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java.lang.Objectorg.faceless.pdf2.SignatureHandler
This class is the baseline handler for all digital signatures - it could
theoretically be used for any type of signature, using biometrics, public/private
key and so on. Four concrete implementations exist out-of-the-box - three subclasses
of PKCS7SignatureHandler
returned by FormSignature.HANDLER_SELFSIGN
,
FormSignature.HANDLER_VERISIGN
and FormSignature.HANDLER_ACROBATSIX
,
and since 2.3 the DSEHandler
class.
For 99% of users, it is enough to look at the examples in the FormSignature
API
documentation, which details how to sign and verify documents using the standard
handlers. For those wanting to write their own signature handlers however, read on.
The SignatureHandler class has several methods which need to be implemented by concrete
implementations of this class. They are at a minimum getFilter()
, the verify()
method (if the handler is to be used to verify signatures), and/or the
prepareToSign()
and sign()
methods if the handler is to be used to sign
signatures.
In addition, when signing if the signature is to have a visible appearance on the page,
something useful should be returned from getLayerNames()
and
getLayerAppearance()
.
The idea behind the handler is that when signing, first any annotations associated with the
signature are created and filled using the values returned from the
getLayerAppearnace()
method. Then the prepareToSign()
method is
called, which should set all the values in the "V" dictionary and generally do everything
required to set up the signature in preparation for signing. Finally the sign()
method
is called, it's return value is stored in the "Contents" field.
The SignatureHandler works in a similar way to the EncryptionHandler
class. There
are a number of get...Value
and put...Value
methods which can
be used to get/set values in the "V" dictionary of the Signature dictionary. See the
discussion in the EncryptionHandler
class documentation for details on how these
methods work. As an example, the SelfSign handler includes the following lines in it's
prepareToSign()
method:
putNameValue("Filter", "Adobe.PPKLite"); putNameValue("SubFilter", "adbe.x509.rsa_sha1"); putNumericValue("R", 65539); putStringValue("Cert", certificatebytearray);
As a slightly more complicated example, to add
/MyArray [ 100 << /Type /MyHandler >> ]
to the "V" dictionary, just do:
putArrayValue("MyArray"); putNumericValue("MyArray.0", 100); putDictionaryValue("MyArray.1"); putNameValue("MyArray.1.Type", "MyHandler");
The getFilter()
method should return an appropriate value - so again, the SelfSign
handler will return the string "Adobe.PPKLite".
For a concrete example of a working, if somewhat brain-dead signature handler, see the
DummySignatureHandler.java
example, supplied with the download package.
FormSignature
,
SignatureHandlerFactory
Constructor Summary | |
SignatureHandler()
|
Method Summary | |
protected boolean |
containsKey(String key)
Return true if the V dictionary contains the specified key |
protected int |
getArrayValueSize(String key)
Return the size of the specified Array from the V dictionary,
or -1 if no such field exists |
protected boolean |
getBooleanValue(String key)
Return a Boolean from the V dictionary as a boolean
or false if no such field exists |
protected Set |
getDictionaryValueKeys(String key)
Return the Set of keys of the specified Dictionary from the V dictionary,
or null if no such field exists. |
abstract String |
getFilter()
Return the name of the filter, eg "Adobe.PPKLite". |
abstract PDFCanvas |
getLayerAppearance(String layername,
PDFStyle style)
Return a PDFCanvas for the specified layer.
|
abstract String[] |
getLayerNames()
Return the list of appearance layer names used by this Signature Handler to create a visible appearance on the page, in the order they should be drawn. |
protected String |
getNameValue(String key)
Return a Name from the V dictionary as a String
or null if no such field exists |
protected float |
getNumericValue(String key)
Return a Number from the V dictionary as a float
or Float.NaN if no such field exists |
protected byte[] |
getStringValue(String key)
Return a String from the V dictionary as a byte array
or null if no such field exists |
protected String |
getTextStringValue(String key)
Return a Text String from the V dictionary as a String
or null if no such field exists |
byte[] |
getVariable(String name)
This method returns the contents of the variable specified by name .
|
Map |
getVariables()
Return the list of "variables" which will be set by the handler after the PDF is rendered. |
protected boolean |
isPDFObjectSignature()
Whether this handler returns it's token in the form of a byte array which should be encoded as a string (false), or whether it returns it as raw bytes which should be inserted directly into the PDF (true). |
protected void |
prepareToSign(KeyStore keystore,
String alias,
char[] password)
This method initialized the handler using the specified values into a state where it's ready to sign. |
protected void |
putArrayValue(String key)
Add (or replace) an Array to the V dictionary. |
protected void |
putBooleanValue(String key,
boolean val)
Add (or replace) a Boolean to the V dictionary. |
protected void |
putDictionaryValue(String key)
Add (or replace) a Dictionary to the V dictionary. |
protected void |
putNameValue(String key,
String val)
Add (or replace) a Name to the V dictionary.
|
protected void |
putNumericValue(String key,
float val)
Add (or replace) a Number to the V dictionary.
|
protected void |
putStringValue(String key,
byte[] val)
Add (or replace) a String to the V dictionary.
|
protected void |
putTextStringValue(String key,
String val)
Add (or replace) a Text String to the V dictionary.
|
abstract byte[] |
sign(InputStream in)
Return a signature token corresponding to the specified InputStream .
|
abstract boolean |
verify(InputStream in)
Return a boolean indicating whether or not the signature handler can verify the specified InputStream . |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
public SignatureHandler()
Method Detail |
protected boolean containsKey(String key)
V
dictionary contains the specified key
protected final byte[] getStringValue(String key)
V
dictionary as a byte array
or null
if no such field exists
protected final String getTextStringValue(String key)
V
dictionary as a String
or null
if no such field exists
protected final String getNameValue(String key)
V
dictionary as a String
or null
if no such field exists
protected final float getNumericValue(String key)
V
dictionary as a float
or Float.NaN
if no such field exists
protected final boolean getBooleanValue(String key)
V
dictionary as a boolean
or false
if no such field exists
protected final int getArrayValueSize(String key)
V
dictionary,
or -1
if no such field exists
protected final Set getDictionaryValueKeys(String key)
V
dictionary,
or null
if no such field exists.
protected final void putStringValue(String key, byte[] val)
V
dictionary.
A value of null
removes the entry.
protected final void putTextStringValue(String key, String val)
V
dictionary.
A value of null
removes the entry
protected final void putNumericValue(String key, float val)
V
dictionary.
A value of Float.NaN
removes the entry.
protected final void putNameValue(String key, String val)
V
dictionary.
A value of null
removes the entry.
protected final void putBooleanValue(String key, boolean val)
V
dictionary.
protected final void putArrayValue(String key)
V
dictionary.
protected final void putDictionaryValue(String key)
V
dictionary.
protected boolean isPDFObjectSignature()
Whether this handler returns it's token in the form of a byte array which should be encoded as a string (false), or whether it returns it as raw bytes which should be inserted directly into the PDF (true).
By default this method returns true, but if you need to set Contents to something other than a String, or add other fields which will not be included in the checksummed area, then you can encode these yourself and return true from this method. One other effect of setting this to true is the "M" value (the signature date) is not set - you need to set it yourself.
public Map getVariables() throws GeneralSecurityException
Return the list of "variables" which will be set by the handler after the
PDF is rendered. Entries in the returned map should have a String
as a key and a byte[]
as a value. The byte array should be empty
(ie all zeros), and should be long enough to hold the token that will eventually
be substituted into it from the getVariable(java.lang.String)
method.
For most SignatureHandlers, the only variable is the "Contents" array containing the signature token, which is what this method returns (it may be overridden if more variables are required).
This method and getVariable(java.lang.String)
replace the isPDFObjectSignature
method which was added in 2.2.4 but has been removed in favour of this considerably
more flexible approach.
GeneralSecurityException
public byte[] getVariable(String name) throws GeneralSecurityException
name
.
It is called after the sign(java.io.InputStream)
method. The returned byte array should not be longer
than the array returned by getVariables()
, and as it will be substituted straight
into the PDF should contain any PDF formatting that's required - for example, if returning
a string, you need to make sure the "(" and ")" characters are added around the String and
that any nested "(" characters are escaped.
This method will be called once for each item returned from the getVariables()
method,
except for "Content" (which is handled seperately).
name
- the name of a variable - guaranteed to be one of the keys returned from getVariables()
GeneralSecurityException
public abstract String getFilter()
public abstract byte[] sign(InputStream in) throws GeneralSecurityException, IOException
InputStream
.
This method will be called more than once - the first time with a
zero-length stream, to calculate the length of the token, the second time
with the actual data to sign. The returned byte array will be stored
as the "Contents" value of the Signature dictionary.
GeneralSecurityException
- if the signature cannot be applied for some cryptographic reason
IOException
- if the InputStream cannot be readpublic abstract boolean verify(InputStream in) throws GeneralSecurityException, IOException
InputStream
.
GeneralSecurityException
- if the signature cannot be verified for some cryptographic reason
IOException
- if the InputStream cannot be readprotected void prepareToSign(KeyStore keystore, String alias, char[] password) throws GeneralSecurityException
This method initialized the handler using the specified values into a state where it's ready to sign. This method should be used to set any additional fields in the Signature dictionary, for example "Certs" for the Self-Sign handler.
Those overriding this method must call super.prepareToSign()
before doing anything else.
keystore
- the KeyStore holding the signing keyalias
- which key in the KeyStore to usepassword
- the password to use to decode the key from the keystore
GeneralSecurityException
public abstract String[] getLayerNames()
FormSignature
class
when drawing the signature annotations on the page.
For more information see the document "Digital Signature Appearances for Public-Key Interoperability", from Adobes website.
As an example, both the Verisign and the SelfSign handlers return the array
[ "n0", "n1", "n2", "n3" ]
.
getLayerAppearance(java.lang.String, org.faceless.pdf2.PDFStyle)
public abstract PDFCanvas getLayerAppearance(String layername, PDFStyle style)
PDFCanvas
for the specified layer.
This method is called internally by the FormSignature
class
when drawing the signature annotations on the page.
For more information see the document "Digital Signature Appearances for Public-Key Interoperability", from Adobes website.
layername
- the layer to create (from the list returned by getLayerNames()
)style
- the style in which to draw the text, if any
PDFCanvas
of any size containing the specified layer.getLayerNames()
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