CipherReadOnlyFile (TrueZIP Driver ZIP 7.4.1 API)

java.lang.Object
- de.schlichtherle.truezip.rof.AbstractReadOnlyFile
- - de.schlichtherle.truezip.rof.DecoratingReadOnlyFile
  - - de.schlichtherle.truezip.crypto.CipherReadOnlyFile

All Implemented Interfaces:

ReadOnlyFile, Closeable, AutoCloseable

Direct Known Subclasses:

WinZipAesEntryReadOnlyFile
```
@NotThreadSafe
@DefaultAnnotation(value=edu.umd.cs.findbugs.annotations.NonNull.class)
public abstract class CipherReadOnlyFile
extends DecoratingReadOnlyFile
```
A read only file for transparent random read access to an encrypted file. The client must call init(SeekableBlockCipher, long, long) before it can actually read anything!
Note that this class implements its own virtual file pointer. Thus, if you would like to access the underlying ReadOnlyFile again after you have finished working with an instance of this class, you should synchronize their file pointers using the pattern as described in the base class DecoratingReadOnlyFile.

Author:

Christian Schlichtherle

See Also:
CipherOutputStream

Field Summary

Fields
Modifier and Type	Field and Description
`private byte[]`	`block` The block buffer to use for decryption of partial blocks.
`private long`	`blockOff` The current offset in the encrypted file where the data starts that has been decrypted to the block.
`private SeekableBlockCipher`	`cipher` The seekable block cipher which allows random access.
`private boolean`	`closed` Whether this read only file has been closed or not.
`private long`	`fp` The virtual file pointer in the encrypted data.
`private long`	`length` The length of the encrypted data.
`private static int`	`MAX_WINDOW_LEN` The maximum buffer length of the window to the encrypted file.
`private long`	`start` Start offset of the encrypted data.
`private byte[]`	`window` The buffer window to the encrypted file.
`private long`	`windowOff` The current offset in the encrypted file where the buffer window starts.

Fields inherited from class de.schlichtherle.truezip.rof.DecoratingReadOnlyFile
delegate

Constructor Summary

Constructors
Modifier Constructor and Description

protected CipherReadOnlyFile(ReadOnlyFile rof)
Creates a read only file for transparent random read access to an encrypted file.

Constructors
Modifier	Constructor and Description
`protected`	`CipherReadOnlyFile(ReadOnlyFile rof)` Creates a read only file for transparent random read access to an encrypted file.

Method Summary

Methods
Modifier and Type	Method and Description
`private void`	`assertOpen()` Asserts that this cipher output stream is in open state, which requires that `cipher` is not `null`.
`void`	`close()` Closes this read only file and releases any resources associated with it.
`protected byte[]`	`computeMac(Mac mac)` Returns the authentication code of the encrypted data in this cipher read only file using the given Message Authentication Code (MAC) object.
`long`	`getFilePointer()`
`protected void`	`init(SeekableBlockCipher cipher, long start, long length)` Initializes this cipher read only file - must be called before first read access!
`long`	`length()`
`private static long`	`min(long a, long b)` Returns the smaller parameter.
`private void`	`positionBlock()` Positions the block with the decrypted data for partial reading so that it contains the current virtual file pointer in the encrypted file.
`private void`	`positionWindow()` Positions the window so that the block containing the current virtual file pointer in the encrypted file is entirely contained in it.
`int`	`read()`
`int`	`read(byte[] buf, int off, int len)`
`void`	`seek(long fp)`

Methods inherited from class de.schlichtherle.truezip.rof.DecoratingReadOnlyFile
toString

Methods inherited from class de.schlichtherle.truezip.rof.AbstractReadOnlyFile
read, readFully, readFully

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - block
```
private byte[] block
```
    The block buffer to use for decryption of partial blocks. Note that this buffer contains decrypted data only.
  - blockOff
```
private long blockOff
```
    The current offset in the encrypted file where the data starts that has been decrypted to the block. This is always a multiple of the block size.
  - cipher
```
@Nullable
private SeekableBlockCipher cipher
```
    The seekable block cipher which allows random access.
  - closed
```
private boolean closed
```
    Whether this read only file has been closed or not.
  - fp
```
private long fp
```
    The virtual file pointer in the encrypted data. This is relative to the start.
  - length
```
private long length
```
    The length of the encrypted data.
  - MAX_WINDOW_LEN
```
private static final int MAX_WINDOW_LEN
```
    The maximum buffer length of the window to the encrypted file. This value has been adjusted to provide optimum performance at minimal size on a Windows XP computer - results may vary. Note that the actual size of the window is a multiple of the cipher's block size and may be smaller than the maximum window size.
    
    See Also:
    Constant Field Values
  - start
```
private long start
```
    Start offset of the encrypted data.
  - window
```
private byte[] window
```
    The buffer window to the encrypted file. Note that this buffer contains encrypted data only. The actual size of the window is a multiple of the cipher's block size and may be slightly smaller than MAX_WINDOW_LEN.
  - windowOff
```
private long windowOff
```
    The current offset in the encrypted file where the buffer window starts. This is always a multiple of the block size.
- Constructor Detail
  - CipherReadOnlyFile
```
protected CipherReadOnlyFile(@Nullable
                  ReadOnlyFile rof)
```
    Creates a read only file for transparent random read access to an encrypted file. The client must call init(SeekableBlockCipher, long, long) before it can actually read anything!
    
    Parameters:
    rof - A read-only file. This may be null, but must be properly initialized before a call to init(de.schlichtherle.truezip.crypto.SeekableBlockCipher, long, long).
- Method Detail
  - assertOpen
```
private void assertOpen()
                 throws IOException
```
    Asserts that this cipher output stream is in open state, which requires that cipher is not null.
    
    Throws:
    
    IOException - If the preconditions do not hold.
  - close
```
public void close()
           throws IOException
```
    Closes this read only file and releases any resources associated with it. This method invalidates the state of this object, causing any subsequent calls to a public method to fail with an IOException.
    
    Specified by:
    
    close in interface ReadOnlyFile
    
    Specified by:
    
    close in interface Closeable
    
    Specified by:
    
    close in interface AutoCloseable
    
    Overrides:
    
    close in class DecoratingReadOnlyFile
    
    Throws:
    
    IOException - If an I/O error occurs.
  - computeMac
```
protected byte[] computeMac(Mac mac)
                     throws IOException
```
    Returns the authentication code of the encrypted data in this cipher read only file using the given Message Authentication Code (MAC) object. It is safe to call this method multiple times to detect if the file has been tampered with meanwhile.
    
    Parameters:
    mac - A properly initialized MAC object.
    
    Throws:
    
    IOException - On any I/O related issue.
  - getFilePointer
```
public long getFilePointer()
                    throws IOException
```
    Specified by:
    
    getFilePointer in interface ReadOnlyFile
    
    Overrides:
    
    getFilePointer in class DecoratingReadOnlyFile
    
    Throws:
    
    IOException
  - init
```
protected final void init(SeekableBlockCipher cipher,
        long start,
        long length)
                   throws IOException
```
    Initializes this cipher read only file - must be called before first read access!
    
    Parameters:
    start - The start offset of the encrypted data in this file.
    length - The length of the encrypted data in this file.
    
    Throws:
    
    IOException - If this read only file has already been closed. This exception is not recoverable.
    
    IllegalStateException - If this object has already been initialized. This exception is not recoverable.
    
    NullPointerException - If DecoratingReadOnlyFile.delegate or cipher is null. This exception is recoverable.
  - length
```
public long length()
            throws IOException
```
    Specified by:
    
    length in interface ReadOnlyFile
    
    Overrides:
    
    length in class DecoratingReadOnlyFile
    
    Throws:
    
    IOException
  - min
```
private static long min(long a,
       long b)
```
    Returns the smaller parameter.
  - positionBlock
```
private void positionBlock()
                    throws IOException
```
    Positions the block with the decrypted data for partial reading so that it contains the current virtual file pointer in the encrypted file.
    
    Throws:
    
    IOException - On any I/O related issue. The block is not moved in this case.
  - positionWindow
```
private void positionWindow()
                     throws IOException
```
    Positions the window so that the block containing the current virtual file pointer in the encrypted file is entirely contained in it.
    
    Throws:
    
    IOException - On any I/O related issue. The window is invalidated in this case.
  - read
```
public int read()
         throws IOException
```
    Specified by:
    
    read in interface ReadOnlyFile
    
    Overrides:
    
    read in class DecoratingReadOnlyFile
    
    Throws:
    
    IOException
  - read
```
public int read(byte[] buf,
       int off,
       int len)
         throws IOException
```
    Specified by:
    
    read in interface ReadOnlyFile
    
    Overrides:
    
    read in class DecoratingReadOnlyFile
    
    Throws:
    
    IOException
  - seek
```
public void seek(long fp)
          throws IOException
```
    Specified by:
    
    seek in interface ReadOnlyFile
    
    Overrides:
    
    seek in class DecoratingReadOnlyFile
    
    Throws:
    
    IOException

Class CipherReadOnlyFile

Field Summary

Fields inherited from class de.schlichtherle.truezip.rof.DecoratingReadOnlyFile

Constructor Summary

Method Summary

Methods inherited from class de.schlichtherle.truezip.rof.DecoratingReadOnlyFile

Methods inherited from class de.schlichtherle.truezip.rof.AbstractReadOnlyFile

Methods inherited from class java.lang.Object

Field Detail

block

blockOff

cipher

closed

fp

length

MAX_WINDOW_LEN

start

window

windowOff

Constructor Detail

CipherReadOnlyFile

Method Detail

assertOpen

close

computeMac

getFilePointer

init

length

min

positionBlock

positionWindow

read

read

seek