Commit 60a5b784 authored by Nick Mathewson's avatar Nick Mathewson
Browse files

Extract the OpenSSL DH functionality to a new file.

parent 99beed15
......@@ -7,6 +7,8 @@
/**
* \file crypto_dh.c
* \brief Block of functions related with DH utilities and operations.
* over Z_p. We aren't using this for any new crypto -- EC is more
* efficient.
**/
#include "lib/crypt_ops/compat_openssl.h"
......@@ -17,495 +19,26 @@
#include "lib/log/log.h"
#include "lib/log/util_bug.h"
DISABLE_GCC_WARNING(redundant-decls)
#include <openssl/dh.h>
ENABLE_GCC_WARNING(redundant-decls)
#include <openssl/bn.h>
#include <string.h>
/** A structure to hold the first half (x, g^x) of a Diffie-Hellman handshake
* while we're waiting for the second.*/
struct crypto_dh_t {
DH *dh; /**< The openssl DH object */
};
static int tor_check_dh_key(int severity, const BIGNUM *bn);
/** Used by tortls.c: Get the DH* from a crypto_dh_t.
*/
DH *
crypto_dh_get_dh_(crypto_dh_t *dh)
{
return dh->dh;
}
/** Our DH 'g' parameter */
#define DH_GENERATOR 2
/** Shared P parameter for our circuit-crypto DH key exchanges. */
static BIGNUM *dh_param_p = NULL;
/** Shared P parameter for our TLS DH key exchanges. */
static BIGNUM *dh_param_p_tls = NULL;
/** Shared G parameter for our DH key exchanges. */
static BIGNUM *dh_param_g = NULL;
/** Validate a given set of Diffie-Hellman parameters. This is moderately
* computationally expensive (milliseconds), so should only be called when
* the DH parameters change. Returns 0 on success, * -1 on failure.
*/
static int
crypto_validate_dh_params(const BIGNUM *p, const BIGNUM *g)
{
DH *dh = NULL;
int ret = -1;
/* Copy into a temporary DH object, just so that DH_check() can be called. */
if (!(dh = DH_new()))
goto out;
#ifdef OPENSSL_1_1_API
BIGNUM *dh_p, *dh_g;
if (!(dh_p = BN_dup(p)))
goto out;
if (!(dh_g = BN_dup(g)))
goto out;
if (!DH_set0_pqg(dh, dh_p, NULL, dh_g))
goto out;
#else /* !(defined(OPENSSL_1_1_API)) */
if (!(dh->p = BN_dup(p)))
goto out;
if (!(dh->g = BN_dup(g)))
goto out;
#endif /* defined(OPENSSL_1_1_API) */
/* Perform the validation. */
int codes = 0;
if (!DH_check(dh, &codes))
goto out;
if (BN_is_word(g, DH_GENERATOR_2)) {
/* Per https://wiki.openssl.org/index.php/Diffie-Hellman_parameters
*
* OpenSSL checks the prime is congruent to 11 when g = 2; while the
* IETF's primes are congruent to 23 when g = 2.
*/
BN_ULONG residue = BN_mod_word(p, 24);
if (residue == 11 || residue == 23)
codes &= ~DH_NOT_SUITABLE_GENERATOR;
}
if (codes != 0) /* Specifics on why the params suck is irrelevant. */
goto out;
/* Things are probably not evil. */
ret = 0;
out:
if (dh)
DH_free(dh);
return ret;
}
/** Set the global Diffie-Hellman generator, used for both TLS and internal
* DH stuff.
*/
static void
crypto_set_dh_generator(void)
{
BIGNUM *generator;
int r;
if (dh_param_g)
return;
generator = BN_new();
tor_assert(generator);
r = BN_set_word(generator, DH_GENERATOR);
tor_assert(r);
dh_param_g = generator;
}
/** Set the global TLS Diffie-Hellman modulus. Use the Apache mod_ssl DH
* modulus. */
void
crypto_set_tls_dh_prime(void)
{
BIGNUM *tls_prime = NULL;
int r;
/* If the space is occupied, free the previous TLS DH prime */
if (BUG(dh_param_p_tls)) {
/* LCOV_EXCL_START
*
* We shouldn't be calling this twice.
*/
BN_clear_free(dh_param_p_tls);
dh_param_p_tls = NULL;
/* LCOV_EXCL_STOP */
}
tls_prime = BN_new();
tor_assert(tls_prime);
/* This is the 1024-bit safe prime that Apache uses for its DH stuff; see
* modules/ssl/ssl_engine_dh.c; Apache also uses a generator of 2 with this
* prime.
*/
r = BN_hex2bn(&tls_prime,
"D67DE440CBBBDC1936D693D34AFD0AD50C84D239A45F520BB88174CB98"
"BCE951849F912E639C72FB13B4B4D7177E16D55AC179BA420B2A29FE324A"
"467A635E81FF5901377BEDDCFD33168A461AAD3B72DAE8860078045B07A7"
"DBCA7874087D1510EA9FCC9DDD330507DD62DB88AEAA747DE0F4D6E2BD68"
"B0E7393E0F24218EB3");
tor_assert(r);
tor_assert(tls_prime);
dh_param_p_tls = tls_prime;
crypto_set_dh_generator();
tor_assert(0 == crypto_validate_dh_params(dh_param_p_tls, dh_param_g));
}
/** Initialize dh_param_p and dh_param_g if they are not already
* set. */
static void
init_dh_param(void)
{
BIGNUM *circuit_dh_prime;
int r;
if (BUG(dh_param_p && dh_param_g))
return; // LCOV_EXCL_LINE This function isn't supposed to be called twice.
circuit_dh_prime = BN_new();
tor_assert(circuit_dh_prime);
/* This is from rfc2409, section 6.2. It's a safe prime, and
supposedly it equals:
2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
*/
r = BN_hex2bn(&circuit_dh_prime,
"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E08"
"8A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B"
"302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9"
"A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE6"
"49286651ECE65381FFFFFFFFFFFFFFFF");
tor_assert(r);
/* Set the new values as the global DH parameters. */
dh_param_p = circuit_dh_prime;
crypto_set_dh_generator();
tor_assert(0 == crypto_validate_dh_params(dh_param_p, dh_param_g));
if (!dh_param_p_tls) {
crypto_set_tls_dh_prime();
}
}
/** Number of bits to use when choosing the x or y value in a Diffie-Hellman
* handshake. Since we exponentiate by this value, choosing a smaller one
* lets our handhake go faster.
*/
#define DH_PRIVATE_KEY_BITS 320
/** Allocate and return a new DH object for a key exchange. Returns NULL on
* failure.
*/
crypto_dh_t *
crypto_dh_new(int dh_type)
{
crypto_dh_t *res = tor_malloc_zero(sizeof(crypto_dh_t));
tor_assert(dh_type == DH_TYPE_CIRCUIT || dh_type == DH_TYPE_TLS ||
dh_type == DH_TYPE_REND);
if (!dh_param_p)
init_dh_param();
if (!(res->dh = DH_new()))
goto err;
#ifdef OPENSSL_1_1_API
BIGNUM *dh_p = NULL, *dh_g = NULL;
if (dh_type == DH_TYPE_TLS) {
dh_p = BN_dup(dh_param_p_tls);
} else {
dh_p = BN_dup(dh_param_p);
}
if (!dh_p)
goto err;
dh_g = BN_dup(dh_param_g);
if (!dh_g) {
BN_free(dh_p);
goto err;
}
if (!DH_set0_pqg(res->dh, dh_p, NULL, dh_g)) {
goto err;
}
if (!DH_set_length(res->dh, DH_PRIVATE_KEY_BITS))
goto err;
#else /* !(defined(OPENSSL_1_1_API)) */
if (dh_type == DH_TYPE_TLS) {
if (!(res->dh->p = BN_dup(dh_param_p_tls)))
goto err;
} else {
if (!(res->dh->p = BN_dup(dh_param_p)))
goto err;
}
if (!(res->dh->g = BN_dup(dh_param_g)))
goto err;
res->dh->length = DH_PRIVATE_KEY_BITS;
#endif /* defined(OPENSSL_1_1_API) */
return res;
/* LCOV_EXCL_START
* This error condition is only reached when an allocation fails */
err:
crypto_openssl_log_errors(LOG_WARN, "creating DH object");
if (res->dh) DH_free(res->dh); /* frees p and g too */
tor_free(res);
return NULL;
/* LCOV_EXCL_STOP */
}
/** Return a copy of <b>dh</b>, sharing its internal state. */
crypto_dh_t *
crypto_dh_dup(const crypto_dh_t *dh)
{
crypto_dh_t *dh_new = tor_malloc_zero(sizeof(crypto_dh_t));
tor_assert(dh);
tor_assert(dh->dh);
dh_new->dh = dh->dh;
DH_up_ref(dh->dh);
return dh_new;
}
/** Return the length of the DH key in <b>dh</b>, in bytes.
*/
int
crypto_dh_get_bytes(crypto_dh_t *dh)
{
tor_assert(dh);
return DH_size(dh->dh);
}
/** Generate \<x,g^x\> for our part of the key exchange. Return 0 on
* success, -1 on failure.
*/
int
crypto_dh_generate_public(crypto_dh_t *dh)
{
#ifndef OPENSSL_1_1_API
again:
#endif
if (!DH_generate_key(dh->dh)) {
/* LCOV_EXCL_START
* To test this we would need some way to tell openssl to break DH. */
crypto_openssl_log_errors(LOG_WARN, "generating DH key");
return -1;
/* LCOV_EXCL_STOP */
}
#ifdef OPENSSL_1_1_API
/* OpenSSL 1.1.x doesn't appear to let you regenerate a DH key, without
* recreating the DH object. I have no idea what sort of aliasing madness
* can occur here, so do the check, and just bail on failure.
*/
const BIGNUM *pub_key, *priv_key;
DH_get0_key(dh->dh, &pub_key, &priv_key);
if (tor_check_dh_key(LOG_WARN, pub_key)<0) {
log_warn(LD_CRYPTO, "Weird! Our own DH key was invalid. I guess once-in-"
"the-universe chances really do happen. Treating as a failure.");
return -1;
}
#else /* !(defined(OPENSSL_1_1_API)) */
if (tor_check_dh_key(LOG_WARN, dh->dh->pub_key)<0) {
/* LCOV_EXCL_START
* If this happens, then openssl's DH implementation is busted. */
log_warn(LD_CRYPTO, "Weird! Our own DH key was invalid. I guess once-in-"
"the-universe chances really do happen. Trying again.");
/* Free and clear the keys, so OpenSSL will actually try again. */
BN_clear_free(dh->dh->pub_key);
BN_clear_free(dh->dh->priv_key);
dh->dh->pub_key = dh->dh->priv_key = NULL;
goto again;
/* LCOV_EXCL_STOP */
}
#endif /* defined(OPENSSL_1_1_API) */
return 0;
}
/** Generate g^x as necessary, and write the g^x for the key exchange
* as a <b>pubkey_len</b>-byte value into <b>pubkey</b>. Return 0 on
* success, -1 on failure. <b>pubkey_len</b> must be \>= DH1024_KEY_LEN.
*/
int
crypto_dh_get_public(crypto_dh_t *dh, char *pubkey, size_t pubkey_len)
{
int bytes;
tor_assert(dh);
const BIGNUM *dh_pub;
#ifdef OPENSSL_1_1_API
const BIGNUM *dh_priv;
DH_get0_key(dh->dh, &dh_pub, &dh_priv);
#else
dh_pub = dh->dh->pub_key;
#endif /* defined(OPENSSL_1_1_API) */
if (!dh_pub) {
if (crypto_dh_generate_public(dh)<0)
return -1;
else {
#ifdef OPENSSL_1_1_API
DH_get0_key(dh->dh, &dh_pub, &dh_priv);
#else
dh_pub = dh->dh->pub_key;
#endif
}
}
tor_assert(dh_pub);
bytes = BN_num_bytes(dh_pub);
tor_assert(bytes >= 0);
if (pubkey_len < (size_t)bytes) {
log_warn(LD_CRYPTO,
"Weird! pubkey_len (%d) was smaller than DH1024_KEY_LEN (%d)",
(int) pubkey_len, bytes);
return -1;
}
memset(pubkey, 0, pubkey_len);
BN_bn2bin(dh_pub, (unsigned char*)(pubkey+(pubkey_len-bytes)));
return 0;
}
/** Check for bad Diffie-Hellman public keys (g^x). Return 0 if the key is
* okay (in the subgroup [2,p-2]), or -1 if it's bad.
* See http://www.cl.cam.ac.uk/ftp/users/rja14/psandqs.ps.gz for some tips.
*/
static int
tor_check_dh_key(int severity, const BIGNUM *bn)
{
BIGNUM *x;
char *s;
tor_assert(bn);
x = BN_new();
tor_assert(x);
if (BUG(!dh_param_p))
init_dh_param(); //LCOV_EXCL_LINE we already checked whether we did this.
BN_set_word(x, 1);
if (BN_cmp(bn,x)<=0) {
log_fn(severity, LD_CRYPTO, "DH key must be at least 2.");
goto err;
}
BN_copy(x,dh_param_p);
BN_sub_word(x, 1);
if (BN_cmp(bn,x)>=0) {
log_fn(severity, LD_CRYPTO, "DH key must be at most p-2.");
goto err;
}
BN_clear_free(x);
return 0;
err:
BN_clear_free(x);
s = BN_bn2hex(bn);
log_fn(severity, LD_CRYPTO, "Rejecting insecure DH key [%s]", s);
OPENSSL_free(s);
return -1;
}
/** Given a DH key exchange object, and our peer's value of g^y (as a
* <b>pubkey_len</b>-byte value in <b>pubkey</b>) generate
* <b>secret_bytes_out</b> bytes of shared key material and write them
* to <b>secret_out</b>. Return the number of bytes generated on success,
* or -1 on failure.
*
* (We generate key material by computing
* SHA1( g^xy || "\x00" ) || SHA1( g^xy || "\x01" ) || ...
* where || is concatenation.)
*/
ssize_t
crypto_dh_compute_secret(int severity, crypto_dh_t *dh,
const char *pubkey, size_t pubkey_len,
char *secret_out, size_t secret_bytes_out)
{
char *secret_tmp = NULL;
BIGNUM *pubkey_bn = NULL;
size_t secret_len=0, secret_tmp_len=0;
int result=0;
tor_assert(dh);
tor_assert(secret_bytes_out/DIGEST_LEN <= 255);
tor_assert(pubkey_len < INT_MAX);
if (!(pubkey_bn = BN_bin2bn((const unsigned char*)pubkey,
(int)pubkey_len, NULL)))
goto error;
if (tor_check_dh_key(severity, pubkey_bn)<0) {
/* Check for invalid public keys. */
log_fn(severity, LD_CRYPTO,"Rejected invalid g^x");
goto error;
}
secret_tmp_len = crypto_dh_get_bytes(dh);
secret_tmp = tor_malloc(secret_tmp_len);
result = DH_compute_key((unsigned char*)secret_tmp, pubkey_bn, dh->dh);
if (result < 0) {
log_warn(LD_CRYPTO,"DH_compute_key() failed.");
goto error;
}
secret_len = result;
if (crypto_expand_key_material_TAP((uint8_t*)secret_tmp, secret_len,
(uint8_t*)secret_out, secret_bytes_out)<0)
goto error;
secret_len = secret_bytes_out;
goto done;
error:
result = -1;
done:
crypto_openssl_log_errors(LOG_WARN, "completing DH handshake");
if (pubkey_bn)
BN_clear_free(pubkey_bn);
if (secret_tmp) {
memwipe(secret_tmp, 0, secret_tmp_len);
tor_free(secret_tmp);
}
if (result < 0)
return result;
else
return secret_len;
}
/** Free a DH key exchange object.
*/
void
crypto_dh_free_(crypto_dh_t *dh)
{
if (!dh)
return;
tor_assert(dh->dh);
DH_free(dh->dh);
tor_free(dh);
}
void
crypto_dh_free_all(void)
{
if (dh_param_p)
BN_clear_free(dh_param_p);
if (dh_param_p_tls)
BN_clear_free(dh_param_p_tls);
if (dh_param_g)
BN_clear_free(dh_param_g);
dh_param_p = dh_param_p_tls = dh_param_g = NULL;
}
const unsigned DH_GENERATOR = 2;
/** This is the 1024-bit safe prime that Apache uses for its DH stuff; see
* modules/ssl/ssl_engine_dh.c; Apache also uses a generator of 2 with this
* prime.
*/
const char TLS_DH_PRIME[] =
"D67DE440CBBBDC1936D693D34AFD0AD50C84D239A45F520BB88174CB98"
"BCE951849F912E639C72FB13B4B4D7177E16D55AC179BA420B2A29FE324A"
"467A635E81FF5901377BEDDCFD33168A461AAD3B72DAE8860078045B07A7"
"DBCA7874087D1510EA9FCC9DDD330507DD62DB88AEAA747DE0F4D6E2BD68"
"B0E7393E0F24218EB3";
/**
* This is from rfc2409, section 6.2. It's a safe prime, and
* supposedly it equals:
* 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
*/
const char OAKLEY_PRIME_2[] =
"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E08"
"8A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B"
"302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9"
"A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE6"
"49286651ECE65381FFFFFFFFFFFFFFFF";
......@@ -19,6 +19,10 @@
typedef struct crypto_dh_t crypto_dh_t;
extern const unsigned DH_GENERATOR;
extern const char TLS_DH_PRIME[];
extern const char OAKLEY_PRIME_2[];
/* Key negotiation */
#define DH_TYPE_CIRCUIT 1
#define DH_TYPE_REND 2
......
/* Copyright (c) 2001, Matej Pfajfar.
* Copyright (c) 2001-2004, Roger Dingledine.
* Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
* Copyright (c) 2007-2018, The Tor Project, Inc. */
/* See LICENSE for licensing information */
/**
* \file crypto_dh_openssl.c
* \brief Implement Tor's Z_p diffie-hellman stuff for OpenSSL.
**/
#include "lib/crypt_ops/compat_openssl.h"
#include "lib/crypt_ops/crypto_dh.h"
#include "lib/crypt_ops/crypto_digest.h"
#include "lib/crypt_ops/crypto_hkdf.h"
#include "lib/crypt_ops/crypto_util.h"
#include "lib/log/log.h"
#include "lib/log/util_bug.h"
DISABLE_GCC_WARNING(redundant-decls)
#include <openssl/dh.h>
ENABLE_GCC_WARNING(redundant-decls)
#include <openssl/bn.h>
#include <string.h>
static int tor_check_dh_key(int severity, const BIGNUM *bn);
/** A structure to hold the first half (x, g^x) of a Diffie-Hellman handshake
* while we're waiting for the second.*/
struct crypto_dh_t {
DH *dh; /**< The openssl DH object */
};
/** Used by tortls.c: Get the DH* from a crypto_dh_t.
*/
DH *
crypto_dh_get_dh_(crypto_dh_t *dh)
{
return dh->dh;
}
/** Shared P parameter for our circuit-crypto DH key exchanges. */
static BIGNUM *dh_param_p = NULL;
/** Shared P parameter for our TLS DH key exchanges. */
static BIGNUM *dh_param_p_tls = NULL;
/** Shared G parameter for our DH key exchanges. */
static BIGNUM *dh_param_g = NULL;
/** Validate a given set of Diffie-Hellman parameters. This is moderately
* computationally expensive (milliseconds), so should only be called when
* the DH parameters change. Returns 0 on success, * -1 on failure.
*/
static int
crypto_validate_dh_params(const BIGNUM *p, const BIGNUM *g)
{
DH *dh = NULL;
int ret = -1;
/* Copy into a temporary DH object, just so that DH_check() can be called. */
if (!(dh = DH_new()))
goto out;
#ifdef OPENSSL_1_1_API
BIGNUM *dh_p, *dh_g;
if (!(dh_p = BN_dup(p)))
goto out;
if (!(dh_g = BN_dup(g)))
goto out;
if (!DH_set0_pqg(dh, dh_p, NULL, dh_g))
goto out;
#else /* !(defined(OPENSSL_1_1_API)) */
if (!(dh->p = BN_dup(p)))
goto out;
if (!(dh->g = BN_dup(g)))
goto out;
#endif /* defined(OPENSSL_1_1_API) */
/* Perform the validation. */
int codes = 0;
if (!DH_check(dh, &codes))
goto out;
if (BN_is_word(g, DH_GENERATOR_2)) {
/* Per https://wiki.openssl.org/index.php/Diffie-Hellman_parameters
*
* OpenSSL checks the prime is congruent to 11 when g = 2; while the
* IETF's primes are congruent to 23 when g = 2.