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docs(ssl): Update TLS/SSL certificate fingerprint instructions #236

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docs(ssl): Update TLS/SSL certificate fingerprint instructions
tyeth Jan 16, 2026
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docs(ssl): Improve comment formatting
tyeth Jan 21, 2026
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24 changes: 20 additions & 4 deletions examples/adafruitio_secure_esp8266/adafruitio_secure_esp8266.ino
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Original file line number Diff line number Diff line change
Expand Up @@ -45,10 +45,26 @@ Adafruit_MQTT_Client mqtt(&client, AIO_SERVER, AIO_SERVERPORT, AIO_USERNAME, AIO

// io.adafruit.com SHA1 fingerprint
/* WARNING - This value was last updated on 07/14/25 and may not be up-to-date!
* If security is a concern for your project, we strongly recommend users impacted by this moving
* to ESP32 which has certificate verification by storing root certs and having a
* chain-of-trust rather than doing individual certificate fingerprints.
* If security is a concern for your project, we strongly recommend users impacted by this move
* to a larger MCU like ESP32 which has certificate verification by storing root certs and having
* a chain-of-trust rather than doing individual certificate fingerprints. */
/* For Mac, Linux and WSL users: Run the following command to get the latest fingerprint (with OpenSSL):
```
openssl s_client -connect [io.adafruit.com]:8883 -showcerts </dev/null 2>/dev/null | openssl x509 -fingerprint -noout | sed 's/:/ /g' | sed 's/SHA1 Fingerprint=//'
```
*/
/* Windows users can use Powershell and not need to install OpenSSL:
```
$tcpClient = New-Object System.Net.Sockets.TcpClient("io.adafruit.com", 8883);
$sslStream = New-Object System.Net.Security.SslStream($tcpClient.GetStream(), $false, ({$True}));
$sslStream.AuthenticateAsClient("io.adafruit.com");
$cert = $sslStream.RemoteCertificate;
$fingerprint = ($cert.GetCertHashString());
Write-Output ($fingerprint -replace '(.{2})', '$1 ' -replace ' $', '');
```
*/

/* Replace the value below with your updated SHA1 fingerprint for io.adafruit.com: */
static const char *fingerprint PROGMEM = "47 D2 CB 14 DF 38 97 59 C6 65 1A 1F 3E 00 1E 53 CC A5 17 E0";

/****************************** Feeds ***************************************/
Expand Down Expand Up @@ -84,7 +100,7 @@ void setup() {
Serial.println("WiFi connected");
Serial.println("IP address: "); Serial.println(WiFi.localIP());

// check the fingerprint of io.adafruit.com's SSL cert
/* Verify SSL fingerprint (see above for instructions to update the SSL fingerprint) */
client.setFingerprint(fingerprint);
}

Expand Down