Package org.loboevolution.pdfview.decrypt

Class CryptFilterDecrypter

java.lang.Object

org.loboevolution.pdfview.decrypt.CryptFilterDecrypter

All Implemented Interfaces:

PDFDecrypter

public class CryptFilterDecrypter
extends Object
implements PDFDecrypter

Implements Version 4 standard decryption, whereby the Encrypt dictionary contains a list of named 'crypt filters', each of which is the equivalent of a PDFDecrypter. In addition to this list of crypt filters, the name of the filter to use for streams and the default filter to use for strings is specified. Requests to decode a stream with a named decrypter (typically Identity) instead of the default decrypter are honoured.

Author Luke Kirby

Constructor Summary

Constructors

Constructor	Description
CryptFilterDecrypter(Map<String,PDFDecrypter> decrypters, String defaultStreamCryptName, String defaultStringCryptName)	Class constructor

Method Summary

Modifier and Type	Method	Description
ByteBuffer	decryptBuffer(String cryptFilterName, PDFObject streamObj, ByteBuffer streamBuf)	Decrypt a buffer of data
String	decryptString(int objNum, int objGen, String inputBasicString)	Decrypt a basic string.
boolean	isEncryptionPresent()	Determine whether this actually applies a decryption other than identity decryption.
boolean	isEncryptionPresent(String cryptFilterName)	Determines whether decryption applies for a given crypt filter name
boolean	isOwnerAuthorised()	Determine whether the password known by the decrypter indicates that the user is the owner of the document.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

CryptFilterDecrypter

public CryptFilterDecrypter(Map<String,PDFDecrypter> decrypters,
 String defaultStreamCryptName,
 String defaultStringCryptName)
                     throws PDFParseException

Class constructor

Parameters:

decrypters - a map of crypt filter names to their corresponding decrypters. Must already contain the Identity filter.

defaultStreamCryptName - the crypt filter name of the default stream decrypter

defaultStringCryptName - the crypt filter name of the default string decrypter

Throws:

PDFParseException - if any.

Method Details

decryptBuffer

public ByteBuffer decryptBuffer(String cryptFilterName,
 PDFObject streamObj,
 ByteBuffer streamBuf)
                         throws PDFParseException

Decrypt a buffer of data

Specified by:

decryptBuffer in interface PDFDecrypter

Parameters:

cryptFilterName - the name of the crypt filter, if V4 encryption is being used, where individual crypt filters may be specified for individual streams. If encryption is not using V4 encryption (indicated by V=4 in the Encrypt dictionary) then this must be null. Null may also be specified with V4 encryption to indicate that the default filter should be used.

streamObj - the object whose stream is being decrypted. The containing object's number and generation contribute to the key used for stream encrypted with the document's default encryption, so this is typically required. Should be null only if a cryptFilterName is specified, as objects with specific stream filters use the general document key, rather than a stream-specific key.

streamBuf - the buffer to decrypt

Returns:

a buffer containing the decrypted stream, positioned at its beginning; will only be the same buffer as streamBuf if the identity decrypter is being used

Throws:

PDFParseException - if any.

decryptString

public String decryptString(int objNum,
 int objGen,
 String inputBasicString)
                     throws PDFParseException

Decrypt a basic string.

Specified by:

decryptString in interface PDFDecrypter

Parameters:

objNum - the object number of the containing object

objGen - the generation number of the containing object

inputBasicString - the string to be decrypted

Returns:

the decrypted string

Throws:

PDFParseException - if any.

isEncryptionPresent

public boolean isEncryptionPresent()

Determine whether this actually applies a decryption other than identity decryption.

Specified by:

isEncryptionPresent in interface PDFDecrypter

Returns:

whether encryption is present

isEncryptionPresent

public boolean isEncryptionPresent(String cryptFilterName)

Determines whether decryption applies for a given crypt filter name

Specified by:

isEncryptionPresent in interface PDFDecrypter

Parameters:

cryptFilterName - the crypt filter name

Returns:

whether the given crypt filter decrypts or not

isOwnerAuthorised

public boolean isOwnerAuthorised()

Determine whether the password known by the decrypter indicates that the user is the owner of the document. Can be used, in conjunction with PDFDecrypter.isEncryptionPresent() to determine whether any permissions apply.

Specified by:

isOwnerAuthorised in interface PDFDecrypter

Returns:

whether owner authentication is being used to decrypt the document