org.apache.poi.hssf.record.crypto.Biff8RC4 Maven / Gradle / Ivy
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package org.apache.poi.hssf.record.crypto;
import org.apache.poi.hssf.record.BOFRecord;
import org.apache.poi.hssf.record.FilePassRecord;
import org.apache.poi.hssf.record.InterfaceHdrRecord;
/**
* Used for both encrypting and decrypting BIFF8 streams. The internal
* {@link RC4} instance is renewed (re-keyed) every 1024 bytes.
*
* @author Josh Micich
*/
final class Biff8RC4 {
private static final int RC4_REKEYING_INTERVAL = 1024;
private RC4 _rc4;
/**
* This field is used to keep track of when to change the {@link RC4}
* instance. The change occurs every 1024 bytes. Every byte passed over is
* counted.
*/
private int _streamPos;
private int _nextRC4BlockStart;
private int _currentKeyIndex;
private boolean _shouldSkipEncryptionOnCurrentRecord;
private final Biff8EncryptionKey _key;
public Biff8RC4(int initialOffset, Biff8EncryptionKey key) {
if (initialOffset >= RC4_REKEYING_INTERVAL) {
throw new RuntimeException("initialOffset (" + initialOffset + ")>"
+ RC4_REKEYING_INTERVAL + " not supported yet");
}
_key = key;
_streamPos = 0;
rekeyForNextBlock();
_streamPos = initialOffset;
for (int i = initialOffset; i > 0; i--) {
_rc4.output();
}
_shouldSkipEncryptionOnCurrentRecord = false;
}
private void rekeyForNextBlock() {
_currentKeyIndex = _streamPos / RC4_REKEYING_INTERVAL;
_rc4 = _key.createRC4(_currentKeyIndex);
_nextRC4BlockStart = (_currentKeyIndex + 1) * RC4_REKEYING_INTERVAL;
}
private int getNextRC4Byte() {
if (_streamPos >= _nextRC4BlockStart) {
rekeyForNextBlock();
}
byte mask = _rc4.output();
_streamPos++;
if (_shouldSkipEncryptionOnCurrentRecord) {
return 0;
}
return mask & 0xFF;
}
public void startRecord(int currentSid) {
_shouldSkipEncryptionOnCurrentRecord = isNeverEncryptedRecord(currentSid);
}
/**
* 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
*/
private 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;
}
return false;
}
/**
* Used when BIFF header fields (sid, size) are being read. The internal
* {@link RC4} instance must step even when unencrypted bytes are read
*/
public void skipTwoBytes() {
getNextRC4Byte();
getNextRC4Byte();
}
public void xor(byte[] buf, int pOffset, int pLen) {
int nLeftInBlock;
nLeftInBlock = _nextRC4BlockStart - _streamPos;
if (pLen <= nLeftInBlock) {
// simple case - this read does not cross key blocks
_rc4.encrypt(buf, pOffset, pLen);
_streamPos += pLen;
return;
}
int offset = pOffset;
int len = pLen;
// start by using the rest of the current block
if (len > nLeftInBlock) {
if (nLeftInBlock > 0) {
_rc4.encrypt(buf, offset, nLeftInBlock);
_streamPos += nLeftInBlock;
offset += nLeftInBlock;
len -= nLeftInBlock;
}
rekeyForNextBlock();
}
// all full blocks following
while (len > RC4_REKEYING_INTERVAL) {
_rc4.encrypt(buf, offset, RC4_REKEYING_INTERVAL);
_streamPos += RC4_REKEYING_INTERVAL;
offset += RC4_REKEYING_INTERVAL;
len -= RC4_REKEYING_INTERVAL;
rekeyForNextBlock();
}
// finish with incomplete block
_rc4.encrypt(buf, offset, len);
_streamPos += len;
}
public int xorByte(int rawVal) {
int mask = getNextRC4Byte();
return (byte) (rawVal ^ mask);
}
public int xorShort(int rawVal) {
int b0 = getNextRC4Byte();
int b1 = getNextRC4Byte();
int mask = (b1 << 8) + (b0 << 0);
return rawVal ^ mask;
}
public int xorInt(int rawVal) {
int b0 = getNextRC4Byte();
int b1 = getNextRC4Byte();
int b2 = getNextRC4Byte();
int b3 = getNextRC4Byte();
int mask = (b3 << 24) + (b2 << 16) + (b1 << 8) + (b0 << 0);
return rawVal ^ mask;
}
public long xorLong(long rawVal) {
int b0 = getNextRC4Byte();
int b1 = getNextRC4Byte();
int b2 = getNextRC4Byte();
int b3 = getNextRC4Byte();
int b4 = getNextRC4Byte();
int b5 = getNextRC4Byte();
int b6 = getNextRC4Byte();
int b7 = getNextRC4Byte();
long mask =
(((long)b7) << 56)
+ (((long)b6) << 48)
+ (((long)b5) << 40)
+ (((long)b4) << 32)
+ (((long)b3) << 24)
+ (b2 << 16)
+ (b1 << 8)
+ (b0 << 0);
return rawVal ^ mask;
}
}