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vtun/auth.c
Frank Denis 91f50be917 Check crypto_scalarmult() return value
2015-11-17 01:28:16 +01:00

481 lines
16 KiB
C
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/*
* Key exchange
*
* Client <-> Server
*
* -> "CKEY " || host || " " || ts || Cpk || Hk(ts || Cpk)
* <- "SKEY " || Spk || Hk(Spk || Hk(ts || Cpk))
* -> "CACK " || Hk("CACK" || Hk(Spk || Hk(ts || Cpk)))
* <- "FLAGS " || flags || " " || Hk(flags || Hk("CACK" || Hk(Spk || Hk(ts || Cpk))))
*
* session_key = Hk(DH)
*
* ts: current timestamp, 4 big-endian bytes
* (Cpk, Csk): client public/secret ephemeral key pair
* (Spk, Ssk): server public/secret ephemeral key pair
* Hk: keyed hash function, key derived from the PSK
*
* DH function: Curve25519
* Keyed hash function: Blake2b
* KDF: Scrypt
*/
#include "config.h"
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <syslog.h>
#include <time.h>
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_NETINET_TCP_H
#include <netinet/tcp.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif
#include <sodium.h>
#include "vtun.h"
#include "lib.h"
#include "lock.h"
#include "auth.h"
static int derive_key(struct vtun_host *host)
{
unsigned char salt[crypto_pwhash_scryptsalsa208sha256_SALTBYTES];
int ret = -1;
size_t bin_len;
if (host->akey != NULL) {
return 0;
}
if ((host->akey = sodium_malloc(crypto_generichash_KEYBYTES)) == NULL) {
return -1;
}
memset(salt, 0xd1, sizeof salt);
if (crypto_pwhash_scryptsalsa208sha256(host->akey, HOST_KEYBYTES,
host->passwd, strlen(host->passwd), salt,
crypto_pwhash_scryptsalsa208sha256_OPSLIMIT_INTERACTIVE,
crypto_pwhash_scryptsalsa208sha256_MEMLIMIT_INTERACTIVE) == 0) {
ret = 0;
}
sodium_memzero(host->passwd, strlen(host->passwd));
free(host->passwd);
host->passwd = NULL;
vtun_syslog(LOG_DEBUG, "Key ready for host [%s]", host->host);
return ret;
}
/*
* Functions to convert binary flags to character string.
* string format: <CS64>
* C - compression, S - speed for shaper and so on.
*/
static char *bf2cf(struct vtun_host *host)
{
static char str[32], * ptr = str;
*(ptr++) = '<';
switch (host->flags & VTUN_PROT_MASK) {
case VTUN_TCP:
*(ptr++) = 'T';
break;
case VTUN_UDP:
*(ptr++) = 'U';
break;
}
switch (host->flags & VTUN_TYPE_MASK) {
case VTUN_TTY:
*(ptr++) = 't';
break;
case VTUN_PIPE:
*(ptr++) = 'p';
break;
case VTUN_ETHER:
*(ptr++) = 'e';
break;
case VTUN_TUN:
*(ptr++) = 'u';
break;
}
if ((host->flags & VTUN_SHAPE) /* && host->spd_in */)
ptr += sprintf(ptr, "S%d", host->spd_in);
if (host->flags & VTUN_ZLIB)
ptr += sprintf(ptr, "C%d", host->zlevel);
if (host->flags & VTUN_LZO)
ptr += sprintf(ptr, "L%d", host->zlevel);
if (host->flags & VTUN_KEEP_ALIVE)
*(ptr++) = 'K';
if (host->flags & VTUN_ENCRYPT) {
ptr += sprintf(ptr, "E%d", host->cipher);
}
strcat(ptr, ">");
return str;
}
/*
* return 0 on success, otherwise -1
* Example: FLAGS: <TuE1>
*/
static int cf2bf(char *str, struct vtun_host *host)
{
char *ptr, *p;
int s;
if (strlen(str) >= 32) {
return -1;
}
if ((ptr = strchr(str, '<'))) {
vtun_syslog(LOG_DEBUG, "Remote Server sends %s.", ptr);
ptr++;
while (*ptr) {
switch (*ptr++) {
case 't':
host->flags |= VTUN_TTY;
break;
case 'p':
host->flags |= VTUN_PIPE;
break;
case 'e':
host->flags |= VTUN_ETHER;
break;
case 'u':
host->flags |= VTUN_TUN;
break;
case 'U':
host->flags &= ~VTUN_PROT_MASK;
host->flags |= VTUN_UDP;
break;
case 'T':
host->flags &= ~VTUN_PROT_MASK;
host->flags |= VTUN_TCP;
break;
case 'K':
host->flags |= VTUN_KEEP_ALIVE;
break;
case 'C':
if ((s = strtol(ptr, &p, 10)) == ERANGE || ptr == p) {
return -1;
}
host->flags |= VTUN_ZLIB;
host->zlevel = s;
ptr = p;
break;
case 'L':
if ((s = strtol(ptr, &p, 10)) == ERANGE || ptr == p) {
return -1;
}
host->flags |= VTUN_LZO;
host->zlevel = s;
ptr = p;
break;
case 'E':
/* new form is 'E10', old form is 'E', so remove the
ptr==p check */
if ((s = strtol(ptr, &p, 10)) == ERANGE) {
vtun_syslog(LOG_ERR, "Garbled encryption method. Bailing out.");
return -1;
}
host->flags |= VTUN_ENCRYPT;
host->cipher = s;
ptr = p;
break;
case 'S':
if ((s = strtol(ptr, &p, 10)) == ERANGE || ptr == p) {
return -1;
}
if (s > 0) {
host->flags |= VTUN_SHAPE;
host->spd_out = s;
}
ptr = p;
break;
case 'F':
/* reserved for Feature transmit */
break;
case '>':
return 0;
default:
return -1;
}
}
}
return -1;
}
/* Authentication (Server side) */
struct vtun_host *auth_server(int fd)
{
char buf[VTUN_MESG_SIZE], *str1, *str2, *str3;
unsigned char cack[crypto_generichash_BYTES];
unsigned char client_pk[crypto_scalarmult_BYTES];
unsigned char server_pk[crypto_scalarmult_BYTES];
unsigned char server_sk[crypto_scalarmult_SCALARBYTES];
unsigned char ckey[4 + crypto_scalarmult_BYTES + crypto_generichash_BYTES];
unsigned char dhkey[crypto_scalarmult_BYTES];
unsigned char skey[crypto_scalarmult_BYTES + crypto_generichash_BYTES];
char skey_hex[2 * (crypto_scalarmult_BYTES + crypto_generichash_BYTES) + 1];
unsigned char hash[crypto_generichash_BYTES];
unsigned char flhash[crypto_generichash_BYTES];
char flhash_hex[2 * crypto_generichash_BYTES + 1];
struct vtun_host *host = NULL;
char *flags;
char *host_name = NULL;
crypto_generichash_state st;
time_t client_now;
size_t bin_len;
int stage;
int success = 0;
set_title("authentication");
print_p(fd, "VTUN server ver %s\n", VTUN_VER);
stage = ST_STEP2;
while (readn_t(fd, buf, VTUN_MESG_SIZE, vtun.timeout) > 0) {
buf[sizeof(buf) - 1] = '\0';
strtok(buf, "\r\n");
if (!(str1 = strtok(buf, " :"))) {
break;
}
if (!(str2 = strtok(NULL, " :"))) {
break;
}
switch (stage) {
case ST_STEP2:
if (!strcmp(str1, "CKEY")) {
if (!(str3 = strtok(NULL, " \t"))) {
break;
}
sodium_hex2bin(ckey, sizeof ckey, str3, strlen(str3), "", &bin_len, NULL);
if (bin_len != sizeof ckey) {
break;
}
client_now = ((time_t) ckey[0]) << 24 | ((time_t) ckey[1]) << 16 |
((time_t) ckey[2]) << 9 | ((time_t) ckey[3]);
(void) client_now;
host_name = str2;
if ((host = find_host(host_name)) == NULL || derive_key(host) != 0) {
break;
}
crypto_generichash(hash, sizeof hash,
ckey, 4 + crypto_scalarmult_BYTES,
host->akey, crypto_generichash_KEYBYTES);
if (sodium_memcmp(hash, ckey + 4 + crypto_scalarmult_BYTES, sizeof hash) != 0) {
break;
}
memcpy(client_pk, ckey + 4, sizeof client_pk);
randombytes_buf(server_sk, crypto_scalarmult_SCALARBYTES);
crypto_scalarmult_base(server_pk, server_sk);
memcpy(skey, server_pk, sizeof server_pk);
memcpy(skey + crypto_scalarmult_BYTES, hash, sizeof hash);
crypto_generichash(skey + crypto_scalarmult_BYTES, crypto_scalarmult_BYTES,
skey, sizeof skey,
host->akey, crypto_generichash_KEYBYTES);
sodium_bin2hex(skey_hex, sizeof skey_hex, skey, sizeof skey);
print_p(fd, "SKEY: %s\n", skey_hex);
stage = ST_STEP3;
continue;
}
break;
case ST_STEP3:
if (!strcmp(str1, "CACK")) {
sodium_hex2bin(cack, sizeof cack, str2, strlen(str2), "", &bin_len, NULL);
if (bin_len != sizeof cack) {
break;
}
crypto_generichash_init(&st, host->akey, crypto_generichash_KEYBYTES,
crypto_generichash_BYTES);
crypto_generichash_update(&st, (const unsigned char *) "CACK", 4);
crypto_generichash_update(&st, skey, sizeof skey);
crypto_generichash_final(&st, hash, sizeof hash);
if (sodium_memcmp(hash, cack, sizeof hash) != 0) {
break;
}
/* Lock host */
if (lock_host(host) < 0) {
/* Multiple connections are denied */
host = NULL;
break;
}
flags = bf2cf(host);
crypto_generichash_init(&st, host->akey, crypto_generichash_KEYBYTES,
crypto_generichash_BYTES);
crypto_generichash_update(&st, (const unsigned char *) flags, strlen(flags));
crypto_generichash_update(&st, cack, sizeof cack);
crypto_generichash_final(&st, flhash, sizeof flhash);
sodium_bin2hex(flhash_hex, sizeof flhash_hex, flhash, sizeof flhash);
print_p(fd, "FLAGS: %s %s\n", flags, flhash_hex);
if (crypto_scalarmult(dhkey, server_sk, client_pk) != 0) {
break;
}
sodium_memzero(server_sk, sizeof server_sk);
if ((host->key = sodium_malloc(HOST_KEYBYTES)) == NULL) {
abort();
}
crypto_generichash(host->key, HOST_KEYBYTES, dhkey, sizeof dhkey,
host->akey, crypto_generichash_KEYBYTES);
sodium_memzero(dhkey, sizeof dhkey);
success = 1;
}
break;
}
break;
}
if (success == 0) {
print_p(fd, "ERR\n");
host = NULL;
}
return host;
}
/* Authentication (Client side) */
int auth_client(int fd, struct vtun_host *host)
{
char buf[VTUN_MESG_SIZE], *str1, *str2, *str3;
unsigned char cack[crypto_generichash_BYTES];
char cack_hex[2 * crypto_generichash_BYTES + 1];
unsigned char flhash[crypto_generichash_BYTES];
unsigned char hash[crypto_generichash_BYTES];
unsigned char client_pk[crypto_scalarmult_BYTES];
unsigned char client_sk[crypto_scalarmult_SCALARBYTES];
unsigned char server_pk[crypto_scalarmult_BYTES];
unsigned char dhkey[crypto_scalarmult_BYTES];
unsigned char ckey[4 + crypto_scalarmult_BYTES + crypto_generichash_BYTES];
char ckey_hex[2 * (4 + crypto_scalarmult_BYTES + crypto_generichash_BYTES) + 1];
unsigned char skey[crypto_scalarmult_BYTES + crypto_generichash_BYTES];
crypto_generichash_state st;
time_t now;
size_t bin_len;
int stage;
int success = 0;
stage = ST_INIT;
if (derive_key(host) != 0) {
return 0;
}
while (readn_t(fd, buf, VTUN_MESG_SIZE, vtun.timeout) > 0) {
buf[sizeof(buf) - 1] = '\0';
strtok(buf, "\r\n");
if (!(str1 = strtok(buf, " :"))) {
break;
}
if (!(str2 = strtok(NULL, " :"))) {
break;
}
switch (stage) {
case ST_INIT:
if (!strcmp(str1, "VTUN")) {
now = time(NULL);
randombytes_buf(client_sk, crypto_scalarmult_SCALARBYTES);
crypto_scalarmult_base(client_pk, client_sk);
ckey[0] = (unsigned char)(now >> 24);
ckey[1] = (unsigned char)(now >> 16);
ckey[2] = (unsigned char)(now >> 8);
ckey[3] = (unsigned char)(now);
memcpy(ckey + 4, client_pk, crypto_scalarmult_BYTES);
crypto_generichash(ckey + 4 + crypto_scalarmult_BYTES, crypto_generichash_BYTES,
ckey, 4 + crypto_scalarmult_BYTES,
host->akey, crypto_generichash_KEYBYTES);
sodium_bin2hex(ckey_hex, sizeof ckey_hex, ckey, sizeof ckey);
stage = ST_STEP2;
print_p(fd, "CKEY: %s %s\n", host->host, ckey_hex);
continue;
}
break;
case ST_STEP2:
if (!strcmp(str1, "SKEY")) {
sodium_hex2bin(skey, sizeof skey, str2, strlen(str2), "", &bin_len, NULL);
if (bin_len != sizeof skey) {
break;
}
crypto_generichash_init(&st, host->akey, crypto_generichash_KEYBYTES,
crypto_generichash_BYTES);
crypto_generichash_update(&st, skey, crypto_scalarmult_BYTES);
crypto_generichash_update(&st, ckey + 4 + crypto_scalarmult_BYTES,
crypto_generichash_BYTES);
crypto_generichash_final(&st, hash, sizeof hash);
if (sodium_memcmp(hash, skey + crypto_scalarmult_BYTES, sizeof hash) != 0) {
break;
}
memcpy(server_pk, skey, sizeof server_pk);
crypto_generichash_init(&st, host->akey, crypto_generichash_KEYBYTES,
crypto_generichash_BYTES);
crypto_generichash_update(&st, (const unsigned char *) "CACK", 4);
crypto_generichash_update(&st, skey, sizeof skey);
crypto_generichash_final(&st, cack, sizeof cack);
sodium_bin2hex(cack_hex, sizeof cack_hex, cack, sizeof cack);
print_p(fd, "CACK: %s\n", cack_hex);
stage = ST_STEP3;
continue;
}
break;
case ST_STEP3:
if (!strcmp(str1, "FLAGS")) {
if (!(str3 = strtok(NULL, " \t"))) {
break;
}
sodium_hex2bin(flhash, sizeof flhash, str3, strlen(str3), "", &bin_len, NULL);
if (bin_len != sizeof flhash) {
break;
}
if (cf2bf(str2, host) != 0) {
break;
}
crypto_generichash_init(&st, host->akey, crypto_generichash_KEYBYTES,
crypto_generichash_BYTES);
crypto_generichash_update(&st, (const unsigned char *) str2, strlen(str2));
crypto_generichash_update(&st, cack, sizeof cack);
crypto_generichash_final(&st, hash, sizeof hash);
if (sodium_memcmp(hash, flhash, sizeof hash) != 0) {
break;
}
if (crypto_scalarmult(dhkey, client_sk, server_pk) != 0) {
break;
}
sodium_memzero(client_sk, sizeof client_sk);
if ((host->key = sodium_malloc(HOST_KEYBYTES)) == NULL) {
abort();
}
crypto_generichash(host->key, HOST_KEYBYTES, dhkey, sizeof dhkey,
host->akey, crypto_generichash_KEYBYTES);
sodium_memzero(dhkey, sizeof dhkey);
success = 1;
}
break;
}
break;
}
return success;
}
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