1 files changed, 478 insertions, 0 deletions

diff --git a/lib/ext/pre_shared_key.c b/lib/ext/pre_shared_key.c
new file mode 100644
index 0000000000..d4ea982cbb
--- /dev/null
+++ b/lib/ext/pre_shared_key.c
@@ -0,0 +1,478 @@
+/*
+ * Copyright (C) 2017-2018 Free Software Foundation, Inc.
+ * Copyright (C) 2018 Red Hat, Inc.
+ *
+ * Author: Ander Juaristi, Nikos Mavrogiannopoulos
+ *
+ * This file is part of GnuTLS.
+ *
+ * The GnuTLS is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published 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 program.  If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+#include "gnutls_int.h"
+#include "auth/psk.h"
+#include "secrets.h"
+#include "tls13/psk_ext_parser.h"
+#include "tls13/finished.h"
+#include "auth/psk_passwd.h"
+#include <ext/pre_shared_key.h>
+#include <assert.h>
+
+typedef struct {
+	uint16_t selected_identity;
+} psk_ext_st;
+
+static int
+compute_binder_key(const mac_entry_st *prf,
+		const uint8_t *key, size_t keylen,
+		void *out)
+{
+	int ret;
+	char label[] = "ext_binder";
+	size_t label_len = sizeof(label) - 1;
+	uint8_t tmp_key[MAX_HASH_SIZE];
+
+	/* Compute HKDF-Extract(0, psk) */
+	ret = _tls13_init_secret2(prf, key, keylen, tmp_key);
+	if (ret < 0)
+		return ret;
+
+	/* Compute Derive-Secret(secret, label, transcript_hash) */
+	ret = _tls13_derive_secret2(prf,
+			label, label_len,
+			NULL, 0,
+			tmp_key,
+			out);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int
+compute_psk_binder(unsigned entity,
+		const mac_entry_st *prf, unsigned binders_length, unsigned hash_size,
+		int exts_length, int ext_offset,
+		const gnutls_datum_t *psk, const gnutls_datum_t *client_hello,
+		void *out)
+{
+	int ret;
+	unsigned extensions_len_pos;
+	gnutls_buffer_st handshake_buf;
+	uint8_t binder_key[MAX_HASH_SIZE];
+
+	_gnutls_buffer_init(&handshake_buf);
+
+	if (entity == GNUTLS_CLIENT) {
+		ret = gnutls_buffer_append_data(&handshake_buf,
+				(const void *)  client_hello->data,
+				client_hello->size);
+		if (ret < 0) {
+			gnutls_assert();
+			goto error;
+		}
+
+		/* This is a ClientHello message */
+		handshake_buf.data[0] = GNUTLS_HANDSHAKE_CLIENT_HELLO;
+
+		/*
+		 * At this point we have not yet added the binders to the ClientHello,
+		 * but we have to overwrite the size field, pretending as if binders
+		 * of the correct length were present.
+		 */
+		_gnutls_write_uint24(handshake_buf.length + binders_length - 2, &handshake_buf.data[1]);
+		_gnutls_write_uint16(handshake_buf.length + binders_length - ext_offset,
+				&handshake_buf.data[ext_offset]);
+
+		extensions_len_pos = handshake_buf.length - exts_length - 2;
+		_gnutls_write_uint16(exts_length + binders_length + 2,
+				&handshake_buf.data[extensions_len_pos]);
+	} else {
+		gnutls_buffer_append_data(&handshake_buf,
+				(const void *) client_hello->data,
+				client_hello->size - binders_length - 3);
+	}
+
+	ret = compute_binder_key(prf,
+			psk->data, psk->size,
+			binder_key);
+	if (ret < 0) {
+		gnutls_assert();
+		goto error;
+	}
+
+	ret = _gnutls13_compute_finished(prf,
+			binder_key, hash_size,
+			&handshake_buf,
+			out);
+	if (ret < 0) {
+		gnutls_assert();
+		goto error;
+	}
+
+	ret = 0;
+error:
+	_gnutls_buffer_clear(&handshake_buf);
+	return ret;
+}
+
+static int
+client_send_params(gnutls_session_t session,
+		   gnutls_buffer_t extdata,
+		   const gnutls_psk_client_credentials_t cred)
+{
+	int ret, ext_offset = 0;
+	uint8_t binder_value[MAX_HASH_SIZE];
+	size_t length, pos;
+	gnutls_datum_t username = {NULL, 0}, key = {NULL, 0}, client_hello;
+	const mac_entry_st *prf = cred->binder_algo;
+	unsigned hash_size = _gnutls_mac_get_algo_len(prf);
+	int free_data;
+
+	if (prf == NULL || hash_size == 0 || hash_size > 255)
+		return gnutls_assert_val(GNUTLS_E_INSUFFICIENT_CREDENTIALS);
+
+	/* Credentials but no username set - this extension is not applicable */
+	if (!_gnutls_have_psk_credentials(cred))
+		return 0;
+
+	ret = _gnutls_find_psk_key(session, cred, &username, &key, &free_data);
+	if (ret < 0)
+		return gnutls_assert_val(ret);
+
+	if (username.size == 0 || username.size > UINT16_MAX) {
+		ret = gnutls_assert_val(GNUTLS_E_INVALID_PASSWORD);
+		goto cleanup;
+	}
+
+	/* placeholder to be filled later */
+	pos = extdata->length;
+	ret = _gnutls_buffer_append_prefix(extdata, 16, 0);
+	if (ret < 0) {
+		gnutls_assert_val(ret);
+		goto cleanup;
+	}
+
+	if ((ret = _gnutls_buffer_append_data_prefix(extdata, 16,
+			username.data, username.size)) < 0) {
+		gnutls_assert();
+		goto cleanup;
+	}
+
+	/* Now append the ticket age, which is always zero for out-of-band PSKs */
+	if ((ret = _gnutls_buffer_append_prefix(extdata, 32, 0)) < 0) {
+		gnutls_assert();
+		goto cleanup;
+	}
+	/* Total length appended is the length of the data, plus six octets */
+	length = (username.size + 6);
+
+	_gnutls_write_uint16(length, &extdata->data[pos]);
+
+	ext_offset = _gnutls_ext_get_extensions_offset(session);
+
+	/* Compute the binders. extdata->data points to the start
+	 * of this client hello. */
+	assert(extdata->length >= sizeof(mbuffer_st));
+	assert(ext_offset >= (ssize_t)sizeof(mbuffer_st));
+	ext_offset -= sizeof(mbuffer_st);
+	client_hello.data = extdata->data+sizeof(mbuffer_st);
+	client_hello.size = extdata->length-sizeof(mbuffer_st);
+
+	ret = compute_psk_binder(GNUTLS_CLIENT, prf,
+				 hash_size+1, hash_size, extdata->length-pos,
+				 ext_offset, &key, &client_hello,
+				 binder_value);
+	if (ret < 0) {
+		gnutls_assert();
+		goto cleanup;
+	}
+
+	/* Associate the selected pre-shared key with the session */
+	session->key.psk.data = key.data;
+	session->key.psk.size = key.size;
+	session->key.psk_needs_free = free_data;
+	key.data = NULL;
+	session->key.proto.tls13.binder_prf = prf;
+
+	/* Now append the binders */
+	ret = _gnutls_buffer_append_prefix(extdata, 16, hash_size+1);
+	if (ret < 0) {
+		gnutls_assert();
+		goto cleanup;
+	}
+
+	/* Add the size of the binder (we only have one) */
+	ret = _gnutls_buffer_append_data_prefix(extdata, 8, binder_value, hash_size);
+	if (ret < 0) {
+		gnutls_assert();
+		goto cleanup;
+	}
+
+	ret = 0;
+
+cleanup:
+	if (free_data) {
+		_gnutls_free_datum(&username);
+		_gnutls_free_temp_key_datum(&key);
+	}
+	return ret;
+}
+
+static int
+server_send_params(gnutls_session_t session, gnutls_buffer_t extdata)
+{
+	int ret;
+
+	if (!(session->internals.hsk_flags & HSK_PSK_SELECTED))
+		return 0;
+
+	ret = _gnutls_buffer_append_prefix(extdata, 16,
+			session->key.proto.tls13.psk_index);
+	if (ret < 0)
+		return gnutls_assert_val(ret);
+
+	return 2;
+}
+
+static int server_recv_params(gnutls_session_t session,
+			      const unsigned char *data, size_t len,
+			      const gnutls_psk_server_credentials_t pskcred)
+{
+	int ret;
+	const mac_entry_st *prf;
+	gnutls_datum_t full_client_hello;
+	uint8_t binder_value[MAX_HASH_SIZE];
+	int psk_index = -1;
+	gnutls_datum_t binder_recvd = { NULL, 0 };
+	gnutls_datum_t key;
+	unsigned hash_size;
+	psk_ext_parser_st psk_parser;
+	struct psk_st psk;
+	psk_auth_info_t info;
+
+	ret = _gnutls13_psk_ext_parser_init(&psk_parser, data, len);
+	if (ret < 0) {
+		if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) /* No PSKs advertised by client */
+			return 0;
+		return gnutls_assert_val(ret);
+	}
+
+	while ((ret = _gnutls13_psk_ext_parser_next_psk(&psk_parser, &psk)) >= 0) {
+		if (psk.ob_ticket_age == 0) {
+			/* _gnutls_psk_pwd_find_entry() expects 0-terminated identities */
+			if (psk.identity.size > 0 && psk.identity.size <= MAX_USERNAME_SIZE) {
+				char identity_str[psk.identity.size + 1];
+
+				memcpy(identity_str, psk.identity.data, psk.identity.size);
+				identity_str[psk.identity.size] = 0;
+
+				ret = _gnutls_psk_pwd_find_entry(session, identity_str, &key);
+				if (ret == 0)
+					psk_index = ret;
+			}
+		}
+	}
+
+	if (psk_index < 0)
+		return 0;
+
+	ret = _gnutls13_psk_ext_parser_find_binder(&psk_parser, psk_index,
+						   &binder_recvd);
+	if (ret < 0)
+		return gnutls_assert_val(ret);
+
+	/* Get full ClientHello */
+	if (!_gnutls_ext_get_full_client_hello(session, &full_client_hello))
+		return 0;
+
+	/* Compute the binder value for this PSK */
+	prf = pskcred->binder_algo;
+	hash_size = prf->output_size;
+	ret = compute_psk_binder(GNUTLS_SERVER, prf, hash_size, hash_size, 0, 0,
+				 &key, &full_client_hello,
+				 binder_value);
+	if (ret < 0)
+		return gnutls_assert_val(ret);
+
+	if (_gnutls_mac_get_algo_len(prf) != binder_recvd.size ||
+	    safe_memcmp(binder_value, binder_recvd.data, binder_recvd.size)) {
+		gnutls_free(key.data);
+		return gnutls_assert_val(GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
+	}
+
+	if (session->internals.hsk_flags & HSK_PSK_KE_MODE_DHE_PSK)
+		_gnutls_handshake_log("EXT[%p]: Selected DHE-PSK mode\n", session);
+	else {
+		reset_cand_groups(session);
+		_gnutls_handshake_log("EXT[%p]: Selected PSK mode\n", session);
+	}
+
+	/* save the username in psk_auth_info to make it available
+	 * using gnutls_psk_server_get_username() */
+	if (psk.ob_ticket_age == 0) {
+		if (psk.identity.size >= sizeof(info->username))
+			return gnutls_assert_val(GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER);
+
+		ret = _gnutls_auth_info_set(session, GNUTLS_CRD_PSK, sizeof(psk_auth_info_st), 1);
+		if (ret < 0)
+			return gnutls_assert_val(ret);
+
+		info = _gnutls_get_auth_info(session, GNUTLS_CRD_PSK);
+		assert(info != NULL);
+
+		memcpy(info->username, psk.identity.data, psk.identity.size);
+		info->username[psk.identity.size] = 0;
+	}
+
+	session->internals.hsk_flags |= HSK_PSK_SELECTED;
+
+	/* Reference the selected pre-shared key */
+	session->key.psk.data = key.data;
+	session->key.psk.size = key.size;
+	session->key.psk_needs_free = 1;
+
+	session->key.proto.tls13.psk_index = psk_index;
+	session->key.proto.tls13.binder_prf = prf;
+
+	return 0;
+}
+
+/*
+ * Return values for this function:
+ *  -  0 : Not applicable.
+ *  - >0 : Ok. Return size of extension data.
+ *  - GNUTLS_E_INT_RET_0 : Size of extension data is zero.
+ *  - <0 : There's been an error.
+ *
+ * In the client, generates the PskIdentity and PskBinderEntry messages.
+ *
+ *      PskIdentity identities<7..2^16-1>;
+ *      PskBinderEntry binders<33..2^16-1>;
+ *
+ *      struct {
+ *          opaque identity<1..2^16-1>;
+ *          uint32 obfuscated_ticket_age;
+ *      } PskIdentity;
+ *
+ *      opaque PskBinderEntry<32..255>;
+ *
+ * The server sends the selected identity, which is a zero-based index
+ * of the PSKs offered by the client:
+ *
+ *      struct {
+ *          uint16 selected_identity;
+ *      } PreSharedKeyExtension;
+ */
+static int _gnutls_psk_send_params(gnutls_session_t session,
+				   gnutls_buffer_t extdata)
+{
+	gnutls_psk_client_credentials_t cred = NULL;
+	const version_entry_st *vers;
+
+	if (session->security_parameters.entity == GNUTLS_CLIENT) {
+		vers = _gnutls_version_max(session);
+
+		if (!vers || !vers->tls13_sem)
+			return 0;
+
+		if (session->internals.hsk_flags & HSK_PSK_KE_MODES_SENT) {
+			cred = (gnutls_psk_client_credentials_t)
+					_gnutls_get_cred(session, GNUTLS_CRD_PSK);
+			/* If there are no PSK credentials, this extension is not applicable,
+			 * so we return zero. */
+			if (cred == NULL || !session->internals.priorities->have_psk)
+				return 0;
+
+			return client_send_params(session, extdata, cred);
+		} else {
+			return 0;
+		}
+	} else {
+		vers = get_version(session);
+
+		if (!vers || !vers->tls13_sem)
+			return 0;
+
+		cred = (gnutls_psk_client_credentials_t)
+				_gnutls_get_cred(session, GNUTLS_CRD_PSK);
+		if (cred == NULL || !session->internals.priorities->have_psk)
+			return 0;
+
+		if (session->internals.hsk_flags & HSK_PSK_KE_MODES_RECEIVED)
+			return server_send_params(session, extdata);
+		else
+			return 0;
+	}
+}
+
+/*
+ * Return values for this function:
+ *  -  0 : Not applicable.
+ *  - >0 : Ok. Return size of extension data.
+ *  - <0 : There's been an error.
+ */
+static int _gnutls_psk_recv_params(gnutls_session_t session,
+				   const unsigned char *data, size_t len)
+{
+	gnutls_psk_server_credentials_t pskcred;
+	const version_entry_st *vers = get_version(session);
+
+	if (!vers || !vers->tls13_sem)
+		return 0;
+
+	if (session->security_parameters.entity == GNUTLS_CLIENT) {
+		if (session->internals.hsk_flags & HSK_PSK_KE_MODES_SENT) {
+			uint16_t selected_identity = _gnutls_read_uint16(data);
+
+			if (selected_identity == 0) {
+				_gnutls_handshake_log("EXT[%p]: Selected PSK mode\n", session);
+				session->internals.hsk_flags |= HSK_PSK_SELECTED;
+			}
+			return 0;
+		} else {
+			return gnutls_assert_val(GNUTLS_E_RECEIVED_ILLEGAL_EXTENSION);
+		}
+	} else {
+		if (session->internals.hsk_flags & HSK_PSK_KE_MODES_RECEIVED) {
+			if (session->internals.hsk_flags & HSK_PSK_KE_MODE_INVALID) {
+				/* We received a "psk_ke_modes" extension, but with a value we don't support */
+				return 0;
+			}
+
+			pskcred = (gnutls_psk_server_credentials_t)
+					_gnutls_get_cred(session, GNUTLS_CRD_PSK);
+
+			/* If there are no PSK credentials, this extension is not applicable,
+			 * so we return zero. */
+			if (pskcred == NULL)
+				return 0;
+
+			return server_recv_params(session, data, len, pskcred);
+		} else {
+			return gnutls_assert_val(GNUTLS_E_RECEIVED_ILLEGAL_EXTENSION);
+		}
+	}
+}
+
+const hello_ext_entry_st ext_pre_shared_key = {
+	.name = "Pre Shared Key",
+	.tls_id = 41,
+	.gid = GNUTLS_EXTENSION_PRE_SHARED_KEY,
+	.parse_type = GNUTLS_EXT_TLS,
+	.validity = GNUTLS_EXT_FLAG_CLIENT_HELLO | GNUTLS_EXT_FLAG_TLS13_SERVER_HELLO,
+	.send_func = _gnutls_psk_send_params,
+	.recv_func = _gnutls_psk_recv_params
+};