Simulated TLS handshake protocol implementation

This is a mutual authentication protocol for eCTF 2024 where an embedded application processor (AP) and a component must verify each other, based on certificates that are generated for both at build-time and signed by a host.

Both AP and component will use ephemeral Diffie-Hellman for forward secrecy, which involves generating an additional ECC keypair on each side following an exchange of those public keys and combining them to derive a shared secret.

➡️ Client (AP) sends:

1. ap_pubkey
2. ap_dh_pubkey
3. Signature of (1) and (2) with ap_pubkey
4. cert sig: signature of (ap_pubkey + ap_name) signed by host_pubkey

(3) proves that AP owns the DH key and (4) proves that host certified the AP

Server (component) receives message. Component validates ap_pubkey from certificate and host_pubkey, and then verifies signature of entire message with ap_pubkey.

Component generates it's own DH keypair and derives shared_key using ap_dh_pubkey.

⬅️ Component sends:

1. comp_pubkey
2. comp_dh_pubkey
3. Signature of (1) and (2) with comp_pubkey
4. Certificate: signature of (comp_pubkey + comp_id) by host_pubkey

Component also sends (separately due to package size restrictions)

• Signature of ap_dh_pubkey using comp_pubkey (this additional parameter is the challenge response from component's side)

AP receives message, validates the certificate & message signature, and derives the shared_key in a similar fashion.

AP also verifies the signature of the ap_dh_public_parameter, which is enough to conclude if the component is genuine.

➡️ AP responds with:

1. Signature of comp_dh_pubkey using ap_pubkey

(AP can then continue validating other components if proceeding to boot or wait for a response if requesting attestation data. )

Component validates the signature and concludes that the AP is genuine.
The handshake is complete.

build wolfSSL

# go to wolfssl directory (eg. wolfssl-5.6.6)
sudo ./configure --enable-staticmemory --enable-ecc --enable-ecccustcurves=all --enable-fastmath --enable-compkey --enable-ed25519 --disable-harden --enable-curve25519 CFLAGS="-DWOLFSSL_PUBLIC_MP"
sudo make
sudo make install

build and run project

make
./out