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Add JWS and JSON Web Token example
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‎examples/JSONWebToken/JSONWebToken.ino‎

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/*
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ArduinoSecureElement - JSON Web Token
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This sketch can be used to generate a JSON Web Token from a private key
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stored in an ECC508/ECC608 or SE050 crypto chip slot.
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If the SecureElement is not configured and locked it prompts
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the user to configure and lock the chip with a default TLS
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configuration.
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The user can also select the slot number to use for the private key.
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A new private key can also be generated in this slot.
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The circuit:
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- A board equipped with ECC508 or ECC608 or SE050 chip
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This example code is in the public domain.
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*/
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#include <Arduino_SecureElement.h>
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#include <Arduino_JSON.h>
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#include <utility/SElementJWS.h>
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void setup() {
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Serial.begin(9600);
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while (!Serial);
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SecureElement secureElement;
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if (!secureElement.begin()) {
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Serial.println("No SecureElement present!");
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while (1);
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}
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String serialNumber = secureElement.serialNumber();
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Serial.print("SecureElement Serial Number = ");
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Serial.println(serialNumber);
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Serial.println();
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if (!secureElement.locked()) {
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String lock = promptAndReadLine("The SecureElement on your board is not locked, would you like to PERMANENTLY configure and lock it now? (y/N)", "N");
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lock.toLowerCase();
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if (!lock.startsWith("y")) {
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Serial.println("Unfortunately you can't proceed without locking it :(");
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while (1);
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}
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if (!secureElement.writeConfiguration()) {
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Serial.println("Writing SecureElement configuration failed!");
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while (1);
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}
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if (!secureElement.lock()) {
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Serial.println("Locking SecureElement configuration failed!");
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while (1);
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}
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Serial.println("SecureElement locked successfully");
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Serial.println();
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}
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Serial.println("Hi there, in order to generate a PEM public key for your board, we'll need the following information ...");
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Serial.println();
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String slot = promptAndReadLine("What slot would you like to use? (0 - 4)", "0");
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String generateNewKey = promptAndReadLine("Would you like to generate a new private key? (Y/n)", "Y");
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String issuer = promptAndReadLine("Issuer (Device UID)", "");
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String iat = promptAndReadLine("Issued at (Unix Timestamp)", "");
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String exp = promptAndReadLine("Expires at (Unix Timestamp)", "");
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Serial.println();
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generateNewKey.toLowerCase();
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SElementJWS jws;
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String publicKeyPem = jws.publicKey(secureElement, slot.toInt(), generateNewKey.startsWith("y"));
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if (!publicKeyPem || publicKeyPem == "") {
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Serial.println("Error generating public key!");
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while (1);
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}
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Serial.println("Here's your public key PEM, enjoy!");
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Serial.println();
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Serial.println(publicKeyPem);
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JSONVar jwtHeader;
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JSONVar jwtClaim;
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jwtHeader["alg"] = "ES256";
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jwtHeader["typ"] = "JWT";
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jwtClaim["iss"] = issuer;
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jwtClaim["iat"] = iat.toInt();
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jwtClaim["exp"] = exp.toInt();
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String token = jws.sign(secureElement, slot.toInt(), JSON.stringify(jwtHeader), JSON.stringify(jwtClaim));
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Serial.println("Here's your JSON Web Token, enjoy!");
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Serial.println();
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Serial.println(token);
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}
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void loop() {
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// do nothing
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}
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String promptAndReadLine(const char* prompt, const char* defaultValue) {
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Serial.print(prompt);
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Serial.print(" [");
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Serial.print(defaultValue);
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Serial.print("]: ");
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String s = readLine();
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if (s.length() == 0) {
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s = defaultValue;
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}
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Serial.println(s);
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return s;
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}
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String readLine() {
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String line;
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while (1) {
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if (Serial.available()) {
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char c = Serial.read();
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if (c == '\r') {
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// ignore
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continue;
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} else if (c == '\n') {
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break;
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}
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line += c;
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}
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}
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return line;
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}

‎src/utility/SElementJWS.cpp‎

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/*
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This file is part of the Arduino_SecureElement library.
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Copyright (c) 2024 Arduino SA
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This Source Code Form is subject to the terms of the Mozilla Public
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License, v. 2.0. If a copy of the MPL was not distributed with this
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file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*/
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/******************************************************************************
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* INCLUDE
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******************************************************************************/
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#include <utility/SElementJWS.h>
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#include <utility/ASN1Utils.h>
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#include <utility/PEMUtils.h>
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static String base64urlEncode(const byte in[], unsigned int length)
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{
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static const char* CODES = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_=";
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int b;
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String out;
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int reserveLength = 4 * ((length + 2) / 3);
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out.reserve(reserveLength);
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for (unsigned int i = 0; i < length; i += 3) {
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b = (in[i] & 0xFC) >> 2;
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out += CODES[b];
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b = (in[i] & 0x03) << 4;
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if (i + 1 < length) {
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b |= (in[i + 1] & 0xF0) >> 4;
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out += CODES[b];
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b = (in[i + 1] & 0x0F) << 2;
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if (i + 2 < length) {
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b |= (in[i + 2] & 0xC0) >> 6;
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out += CODES[b];
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b = in[i + 2] & 0x3F;
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out += CODES[b];
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} else {
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out += CODES[b];
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}
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} else {
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out += CODES[b];
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}
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}
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while (out.lastIndexOf('=') != -1) {
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out.remove(out.length() - 1);
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}
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return out;
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}
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String SElementJWS::publicKey(SecureElement & se, int slot, bool newPrivateKey)
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{
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if (slot < 0 || slot > 8) {
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return "";
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}
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byte publicKey[64];
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if (newPrivateKey) {
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if (!se.generatePrivateKey(slot, publicKey)) {
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return "";
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}
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} else {
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if (!se.generatePublicKey(slot, publicKey)) {
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return "";
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}
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}
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int length = ASN1Utils.publicKeyLength();
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byte out[length];
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ASN1Utils.appendPublicKey(publicKey, out);
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return PEMUtils.base64Encode(out, length, "-----BEGIN PUBLIC KEY-----\n", "\n-----END PUBLIC KEY-----\n");
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}
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String SElementJWS::sign(SecureElement & se, int slot, const char* header, const char* payload)
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{
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if (slot < 0 || slot > 8) {
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return "";
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}
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String encodedHeader = base64urlEncode((const byte*)header, strlen(header));
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String encodedPayload = base64urlEncode((const byte*)payload, strlen(payload));
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String toSign;
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toSign.reserve(encodedHeader.length() + 1 + encodedPayload.length());
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toSign += encodedHeader;
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toSign += '.';
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toSign += encodedPayload;
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byte toSignSha256[32];
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byte signature[64];
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se.SHA256((const uint8_t*)toSign.c_str(), toSign.length(), toSignSha256);
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if (!se.ecSign(slot, toSignSha256, signature)) {
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return "";
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}
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String encodedSignature = base64urlEncode(signature, sizeof(signature));
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String result;
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result.reserve(toSign.length() + 1 + encodedSignature.length());
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result += toSign;
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result += '.';
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result += encodedSignature;
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return result;
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}
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String SElementJWS::sign(SecureElement & se, int slot, const String& header, const String& payload)
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{
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return sign(se, slot, header.c_str(), payload.c_str());
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}

‎src/utility/SElementJWS.h‎

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/*
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This file is part of the Arduino_SecureElement library.
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Copyright (c) 2024 Arduino SA
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This Source Code Form is subject to the terms of the Mozilla Public
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License, v. 2.0. If a copy of the MPL was not distributed with this
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file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*/
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#ifndef SECURE_ELEMENT_JWS_H_
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#define SECURE_ELEMENT_JWS_H_
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/******************************************************************************
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* INCLUDE
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******************************************************************************/
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#include <Arduino_SecureElement.h>
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/******************************************************************************
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* CLASS DECLARATION
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******************************************************************************/
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class SElementJWS
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{
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public:
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String publicKey(SecureElement & se, int slot, bool newPrivateKey = true);
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String sign(SecureElement & se, int slot, const char* header, const char* payload);
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String sign(SecureElement & se, int slot, const String& header, const String& payload);
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};
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#endif /* SECURE_ELEMENT_JWS_H_ */

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