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WireGuard: implement peer identification based on MAC1 

Using long-term static public keys, it is possible to identify the
recipient of a handshake message. Add a new UAT where such keys can be
configured. Allow private keys to be configured as well since this
enables decryption of the Initiation handshake message.

Bug: 15011
Change-Id: I0d4df046824eac6c333e0df75f69f73d10ed8e5e
Reviewed-on: https://code.wireshark.org/review/28988
Reviewed-by: Anders Broman <a.broman58@gmail.com>
This commit is contained in:
Peter Wu 2018-06-22 19:36:11 +02:00 committed by Anders Broman
parent d7187e0b1b
commit cf9f1cac07
3 changed files with 422 additions and 0 deletions
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369
epan/dissectors/packet-wireguard.c
View File

@ -19,6 +19,14 @@
#include <epan/expert.h>
#include <epan/prefs.h>
#include <epan/proto_data.h>
#include <epan/uat.h>
#include <wsutil/wsgcrypt.h>
#include <wsutil/curve25519.h>
#if GCRYPT_VERSION_NUMBER >= 0x010800 /* 1.8.0 */
/* Decryption requires Curve25519, ChaCha20-Poly1305 (1.7) and Blake2s (1.8). */
#define WG_DECRYPTION_SUPPORTED
#endif
void proto_reg_handoff_wg(void);
void proto_register_wg(void);
@ -41,8 +49,11 @@ static int hf_wg_encrypted_packet = -1;
static int hf_wg_stream = -1;
static int hf_wg_response_in = -1;
static int hf_wg_response_to = -1;
static int hf_wg_receiver_pubkey = -1;
static int hf_wg_receiver_pubkey_known_privkey = -1;
static gint ett_wg = -1;
static gint ett_key_info = -1;
static expert_field ei_wg_bad_packet_length = EI_INIT;
static expert_field ei_wg_keepalive = EI_INIT;
@ -66,6 +77,50 @@ static const value_string wg_type_names[] = {
{ 0x00, NULL }
};
#ifdef WG_DECRYPTION_SUPPORTED
/* Decryption types. {{{ */
/*
* Most operations operate on 32 byte units (keys and hash output).
*/
typedef struct {
#define WG_KEY_LEN 32
guchar data[WG_KEY_LEN];
} wg_qqword;
/*
* Static key with the MAC1 key pre-computed and an optional private key.
*/
typedef struct wg_skey {
wg_qqword pub_key;
wg_qqword mac1_key;
wg_qqword priv_key; /* Optional, set to all zeroes if missing. */
} wg_skey_t;
/*
* Set of (long-term) static keys (for guessing the peer based on MAC1).
* Maps the public key to the "wg_skey_t" structure.
* Keys are populated from the UAT and key log file.
*/
static GHashTable *wg_static_keys;
/* UAT adapter for populating wg_static_keys. */
enum { WG_KEY_UAT_PUBLIC, WG_KEY_UAT_PRIVATE };
static const value_string wg_key_uat_type_vals[] = {
{ WG_KEY_UAT_PUBLIC, "Public" },
{ WG_KEY_UAT_PRIVATE, "Private" },
{ 0, NULL }
};
typedef struct {
guint key_type; /* See "wg_key_uat_type_vals". */
char *key;
} wg_key_uat_record_t;
static wg_key_uat_record_t *wg_key_records;
static guint num_wg_key_records;
/* Decryption types. }}} */
#endif /* WG_DECRYPTION_SUPPORTED */
/*
* Information required to process and link messages as required on the first
* sequential pass. After that it can be erased.
@ -102,6 +157,206 @@ static wmem_map_t *sessions;
static guint32 wg_session_count;
#ifdef WG_DECRYPTION_SUPPORTED
/* Key conversion routines. {{{ */
/* Import external random data as private key. */
static void
set_private_key(wg_qqword *privkey, const wg_qqword *inkey)
{
// The 254th bit of a Curve25519 secret will always be set in calculations,
// use this property to recognize whether a private key is set.
*privkey = *inkey;
privkey->data[31] |= 64;
}
/* Whether a private key is initialized (see set_private_key). */
static inline gboolean
has_private_key(const wg_qqword *secret)
{
return !!(secret->data[31] & 64);
}
/**
* Compute the Curve25519 public key from a private key.
*/
static void
priv_to_pub(wg_qqword *pub, const wg_qqword *priv)
{
int r = crypto_scalarmult_curve25519_base(pub->data, priv->data);
/* The computation should always be possible. */
DISSECTOR_ASSERT(r == 0);
}
/*
* Returns the string representation (base64) of a public key.
* The returned value is allocated with wmem_packet_scope.
*/
static const char *
pubkey_to_string(const wg_qqword *pubkey)
{
gchar *str = g_base64_encode(pubkey->data, WG_KEY_LEN);
gchar *ret = wmem_strdup(wmem_packet_scope(), str);
g_free(str);
return ret;
}
static gboolean
decode_base64_key(wg_qqword *out, const char *str)
{
gsize out_len;
gchar tmp[45];
if (strlen(str) + 1 != sizeof(tmp)) {
return FALSE;
}
memcpy(tmp, str, sizeof(tmp));
g_base64_decode_inplace(tmp, &out_len);
if (out_len != WG_KEY_LEN) {
return FALSE;
}
memcpy(out->data, tmp, WG_KEY_LEN);
return TRUE;
}
/* Key conversion routines. }}} */
static gboolean
wg_pubkey_equal(gconstpointer v1, gconstpointer v2)
{
const wg_qqword *pubkey1 = (const wg_qqword *)v1;
const wg_qqword *pubkey2 = (const wg_qqword *)v2;
return !memcmp(pubkey1->data, pubkey2->data, WG_KEY_LEN);
}
/* Protocol-specific crypto routines. {{{ */
/**
* Computes MAC1. Caller must ensure that GCRY_MD_BLAKE2S_256 is available.
*/
static void
wg_mac1_key(const wg_qqword *static_public, wg_qqword *mac_key_out)
{
gcry_md_hd_t hd;
if (gcry_md_open(&hd, GCRY_MD_BLAKE2S_256, 0) == 0) {
const char wg_label_mac1[] = "mac1----";
gcry_md_write(hd, wg_label_mac1, strlen(wg_label_mac1));
gcry_md_write(hd, static_public->data, sizeof(wg_qqword));
memcpy(mac_key_out->data, gcry_md_read(hd, 0), sizeof(wg_qqword));
gcry_md_close(hd);
return;
}
// caller should have checked this.
DISSECTOR_ASSERT_NOT_REACHED();
}
/*
* Verify that MAC(mac_key, data) matches "mac_output".
*/
static gboolean
wg_mac_verify(const wg_qqword *mac_key,
const guchar *data, guint data_len, const guint8 mac_output[16])
{
gboolean ok = FALSE;
gcry_md_hd_t hd;
if (gcry_md_open(&hd, GCRY_MD_BLAKE2S_128, 0) == 0) {
gcry_error_t r;
// not documented by Libgcrypt, but required for keyed blake2s
r = gcry_md_setkey(hd, mac_key->data, WG_KEY_LEN);
DISSECTOR_ASSERT(r == 0);
gcry_md_write(hd, data, data_len);
ok = memcmp(mac_output, gcry_md_read(hd, 0), 16) == 0;
gcry_md_close(hd);
} else {
// caller should have checked this.
DISSECTOR_ASSERT_NOT_REACHED();
}
return ok;
}
/* Protocol-specific crypto routines. }}} */
/*
* Add a static public or private key to "wg_static_keys".
*/
static void
wg_add_static_key(const wg_qqword *tmp_key, gboolean is_private)
{
wg_skey_t *key = g_new0(wg_skey_t, 1);
if (is_private) {
set_private_key(&key->priv_key, tmp_key);
priv_to_pub(&key->pub_key, tmp_key);
} else {
key->pub_key = *tmp_key;
}
// If a previous pubkey exists, skip adding the new key. Do add the
// secret if it has become known in meantime.
wg_skey_t *oldkey = (wg_skey_t *)g_hash_table_lookup(wg_static_keys, &key->pub_key);
if (oldkey) {
if (!has_private_key(&oldkey->priv_key) && is_private) {
oldkey->priv_key = key->priv_key;
}
g_free(key);
return;
}
// New key, precompute the MAC1 label.
wg_mac1_key(&key->pub_key, &key->mac1_key);
g_hash_table_insert(wg_static_keys, &key->pub_key, key);
}
/* UAT and key configuration. {{{ */
static gboolean
wg_key_uat_record_update_cb(void *r, char **error)
{
wg_key_uat_record_t *rec = (wg_key_uat_record_t *)r;
wg_qqword key;
/* Check for valid base64-encoding. */
if (!decode_base64_key(&key, rec->key)) {
*error = g_strdup("Invalid key");
return FALSE;
}
return TRUE;
}
static void
wg_key_uat_apply(void)
{
if (!wg_static_keys) {
// The first field of "wg_skey_t" is the pubkey (and the table key),
// its initial four bytes should be good enough as key hash.
wg_static_keys = g_hash_table_new_full(g_int_hash, wg_pubkey_equal, NULL, g_free);
} else {
g_hash_table_remove_all(wg_static_keys);
}
/* Convert base64-encoded strings to wg_skey_t and derive pubkey. */
for (guint i = 0; i < num_wg_key_records; i++) {
wg_key_uat_record_t *rec = &wg_key_records[i];
wg_qqword tmp_key; /* Either public or private, not sure yet. */
/* Populate public (and private) keys. */
gboolean decoded = decode_base64_key(&tmp_key, rec->key);
DISSECTOR_ASSERT(decoded);
wg_add_static_key(&tmp_key, rec->key_type == WG_KEY_UAT_PRIVATE);
}
}
static void
wg_key_uat_reset(void)
{
/* Erase keys when the UAT is unloaded. */
g_hash_table_destroy(wg_static_keys);
wg_static_keys = NULL;
}
UAT_VS_DEF(wg_key_uat, key_type, wg_key_uat_record_t, guint, WG_KEY_UAT_PUBLIC, "Public")
UAT_CSTRING_CB_DEF(wg_key_uat, key, wg_key_uat_record_t)
/* UAT and key configuration. }}} */
#endif /* WG_DECRYPTION_SUPPORTED */
static void
wg_sessions_insert(guint32 id, wg_session_t *session)
{
@ -210,6 +465,39 @@ wg_sessions_lookup(packet_info *pinfo, guint32 receiver_id, gboolean *receiver_i
return NULL;
}
#ifdef WG_DECRYPTION_SUPPORTED
/*
* Finds the static public key for the receiver of this message based on the
* MAC1 value.
* TODO on PINFO_FD_VISITED, reuse previously discovered keys from session?
*/
static const wg_skey_t *
wg_mac1_key_probe(tvbuff_t *tvb, gboolean is_initiation)
{
const int mac1_offset = is_initiation ? 116 : 60;
// Shortcut: skip MAC1 validation if no pubkeys are configured.
if (g_hash_table_size(wg_static_keys) == 0) {
return NULL;
}
const guint8 *mac1_msgdata = tvb_get_ptr(tvb, 0, mac1_offset);
const guint8 *mac1_output = tvb_get_ptr(tvb, mac1_offset, 16);
// Find public key that matches the 16-byte MAC1 field.
GHashTableIter iter;
gpointer value;
g_hash_table_iter_init(&iter, wg_static_keys);
while (g_hash_table_iter_next(&iter, NULL, &value)) {
const wg_skey_t *skey = (wg_skey_t *)value;
if (wg_mac_verify(&skey->mac1_key, mac1_msgdata, (guint)mac1_offset, mac1_output)) {
return skey;
}
}
return NULL;
}
#endif /* WG_DECRYPTION_SUPPORTED */
static void
wg_dissect_pubkey(proto_tree *tree, tvbuff_t *tvb, int offset, gboolean is_ephemeral)
@ -223,18 +511,43 @@ wg_dissect_pubkey(proto_tree *tree, tvbuff_t *tvb, int offset, gboolean is_ephem
proto_tree_add_string(tree, hf_id, tvb, offset, 32, key_str);
}
#ifdef WG_DECRYPTION_SUPPORTED
static void
wg_dissect_mac1_pubkey(proto_tree *tree, tvbuff_t *tvb, const wg_skey_t *skey)
{
proto_item *ti;
if (!skey) {
return;
}
ti = proto_tree_add_string(tree, hf_wg_receiver_pubkey, tvb, 0, 0, pubkey_to_string(&skey->pub_key));
PROTO_ITEM_SET_GENERATED(ti);
proto_tree *key_tree = proto_item_add_subtree(ti, ett_key_info);
ti = proto_tree_add_boolean(key_tree, hf_wg_receiver_pubkey_known_privkey, tvb, 0, 0, !!has_private_key(&skey->priv_key));
PROTO_ITEM_SET_GENERATED(ti);
}
#endif /* WG_DECRYPTION_SUPPORTED */
static int
wg_dissect_handshake_initiation(tvbuff_t *tvb, packet_info *pinfo, proto_tree *wg_tree, wg_packet_info_t *wg_pinfo)
{
guint32 sender_id;
proto_item *ti;
#ifdef WG_DECRYPTION_SUPPORTED
const wg_skey_t *skey_r = wg_mac1_key_probe(tvb, TRUE);
#endif /* WG_DECRYPTION_SUPPORTED */
proto_tree_add_item_ret_uint(wg_tree, hf_wg_sender, tvb, 4, 4, ENC_LITTLE_ENDIAN, &sender_id);
col_append_fstr(pinfo->cinfo, COL_INFO, ", sender=0x%08X", sender_id);
wg_dissect_pubkey(wg_tree, tvb, 8, TRUE);
proto_tree_add_item(wg_tree, hf_wg_encrypted_static, tvb, 40, 32 + AUTH_TAG_LENGTH, ENC_NA);
proto_tree_add_item(wg_tree, hf_wg_encrypted_timestamp, tvb, 88, 12 + AUTH_TAG_LENGTH, ENC_NA);
proto_tree_add_item(wg_tree, hf_wg_mac1, tvb, 116, 16, ENC_NA);
#ifdef WG_DECRYPTION_SUPPORTED
wg_dissect_mac1_pubkey(wg_tree, tvb, skey_r);
#endif /* WG_DECRYPTION_SUPPORTED */
proto_tree_add_item(wg_tree, hf_wg_mac2, tvb, 132, 16, ENC_NA);
if (!PINFO_FD_VISITED(pinfo)) {
@ -265,6 +578,10 @@ wg_dissect_handshake_response(tvbuff_t *tvb, packet_info *pinfo, proto_tree *wg_
guint32 sender_id, receiver_id;
proto_item *ti;
#ifdef WG_DECRYPTION_SUPPORTED
const wg_skey_t *skey_i = wg_mac1_key_probe(tvb, FALSE);
#endif /* WG_DECRYPTION_SUPPORTED */
proto_tree_add_item_ret_uint(wg_tree, hf_wg_sender, tvb, 4, 4, ENC_LITTLE_ENDIAN, &sender_id);
col_append_fstr(pinfo->cinfo, COL_INFO, ", sender=0x%08X", sender_id);
proto_tree_add_item_ret_uint(wg_tree, hf_wg_receiver, tvb, 8, 4, ENC_LITTLE_ENDIAN, &receiver_id);
@ -272,6 +589,9 @@ wg_dissect_handshake_response(tvbuff_t *tvb, packet_info *pinfo, proto_tree *wg_
wg_dissect_pubkey(wg_tree, tvb, 12, TRUE);
proto_tree_add_item(wg_tree, hf_wg_encrypted_empty, tvb, 44, 16, ENC_NA);
proto_tree_add_item(wg_tree, hf_wg_mac1, tvb, 60, 16, ENC_NA);
#ifdef WG_DECRYPTION_SUPPORTED
wg_dissect_mac1_pubkey(wg_tree, tvb, skey_i);
#endif /* WG_DECRYPTION_SUPPORTED */
proto_tree_add_item(wg_tree, hf_wg_mac2, tvb, 76, 16, ENC_NA);
wg_session_t *session;
@ -440,6 +760,9 @@ wg_init(void)
void
proto_register_wg(void)
{
#ifdef WG_DECRYPTION_SUPPORTED
module_t *wg_module;
#endif /* WG_DECRYPTION_SUPPORTED */
expert_module_t *expert_wg;
static hf_register_info hf[] = {
@ -538,10 +861,23 @@ proto_register_wg(void)
FT_FRAMENUM, BASE_NONE, FRAMENUM_TYPE(FT_FRAMENUM_REQUEST), 0x0,
"This is a response to the initiation message in this frame", HFILL }
},
/* Additional fields. */
{ &hf_wg_receiver_pubkey,
{ "Receiver Static Public Key", "wg.receiver_pubkey",
FT_STRING, BASE_NONE, NULL, 0x0,
"Public key of the receiver (matched based on MAC1)", HFILL }
},
{ &hf_wg_receiver_pubkey_known_privkey,
{ "Has Private Key", "wg.receiver_pubkey.known_privkey",
FT_BOOLEAN, BASE_NONE, NULL, 0x0,
"Whether the corresponding private key is known (configured via prefs)", HFILL }
},
};
static gint *ett[] = {
&ett_wg,
&ett_key_info,
};
static ei_register_info ei[] = {
@ -555,6 +891,15 @@ proto_register_wg(void)
},
};
#ifdef WG_DECRYPTION_SUPPORTED
/* UAT for header fields */
static uat_field_t wg_key_uat_fields[] = {
UAT_FLD_VS(wg_key_uat, key_type, "Key type", wg_key_uat_type_vals, "Public or Private"),
UAT_FLD_CSTRING(wg_key_uat, key, "Key", "Base64-encoded key"),
UAT_END_FIELDS
};
#endif /* WG_DECRYPTION_SUPPORTED */
proto_wg = proto_register_protocol("WireGuard Protocol", "WireGuard", "wg");
proto_register_field_array(proto_wg, hf, array_length(hf));
@ -565,6 +910,30 @@ proto_register_wg(void)
register_dissector("wg", dissect_wg, proto_wg);
#ifdef WG_DECRYPTION_SUPPORTED
wg_module = prefs_register_protocol(proto_wg, NULL);
uat_t *wg_keys_uat = uat_new("WireGuard static keys",
sizeof(wg_key_uat_record_t),
"wg_keys", /* filename */
TRUE, /* from_profile */
&wg_key_records, /* data_ptr */
&num_wg_key_records, /* numitems_ptr */
UAT_AFFECTS_DISSECTION, /* affects dissection of packets, but not set of named fields */
NULL, /* Help section (currently a wiki page) */
NULL, /* copy_cb */
wg_key_uat_record_update_cb, /* update_cb */
NULL, /* free_cb */
wg_key_uat_apply, /* post_update_cb */
wg_key_uat_reset, /* reset_cb */
wg_key_uat_fields);
prefs_register_uat_preference(wg_module, "keys",
"WireGuard static keys",
"A table of long-term static keys to enable WireGuard peer identification or partial decryption",
wg_keys_uat);
#endif /* WG_DECRYPTION_SUPPORTED */
register_init_routine(wg_init);
sessions = wmem_map_new_autoreset(wmem_epan_scope(), wmem_file_scope(), g_direct_hash, g_direct_equal);
}

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test/captures/wireguard-ping-tcp.pcap Normal file
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53
test/suite_decryption.py
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@ -485,3 +485,56 @@ class case_decrypt_kerberos(subprocesstest.SubprocessTestCase):
env=config.test_env)
# keyvalue: ccda7d48219f73c3b28311c4ba7242b3
self.assertTrue(self.grepOutput('cc:da:7d:48:21:9f:73:c3:b2:83:11:c4:ba:72:42:b3'))
class case_decrypt_wireguard(subprocesstest.SubprocessTestCase):
key_Spriv_i = 'AKeZaHwBxjiKLFnkY2unvEdOTtg4AL+M9dQXfopFVFk='
key_Spub_i = 'Igge9KzRytKNwrgkzDE/8hrLu6Ly0OqVdvOPWhA5KR4='
key_Spriv_r = 'cFIxTUyBs1Qil414hBwEgvasEax8CKJ5IS5ZougplWs='
key_Spub_r = 'YDCttCs9e1J52/g9vEnwJJa+2x6RqaayAYMpSVQfGEY='
key_Epriv_i0 = 'sLGLJSOQfyz7JNJ5ZDzFf3Uz1rkiCMMjbWerNYcPFFU='
key_Epriv_r0 = 'QC4/FZKhFf0b/eXEcCecmZNt6V6PXmRa4EWG1PIYTU4='
key_Epriv_i1 = 'ULv83D+y3vA0t2mgmTmWz++lpVsrP7i4wNaUEK2oX0E='
key_Epriv_r1 = 'sBv1dhsm63cbvWMv/XML+bvynBp9PTdY9Vvptu3HQlg='
def runOne(self, args, pcap_file='wireguard-ping-tcp.pcap'):
if not config.have_libgcrypt17:
self.skipTest('Requires Gcrypt 1.7 or later')
capture_file = os.path.join(config.capture_dir, pcap_file)
proc = self.runProcess([config.cmd_tshark, '-r', capture_file] + args,
env=config.test_env)
lines = proc.stdout_str.splitlines()
return lines
def test_mac1_public(self):
"""Check that MAC1 identification using public keys work."""
lines = self.runOne([
'-ouat:wg_keys:"Public","%s"' % self.key_Spub_i,
'-ouat:wg_keys:"Public","%s"' % self.key_Spub_r,
'-Y', 'wg.receiver_pubkey',
'-Tfields',
'-e', 'frame.number',
'-e', 'wg.receiver_pubkey',
'-e', 'wg.receiver_pubkey.known_privkey',
])
self.assertEqual(4, len(lines))
self.assertIn('1\t%s\t0' % self.key_Spub_r, lines)
self.assertIn('2\t%s\t0' % self.key_Spub_i, lines)
self.assertIn('13\t%s\t0' % self.key_Spub_r, lines)
self.assertIn('14\t%s\t0' % self.key_Spub_i, lines)
def test_mac1_private(self):
"""Check that MAC1 identification using private keys work."""
lines = self.runOne([
'-ouat:wg_keys:"Private","%s"' % self.key_Spriv_i,
'-ouat:wg_keys:"Private","%s"' % self.key_Spriv_r,
'-Y', 'wg.receiver_pubkey',
'-Tfields',
'-e', 'frame.number',
'-e', 'wg.receiver_pubkey',
'-e', 'wg.receiver_pubkey.known_privkey',
])
self.assertEqual(4, len(lines))
self.assertIn('1\t%s\t1' % self.key_Spub_r, lines)
self.assertIn('2\t%s\t1' % self.key_Spub_i, lines)
self.assertIn('13\t%s\t1' % self.key_Spub_r, lines)
self.assertIn('14\t%s\t1' % self.key_Spub_i, lines)