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totp.c
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totp.c
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/*
* libmutotp - a library for using and making TOTP QR codes
* Copyright (C) 2020 kmeow
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as publ-
* ished by the Free Software Foundation; either version 2.1 of the
* License, or (at your option) any later version.
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301 USA
*/
#include "totp.h"
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "sha1.h"
#include "base32codec.h"
#include "qrcode/qrcode.h"
void totpuri_init(struct totpuri* uri, const char* label, const char* issuer,
const char* secret)
{
memset(uri, 0, sizeof(struct totpuri));
//The uri format string text alone takes up 33 characters
//The maximum length of the URI is 106 characters in a version 5 QR code
snprintf(uri->label, sizeof(uri->label), label);
snprintf(uri->secret, sizeof(uri->secret), secret);
snprintf(uri->issuer, sizeof(uri->issuer), issuer);
snprintf(uri->uristr, sizeof(uri->uristr), "otpauth://totp/%s?secret=%s&issuer=%s",
uri->label, uri->secret, uri->issuer);
}
char* create_totp_qrcode(const char* label, const char* issuer, const char* secret)
{
QRCode qrcode;
uint8_t qrcodever = 4;
size_t qrcodelen = qrcode_getBufferSize(qrcodever);
uint8_t* qrcodedata = (char*) malloc(qrcodelen);
struct totpuri uri;
totpuri_init(&uri, label, issuer, secret);
qrcode_initText(&qrcode, qrcodedata, qrcodever, ECC_LOW, uri.uristr);
uint8_t y = 0, x = 0;
uint32_t i = 0;
static const char* rev = "\x1B[07m";
static const char* def = "\x1B[0m";
size_t qrcodeansilen = (7 * qrcode.size * qrcode.size) + 1;
uint8_t* qrcodeansi = (char*) malloc(qrcodeansilen);
memset(qrcodeansi, 0 , qrcodeansilen);
size_t idx = 0;
uint8_t lastansi = 0;
for(y = 0; y < qrcode.size; ++y)
{
for(x = 0; x < qrcode.size; ++x)
{
if(qrcode_getModule(&qrcode, x, y))
{
idx += snprintf(&qrcodeansi[idx], qrcodeansilen - idx, "%s ",
1 == lastansi ? "" : rev);
lastansi = 1;
}
else
{
idx += snprintf(&qrcodeansi[idx], qrcodeansilen - idx, "%s ",
0 == lastansi ? "" : def);
lastansi = 0;
}
}
idx += snprintf(&qrcodeansi[idx], qrcodeansilen - idx, "\n");
}
idx += snprintf(&qrcodeansi[idx], qrcodeansilen - idx, "%s", def);
free(qrcodedata);
return qrcodeansi;
}
static time_t flip_ts_endianness(time_t timestamp)
{
size_t idx = 0, len = sizeof(time_t);
time_t output = 0;
char* pOutput = (char*) &output;
for(; idx < len; ++idx)
{
pOutput[idx] = (timestamp >> ((len - idx - 1) << 3)) & 0xff;
}
return output;
}
int generate_random_secret(char* out, size_t outlen, int32_t (*rgen)(uint8_t*, size_t))
{
//Generate a 160-bit random value encoded in a 32 character long base32
//encoded ASCII string
if(outlen < 33)
{
return -1;
}
uint8_t secret[20] = {0};
if(rgen(secret, 20) < 0)
{
return -1;
}
return base32encode(secret, 20, out, outlen);
}
int32_t compute_totp(const char* secret, size_t secretlen,
time_t timestamp, size_t timestep, size_t digits)
{
static const int32_t ddivisor[] =
{
1, 10, 100, 1000, 10000, 100000, 1000000,
10000000, 100000000
};
if(digits >= sizeof(ddivisor)/sizeof(uint32_t))
{
return -1;
}
uint8_t result[20] = {0};
uint8_t hexstr[41] = {0};
time_t counter = timestamp / timestep;
//TODO: This only needs to be done on little endian machines
time_t counterbe = flip_ts_endianness(counter);
hmacsha1(result, secret, secretlen,
(char*) &counterbe, sizeof(time_t));
int32_t offset = result[19] & 0x0f;
int32_t truncated = ((result[offset] & 0x7f) << 24) |
((result[offset + 1] & 0xff) << 16) |
((result[offset + 2] & 0xff) << 8) |
(result[offset + 3] & 0xff);
return truncated % ddivisor[digits];
}
#ifndef min
#define min(a, b) (a < b ? a : b)
#endif
void hmacsha1(char* output, const char* key, size_t key_len, const char* message, size_t message_len)
{
char okeypad[64] = {0};
char ikeypad[64] = {0};
char keybuf[128] = {0};
memcpy(keybuf, key, min(128, key_len));
if(strnlen(keybuf, 128) > 64)
{
//Hash a key which is longer than the SHA1 block size (64 bytes)
char keyout[128] = {0};
SHA1(keyout, keybuf, strnlen(keybuf, 128));
memset(keybuf, 0, 128);
memcpy(keybuf, keyout, 128);
}
size_t idx = 0;
for(; idx < 16; ++idx)
{
((unsigned int*) okeypad)[idx] = ((unsigned int*) keybuf)[idx] ^ 0x5c5c5c5c;
((unsigned int*) ikeypad)[idx] = ((unsigned int*) keybuf)[idx] ^ 0x36363636;
}
//bc = ikeypad + message
//a = okeypad + Hash(bc)
//HMAC = Hash(a)
size_t bc_len = 64 + message_len;
size_t a_len = 84; //64 + 20
char* bc = malloc(bc_len + 1);
char* a = malloc(a_len + 1);
memcpy(bc, ikeypad, 64);
memcpy(&bc[64], message, message_len);
memcpy(a, okeypad, 64);
SHA1(&a[64], bc, bc_len);
SHA1(output, a, a_len);
free(a);
free(bc);
}