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google-authenticator.c
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google-authenticator.c
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// Helper program to generate a new secret for use in two-factor
// authentication.
//
// Copyright 2010 Google Inc.
// Author: Markus Gutschke
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "config.h"
#include <assert.h>
#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
#include "base32.h"
#include "hmac.h"
#include "sha1.h"
#define SECRET "/.google_authenticator"
#define SECRET_BITS 128 // Must be divisible by eight
#define VERIFICATION_CODE_MODULUS (1000*1000) // Six digits
#define SCRATCHCODES 5 // Default number of initial scratchcodes
#define MAX_SCRATCHCODES 10 // Max number of initial scratchcodes
#define SCRATCHCODE_LENGTH 8 // Eight digits per scratchcode
#define BYTES_PER_SCRATCHCODE 4 // 32bit of randomness is enough
#define BITS_PER_BASE32_CHAR 5 // Base32 expands space by 8/5
static enum { QR_UNSET=0, QR_NONE, QR_ANSI, QR_UTF8 } qr_mode = QR_UNSET;
static int generateCode(const char *key, unsigned long tm) {
uint8_t challenge[8];
for (int i = 8; i--; tm >>= 8) {
challenge[i] = tm;
}
// Estimated number of bytes needed to represent the decoded secret. Because
// of white-space and separators, this is an upper bound of the real number,
// which we later get as a return-value from base32_decode()
int secretLen = (strlen(key) + 7)/8*BITS_PER_BASE32_CHAR;
// Sanity check, that our secret will fixed into a reasonably-sized static
// array.
if (secretLen <= 0 || secretLen > 100) {
return -1;
}
// Decode secret from Base32 to a binary representation, and check that we
// have at least one byte's worth of secret data.
uint8_t secret[100];
if ((secretLen = base32_decode((const uint8_t *)key, secret, secretLen))<1) {
return -1;
}
// Compute the HMAC_SHA1 of the secret and the challenge.
uint8_t hash[SHA1_DIGEST_LENGTH];
hmac_sha1(secret, secretLen, challenge, 8, hash, SHA1_DIGEST_LENGTH);
// Pick the offset where to sample our hash value for the actual verification
// code.
const int offset = hash[SHA1_DIGEST_LENGTH - 1] & 0xF;
// Compute the truncated hash in a byte-order independent loop.
unsigned int truncatedHash = 0;
for (int i = 0; i < 4; ++i) {
truncatedHash <<= 8;
truncatedHash |= hash[offset + i];
}
// Truncate to a smaller number of digits.
truncatedHash &= 0x7FFFFFFF;
truncatedHash %= VERIFICATION_CODE_MODULUS;
return truncatedHash;
}
// return the user name in heap-allocated buffer.
// Caller frees.
static const char *getUserName(uid_t uid) {
struct passwd pwbuf, *pw;
char *buf;
#ifdef _SC_GETPW_R_SIZE_MAX
int len = sysconf(_SC_GETPW_R_SIZE_MAX);
if (len <= 0) {
len = 4096;
}
#else
int len = 4096;
#endif
buf = malloc(len);
char *user;
if (getpwuid_r(uid, &pwbuf, buf, len, &pw) || !pw) {
user = malloc(32);
snprintf(user, 32, "%d", uid);
} else {
user = strdup(pw->pw_name);
if (!user) {
perror("malloc()");
_exit(1);
}
}
free(buf);
return user;
}
static const char *urlEncode(const char *s) {
const size_t size = 3 * strlen(s) + 1;
if (size > 10000) {
// Anything "too big" is too suspect to let through.
fprintf(stderr, "Error: Generated URL would be unreasonably large.\n");
exit(1);
}
char *ret = malloc(size);
char *d = ret;
do {
switch (*s) {
case '%':
case '&':
case '?':
case '=':
encode:
snprintf(d, size-(d-ret), "%%%02X", (unsigned char)*s);
d += 3;
break;
default:
if ((*s && *s <= ' ') || *s >= '\x7F') {
goto encode;
}
*d++ = *s;
break;
}
} while (*s++);
char* newret = realloc(ret, strlen(ret) + 1);
if (newret) {
ret = newret;
}
return ret;
}
static const char *getURL(const char *secret, const char *label,
const int use_totp, const char *issuer) {
const char *encodedLabel = urlEncode(label);
char *url;
const char totp = use_totp ? 't' : 'h';
if (asprintf(&url, "otpauth://%cotp/%s?secret=%s", totp, encodedLabel, secret) < 0) {
fprintf(stderr, "String allocation failed, probably running out of memory.\n");
_exit(1);
}
if (issuer != NULL && strlen(issuer) > 0) {
// Append to URL &issuer=<issuer>
const char *encodedIssuer = urlEncode(issuer);
char *newUrl;
if (asprintf(&newUrl, "%s&issuer=%s", url, encodedIssuer) < 0) {
fprintf(stderr, "String allocation failed, probably running out of memory.\n");
_exit(1);
}
free((void *)encodedIssuer);
free(url);
url = newUrl;
}
free((void *)encodedLabel);
return url;
}
#define ANSI_RESET "\x1B[0m"
#define ANSI_BLACKONGREY "\x1B[30;47;27m"
#define ANSI_WHITE "\x1B[27m"
#define ANSI_BLACK "\x1B[7m"
#define UTF8_BOTH "\xE2\x96\x88"
#define UTF8_TOPHALF "\xE2\x96\x80"
#define UTF8_BOTTOMHALF "\xE2\x96\x84"
// Display QR code visually. If not possible, return 0.
static int displayQRCode(const char* url) {
void *qrencode = dlopen("libqrencode.so.2", RTLD_NOW | RTLD_LOCAL);
if (!qrencode) {
qrencode = dlopen("libqrencode.so.3", RTLD_NOW | RTLD_LOCAL);
}
if (!qrencode) {
qrencode = dlopen("libqrencode.so.4", RTLD_NOW | RTLD_LOCAL);
}
if (!qrencode) {
qrencode = dlopen("libqrencode.3.dylib", RTLD_NOW | RTLD_LOCAL);
}
if (!qrencode) {
qrencode = dlopen("libqrencode.4.dylib", RTLD_NOW | RTLD_LOCAL);
}
if (!qrencode) {
return 0;
}
typedef struct {
int version;
int width;
unsigned char *data;
} QRcode;
QRcode *(*QRcode_encodeString8bit)(const char *, int, int) =
(QRcode *(*)(const char *, int, int))
dlsym(qrencode, "QRcode_encodeString8bit");
void (*QRcode_free)(QRcode *qrcode) =
(void (*)(QRcode *))dlsym(qrencode, "QRcode_free");
if (!QRcode_encodeString8bit || !QRcode_free) {
dlclose(qrencode);
return 0;
}
QRcode *qrcode = QRcode_encodeString8bit(url, 0, 1);
const char *ptr = (char *)qrcode->data;
// Output QRCode using ANSI colors. Instead of black on white, we
// output black on grey, as that works independently of whether the
// user runs their terminal in a black on white or white on black color
// scheme.
// But this requires that we print a border around the entire QR Code.
// Otherwise readers won't be able to recognize it.
if (qr_mode != QR_UTF8) {
for (int i = 0; i < 2; ++i) {
printf(ANSI_BLACKONGREY);
for (int x = 0; x < qrcode->width + 4; ++x) printf(" ");
puts(ANSI_RESET);
}
for (int y = 0; y < qrcode->width; ++y) {
printf(ANSI_BLACKONGREY" ");
int isBlack = 0;
for (int x = 0; x < qrcode->width; ++x) {
if (*ptr++ & 1) {
if (!isBlack) {
printf(ANSI_BLACK);
}
isBlack = 1;
} else {
if (isBlack) {
printf(ANSI_WHITE);
}
isBlack = 0;
}
printf(" ");
}
if (isBlack) {
printf(ANSI_WHITE);
}
puts(" "ANSI_RESET);
}
for (int i = 0; i < 2; ++i) {
printf(ANSI_BLACKONGREY);
for (int x = 0; x < qrcode->width + 4; ++x) printf(" ");
puts(ANSI_RESET);
}
} else {
// Drawing the QRCode with Unicode block elements is desirable as
// it makes the code much smaller, which is often easier to scan.
// Unfortunately, many terminal emulators do not display these
// Unicode characters properly.
printf(ANSI_BLACKONGREY);
for (int i = 0; i < qrcode->width + 4; ++i) {
printf(" ");
}
puts(ANSI_RESET);
for (int y = 0; y < qrcode->width; y += 2) {
printf(ANSI_BLACKONGREY" ");
for (int x = 0; x < qrcode->width; ++x) {
const int top = qrcode->data[y*qrcode->width + x] & 1;
int bottom = 0;
if (y+1 < qrcode->width) {
bottom = qrcode->data[(y+1)*qrcode->width + x] & 1;
}
if (top) {
if (bottom) {
printf(UTF8_BOTH);
} else {
printf(UTF8_TOPHALF);
}
} else {
if (bottom) {
printf(UTF8_BOTTOMHALF);
} else {
printf(" ");
}
}
}
puts(" "ANSI_RESET);
}
printf(ANSI_BLACKONGREY);
for (int i = 0; i < qrcode->width + 4; ++i) {
printf(" ");
}
puts(ANSI_RESET);
}
QRcode_free(qrcode);
dlclose(qrencode);
return 1;
}
// Display to the user what they need to provision their app.
static void displayEnrollInfo(const char *secret, const char *label,
const int use_totp, const char *issuer) {
if (qr_mode == QR_NONE) {
return;
}
const char *url = getURL(secret, label, use_totp, issuer);
// Only newer systems have support for libqrencode. So instead of requiring
// it at build-time we look for it at run-time. If it cannot be found, the
// user can still type the code in manually or copy the URL into
// their browser.
if (isatty(STDOUT_FILENO)) {
if (!displayQRCode(url)) {
printf(
"Failed to use libqrencode to show QR code visually for scanning.\n"
"Consider typing the OTP secret into your app manually.\n");
}
}
free((char *)url);
}
// ask for a code. Return code, or some garbage if no number given. That's fine
// because bad data also won't match code.
static int ask_code(const char* msg) {
char line[128];
printf("%s ", msg);
fflush(stdout);
line[sizeof(line)-1] = 0;
if (NULL == fgets(line, sizeof line, stdin)) {
if (errno == 0) {
printf("\n");
} else {
perror("getline()");
}
exit(1);
}
return strtol(line, NULL, 10);
}
// ask y/n, and return 0 for no, 1 for yes.
static int maybe(const char *msg) {
printf("\n");
for (;;) {
char line[128];
printf("%s (y/n) ", msg);
fflush(stdout);
line[sizeof(line)-1] = 0;
if (NULL == fgets(line, sizeof(line), stdin)) {
if (errno == 0) {
printf("\n");
} else {
perror("getline()");
}
exit(1);
}
switch (line[0]) {
case 'Y':
case 'y':
return 1;
case 'N':
case 'n':
return 0;
}
}
}
static char *addOption(char *buf, size_t nbuf, const char *option) {
assert(strlen(buf) + strlen(option) < nbuf);
char *scratchCodes = strchr(buf, '\n');
assert(scratchCodes);
scratchCodes++;
memmove(scratchCodes + strlen(option), scratchCodes,
strlen(scratchCodes) + 1);
memcpy(scratchCodes, option, strlen(option));
return buf;
}
static char *maybeAddOption(const char *msg, char *buf, size_t nbuf,
const char *option) {
if (maybe(msg)) {
buf = addOption(buf, nbuf, option);
}
return buf;
}
static void
print_version() {
puts("google-authenticator "VERSION);
}
static void usage(void) {
print_version();
puts(
"google-authenticator [<options>]\n"
" -h, --help Print this message\n"
" --version Print version\n"
" -c, --counter-based Set up counter-based (HOTP) verification\n"
" -C, --no-confirm Don't confirm code. For non-interactive setups\n"
" -t, --time-based Set up time-based (TOTP) verification\n"
" -d, --disallow-reuse Disallow reuse of previously used TOTP tokens\n"
" -D, --allow-reuse Allow reuse of previously used TOTP tokens\n"
" -f, --force Write file without first confirming with user\n"
" -l, --label=<label> Override the default label in \"otpauth://\" URL\n"
" -i, --issuer=<issuer> Override the default issuer in \"otpauth://\" URL\n"
" -q, --quiet Quiet mode\n"
" -Q, --qr-mode={NONE,ANSI,UTF8} QRCode output mode\n"
" -r, --rate-limit=N Limit logins to N per every M seconds\n"
" -R, --rate-time=M Limit logins to N per every M seconds\n"
" -u, --no-rate-limit Disable rate-limiting\n"
" -s, --secret=<file> Specify a non-standard file location\n"
" -S, --step-size=S Set interval between token refreshes\n"
" -w, --window-size=W Set window of concurrently valid codes\n"
" -W, --minimal-window Disable window of concurrently valid codes\n"
" -e, --emergency-codes=N Number of emergency codes to generate");
}
int main(int argc, char *argv[]) {
uint8_t buf[SECRET_BITS/8 + MAX_SCRATCHCODES*BYTES_PER_SCRATCHCODE];
static const char hotp[] = "\" HOTP_COUNTER 1\n";
static const char totp[] = "\" TOTP_AUTH\n";
static const char disallow[] = "\" DISALLOW_REUSE\n";
static const char step[] = "\" STEP_SIZE 30\n";
static const char window[] = "\" WINDOW_SIZE 17\n";
static const char ratelimit[] = "\" RATE_LIMIT 3 30\n";
char secret[(SECRET_BITS + BITS_PER_BASE32_CHAR-1)/BITS_PER_BASE32_CHAR +
1 /* newline */ +
sizeof(hotp) + // hotp and totp are mutually exclusive.
sizeof(disallow) +
sizeof(step) +
sizeof(window) +
sizeof(ratelimit) + 5 + // NN MMM (total of five digits)
SCRATCHCODE_LENGTH*(MAX_SCRATCHCODES + 1 /* newline */) +
1 /* NUL termination character */];
enum { ASK_MODE, HOTP_MODE, TOTP_MODE } mode = ASK_MODE;
enum { ASK_REUSE, DISALLOW_REUSE, ALLOW_REUSE } reuse = ASK_REUSE;
int force = 0, quiet = 0;
int r_limit = 0, r_time = 0;
char *secret_fn = NULL;
char *label = NULL;
char *issuer = NULL;
int step_size = 0;
int confirm = 1;
int window_size = 0;
int emergency_codes = -1;
int idx;
for (;;) {
static const char optstring[] = "+hcCtdDfl:i:qQ:r:R:us:S:w:We:";
static struct option options[] = {
{ "help", 0, 0, 'h' },
{ "version", 0, 0, 0},
{ "counter-based", 0, 0, 'c' },
{ "no-confirm", 0, 0, 'C' },
{ "time-based", 0, 0, 't' },
{ "disallow-reuse", 0, 0, 'd' },
{ "allow-reuse", 0, 0, 'D' },
{ "force", 0, 0, 'f' },
{ "label", 1, 0, 'l' },
{ "issuer", 1, 0, 'i' },
{ "quiet", 0, 0, 'q' },
{ "qr-mode", 1, 0, 'Q' },
{ "rate-limit", 1, 0, 'r' },
{ "rate-time", 1, 0, 'R' },
{ "no-rate-limit", 0, 0, 'u' },
{ "secret", 1, 0, 's' },
{ "step-size", 1, 0, 'S' },
{ "window-size", 1, 0, 'w' },
{ "minimal-window", 0, 0, 'W' },
{ "emergency-codes", 1, 0, 'e' },
{ 0, 0, 0, 0 }
};
idx = -1;
const int c = getopt_long(argc, argv, optstring, options, &idx);
if (c > 0) {
for (int i = 0; options[i].name; i++) {
if (options[i].val == c) {
idx = i;
break;
}
}
} else if (c < 0) {
break;
}
if (idx-- <= 0) {
// Help (or invalid argument)
err:
usage();
if (idx < -1) {
fprintf(stderr, "Failed to parse command line\n");
_exit(1);
}
exit(0);
} else if (!idx--) {
// --version
print_version();
exit(0);
} else if (!idx--) {
// counter-based, -c
if (mode != ASK_MODE) {
fprintf(stderr, "Duplicate -c and/or -t option detected\n");
_exit(1);
}
if (reuse != ASK_REUSE) {
reuse_err:
fprintf(stderr, "Reuse of tokens is not a meaningful parameter "
"in counter-based mode\n");
_exit(1);
}
mode = HOTP_MODE;
} else if (!idx--) {
// don't confirm code provisioned, -C
confirm = 0;
} else if (!idx--) {
// time-based
if (mode != ASK_MODE) {
fprintf(stderr, "Duplicate -c and/or -t option detected\n");
_exit(1);
}
mode = TOTP_MODE;
} else if (!idx--) {
// disallow-reuse
if (reuse != ASK_REUSE) {
fprintf(stderr, "Duplicate -d and/or -D option detected\n");
_exit(1);
}
if (mode == HOTP_MODE) {
goto reuse_err;
}
reuse = DISALLOW_REUSE;
} else if (!idx--) {
// allow-reuse
if (reuse != ASK_REUSE) {
fprintf(stderr, "Duplicate -d and/or -D option detected\n");
_exit(1);
}
if (mode == HOTP_MODE) {
goto reuse_err;
}
reuse = ALLOW_REUSE;
} else if (!idx--) {
// force
if (force) {
fprintf(stderr, "Duplicate -f option detected\n");
_exit(1);
}
force = 1;
} else if (!idx--) {
// label
if (label) {
fprintf(stderr, "Duplicate -l option detected\n");
_exit(1);
}
label = strdup(optarg);
} else if (!idx--) {
// issuer
if (issuer) {
fprintf(stderr, "Duplicate -i option detected\n");
_exit(1);
}
issuer = strdup(optarg);
} else if (!idx--) {
// quiet
if (quiet) {
fprintf(stderr, "Duplicate -q option detected\n");
_exit(1);
}
quiet = 1;
} else if (!idx--) {
// qr-mode
if (qr_mode != QR_UNSET) {
fprintf(stderr, "Duplicate -Q option detected\n");
_exit(1);
}
if (!strcasecmp(optarg, "none")) {
qr_mode = QR_NONE;
} else if (!strcasecmp(optarg, "ansi")) {
qr_mode = QR_ANSI;
} else if (!strcasecmp(optarg, "utf8")) {
qr_mode = QR_UTF8;
} else {
fprintf(stderr, "Invalid qr-mode \"%s\"\n", optarg);
_exit(1);
}
} else if (!idx--) {
// rate-limit
if (r_limit > 0) {
fprintf(stderr, "Duplicate -r option detected\n");
_exit(1);
} else if (r_limit < 0) {
fprintf(stderr, "-u is mutually exclusive with -r\n");
_exit(1);
}
char *endptr;
errno = 0;
const long l = strtol(optarg, &endptr, 10);
if (errno || endptr == optarg || *endptr || l < 1 || l > 10) {
fprintf(stderr, "-r requires an argument in the range 1..10\n");
_exit(1);
}
r_limit = (int)l;
} else if (!idx--) {
// rate-time
if (r_time > 0) {
fprintf(stderr, "Duplicate -R option detected\n");
_exit(1);
} else if (r_time < 0) {
fprintf(stderr, "-u is mutually exclusive with -R\n");
_exit(1);
}
char *endptr;
errno = 0;
const long l = strtol(optarg, &endptr, 10);
if (errno || endptr == optarg || *endptr || l < 15 || l > 600) {
fprintf(stderr, "-R requires an argument in the range 15..600\n");
_exit(1);
}
r_time = (int)l;
} else if (!idx--) {
// no-rate-limit
if (r_limit > 0 || r_time > 0) {
fprintf(stderr, "-u is mutually exclusive with -r/-R\n");
_exit(1);
}
if (r_limit < 0) {
fprintf(stderr, "Duplicate -u option detected\n");
_exit(1);
}
r_limit = r_time = -1;
} else if (!idx--) {
// secret
if (secret_fn) {
fprintf(stderr, "Duplicate -s option detected\n");
_exit(1);
}
if (!*optarg) {
fprintf(stderr, "-s must be followed by a filename\n");
_exit(1);
}
secret_fn = strdup(optarg);
if (!secret_fn) {
perror("malloc()");
_exit(1);
}
} else if (!idx--) {
// step-size
if (step_size) {
fprintf(stderr, "Duplicate -S option detected\n");
_exit(1);
}
char *endptr;
errno = 0;
const long l = strtol(optarg, &endptr, 10);
if (errno || endptr == optarg || *endptr || l < 1 || l > 60) {
fprintf(stderr, "-S requires an argument in the range 1..60\n");
_exit(1);
}
step_size = (int)l;
} else if (!idx--) {
// window-size
if (window_size) {
fprintf(stderr, "Duplicate -w/-W option detected\n");
_exit(1);
}
char *endptr;
errno = 0;
const long l = strtol(optarg, &endptr, 10);
if (errno || endptr == optarg || *endptr || l < 1 || l > 21) {
fprintf(stderr, "-w requires an argument in the range 1..21\n");
_exit(1);
}
window_size = (int)l;
} else if (!idx--) {
// minimal-window
if (window_size) {
fprintf(stderr, "Duplicate -w/-W option detected\n");
_exit(1);
}
window_size = -1;
} else if (!idx--) {
// emergency-codes
if (emergency_codes >= 0) {
fprintf(stderr, "Duplicate -e option detected\n");
_exit(1);
}
char *endptr;
errno = 0;
long l = strtol(optarg, &endptr, 10);
if (errno || endptr == optarg || *endptr || l < 0 || l > MAX_SCRATCHCODES) {
fprintf(stderr, "-e requires an argument in the range 0..%d\n", MAX_SCRATCHCODES);
_exit(1);
}
emergency_codes = (int)l;
} else {
fprintf(stderr, "Error\n");
_exit(1);
}
}
idx = -1;
if (optind != argc) {
goto err;
}
if (reuse != ASK_REUSE && mode != TOTP_MODE) {
fprintf(stderr, "Must select time-based mode, when using -d or -D\n");
_exit(1);
}
if ((r_time && !r_limit) || (!r_time && r_limit)) {
fprintf(stderr, "Must set -r when setting -R, and vice versa\n");
_exit(1);
}
if (emergency_codes < 0) {
emergency_codes = SCRATCHCODES;
}
if (!label) {
const uid_t uid = getuid();
const char *user = getUserName(uid);
char hostname[128] = { 0 };
if (gethostname(hostname, sizeof(hostname)-1)) {
strcpy(hostname, "unix");
}
label = strcat(strcat(strcpy(malloc(strlen(user) + strlen(hostname) + 2),
user), "@"), hostname);
free((char *)user);
}
if (!issuer) {
char hostname[128] = { 0 };
if (gethostname(hostname, sizeof(hostname)-1)) {
strcpy(hostname, "unix");
}
issuer = strdup(hostname);
}
// Not const because 'fd' is reused. TODO.
int fd = open("/dev/urandom", O_RDONLY);
if (fd < 0) {
perror("Failed to open \"/dev/urandom\"");
return 1;
}
if (read(fd, buf, sizeof(buf)) != sizeof(buf)) {
urandom_failure:
perror("Failed to read from \"/dev/urandom\"");
return 1;
}
base32_encode(buf, SECRET_BITS/8, (uint8_t *)secret, sizeof(secret));
int use_totp;
if (mode == ASK_MODE) {
use_totp = maybe("Do you want authentication tokens to be time-based");
} else {
use_totp = mode == TOTP_MODE;
}
if (!quiet) {
displayEnrollInfo(secret, label, use_totp, issuer);
printf("Your new secret key is: %s\n", secret);
// Confirm code.
if (confirm && use_totp) {
for (;;) {
const int test_code = ask_code("Enter code from app (-1 to skip):");
if (test_code < 0) {
printf("Code confirmation skipped\n");
break;
}
const unsigned long tm = time(NULL)/(step_size ? step_size : 30);
const int correct_code = generateCode(secret, tm);
if (test_code == correct_code) {
printf("Code confirmed\n");
break;
}
printf("Code incorrect (correct code %06d). Try again.\n",
correct_code);
}
} else {
const unsigned long tm = 1;
printf("Your verification code for code %lu is %06d\n",
tm, generateCode(secret, tm));
}
printf("Your emergency scratch codes are:\n");
}
free(label);
free(issuer);
strcat(secret, "\n");
if (use_totp) {
strcat(secret, totp);
} else {
strcat(secret, hotp);
}
for (int i = 0; i < emergency_codes; ++i) {
new_scratch_code:;
int scratch = 0;
for (int j = 0; j < BYTES_PER_SCRATCHCODE; ++j) {
scratch = 256*scratch + buf[SECRET_BITS/8 + BYTES_PER_SCRATCHCODE*i + j];
}
int modulus = 1;
for (int j = 0; j < SCRATCHCODE_LENGTH; j++) {
modulus *= 10;
}
scratch = (scratch & 0x7FFFFFFF) % modulus;
if (scratch < modulus/10) {
// Make sure that scratch codes are always exactly eight digits. If they
// start with a sequence of zeros, just generate a new scratch code.
if (read(fd, buf + (SECRET_BITS/8 + BYTES_PER_SCRATCHCODE*i),
BYTES_PER_SCRATCHCODE) != BYTES_PER_SCRATCHCODE) {
goto urandom_failure;
}
goto new_scratch_code;
}
if (!quiet) {
printf(" %08d\n", scratch);
}
snprintf(strrchr(secret, '\000'), sizeof(secret) - strlen(secret),
"%08d\n", scratch);
}
close(fd);
if (!secret_fn) {
const char *home = getenv("HOME");
if (!home || *home != '/') {
fprintf(stderr, "Cannot determine home directory\n");
return 1;
}
secret_fn = malloc(strlen(home) + strlen(SECRET) + 1);
if (!secret_fn) {
perror("malloc()");
_exit(1);
}
strcat(strcpy(secret_fn, home), SECRET);
}
if (!force) {
char s[1024];
snprintf(s, sizeof s, "Do you want me to update your \"%s\" file?",
secret_fn);
if (!maybe(s)) {
exit(0);
}
}
const int size = strlen(secret_fn) + 3;
char* tmp_fn = malloc(size);
if (!tmp_fn) {
perror("malloc()");
_exit(1);
}
snprintf(tmp_fn, size, "%s~", secret_fn);
// Add optional flags.
if (use_totp) {
if (reuse == ASK_REUSE) {
maybeAddOption("Do you want to disallow multiple uses of the same "
"authentication\ntoken? This restricts you to one login "
"about every 30s, but it increases\nyour chances to "
"notice or even prevent man-in-the-middle attacks",
secret, sizeof(secret), disallow);
} else if (reuse == DISALLOW_REUSE) {
addOption(secret, sizeof(secret), disallow);
}
if (step_size) {
char s[80];
snprintf(s, sizeof s, "\" STEP_SIZE %d\n", step_size);
addOption(secret, sizeof(secret), s);
}
if (!window_size) {
maybeAddOption("By default, a new token is generated every 30 seconds by"
" the mobile app.\nIn order to compensate for possible"
" time-skew between the client and the server,\nwe allow"
" an extra token before and after the current time. This"
" allows for a\ntime skew of up to 30 seconds between"
" authentication server and client. If you\nexperience"
" problems with poor time synchronization, you can"
" increase the window\nfrom its default size of 3"
" permitted codes (one previous code, the current\ncode,"
" the next code) to 17 permitted codes (the 8 previous"
" codes, the current\ncode, and the 8 next codes)."
" This will permit for a time skew of up to 4 minutes"
"\nbetween client and server."
"\nDo you want to do so?",
secret, sizeof(secret), window);
} else {
char s[80];
// TODO: Should 3 really be the minimal window size for TOTP?
// If so, the code should not allow -w=1 here.
snprintf(s, sizeof s, "\" WINDOW_SIZE %d\n", window_size > 0 ? window_size : 3);
addOption(secret, sizeof(secret), s);
}
} else {
// Counter based.
if (!window_size) {
maybeAddOption("By default, three tokens are valid at any one time. "
"This accounts for\ngenerated-but-not-used tokens and "
"failed login attempts. In order to\ndecrease the "
"likelihood of synchronization problems, this window "
"can be\nincreased from its default size of 3 to 17. Do "
"you want to do so?",
secret, sizeof(secret), window);
} else {
char s[80];
snprintf(s, sizeof s, "\" WINDOW_SIZE %d\n", window_size > 0 ? window_size : 1);
addOption(secret, sizeof(secret), s);
}
}
if (!r_limit && !r_time) {
maybeAddOption("If the computer that you are logging into isn't hardened "
"against brute-force\nlogin attempts, you can enable "
"rate-limiting for the authentication module.\nBy default, "
"this limits attackers to no more than 3 login attempts "
"every 30s.\nDo you want to enable rate-limiting?",
secret, sizeof(secret), ratelimit);
} else if (r_limit > 0 && r_time > 0) {
char s[80];
snprintf(s, sizeof s, "\" RATE_LIMIT %d %d\n", r_limit, r_time);
addOption(secret, sizeof(secret), s);
}
fd = open(tmp_fn, O_WRONLY|O_EXCL|O_CREAT|O_NOFOLLOW|O_TRUNC, 0400);
if (fd < 0) {
fprintf(stderr, "Failed to create \"%s\" (%s)",
secret_fn, strerror(errno));
goto errout;
}
if (write(fd, secret, strlen(secret)) != (ssize_t)strlen(secret) ||
rename(tmp_fn, secret_fn)) {
perror("Failed to write new secret");
unlink(secret_fn);
goto errout;
}
free(tmp_fn);
free(secret_fn);
close(fd);
return 0;
errout:
if (fd > 0) {
close(fd);
}
free(secret_fn);
free(tmp_fn);
return 1;
}
/* ---- Emacs Variables ----
* Local Variables:
* c-basic-offset: 2
* indent-tabs-mode: nil
* End:
*/