mirror of https://gitlab.com/octospacc/SmolOTP.git
97 lines
2.4 KiB
C
97 lines
2.4 KiB
C
/*
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*
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* TOTP: Time-Based One-Time Password Algorithm
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* Copyright (c) 2017, fmount <fmount9@autistici.org>
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*
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* This software is distributed under MIT License
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*
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* Compute the hmac using openssl library.
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* SHA-1 engine is used by default, but you can pass another one,
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*
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* e.g EVP_md5(), EVP_sha224, EVP_sha512, etc
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*
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*/
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#include <stdio.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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#include <math.h>
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#include "hmac.h"
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char currentHmacResult[HMAC_SHA1_HASH_SIZE];
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uint8_t *hmac(unsigned char *key, int kl, uint64_t interval)
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{
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hmac_sha1(key, kl, &interval, sizeof(interval), ¤tHmacResult);
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return currentHmacResult;
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}
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uint32_t DT(uint8_t *digest)
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{
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uint64_t offset;
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uint32_t bin_code;
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#ifdef DEBUG
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char mdString[40];
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for (int i = 0; i < 20; i++)
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sprintf(&mdString[i*2], "%02x", (unsigned int)digest[i]);
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printf("HMAC digest: %s\n", mdString);
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#endif
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// dynamically truncates hash
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offset = digest[19] & 0x0f;
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bin_code = (digest[offset] & 0x7f) << 24
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| (digest[offset+1] & 0xff) << 16
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| (digest[offset+2] & 0xff) << 8
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| (digest[offset+3] & 0xff);
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// truncates code to 6 digits
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#ifdef DEBUG
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printf("OFFSET: %d\n", offset);
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printf("\nDBC1: %d\n", bin_code);
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#endif
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return bin_code;
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}
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uint32_t mod_hotp(uint32_t bin_code, int digits)
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{
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int power = pow(10, digits);
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uint32_t otp = bin_code % power;
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return otp;
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}
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uint32_t HOTP(uint8_t *key, size_t kl, uint64_t interval, int digits)
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{
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uint8_t *digest;
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uint32_t result;
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uint32_t endianness;
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#ifdef DEBUG
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printf("KEY IS: %s\n", key);
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printf("KEY LEN IS: %d\n", kl);
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printf("COUNTER IS: %d\n", interval);
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#endif
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endianness = 0xdeadbeef;
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if ((*(const uint8_t *)&endianness) == 0xef) {
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interval = ((interval & 0x00000000ffffffff) << 32) | ((interval & 0xffffffff00000000) >> 32);
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interval = ((interval & 0x0000ffff0000ffff) << 16) | ((interval & 0xffff0000ffff0000) >> 16);
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interval = ((interval & 0x00ff00ff00ff00ff) << 8) | ((interval & 0xff00ff00ff00ff00) >> 8);
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};
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//First Phase, get the digest of the message using the provided key ...
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digest = (uint8_t *)hmac(key, kl, interval);
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//Second Phase, get the dbc from the algorithm
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uint32_t dbc = DT(digest);
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//Third Phase: calculate the mod_k of the dbc to get the correct number
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result = mod_hotp(dbc, digits);
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return result;
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}
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