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Apache POI - Java API To Access Microsoft Format Files
/* ====================================================================
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==================================================================== */
package org.apache.poi.hssf.record.crypto;
import java.io.InputStream;
import java.io.PushbackInputStream;
import org.apache.poi.hssf.record.BOFRecord;
import org.apache.poi.hssf.record.BiffHeaderInput;
import org.apache.poi.hssf.record.FilePassRecord;
import org.apache.poi.hssf.record.InterfaceHdrRecord;
import org.apache.poi.hssf.record.RecordFormatException;
import org.apache.poi.poifs.crypt.ChunkedCipherInputStream;
import org.apache.poi.poifs.crypt.Decryptor;
import org.apache.poi.poifs.crypt.EncryptionInfo;
import org.apache.poi.util.LittleEndian;
import org.apache.poi.util.LittleEndianConsts;
import org.apache.poi.util.LittleEndianInput;
public final class Biff8DecryptingStream implements BiffHeaderInput, LittleEndianInput {
public static final int RC4_REKEYING_INTERVAL = 1024;
private final EncryptionInfo info;
private ChunkedCipherInputStream ccis;
private final byte buffer[] = new byte[LittleEndianConsts.LONG_SIZE];
private boolean shouldSkipEncryptionOnCurrentRecord = false;
public Biff8DecryptingStream(InputStream in, int initialOffset, EncryptionInfo info) throws RecordFormatException {
try {
byte initialBuf[] = new byte[initialOffset];
InputStream stream;
if (initialOffset == 0) {
stream = in;
} else {
stream = new PushbackInputStream(in, initialOffset);
((PushbackInputStream)stream).unread(initialBuf);
}
this.info = info;
Decryptor dec = this.info.getDecryptor();
dec.setChunkSize(RC4_REKEYING_INTERVAL);
ccis = (ChunkedCipherInputStream)dec.getDataStream(stream, Integer.MAX_VALUE, 0);
if (initialOffset > 0) {
ccis.readFully(initialBuf);
}
} catch (Exception e) {
throw new RecordFormatException(e);
}
}
@Override
public int available() {
return ccis.available();
}
/**
* Reads an unsigned short value without decrypting
*/
@Override
public int readRecordSID() {
readPlain(buffer, 0, LittleEndianConsts.SHORT_SIZE);
int sid = LittleEndian.getUShort(buffer, 0);
shouldSkipEncryptionOnCurrentRecord = isNeverEncryptedRecord(sid);
return sid;
}
/**
* Reads an unsigned short value without decrypting
*/
@Override
public int readDataSize() {
readPlain(buffer, 0, LittleEndianConsts.SHORT_SIZE);
int dataSize = LittleEndian.getUShort(buffer, 0);
ccis.setNextRecordSize(dataSize);
return dataSize;
}
@Override
public double readDouble() {
long valueLongBits = readLong();
double result = Double.longBitsToDouble(valueLongBits);
if (Double.isNaN(result)) {
// (Because Excel typically doesn't write NaN
throw new RuntimeException("Did not expect to read NaN");
}
return result;
}
@Override
public void readFully(byte[] buf) {
readFully(buf, 0, buf.length);
}
@Override
public void readFully(byte[] buf, int off, int len) {
if (shouldSkipEncryptionOnCurrentRecord) {
readPlain(buf, off, buf.length);
} else {
ccis.readFully(buf, off, len);
}
}
@Override
public int readUByte() {
return readByte() & 0xFF;
}
@Override
public byte readByte() {
if (shouldSkipEncryptionOnCurrentRecord) {
readPlain(buffer, 0, LittleEndianConsts.BYTE_SIZE);
return buffer[0];
} else {
return ccis.readByte();
}
}
@Override
public int readUShort() {
return readShort() & 0xFFFF;
}
@Override
public short readShort() {
if (shouldSkipEncryptionOnCurrentRecord) {
readPlain(buffer, 0, LittleEndianConsts.SHORT_SIZE);
return LittleEndian.getShort(buffer);
} else {
return ccis.readShort();
}
}
@Override
public int readInt() {
if (shouldSkipEncryptionOnCurrentRecord) {
readPlain(buffer, 0, LittleEndianConsts.INT_SIZE);
return LittleEndian.getInt(buffer);
} else {
return ccis.readInt();
}
}
@Override
public long readLong() {
if (shouldSkipEncryptionOnCurrentRecord) {
readPlain(buffer, 0, LittleEndianConsts.LONG_SIZE);
return LittleEndian.getLong(buffer);
} else {
return ccis.readLong();
}
}
/**
* @return the absolute position in the stream
*/
public long getPosition() {
return ccis.getPos();
}
/**
* TODO: Additionally, the lbPlyPos (position_of_BOF) field of the BoundSheet8 record MUST NOT be encrypted.
*
* @return true if record type specified by sid is never encrypted
*/
public static boolean isNeverEncryptedRecord(int sid) {
switch (sid) {
case BOFRecord.sid:
// sheet BOFs for sure
// TODO - find out about chart BOFs
case InterfaceHdrRecord.sid:
// don't know why this record doesn't seem to get encrypted
case FilePassRecord.sid:
// this only really counts when writing because FILEPASS is read early
// UsrExcl(0x0194)
// FileLock
// RRDInfo(0x0196)
// RRDHead(0x0138)
return true;
default:
return false;
}
}
@Override
public void readPlain(byte b[], int off, int len) {
ccis.readPlain(b, off, len);
}
}