RSASSA-PKCS1-v1_5 algorithms
+  - RSASSA-PSS algorithms
+
+Implementation of all algorithms (except x25519 & ed25519) are directly sourced from the [RustCrypto](https://github.com/RustCrypto) project.
+
+Implementation of x25519 & ed25519 algorithms are directly sourced from the [dalek-cryptography](https://github.com/dalek-cryptography) project.
+
+Algorithms not listed above are __NOT__ supported. Using certificates with unsupported algorithms will cause handshake/communication failure.
+
+This crate supports these handshake features:
+- Certificate verification, with a single self-signed certificate
+- (Client) Client certificate verification, if requested by remote server
+- (Server) Send Client Certificate Request to remote client
+
+These handshake features are __NOT__ supported:
+- HelloRetryRequest
+- Pre-shared key & New session ticket
+- Early data
+- 0-RTT handshake
+- Verification of non-self-signed certificates, including certificate chain
+
+## TLS Socket
+To create a TLS socket, the following items are needed:
+- TCP Socket from smoltcp
+- Random number generator (cryptographically secure RNG is recommended)
+- (Optional) Client certificates in x509 certificate & the associated private key
+
+The RNG requires the `TlsRng` trait to be implemented, which further include these traits:
+- `RngCore` from rand_core
+- `CryptoRng` from rand_core
+
+TLS socket can be instantiated by the following lines of code:
+```rust
+    // Typical TCP socket from smoltcp
+    let mut tx_storage = [0; 4096];
+    let mut rx_storage = [0; 4096];
+    let tx_buffer = net::socket::TcpSocketBuffer::new(&mut tx_storage[..]);
+    let rx_buffer = net::socket::TcpSocketBuffer::new(&mut rx_storage[..]);
+    let mut tcp_socket = net::socket::TcpSocket::new(rx_buffer, tx_buffer);
+
+    // TLS socket constructor
+    let tls_socket = TlsSocket::new(
+        tcp_socket,
+        &mut rng,   // Assume rng is from a struct that implements TlsRng
+        None
+    );
+```
+
+## Socket Storage & Access
+Similar to smoltcp, a `TlsSocketSet` is needed to hold the sockets.
+Use `TlsSocketHandle` to gain access to a TLS Socket indirectly.
+```rust
+    // Prepare a socket set for TLS sockets
+    let mut tls_socket_entries: [_; 1] = Default::default();
+    let mut tls_socket_set = smoltcp_tls::set::TlsSocketSet::new(
+        &mut tls_socket_entries[..]
+    );
+    // Use TLS socket set & handle to access TLS socket
+    let tls_handle = tls_socket_set.add(tls_socket);
+    {
+        let mut tls_socket = tls_socket_set.get(tls_handle);
+        /* Socket manipulations */
+    }
+```
+
+## Polling
+The `poll(..)` function substitutes the `EthernetInterface.poll(..)` function in smoltcp.
+```rust
+    smoltcp_tls::poll(
+        Some(&mut smoltcp_sockets),     // Optional socket set from smoltcp
+        &mut tls_socket_set,
+        &mut ethernet_interface,
+        smoltcp::time::Instant::from_millis(time)
+    );
+```
+Sockets in either `smoltcp_sockets` or `tls_socket_set` will be updated.
+
+## Feature `nal_tcp_stack`
+Implements `TcpStack` in embedded-nal (v0.1.0) for `TlsSocket`. This disguises `TlsSocket` as just another TCP socket, potentially useful for implementating application layer protocols (e.g. MQTT in minimq).