mariadb/storage/innobase/fil/fil0pageencryption.cc

/*****************************************************************************

Copyright (C) 2014 eperi GmbH. All Rights Reserved.

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; version 2 of the License.

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, write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

*****************************************************************************/

/*****************************************************************
 @file fil/fil0pageencryption.cc
 Implementation for page encryption file spaces.

 Created  08/25/2014 Ludger Göckel eperi-GmbH
 Modified 11/26/2014 Jan Lindström MariaDB Corporation
 ***********************************************************************/

#include "fil0fil.h"
#include "fil0pageencryption.h"
#include "fsp0pageencryption.h"
#include "my_dbug.h"
#include "page0zip.h"

#include "buf0checksum.h"

#include <my_aes.h>
#include <KeySingleton.h>
#include <math.h>

/*
 * derived from libFLAC, which is gpl v2
 */
byte crc_table[] = {
		0x00,0x07,0x0E,0x09,0x1C,0x1B,0x12,0x15,0x38,0x3F,0x36,0x31,0x24,0x23,0x2A,0x2D,0x70,0x77,0x7E,0x79,
		0x6C,0x6B,0x62,0x65,0x48,0x4F,0x46,0x41,0x54,0x53,0x5A,0x5D,0xE0,0xE7,0xEE,0xE9,0xFC,0xFB,0xF2,0xF5,
		0xD8,0xDF,0xD6,0xD1,0xC4,0xC3,0xCA,0xCD,0x90,0x97,0x9E,0x99,0x8C,0x8B,0x82,0x85,0xA8,0xAF,0xA6,0xA1,
		0xB4,0xB3,0xBA,0xBD,0xC7,0xC0,0xC9,0xCE,0xDB,0xDC,0xD5,0xD2,0xFF,0xF8,0xF1,0xF6,0xE3,0xE4,0xED,0xEA,
		0xB7,0xB0,0xB9,0xBE,0xAB,0xAC,0xA5,0xA2,0x8F,0x88,0x81,0x86,0x93,0x94,0x9D,0x9A,0x27,0x20,0x29,0x2E,
		0x3B,0x3C,0x35,0x32,0x1F,0x18,0x11,0x16,0x03,0x04,0x0D,0x0A,0x57,0x50,0x59,0x5E,0x4B,0x4C,0x45,0x42,
		0x6F,0x68,0x61,0x66,0x73,0x74,0x7D,0x7A,0x89,0x8E,0x87,0x80,0x95,0x92,0x9B,0x9C,0xB1,0xB6,0xBF,0xB8,
		0xAD,0xAA,0xA3,0xA4,0xF9,0xFE,0xF7,0xF0,0xE5,0xE2,0xEB,0xEC,0xC1,0xC6,0xCF,0xC8,0xDD,0xDA,0xD3,0xD4,
		0x69,0x6E,0x67,0x60,0x75,0x72,0x7B,0x7C,0x51,0x56,0x5F,0x58,0x4D,0x4A,0x43,0x44,0x19,0x1E,0x17,0x10,
		0x05,0x02,0x0B,0x0C,0x21,0x26,0x2F,0x28,0x3D,0x3A,0x33,0x34,0x4E,0x49,0x40,0x47,0x52,0x55,0x5C,0x5B,
		0x76,0x71,0x78,0x7F,0x6A,0x6D,0x64,0x63,0x3E,0x39,0x30,0x37,0x22,0x25,0x2C,0x2B,0x06,0x01,0x08,0x0F,
		0x1A,0x1D,0x14,0x13,0xAE,0xA9,0xA0,0xA7,0xB2,0xB5,0xBC,0xBB,0x96,0x91,0x98,0x9F,0x8A,0x8D,0x84,0x83,
		0xDE,0xD9,0xD0,0xD7,0xC2,0xC5,0xCC,0xCB,0xE6,0xE1,0xE8,0xEF,0xFA,0xFD,0xF4,0xF3

};

/****************************************************************//**
Calculate checksum for encrypted pages
@return checksum */
static
byte
fil_page_encryption_calc_checksum(
/*==============================*/
	unsigned char* 	buf, 	/*!<in: buffer where to calculate checksum */
	ulint 	 	len) 	/*!<in: buffer length */
{
	byte crc = 0;
	for (ulint i = 0; i < len; i++) {
		crc = crc_table[(crc ^ buf[i]) & 0xff];
	}
        return crc;
}

/****************************************************************//**
Recalculate checksum for encrypted pages */
static
void
do_check_sum(
/*=========*/
	ulint 	page_size, 	/*!< in: page size */
	ulint 	zip_size, 	/*!< in: compressed page size */
	byte* 	buf) 	 	/*!< in: buffer */
{
	ib_uint32_t checksum = 0;

	if (zip_size) {
		checksum = page_zip_calc_checksum(buf,zip_size,
			static_cast<srv_checksum_algorithm_t>(
				srv_checksum_algorithm));

		mach_write_to_4(buf + FIL_PAGE_SPACE_OR_CHKSUM, checksum);
		return;
	}

	switch ((srv_checksum_algorithm_t) srv_checksum_algorithm) {
	case SRV_CHECKSUM_ALGORITHM_CRC32:
	case SRV_CHECKSUM_ALGORITHM_STRICT_CRC32:
		checksum = buf_calc_page_crc32(buf);
		break;
	case SRV_CHECKSUM_ALGORITHM_INNODB:
	case SRV_CHECKSUM_ALGORITHM_STRICT_INNODB:
		checksum = (ib_uint32_t) buf_calc_page_new_checksum(buf);
		break;
	case SRV_CHECKSUM_ALGORITHM_NONE:
	case SRV_CHECKSUM_ALGORITHM_STRICT_NONE:
		checksum = BUF_NO_CHECKSUM_MAGIC;
		break;
		/* no default so the compiler will emit a warning if new enum
		 is added and not handled here */
	}

	mach_write_to_4(buf + FIL_PAGE_SPACE_OR_CHKSUM, checksum);

	/* old style checksum is omitted */
}

/****************************************************************//**
 For page encrypted pages encrypt the page before actual write
 operation.

 Note, that FIL_PAGE_TYPE_FSP_HDR and FIL_PAGE_TYPE_XDES type pages
 are not encrypted!

 Pages are encrypted with AES/CBC/NoPadding algorithm.

 "No padding" is used to ensure, that the encrypted page does not
 exceed the page size. If "no padding" is used, the input for encryption
 must be of size (multiple * AES blocksize). AES Blocksize is usually 16
 (bytes).

 Everything in the page is encrypted except for the 38 byte FIL header.
 Since the length of the payload is not a multiple of the AES blocksize,
 and to ensure that every byte of the payload is encrypted, two encryption
 operations are done. Each time with a block of adequate size as input.
 1st block contains everything from beginning of payload bytes except for
 the remainder. 2nd block is of size 64 and contains the remainder and
 the last (64 - sizeof(remainder)) bytes of the encrypted 1st block.

 Each encrypted page receives a new page type for PAGE_ENCRYPTION.
 The original page type (2 bytes) is stored in the Checksum header of the
 page (position FIL_PAGE_SPACE_OR_CHKSUM). Additionally the encryption
 key identifier is stored in the Checksum Header. This uses 1 byte.
 Checksum verification for encrypted pages is disabled. This checksum
 should be restored after decryption.

 To be able to verify decryption in a later stage, a 1-byte checksum at
 position 4 of the FIL_PAGE_SPACE_OR_CHKSUM header is stored.
 For page compressed table pages the log base 2 of the length of the
 encrypted data is stored.

 @return encrypted page or original page if encryption failed to be
 written*/
UNIV_INTERN
byte*
fil_encrypt_page(
/*==============*/
	ulint 		space_id, 	/*!< in: tablespace id of the table. */
	byte* 		buf, 		/*!< in: buffer from which to write; in aio
					this must be appropriately aligned */
	byte* 		out_buf, 	/*!< out: encrypted buffer */
	ulint 		len, 		/*!< in: length of input buffer.*/
	ulint 		encryption_key, /*!< in: encryption key */
	ulint* 		out_len, 	/*!< out: actual length of encrypted page */
	ulint* 		errorCode, 	/*!< out: an error code. set,
					if page is intentionally not encrypted */
	byte*  		tmp_encryption_buf) /*!< in: temporary buffer or NULL */
{

	int err = AES_OK;
	int key = 0;
	uint32 data_size = 0;
	ulint orig_page_type = 0;
	uint32 write_size = 0;
	fil_space_t* space = NULL;
	byte* tmp_buf = NULL;
	ulint page_len = 0;
	ulint offset = 0;

	ut_ad(buf);ut_ad(out_buf);
	key = encryption_key;

	*errorCode = AES_OK;

	ut_ad(fil_space_is_page_encrypted(space_id));
	fil_system_enter();
	space = fil_space_get_by_id(space_id);
	fil_system_exit();

#ifdef UNIV_DEBUG_PAGEENCRYPTION
	ulint pageno = mach_read_from_4(buf + FIL_PAGE_OFFSET);
	fprintf(stderr,
		"InnoDB: Note: Preparing for encryption for space %lu name %s len %lu, page no %lu\n",
		space_id, fil_space_name(space), len, pageno);
#endif /* UNIV_DEBUG_PAGEENCRYPTION */

	/* read original page type */
	orig_page_type = mach_read_from_2(buf + FIL_PAGE_TYPE);

	/* Do not encrypt file space header or extend descriptor */
	if ((orig_page_type == FIL_PAGE_TYPE_FSP_HDR)
	     || (orig_page_type == FIL_PAGE_TYPE_XDES) ) {
		*errorCode = PAGE_ENCRYPTION_WILL_NOT_ENCRYPT;
		*out_len = len;
		return (buf);
	}

	if (FIL_PAGE_PAGE_COMPRESSED == orig_page_type) {
		page_len = log10((double)len)/log10((double)2);
	}

	byte checksum_byte = fil_page_encryption_calc_checksum(buf + FIL_PAGE_DATA, len - FIL_PAGE_DATA);

	/* data_size bytes will be encrypted at first.
	 * data_size will be the length of the cipher text since no padding is used.*/
	data_size = ((len - FIL_PAGE_DATA - FIL_PAGE_DATA_END) / MY_AES_BLOCK_SIZE) * MY_AES_BLOCK_SIZE;


	const unsigned char rkey[] = {0xbd, 0xe4, 0x72, 0xa2, 0x95, 0x67, 0x5c, 0xa9,
				      0x2e, 0x04, 0x67, 0xea, 0xdb, 0xc0, 0xe0, 0x23,
				      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
				      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
	uint8 key_len = 16;

	const unsigned char iv[] = {0x2d, 0x1a, 0xf8, 0xd3, 0x97, 0x4e, 0x0b, 0xd3, 0xef, 0xed,
		0x5a, 0x6f, 0x82, 0x59, 0x4f,0x5e};

	ulint iv_len = 16;

	KeySingleton& keys = KeySingleton::getInstance();

	if (!keys.isAvailable()) {
		err = AES_KEY_CREATION_FAILED;
	} else if (keys.getKeys(encryption_key) == NULL) {
		err = PAGE_ENCRYPTION_KEY_MISSING;
	} else {
		char* keyString = keys.getKeys(encryption_key)->key;
		char* ivString = keys.getKeys(encryption_key)->iv;

		if (keyString == NULL || ivString == NULL) {
			*errorCode = PAGE_ENCRYPTION_WILL_NOT_ENCRYPT;
			*out_len = len;
			return (buf);
		}
		key_len = strlen(keyString)/2;
		my_aes_hexToUint(keyString, (unsigned char*)&rkey, key_len);
		my_aes_hexToUint(ivString, (unsigned char*)&iv, 16);
	}

	/* 1st encryption: data_size bytes starting from FIL_PAGE_DATA */
	if (err == AES_OK) {
		err = my_aes_encrypt_cbc(
			(char*) buf + FIL_PAGE_DATA,
			data_size,
			(char *) out_buf + FIL_PAGE_DATA,
			&write_size,
			(const unsigned char *) &rkey,
			key_len,
			(const unsigned char *) &iv,
			iv_len,
			1);

		ut_ad(write_size == data_size);

		if (err == AES_OK) {
			/* copy remaining bytes from input buffer to output buffer.
			 * Note, that this copies the final 8 bytes of a
			 * page, which consists of the
			 * Old-style checksum and the "Low 32 bits of LSN */
			memcpy(out_buf + FIL_PAGE_DATA + data_size,
			       buf + FIL_PAGE_DATA + data_size ,
			       len - FIL_PAGE_DATA -data_size);

			if (tmp_encryption_buf == NULL) {
				//create temporary buffer for 2nd encryption
				tmp_buf = static_cast<byte *>(ut_malloc(64));
			} else {
				tmp_buf = tmp_encryption_buf;
			}

			/* 2nd encryption: 64 bytes from out_buf,
			result length is 64 bytes */
			err = my_aes_encrypt_cbc((char*)out_buf + len -offset -64,
					64,
					(char*)tmp_buf,
					&write_size,
					(const unsigned char *)&rkey,
					key_len,
					(const unsigned char *)&iv,
					iv_len, 1);
			ut_ad(write_size == 64);

			/* copy 64 bytes from 2nd encryption to out_buf*/
			memcpy(out_buf + len - offset -64, tmp_buf, 64);
		}

	}

	/* error handling */
	if (err != AES_OK) {
		/* If an error occurred we leave the actual page as it was */

		fprintf(stderr,
			"InnoDB: Warning: Encryption failed for space %lu "
			"name %s len %lu rt %d write %lu, error: %d\n",
			space_id, fil_space_name(space), len, err, (ulint)data_size, err);
		fflush(stderr);
		srv_stats.pages_page_encryption_error.inc();
		*out_len = len;

		/* free temporary buffer */
		if (tmp_buf!=NULL && tmp_encryption_buf == NULL) {
			ut_free(tmp_buf);
		}
		*errorCode = err;

		return (buf);
	}

	/* Set up the page header. Copied from input buffer*/
	memcpy(out_buf, buf, FIL_PAGE_DATA);

	/* Set up the correct page type */
	mach_write_to_2(out_buf + FIL_PAGE_TYPE, FIL_PAGE_PAGE_ENCRYPTED);

	/* The 1st checksum field is used to store original page type, etc.
	 * checksum check for page encrypted pages is omitted.
	 */

	/* Set up the encryption key. Written to the 1st byte of
	the checksum header field. This header is currently used to store data. */
	mach_write_to_1(out_buf + FIL_PAGE_SPACE_OR_CHKSUM, key);

	/* store original page type. Written to 2nd and 3rd byte
	of the checksum header field */
	mach_write_to_2(out_buf + FIL_PAGE_SPACE_OR_CHKSUM + 1, orig_page_type);

	if (FIL_PAGE_PAGE_COMPRESSED == orig_page_type) {
		/* set byte 4 of checksum field to page length (ln(len)) */
		memset(out_buf + FIL_PAGE_SPACE_OR_CHKSUM + 3, page_len, 1);
	} else {
		/* set byte 4 of checksum field to checksum byte */
		memset(out_buf + FIL_PAGE_SPACE_OR_CHKSUM + 3, checksum_byte, 1);
	}

#ifdef UNIV_DEBUG
	/* Verify */
	ut_ad(fil_page_is_encrypted(out_buf));

#endif /* UNIV_DEBUG */

	srv_stats.pages_page_encrypted.inc();
	*out_len = len;

	/* free temporary buffer */
	if (tmp_buf!=NULL && tmp_encryption_buf == NULL) {
		ut_free(tmp_buf);
	}

	return (out_buf);
}

/****************************************************************//**
 For page encrypted pages decrypt the page after actual read
 operation.

 See fil_encrypt_page for details, how the encryption works.

 If the decryption can be verified, original page should be completely restored.
 This includes original page type, 4-byte checksum field at page start.
 If it is not a page compressed table's page, decryption is verified against
 a 1-byte checksum built over the plain data bytes. If this verification
 fails, an error state is returned.

 @return decrypted page */
ulint
fil_decrypt_page(
/*=============*/
	byte* 		page_buf, 	/*!< in: preallocated buffer or NULL */
	byte* 		buf, 		/*!< in/out: buffer from which to read; in aio
					this must be appropriately aligned */
	ulint 		len, 		/*!< in: length buffer, which should be decrypted.*/
	ulint* 		write_size, 	/*!< out: size of the decrypted
					data. If no error occurred equal to len */
	ibool* 		page_compressed,/*!<out: is page compressed.*/
	byte*  		tmp_encryption_buf) /*!< in: temporary buffer or NULL */
{
	int err = AES_OK;
	ulint page_decryption_key;
	uint32 data_size = 0;
	ulint orig_page_type = 0;
	uint32 tmp_write_size = 0;
	ulint offset = 0;
	byte *in_buf = NULL;
	byte *tmp_buf = NULL;
	fil_space_t* space = NULL;

	ulint page_compression_flag = 0;

	ut_ad(buf);
	ut_ad(len);

	/* Before actual decrypt, make sure that page type is correct */
	ulint current_page_type = mach_read_from_2(buf + FIL_PAGE_TYPE);

	if ((current_page_type == FIL_PAGE_TYPE_FSP_HDR)
	    || (current_page_type == FIL_PAGE_TYPE_XDES)) {
		/* assumed as unencrypted */
		if (write_size!=NULL)  {
			*write_size = len;
		}
		return AES_OK;
	}

	if (current_page_type != FIL_PAGE_PAGE_ENCRYPTED) {

		fprintf(stderr, "InnoDB: Corruption: We try to decrypt corrupted page\n"
				"InnoDB: CRC %lu type %lu.\n"
				"InnoDB: len %lu\n",
				mach_read_from_4(buf + FIL_PAGE_SPACE_OR_CHKSUM),
				mach_read_from_2(buf + FIL_PAGE_TYPE), len);

		fflush(stderr);
		return PAGE_ENCRYPTION_WRONG_PAGE_TYPE;
	}

	/* 1st checksum field is used to store original page type, etc.
	 * checksum check for page encrypted pages is omitted.
	 */

	/* read page encryption key */
	page_decryption_key = mach_read_from_1(buf + FIL_PAGE_SPACE_OR_CHKSUM);

	/* Get the page type */
	orig_page_type = mach_read_from_2(buf + FIL_PAGE_SPACE_OR_CHKSUM + 1);

	/* read checksum byte */
	byte stored_checksum_byte = mach_read_from_1(buf + FIL_PAGE_SPACE_OR_CHKSUM + 3);

	if (FIL_PAGE_PAGE_COMPRESSED == orig_page_type) {
		if (page_compressed != NULL) {
			*page_compressed = 1L;
		}
		page_compression_flag = 1;
		len = pow((double)2, (double)((int)stored_checksum_byte));
		offset = 0;
	}

	data_size = ((len - FIL_PAGE_DATA - FIL_PAGE_DATA_END) / MY_AES_BLOCK_SIZE) * MY_AES_BLOCK_SIZE;

	const unsigned char rkey[] = {0xbd, 0xe4, 0x72, 0xa2, 0x95, 0x67, 0x5c, 0xa9,
			0x2e, 0x04, 0x67, 0xea, 0xdb, 0xc0,0xe0, 0x23,
			0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
			0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00};
	uint8 key_len = 16;
	const unsigned char iv[] = {0x2d, 0x1a, 0xf8, 0xd3, 0x97, 0x4e, 0x0b, 0xd3, 0xef, 0xed,
			0x5a, 0x6f, 0x82, 0x59, 0x4f,0x5e};

	uint8 iv_len = 16;

	KeySingleton& keys = KeySingleton::getInstance();

	if (!keys.isAvailable()) {
		err = PAGE_ENCRYPTION_ERROR;
	} else if (keys.getKeys(page_decryption_key) == NULL) {
		err = PAGE_ENCRYPTION_KEY_MISSING;
	} else {
		char* keyString = keys.getKeys(page_decryption_key)->key;
		char* ivString = keys.getKeys(page_decryption_key)->iv;
		key_len = strlen(keyString)/2;
		if (keyString == NULL || ivString == NULL) {
			return err;
		}

		my_aes_hexToUint(keyString, (unsigned char*)&rkey, key_len);
		my_aes_hexToUint(ivString, (unsigned char*)&iv, 16);
	}

	if (err != AES_OK) {
		/* surely key could not be determined. */
		fprintf(stderr, "InnoDB: Corruption: Page is marked as encrypted\n"
				"InnoDB: but decrypt failed with error %d, encryption key %d.\n",
				err, (int)page_decryption_key);
		fflush(stderr);

		return err;
	}

	if (tmp_encryption_buf == NULL) {
		tmp_buf= static_cast<byte *>(ut_malloc(64));
	} else {
		tmp_buf = tmp_encryption_buf;
	}

	// If no buffer was given, we need to allocate temporal buffer
	if (page_buf == NULL) {
#ifdef UNIV_PAGECOMPRESS_DEBUG
		fprintf(stderr,
			"InnoDB: Note: FIL: Encryption buffer not given, allocating...\n");
#endif /* UNIV_PAGECOMPRESS_DEBUG */
		in_buf = static_cast<byte *>(ut_malloc(UNIV_PAGE_SIZE*2));
	} else {
		in_buf = page_buf;
	}

	/* 1st decryption: 64 bytes */
	/* 64 bytes from data area are copied to temporary buffer.
	 * These are the last 64 of the (encrypted) payload */
	memcpy(tmp_buf, buf + len - offset - 64, 64);

	err = my_aes_decrypt_cbc(
		(const char*) tmp_buf,
		64,
		(char *) in_buf + len - offset - 64,
		&tmp_write_size,
		(const unsigned char *) &rkey,
		key_len,
		(const unsigned char *) &iv,
		iv_len,
		1);

	ut_ad(tmp_write_size == 64);

	/* If decrypt fails it means that page is corrupted or has an unknown key */
	if (err != AES_OK) {
		fprintf(stderr, "InnoDB: Corruption: Page is marked as encrypted\n"
			"InnoDB: but decrypt failed with error %d.\n"
			"InnoDB: size %lu len %lu, key %d\n", err, (ulint)data_size,
			len, (int)page_decryption_key);
		fflush(stderr);

		if (tmp_encryption_buf == NULL) {
			ut_free(tmp_buf);
		}

		if (page_buf == NULL) {
			ut_free(in_buf);
		}
		return err;
	}

	ut_ad(tmp_write_size == 64);

	/* copy 1st part of payload from buf to in_buf */
	/* do not override result of 1st decryption */
	memcpy(in_buf + FIL_PAGE_DATA, buf + FIL_PAGE_DATA, len -offset -64 - FIL_PAGE_DATA);


	/* Decrypt rest of the page */
	err = my_aes_decrypt_cbc((char*) in_buf + FIL_PAGE_DATA,
			data_size,
			(char *) buf + FIL_PAGE_DATA,
			&tmp_write_size,
			(const unsigned char *)&rkey,
			key_len,
			(const unsigned char *)&iv,
			iv_len,
			1);

	ut_ad(tmp_write_size = data_size);

	/* copy remaining bytes from in_buf to buf.
	 */
	ulint bytes_to_copy = len - FIL_PAGE_DATA - data_size - offset;
	memcpy(buf + FIL_PAGE_DATA + data_size, in_buf + FIL_PAGE_DATA + data_size, bytes_to_copy);

	/* apart from header data everything is now in in_buf */

	if (tmp_encryption_buf == NULL) {
		ut_free(tmp_buf);
	}

#ifdef UNIV_PAGEENCRIPTION_DEBUG
	fprintf(stderr, "InnoDB: Note: Decryption succeeded for len %lu\n", len);
	fflush(stderr);
#endif

	if (page_buf == NULL) {
		ut_free(in_buf);
	}

	/* setting original page type */
	mach_write_to_2(buf + FIL_PAGE_TYPE, orig_page_type);

	ulint pageno = mach_read_from_4(buf + FIL_PAGE_OFFSET);
	ulint flags = 0;
	ulint zip_size = 0;

	/* please note, that page with number 0 is not encrypted */
	if (pageno == 0 ) {
		flags = mach_read_from_4(FSP_HEADER_OFFSET + FSP_SPACE_FLAGS + buf);
	} else {
		ulint space_id = mach_read_from_4(buf + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID);
		fil_system_enter();
		space = fil_space_get_by_id(space_id);
		flags = fil_space_flags(space);
		fil_system_exit();
	}

	if (!(page_compression_flag)) {
		zip_size = fsp_flags_get_zip_size(flags);
	}

	if (write_size!=NULL) {
		*write_size = len;
	}

	if (!(page_compression_flag)) {
		byte checksum_byte = fil_page_encryption_calc_checksum(buf + FIL_PAGE_DATA, len - FIL_PAGE_DATA);

		if (checksum_byte != stored_checksum_byte) {
			err = PAGE_ENCRYPTION_WRONG_KEY;
			fprintf(stderr, "InnoDB: Corruption: Page is marked as encrypted\n"
				"InnoDB: but decryption verification failed with error %d,"
				" encryption key %d.\n",
				err, (int)page_decryption_key);
			fflush(stderr);
			return err;
		}

		/* calc check sums and write to the buffer, if page is not of type PAGE_COMPRESSED.
		 * if the decryption is verified, it is assumed that the
		 * original page was restored, re-calculating the original
		 * checksums should be ok
		 */
		do_check_sum(len, zip_size, buf);
	} else {
		/* page_compression uses BUF_NO_CHECKSUM_MAGIC as checksum */
		mach_write_to_4(buf + FIL_PAGE_SPACE_OR_CHKSUM, BUF_NO_CHECKSUM_MAGIC);
	}

	srv_stats.pages_page_decrypted.inc();

	return err;
}