RFC 5077 TLS session tickets

Author: Ivan Kostoski

src/HTTPSConnection.cpp

@@ -6,6 +6,7 @@ namespace httpsserver {
 HTTPSConnection::HTTPSConnection(ResourceResolver * resResolver):
   HTTPConnection(resResolver) {
   _ssl = NULL;
+  _TLSTickets = NULL;
 }
 
 HTTPSConnection::~HTTPSConnection() {
@@ -31,6 +32,7 @@ int HTTPSConnection::initialize(int serverSocketID, SSL_CTX * sslCtx, HTTPHeader
     if (resSocket >= 0) {
 
       _ssl = SSL_new(sslCtx);
+      if (_TLSTickets != NULL) _TLSTickets->enable(_ssl);
 
       if (_ssl) {
         // Bind SSL to the socket

src/HTTPSConnection.hpp

@@ -23,6 +23,7 @@
 #include "ResourceNode.hpp"
 #include "HTTPRequest.hpp"
 #include "HTTPResponse.hpp"
+#include "TLSTickets.hpp"
 
 namespace httpsserver {
 
@@ -50,6 +51,7 @@ class HTTPSConnection : public HTTPConnection {
 private:
   // SSL context for this connection
   SSL * _ssl;
+	TLSTickets * _TLSTickets;
 
 };
 

src/HTTPSServer.cpp

@@ -9,6 +9,7 @@ HTTPSServer::HTTPSServer(SSLCert * cert, const uint16_t port, const uint8_t maxC
 
   // Configure runtime data
   _sslctx = NULL;
+  _TLSTickets = NULL;
 }
 
 HTTPSServer::~HTTPSServer() {
@@ -45,6 +46,10 @@ uint8_t HTTPSServer::setupSocket() {
   }
 }
 
+void HTTPSServer::enableTLSTickets(uint32_t liftimeSeconds, bool useHardwareRNG) {
+  _TLSTickets = new TLSTickets("esp32_https_server", liftimeSeconds, useHardwareRNG);
+}
+
 void HTTPSServer::teardownSocket() {
 
   HTTPServer::teardownSocket();

src/HTTPSServer.hpp

@@ -21,6 +21,7 @@
 #include "ResolvedResource.hpp"
 #include "HTTPSConnection.hpp"
 #include "SSLCert.hpp"
+#include "TLSTickets.hpp"
 
 namespace httpsserver {
 
@@ -32,13 +33,17 @@ class HTTPSServer : public HTTPServer {
   HTTPSServer(SSLCert * cert, const uint16_t portHTTPS = 443, const uint8_t maxConnections = 4, const in_addr_t bindAddress = 0);
   virtual ~HTTPSServer();
 
+  // RFC 5077 TLS session tickets
+  void enableTLSTickets(uint32_t liftimeSeconds = 86400, bool useHardwareRNG = false);
+
 private:
   // Static configuration. Port, keys, etc. ====================
   // Certificate that should be used (includes private key)
   SSLCert * _cert;
 
   //// Runtime data ============================================
   SSL_CTX * _sslctx;
+  TLSTickets * _TLSTickets;
   // Status of the server: Are we running, or not?
 
   // Setup functions

src/TLSTickets.cpp

@@ -0,0 +1,91 @@
+#include "TLSTickets.hpp"
+#include "HTTPSServerConstants.hpp"
+
+#include "mbedtls/net_sockets.h"
+
+// Low level SSL implementation on ESP32
+// Copied from esp-idf/components/openssl/platform/ssl_pm.c 
+struct ssl_pm {    
+  mbedtls_net_context fd;
+  mbedtls_net_context cl_fd;
+  mbedtls_ssl_config conf; 
+  mbedtls_ctr_drbg_context ctr_drbg;
+  mbedtls_ssl_context ssl;
+  mbedtls_entropy_context entropy;
+};
+
+namespace httpsserver {
+
+int TLSTickets::hardware_random(void * p_rng, unsigned char * output, size_t output_len) {
+   esp_fill_random(output, output_len);
+   return 0;
+}
+
+TLSTickets::TLSTickets(const char* tag, uint32_t lifetimeSeconds, bool useHWRNG) {
+  _initOk = false;
+  _useHWRNG = useHWRNG;
+
+  // Setup TLS tickets context
+  int ret = -1;
+  if (_useHWRNG) {
+    mbedtls_ssl_ticket_init(&_ticketCtx);
+    ret = mbedtls_ssl_ticket_setup(
+      &_ticketCtx,
+      TLSTickets::hardware_random,
+      NULL,
+      MBEDTLS_CIPHER_AES_256_GCM, 
+      lifetimeSeconds
+    );
+  } else {
+		mbedtls_entropy_init(&_entropy); 			
+    mbedtls_ctr_drbg_init(&_ctr_drbg);
+    mbedtls_ssl_ticket_init(&_ticketCtx);
+    ret = mbedtls_ctr_drbg_seed(
+      &_ctr_drbg, 
+      mbedtls_entropy_func, 
+      &_entropy, 
+      (unsigned char*)tag, 
+      strlen(tag)
+    );
+    if (ret == 0) {
+      ret = mbedtls_ssl_ticket_setup(
+        &_ticketCtx,
+        mbedtls_ctr_drbg_random,
+        &_ctr_drbg,
+        MBEDTLS_CIPHER_AES_256_GCM, 
+        lifetimeSeconds
+      );    
+    }
+  }
+  if (ret != 0) return;
+
+  _initOk = true;
+  HTTPS_LOGI("Using TLS session tickets");
+}
+
+TLSTickets::~TLSTickets() {
+  if (!_useHWRNG) {
+    mbedtls_ctr_drbg_free(&_ctr_drbg);
+    mbedtls_entropy_free(&_entropy);
+  }
+  mbedtls_ssl_ticket_free(&_ticketCtx);
+}
+  
+bool TLSTickets::enable(SSL * ssl) {
+  bool res = false;
+  if (_initOk && ssl && ssl->ssl_pm) {      
+    // Get handle of low-level mbedtls structures for the session
+    struct ssl_pm * ssl_pm = (struct ssl_pm *) ssl->ssl_pm;
+    // Configure TLS ticket callbacks using default MbedTLS implementation
+    mbedtls_ssl_conf_session_tickets_cb(
+      &ssl_pm->conf,
+      mbedtls_ssl_ticket_write,
+      mbedtls_ssl_ticket_parse,
+      &_ticketCtx
+    );        
+    res = true;
+  }
+  return res;
+}
+    
+} /* namespace httpsserver */

src/TLSTickets.hpp

@@ -0,0 +1,57 @@
+#ifndef SRC_TLSTICKETS_HPP_
+#define SRC_TLSTICKETS_HPP_
+
+#include <cstdint>
+#include "mbedtls/entropy.h"
+#include "mbedtls/ctr_drbg.h"
+#include "mbedtls/ssl_ticket.h"
+#include "openssl/ssl.h"
+
+namespace httpsserver {
+
+/**
+ * Enables handling of RFC 5077 TLS session tickets
+ */
+class TLSTickets {
+
+public:
+  TLSTickets(const char* tag, uint32_t liftimeSecs, bool useHWRNG);
+  ~TLSTickets();
+
+  /**
+   * Enables TLS ticket processing for SSL session 
+   */
+  bool enable(SSL * ssl);
+
+protected:
+  bool _initOk;
+  bool _useHWRNG;
+
+  /**
+   * Holds TLS ticket keys
+   */
+  mbedtls_ssl_ticket_context _ticketCtx;
+
+  /**
+   * mbedTLS random number generator state
+   */
+	mbedtls_entropy_context _entropy; 			
+  mbedtls_ctr_drbg_context _ctr_drbg;  
+
+  /**
+   * MbedTLS Random Number Generator using ESP32's hardware RNG
+   * 
+   * NOTE: Radio (WiFi/Bluetooth) MUST be running for hardware
+   * entropy to be gathered. Otherwise this function is PRNG!
+   * 
+   * See more details about esp_random(), here:
+   * https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/system/system.html
+   * 
+   */
+  static int hardware_random(void * p_rng, unsigned char * output, size_t output_len);
+
+};
+
+} /* namespace httpsserver */
+
+#endif // SRC_TLSTICKETS_HPP_