Secure Diagnostics (UDS Security)

/* UDS SecurityAccess SID 0x27 — seed-key authentication */
/* AUTOSAR DCM: SecurityAccess service handler */

#include "Dcm.h"
#include "Csm.h"

static uint8  sa_seed[32];      /* 256-bit random seed per ISO/SAE 21434 */
static uint8  sa_attempt_count; /* failed attempt counter per level */
static uint32 sa_lockout_timer; /* exponential backoff timer (ms) */

Dcm_StatusType DCM_SecurityAccess_RequestSeed(uint8 security_level,
                                               uint8* seed_out, uint8* seed_len)
{
    /* Check lockout: 3 failures → exponential backoff */
    if (sa_attempt_count >= 3 && sa_lockout_timer > 0) {
        return DCM_E_REQUEST_OUT_OF_RANGE;  /* NRC 0x31 */
    }

    /* Generate 256-bit cryptographically secure random seed */
    Csm_RandomGenerate(CSM_JOB_RANDOM_256BIT, sa_seed, 32);

    memcpy(seed_out, sa_seed, 32);
    *seed_len = 32;
    return DCM_E_OK;
}

Dcm_StatusType DCM_SecurityAccess_CompareKey(uint8 security_level,
                                              const uint8* received_key, uint8 key_len)
{
    uint8 expected_key[32];

    /* Expected key = HMAC-SHA256(sa_seed || ECU_ID, secret_key) truncated to 32B */
    /* secret_key stored in HSM KEY_2 slot — never exported */
    Csm_MacGenerate(CSM_JOB_HMAC_SHA256_KEY2,
                    sa_seed, 32, expected_key);

    /* CRITICAL: constant-time comparison — no timing oracle */
    uint8 diff = 0;
    for (uint8 i = 0; i < 32; i++) {
        diff |= expected_key[i] ^ received_key[i];
    }

    if (diff != 0) {
        sa_attempt_count++;
        if (sa_attempt_count >= 3) {
            sa_lockout_timer = 10000u * (1u << (sa_attempt_count - 3u)); /* exp backoff */
        }
        return DCM_E_INVALID_KEY;  /* NRC 0x35 */
    }

    sa_attempt_count = 0;
    DCM_SetSecurityLevel(security_level);
    return DCM_E_OK;
}

#!/usr/bin/env python3
# DoIP over TLS: secure routing activation with mTLS client cert verification

import ssl, socket, struct

def create_doip_tls_connection(vehicle_ip: str, doip_port: int = 13400,
                                client_cert: str = "workshop_tool.pem",
                                client_key:  str = "workshop_tool.key",
                                ca_cert:     str = "oem_root_ca.pem") -> ssl.SSLSocket:
    """Establish mTLS-secured DoIP TCP connection per ISO 13400-2"""
    ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
    ctx.minimum_version = ssl.TLSVersion.TLSv1_3  # enforce TLS 1.3 minimum
    ctx.verify_mode = ssl.CERT_REQUIRED
    ctx.load_verify_locations(ca_cert)             # verify vehicle's ECU cert
    ctx.load_cert_chain(client_cert, client_key)   # present workshop tool cert

    sock = socket.create_connection((vehicle_ip, doip_port), timeout=5)
    tls_sock = ctx.wrap_socket(sock, server_hostname=vehicle_ip)

    # DoIP RoutingActivation (0x0005) — authentication token extension
    routing_req = struct.pack(">HHIB",
        0xFFFE,   # Source address (test equipment)
        0x0005,   # RoutingActivation payload type
        0x00000001, # Length
        0x00        # Default activation type (client cert already validated by TLS)
    )
    tls_sock.sendall(routing_req)
    response = tls_sock.recv(1024)
    print(f"DoIP RoutingActivation response: {response.hex()}")
    return tls_sock