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## org.faceless.pdf2
Class SignatureHandler

    java.lang.Object
      org.faceless.pdf2.SignatureHandler

Direct Known Subclasses:
  DSE200Handler, EGIZSignatureHandler, PKCS7SignatureHandler

    public abstract class SignatureHandler

extends Object

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. Two main implementations are provided with this package, those returned by `AcrobatSignatureHandlerFactory` and thoe returned by the `DSE200HandlerFactory`. Typically an object of this type will be a `PKCS7SignatureHandler`.

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()`, `getMessageDigest()` 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 `getLayerAppearance()` 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.

Since:
  2.0
See Also:
  `FormSignature`, `SignatureHandlerFactory`

Nested Class Summary
`static class` | `SignatureHandler.Placeholder` A Placeholder can be used to mark a point in the PDF which needs to be updated after the signature has been applied

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
`String` | `getDefaultName()` Returns an optional default value that can be used to initialize `FormSignature.setName(java.lang.String)`, or `null` if no such name is available.
`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.
`int` | `getEstimatedContentSize(int contentsize)` Return the estimated size of the signature object to be embedded, or <= 0 if this cannot be determined.
`abstract String` | `getFilter()` Return the name of the filter, eg "Adobe.PPKLite".
`FormSignature` | `getFormSignature()` Get the `FormSignature` this handler is attaached to
`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 abstract MessageDigest` | `getMessageDigest()` Return a MessageDigest that will be used to calculate the digest of the PDF for signing.
`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 InputStream` | `getStreamValue(String key)` Return the contents of a Stream from the `V` dictionary, or `false` 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
`Map` | `getVariables()` Return the list of "variables" which will be set by the handler after the PDF is rendered.
`protected void` | `postDigest(long filelength, Map variables)` Update any Variables that need to be updated after the Digest is calculated (eg Contents).
`protected void` | `preDigest(long filelength, Map variables)` Update any Variables that need to be updated before the Digest is calculated (eg ByteRange).
`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` | `putStreamValue(String key, byte[] val)` Add (or replace) the contents of a Stream in 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.
`protected byte[]` | `sign()` Finish the digest calculation on the digest returned from `getMessageDigest()` and return a signature token the signs it.
`protected 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

### SignatureHandler

    public SignatureHandler()

Method Detail

### containsKey

    protected boolean containsKey(String key)

  Return true if the `V` dictionary contains the specified key

### getStringValue

    protected final byte[] getStringValue(String key)

  Return a String from the `V` dictionary as a byte array or `null` if no such field exists

### getTextStringValue

    protected final String getTextStringValue(String key)

  Return a Text String from the `V` dictionary as a String or `null` if no such field exists

### getNameValue

    protected final String getNameValue(String key)

  Return a Name from the `V` dictionary as a String or `null` if no such field exists

### getNumericValue

    protected final float getNumericValue(String key)

  Return a Number from the `V` dictionary as a float or `Float.NaN` if no such field exists

### getBooleanValue

    protected final boolean getBooleanValue(String key)

  Return a Boolean from the `V` dictionary as a boolean or `false` if no such field exists

### getArrayValueSize

    protected final int getArrayValueSize(String key)

  Return the size of the specified Array from the `V` dictionary, or `-1` if no such field exists

### getDictionaryValueKeys

    protected final Set getDictionaryValueKeys(String key)

  Return the Set of keys of the specified Dictionary from the `V` dictionary, or `null` if no such field exists.

### getStreamValue

    protected final InputStream getStreamValue(String key)

  Return the contents of a Stream from the `V` dictionary, or `false` if no such field exists

  Since:
    2.6.5

### putStringValue

    protected final void putStringValue(String key,
                                        byte[] val)

  Add (or replace) a String to the `V` dictionary. A value of `null` removes the entry.

### putTextStringValue

    protected final void putTextStringValue(String key,
                                            String val)

  Add (or replace) a Text String to the `V` dictionary. A value of `null` removes the entry

### putNumericValue

    protected final void putNumericValue(String key,
                                         float val)

  Add (or replace) a Number to the `V` dictionary. A value of `Float.NaN` removes the entry.

### putNameValue

    protected final void putNameValue(String key,
                                      String val)

  Add (or replace) a Name to the `V` dictionary. A value of `null` removes the entry.

### putBooleanValue

    protected final void putBooleanValue(String key,
                                         boolean val)

  Add (or replace) a Boolean to the `V` dictionary.

### putArrayValue

    protected final void putArrayValue(String key)

  Add (or replace) an Array to the `V` dictionary.

### putDictionaryValue

    protected final void putDictionaryValue(String key)

  Add (or replace) a Dictionary to the `V` dictionary.

### putStreamValue

    protected final void putStreamValue(String key,
                                        byte[] val)

  Add (or replace) the contents of a Stream in the `V` dictionary.

  Since:
    2.6.5

### getVariables

    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 `SignatureHandler.Placeholder` as a value. These placeholders will be inserted into the PDF at the correct points.

  For most SignatureHandlers, the only variables are the "ByteRange" and "Contents" array containing the signature token, which is what this method returns (it may be overridden if more variables are required).

  This method was updated for a new signing architecture in release 2.11.12.

  Returns:
    a Map containing the variables to be substituted into the PDF during signing
  Throws:
    `GeneralSecurityException`
  Since:
    2.3
  See Also:
    `AcrobatSignatureHandlerFactory.setContentSize(int)`

### getEstimatedContentSize

    public int getEstimatedContentSize(int contentsize)

  Return the estimated size of the signature object to be embedded, or <= 0 if this cannot be determined. The default implementation returns 0.

  Parameters:
    `contentsize` - the negation of any value previously passed into `setContentSize(int)`
  Since:
    2.11.21

### getFilter

    public abstract String getFilter()

  Return the name of the filter, eg "Adobe.PPKLite".

### preDigest

    protected void preDigest(long filelength,
                             Map variables)
                      throws Exception

  Update any Variables that need to be updated before the Digest is calculated (eg ByteRange).

  Parameters:
    `filelength` - the length of the PDF file, in bytes
    `variables` - the Map of variables, ordered by their position in the file.
  Throws:
    `Exception`
  Since:
    2.11.12

### postDigest

    protected void postDigest(long filelength,
                              Map variables)
                       throws Exception

  Update any Variables that need to be updated after the Digest is calculated (eg Contents).

  Parameters:
    `filelength` - the length of the PDF file, in bytes
    `variables` - the Map of variables, ordered by their position in the file.
  Throws:
    `Exception`
  Since:
    2.11.12

### sign

    protected byte[] sign()
                   throws GeneralSecurityException,
                          IOException

  Finish the digest calculation on the digest returned from `getMessageDigest()` and return a signature token the signs it. The returned byte array will be stored as the "Contents" value of the Signature dictionary.

  As well as being called to perform the actual signing, the default behaviour of the `getVariables()` method is also to call this method with an empty digest, to determine the size of the token to store in the PDF (the `getMessageDigest()` method is called twice as well). This can be overridden, by calling `AcrobatSignatureHandlerFactory.setContentSize(int)` for handlers created by that factory or, if you're implementing a custom signature handler, by writing your own `getVariables()` method.

  Returns:
    a byte array representing the signature token
  Throws:
    `GeneralSecurityException` - if the signature cannot be applied for some cryptographic reason
    `IOException` - if the InputStream cannot be read
  Since:
    2.10 (this method existed earlier but took an InputStream as a parameter, and was required to create the digest now returned from `getMessageDigest()` internally)

### getMessageDigest

    protected abstract MessageDigest getMessageDigest()

  Return a MessageDigest that will be used to calculate the digest of the PDF for signing. This message will be called before `sign()` - see the API docs for that method for more details.

  Since:
    2.10

### verify

    protected abstract boolean verify(InputStream in)
                               throws GeneralSecurityException,
                                      IOException

  Return a boolean indicating whether or not the signature handler can verify the specified `InputStream`.

  Returns:
    true if the signature matches the specified InputStream
  Throws:
    `GeneralSecurityException` - if the signature cannot be verified for some cryptographic reason
    `IOException` - if the InputStream cannot be read

### prepareToSign

    protected 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.

  Parameters:
    `keystore` - the KeyStore
    `alias` - which key to use
    `password` - the password to use to decode the key
  Throws:
    `GeneralSecurityException`

### getLayerNames

    public 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. 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.

  As an example, both the Verisign and the SelfSign handlers return the array `[ "n0", "n1", "n2", "n3" ]`.

  Returns:
    the ordered list of layer names that should to used to create a visible representation of this signature on a page.
  See Also:
    `getLayerAppearance(java.lang.String, org.faceless.pdf2.PDFStyle)`

### getLayerAppearance

    public abstract PDFCanvas getLayerAppearance(String layername,
                                                 PDFStyle style)

  Return a `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.

  Parameters:
    `layername` - the layer to create (from the list returned by `getLayerNames()`)
    `style` - the style in which to draw the text, if any
  Returns:
    a new `PDFCanvas` of any size containing the specified layer.
  See Also:
    `getLayerNames()`

### getDefaultName

    public String getDefaultName()

  Returns an optional default value that can be used to initialize `FormSignature.setName(java.lang.String)`, or `null` if no such name is available.

  Since:
    2.11

### getFormSignature

    public FormSignature getFormSignature()

  Get the `FormSignature` this handler is attaached to

  Since:
    2.11.12

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