feature: create a Trust on First Use example (#9103)
* feature: create a Trust on First Use example the quell the increasingly common copy & paste of the insecure approach making it to production * Quell CI/CD runs on non-WiFi supporting hardare * Update libraries/WiFiClientSecure/examples/WiFiClientInsecure/WiFiClientInsecure.ino typo/improvement to text Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com> * Update libraries/WiFiClientSecure/examples/WiFiClientTrustOnFirstUse/WiFiClientTrustOnFirstUse.ino typo/improvement to text Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com> * Update libraries/WiFiClientSecure/examples/WiFiClientTrustOnFirstUse/WiFiClientTrustOnFirstUse.ino Fix formatting Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com> * Update libraries/WiFiClientSecure/examples/WiFiClientTrustOnFirstUse/WiFiClientTrustOnFirstUse.ino typo/improvement to text Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com> * Update libraries/WiFiClientSecure/examples/WiFiClientTrustOnFirstUse/WiFiClientTrustOnFirstUse.ino typo/improvement to text Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com> * Update libraries/WiFiClientSecure/examples/WiFiClientTrustOnFirstUse/WiFiClientTrustOnFirstUse.ino typo/improvement to text Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com> * Update libraries/WiFiClientSecure/examples/WiFiClientTrustOnFirstUse/WiFiClientTrustOnFirstUse.ino typo/improvement to text Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com> * Update libraries/WiFiClientSecure/examples/WiFiClientTrustOnFirstUse/WiFiClientTrustOnFirstUse.ino typo/improvement to text Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com> * Various things can all stop_ssl_socket() which sets the socket to -1; but the WiFiClientSecure checks for _connected. So we want to make sure the latter is always set. And thus have moved the state handling around *ssl_client down into the C code; below WiFiClientSecure. * Unitialized NVRAM/EEPROM is actual set to 0xFF; so adjust for this. And print the LF/CR for the header lines. * Update libraries/WiFiClientSecure/examples/WiFiClientTrustOnFirstUse/WiFiClientTrustOnFirstUse.ino --------- Co-authored-by: Me No Dev <me-no-dev@users.noreply.github.com> Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com>
This commit is contained in:
Dirk-Willem van Gulik
GitHub
parent
58bea5c131
commit
13fac0876b
4 changed files with 277 additions and 8 deletions
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@ -1,5 +1,13 @@
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#include <WiFiClientSecure.h>
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/* This is a very INSECURE approach.
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* If for some reason the secure, proper example WiFiClientSecure
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* does not work for you; then you may want to check the
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* WiFiClientTrustOnFirstUse example first. It is less secure than
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* WiFiClientSecure, but a lot better than this totally insecure
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* approach shown below.
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*/
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const char* ssid = "your-ssid"; // your network SSID (name of wifi network)
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const char* password = "your-password"; // your network password
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@ -0,0 +1,264 @@
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/* For any secure connection - it is (at least) essential for the
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the client to verify that it is talking with the server it
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thinks it is talking to. And not some (invisible) man in the middle.
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See https://en.wikipedia.org/wiki/Man-in-the-middle_attack,
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https://www.ai.rug.nl/mas/finishedprojects/2011/TLS/hermsencomputerservices.nl/mas/mitm.html or
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https://medium.com/@munteanu210/ssl-certificates-vs-man-in-the-middle-attacks-3fb7846fa5db
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for some background on this.
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Unfortunatley this means that one needs to hardcode a server
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public key, certificate or some cryptographically strong hash
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thereoff into the code, to verify that you are indeed talking to
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the right server. This is sometimes somewhat impractical. Especially
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if you do not know the server in advance; or if your code needs to be
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stable ovr very long times - during which the server may change.
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However completely dispensing with any checks (See the WifiClientInSecure
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example) is also not a good idea either.
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This example gives you some middle ground; "Trust on First Use" --
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TOFU - see https://developer.mozilla.org/en-US/docs/Glossary/TOFU or
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https://en.wikipedia.org/wiki/Trust_on_first_use).
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In this scheme; we start the very first time without any security checks
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but once we have our first connection; we store the public crytpographic
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details (or a proxy, such as a sha256 of this). And then we use this for
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any subsequent connections.
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The assumption here is that we do our very first connection in a somewhat
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trusted network environment; where the chance of a man in the middle is
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very low; or one where the person doing the first run can check the
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details manually.
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So this is not quite as good as building a CA certificate into your
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code (as per the WifiClientSecure example). But not as bad as something
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with no trust management at all.
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To make it possible for the enduser to 'reset' this trust; the
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startup sequence checks if a certain GPIO is low (assumed to be wired
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to some physical button or jumper on the PCB). And we only allow
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the TOFU to be configured when this pin is LOW.
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*/
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#ifndef WIFI_NETWORK
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#define WIFI_NETWORK "Your Wifi SSID"
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#endif
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#ifndef WIFI_PASSWD
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#define WIFI_PASSWD "your-secret-wifi-password"
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#endif
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const char* ssid = WIFI_NETWORK; // your network SSID (name of wifi network)
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const char* password = WIFI_PASSWD; // your network password
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const char* server = "www.howsmyssl.com"; // Server to test with.
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const int TOFU_RESET_BUTTON = 35; /* Trust reset button wired between GPIO 35 and GND (pulldown) */
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#include <WiFiClientSecure.h>
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#include <EEPROM.h>
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/* Set aside some persistant memory (i.e. memory that is preserved on reboots and
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power cycling; and will generally survive software updates as well.
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*/
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EEPROMClass TOFU("tofu0");
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// Utility function; checks if a given buffer is entirly
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// with with 0 bytes over its full length. Returns 0 on
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// succes; a non zero value on fail.
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//
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static int memcmpzero(unsigned char * ptr, size_t len) {
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while (len--) if (0xff != *ptr++) return -1;
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return 0;
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};
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static void printSHA256(unsigned char * ptr) {
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for (int i = 0; i < 32; i++) Serial.printf("%s%02x", i ? ":" : "", ptr[i]);
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Serial.println("");
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};
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WiFiClientSecure client;
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bool get_tofu();
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bool doTOFU_Protected_Connection(uint8_t * fingerprint_tofu);
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void setup() {
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bool tofu_reset = false;
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//Initialize serial and wait for port to open:
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Serial.begin(115200);
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delay(100);
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if (!TOFU.begin(32)) {
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Serial.println("Could not initialsize the EEPROM");
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return;
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}
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uint8_t fingerprint_tofu[32];
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// reset the trust if the tofu reset button is pressed.
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//
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pinMode(TOFU_RESET_BUTTON, INPUT_PULLUP);
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if (digitalRead(TOFU_RESET_BUTTON) == LOW) {
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Serial.println("The TOFU reset button is pressed.");
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tofu_reset = true;
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}
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/* if the button is not pressed; see if we can get the TOFU
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fingerprint from the EEPROM.
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*/
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else if (32 != TOFU.readBytes(0, fingerprint_tofu, 32)) {
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Serial.println("Failed to get the fingerprint from memory.");
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tofu_reset = true;
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}
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/* And check that the EEPROM value is not all 0's; in which
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case we also need to do a TOFU.
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*/
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else if (!memcmpzero(fingerprint_tofu, 32)) {
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Serial.println("TOFU fingerprint in memory all zero.");
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tofu_reset = true;
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};
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if (!tofu_reset) {
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Serial.print("TOFU pegged to fingerprint: SHA256=");
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printSHA256(fingerprint_tofu);
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Serial.print("Note: You can check this fingerprint by going to the URL\n"
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"<https://");
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Serial.print(server);
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Serial.println("> and then click on the lock icon.\n");
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};
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// attempt to connect to Wifi network:
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Serial.print("Attempting to connect to SSID: ");
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Serial.println(ssid);
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WiFi.begin(ssid, password);
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while (WiFi.status() != WL_CONNECTED) {
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Serial.print(".");
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// wait 1 second for re-trying
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delay(1000);
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}
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Serial.print("Connected to ");
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Serial.println(ssid);
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if (tofu_reset) {
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Serial.println("Resetting trust fingerprint.");
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if (!get_tofu()) {
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Serial.println("Trust reset failed. Giving up");
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return;
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}
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Serial.println("(New) Trust of First used configured. Rebooting in 3 seconds");
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delay(3 * 1000);
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ESP.restart();
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};
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Serial.println("Trying to connect to a server; using TOFU details from the eeprom");
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if (doTOFU_Protected_Connection(fingerprint_tofu))
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Serial.println("ALL OK");
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}
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bool get_tofu() {
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Serial.println("\nStarting our insecure connection to server...");
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client.setInsecure();//skip verification
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if (!client.connect(server, 443)) {
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Serial.println("Connection failed!");
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client.stop();
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return false;
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};
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Serial.println("Connected to server. Extracting trust data.");
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// Now extract the data of the certificate and show it to
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// the user over the serial connection for optional
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// verification.
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const mbedtls_x509_crt* peer = client.getPeerCertificate();
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char buf[1024];
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int l = mbedtls_x509_crt_info(buf, sizeof(buf), "", peer);
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if (l <= 0) {
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Serial.println("Peer conversion to printable buffer failed");
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client.stop();
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return false;
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};
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Serial.println();
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Serial.println(buf);
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// Extract the fingerprint - and store this in our EEPROM
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// to be used for future validation.
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uint8_t fingerprint_remote[32];
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if (!client.getFingerprintSHA256(fingerprint_remote)) {
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Serial.println("Failed to get the fingerprint");
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client.stop();
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return false;
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}
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if (
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(32 != TOFU.writeBytes(0, fingerprint_remote, 32)) ||
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(!TOFU.commit())
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) {
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Serial.println("Could not write the fingerprint to the EEPROM");
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client.stop();
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return false;
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};
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TOFU.end();
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client.stop();
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Serial.print("TOFU pegged to fingerprint: SHA256=");
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printSHA256(fingerprint_remote);
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return true;
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};
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bool doTOFU_Protected_Connection(uint8_t * fingerprint_tofu) {
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// As we're not using a (CA) certificate to check the
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// connection; but the hash of the peer - we need to initially
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// allow the connection to be set up without the CA check.
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client.setInsecure();//skip verification
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if (!client.connect(server, 443)) {
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Serial.println("Connection failed!");
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client.stop();
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return false;
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};
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// Now that we're connected - we can check that we have
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// end to end trust - by comparing the fingerprint we (now)
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// see (of the server certificate) to the one we have stored
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// in our EEPROM as part of an earlier trust-on-first use.
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uint8_t fingerprint_remote[32];
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if (!client.getFingerprintSHA256(fingerprint_remote)) {
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Serial.println("Failed to get the fingerprint of the server");
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client.stop();
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return false;
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}
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if (memcmp(fingerprint_remote, fingerprint_tofu, 32)) {
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Serial.println("TOFU fingerprint not the same as the one from the server.");
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Serial.print("TOFU : SHA256=");
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printSHA256(fingerprint_tofu);
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Serial.print("Remote: SHA256=");
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printSHA256(fingerprint_remote);
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Serial.println(" : NOT identical -- Aborting!");
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client.stop();
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return false;
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};
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Serial.println("All well - you are talking to the same server as\n"
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"when you set up TOFU. So we can now do a GET.\n\n");
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client.println("GET /a/check HTTP/1.0");
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client.print("Host: " ); client.println(server);
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client.println("Connection: close");
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client.println();
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bool inhdr = true;
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while (client.connected()) {
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String line = client.readStringUntil('\n');
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Serial.println(line);
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if (inhdr && line == "\r") {
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inhdr = false;
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Serial.println("-- headers received. Payload follows\n\n");
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}
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}
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Serial.println("\n\n-- Payload ended.");
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client.stop();
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return true;
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}
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void loop() {}
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@ -91,15 +91,12 @@ WiFiClientSecure &WiFiClientSecure::operator=(const WiFiClientSecure &other)
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void WiFiClientSecure::stop()
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{
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if (sslclient->socket >= 0) {
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close(sslclient->socket);
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sslclient->socket = -1;
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_connected = false;
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_peek = -1;
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_lastReadTimeout = 0;
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_lastWriteTimeout = 0;
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}
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stop_ssl_socket(sslclient, _CA_cert, _cert, _private_key);
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_connected = false;
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_peek = -1;
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_lastReadTimeout = 0;
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_lastWriteTimeout = 0;
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}
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int WiFiClientSecure::connect(IPAddress ip, uint16_t port)
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