/*
   Unix SMB/CIFS implementation.

   SMB2 Signing Code

   Copyright (C) Andrew Tridgell <tridge@samba.org> 2008

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "libcli/raw/libcliraw.h"
#include "libcli/smb2/smb2.h"
#include "libcli/smb2/smb2_calls.h"

#include <gnutls/gnutls.h>
#include <gnutls/crypto.h>
#include "lib/crypto/gnutls_helpers.h"

/*
  sign an outgoing message
 */
NTSTATUS smb2_sign_message(struct smb2_request_buffer *buf, DATA_BLOB session_key)
{
	uint8_t digest[gnutls_hmac_get_len(GNUTLS_MAC_SHA256)];
	uint64_t session_id;
	size_t hdr_offset;
	int rc;

	if (buf->size < NBT_HDR_SIZE + SMB2_HDR_SIGNATURE + 16) {
		/* can't sign non-SMB2 messages */
		return NT_STATUS_OK;
	}

	hdr_offset = buf->hdr - buf->buffer;

	session_id = BVAL(buf->hdr, SMB2_HDR_SESSION_ID);
	if (session_id == 0) {
		/* we don't sign messages with a zero session_id. See
		   MS-SMB2 3.2.4.1.1 */
		return NT_STATUS_OK;
	}

	if (session_key.length == 0) {
		DEBUG(2,("Wrong session key length %u for SMB2 signing\n",
			 (unsigned)session_key.length));
		return NT_STATUS_ACCESS_DENIED;
	}

	memset(buf->hdr + SMB2_HDR_SIGNATURE, 0, 16);

	SIVAL(buf->hdr, SMB2_HDR_FLAGS, IVAL(buf->hdr, SMB2_HDR_FLAGS) | SMB2_HDR_FLAG_SIGNED);

	rc = gnutls_hmac_fast(GNUTLS_MAC_SHA256,
			      session_key.data,
			      MIN(session_key.length, 16),
			      buf->hdr,
			      buf->size - hdr_offset,
			      digest);
	if (rc < 0) {
		return gnutls_error_to_ntstatus(rc, NT_STATUS_HMAC_NOT_SUPPORTED);
	}

	DEBUG(5,("signed SMB2 message of size %u\n", (unsigned)buf->size - NBT_HDR_SIZE));

	memcpy(buf->hdr + SMB2_HDR_SIGNATURE, digest, 16);

	return NT_STATUS_OK;
}

/*
  check an incoming signature
 */
NTSTATUS smb2_check_signature(struct smb2_request_buffer *buf, DATA_BLOB session_key)
{
	uint64_t session_id;
	uint8_t digest[gnutls_hmac_get_len(GNUTLS_MAC_SHA256)];
	uint8_t sig[16];
	size_t hdr_offset;
	int rc;

	if (buf->size < NBT_HDR_SIZE + SMB2_HDR_SIGNATURE + 16) {
		/* can't check non-SMB2 messages */
		return NT_STATUS_OK;
	}

	hdr_offset = buf->hdr - buf->buffer;

	session_id = BVAL(buf->hdr, SMB2_HDR_SESSION_ID);
	if (session_id == 0) {
		/* don't sign messages with a zero session_id. See
		   MS-SMB2 3.2.4.1.1 */
		return NT_STATUS_OK;
	}

	if (session_key.length == 0) {
		/* we don't have the session key yet */
		return NT_STATUS_OK;
	}

	memcpy(sig, buf->hdr+SMB2_HDR_SIGNATURE, 16);

	memset(buf->hdr + SMB2_HDR_SIGNATURE, 0, 16);

	rc = gnutls_hmac_fast(GNUTLS_MAC_SHA256,
			      session_key.data,
			      MIN(session_key.length, 16),
			      buf->hdr,
			      buf->size - hdr_offset,
			      digest);
	if (rc < 0) {
		return gnutls_error_to_ntstatus(rc, NT_STATUS_HMAC_NOT_SUPPORTED);
	}

	memcpy(buf->hdr + SMB2_HDR_SIGNATURE, digest, 16);

	if (!mem_equal_const_time(digest, sig, 16)) {
		DEBUG(0,("Bad SMB2 signature for message of size %u\n",
			 (unsigned)buf->size-NBT_HDR_SIZE));
		dump_data(0, sig, 16);
		dump_data(0, digest, 16);
		ZERO_ARRAY(digest);
		return NT_STATUS_ACCESS_DENIED;
	}
	ZERO_ARRAY(digest);

	return NT_STATUS_OK;
}