122 lines
4.1 KiB
C++
122 lines
4.1 KiB
C++
/* 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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