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Add initial code and example
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‎LICENSE.txt‎

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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.

‎examples/RFC6238-generator/RFC6238-generator.ino‎

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/* Copyright (c) Dirk-Willem van Gulik, All rights reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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*
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <WiFi.h>
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#include <ESPmDNS.h>
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#include <ArduinoOTA.h>
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#include <WebServer.h>
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#include <lwip/apps/sntp.h>
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#include <TOTP-RC6236-generator.hpp>
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#ifndef WIFI_NETWORK
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#define WIFI_NETWORK "mySecretWiFiPassword"
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#warning "You propably want to change this line!"
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#endif
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#ifndef WIFI_PASSWD
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#define WIFI_PASSWD "mySecretWiFiPassword"
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#warning "You propably want to change this line!"
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#endif
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#ifndef NTP_SERVER
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#define NTP_SERVER "nl.pool.ntp.org"
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#warning "You MUST set an appropriate ntp pool - see http://ntp.org"
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#endif
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#ifndef NTP_DEFAULT_TZ
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#define NTP_DEFAULT_TZ "CET-1CEST,M3.5.0,M10.5.0/3"
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#endif
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const char* ssid = WIFI_NETWORK;
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const char* password = WIFI_PASSWD;
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void setup() {
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Serial.begin(115200);
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while (!Serial) delay(10);
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Serial.println("\n\n" __FILE__ "Started");
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WiFi.mode(WIFI_STA);
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WiFi.begin(ssid, password);
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if (WiFi.waitForConnectResult() != WL_CONNECTED) {
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Serial.println("WiFi Connect Failed! Rebooting...");
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delay(1000);
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ESP.restart();
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}
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// we need a reasonable accurate time for TOTP to work.
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//
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configTzTime(NTP_DEFAULT_TZ, NTP_SERVER);
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}
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void loop() {
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// Print the one time passcode every seconds;
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//
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static unsigned long lst = millis();
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if (millis() - lst < 1000)
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return;
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lst = millis();
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time_t t = time(NULL);
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if (t < 1000000) {
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Serial.println("Not having a stable time yet.. TOTP is not going to work.");
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return;
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};
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// Seed value - as per the QR code; which is in fact a base32 encoded
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// byte array (i.e. it is binary).
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//
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const char * seed = "ORUGKU3FMNZGK5CTMVSWI===";
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// Example of the same thing - but as usually formatted when shown
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// as the 'alternative text to enter'
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//
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// const char * seed = "ORU GKU 3FM NZG K5C TMV SWI";
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String * otp = TOTP::currentOTP(seed);
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Serial.print(ctime(&t));
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Serial.print(" TOTP at this time is: ");
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Serial.println(*otp);
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Serial.println();
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delete otp;
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}
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‎library.properties‎

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name=TOTP-RC6236-generator
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version=1.0.0
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author=Dirk-Willem van Gulik
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license=ASLv2
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maintainer=Dirk-Willem van Gulik <dirkx@webweaving.org>
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sentence=Time based one time password generator; complies with RFC 6238
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paragraph=RFC 6238 time based one time password generator. It will accept the base32 encoded seeds (and all the other parameters typically found in the Qr codes).
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category=Communication
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url=https://github.com/dirkx/Arduino-TOTP-RFC6238-generator
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architectures=*
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depends=Base32-Decode
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includes=TOTP-RC6236-generator.hpp

‎src/TOTP-RC6236-generator.hpp‎

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/* Copyright (c) Dirk-Willem van Gulik, All rights reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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*
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef _TOTP_RFC6238_H
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#define _TOTP_RFC6238_H
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// Needed for the SHA1
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//
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#include <mbedtls/md.h>
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// Needed for base32 decode - origin
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// https://github.com/dirkx/Arduino-Base32-Decode/releases
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//
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#include <Base32-Decode.h>
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class TOTP {
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public:
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// Defaults from RFC 6238
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// Seed assumed in base64 format; and to be a multiple of 8 bits.
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// once decoded.
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static const time_t RFC6238_DEFAULT_interval = 30; // seconds (default)
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static const time_t RFC6238_DEFAULT_epoch = 0; // epoch relative to the unix epoch (jan 1970 is the default)
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static const int RFC6238_DEFAULT_digits = 6; // length (default is 6)
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static String * currentOTP(String seed,
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time_t interval = RFC6238_DEFAULT_interval,
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int digits = RFC6238_DEFAULT_digits,
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time_t epoch = RFC6238_DEFAULT_epoch
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)
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{
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return currentOTP(seed, time(NULL), interval, digits, epoch);
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}
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static String * currentOTP(String seed,
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time_t t,
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time_t interval = RFC6238_DEFAULT_interval,
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int digits = RFC6238_DEFAULT_digits,
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time_t epoch = RFC6238_DEFAULT_epoch
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)
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{
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uint64_t v = t;
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v = (v - epoch) / interval;
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// HMAC is calculated in big-endian (network) order.
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// v = htonll(v);
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// Unfortunately htonll is not exposed
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uint32_t endianness = 0xdeadbeef;
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if ((*(const uint8_t *)&endianness) == 0xef) {
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v = ((v & 0x00000000ffffffff) << 32) | ((v & 0xffffffff00000000) >> 32);
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v = ((v & 0x0000ffff0000ffff) << 16) | ((v & 0xffff0000ffff0000) >> 16);
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v = ((v & 0x00ff00ff00ff00ff) << 8) | ((v & 0xff00ff00ff00ff00) >> 8);
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};
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unsigned char buff[ seed.length() ];
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bzero(buff, sizeof(buff));
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int n = base32decode(seed.c_str(), buff, sizeof(buff));
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if (n < 0) {
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Serial.println("Could not decode base32 seed");
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return NULL;
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}
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#ifdef RFC6238_DEBUG
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Serial.print("Key: ");
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Serial.print(seed);
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Serial.print(" --> ");
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for (int i = 0; i < n; i++) {
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Serial.printf("%02x", buff[i]);
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}
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Serial.printf(" -- bits=%d -- check this against https://cryptotools.net/otp\n",n * 8);
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#endif
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unsigned char digest[20];
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if (mbedtls_md_hmac(mbedtls_md_info_from_type(MBEDTLS_MD_SHA1),
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buff, n, // key
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(unsigned char*) &v, sizeof(v), // input
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digest)) return NULL;
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uint8_t offst = digest[19] & 0x0f;
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uint32_t bin_code = (digest[offst + 0] & 0x7f) << 24
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| (digest[offst + 1] & 0xff) << 16
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| (digest[offst + 2] & 0xff) << 8
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| (digest[offst + 3] & 0xff);
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int power = pow(10, digits);
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#if RFC6238_DEBUG
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// To check against https://cryptotools.net/otp
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//
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for (int i = 0; i < 20; i++) {
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if (offst == i) Serial.print("|");
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Serial.printf("%02x", digest[i]);
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if (offst == i) Serial.print("|");
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}
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Serial.println();
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#endif
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// prefix with zero's - as needed & cut off to right number of digits.
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//
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char outbuff[32];
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snprintf(outbuff, sizeof(outbuff), "%06u", bin_code % power);
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String * otp = new String(outbuff);
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return (otp);
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}
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};
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#endif

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