Initial import of signature models

pdf/model/signature.go

@@ -0,0 +1,238 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
+package model
+
+import "github.com/unidoc/unidoc/pdf/core"
+
+// PdfSignature represents a PDF signature dictionary and is used for signing via form signature fields.
+// (Section 12.8, Table 252 - Entries in a signature dictionary p. 475).
+type PdfSignature struct {
+	container *core.PdfIndirectObject
+	// Type: Sig
+	Filter        *core.PdfObjectName
+	SubFilter     *core.PdfObjectName
+	Contents      *core.PdfObjectString
+	Cert          core.PdfObject
+	ByteRange     *core.PdfObjectArray
+	Reference     *core.PdfObjectArray
+	Changes       *core.PdfObjectArray
+	Name          *core.PdfObjectString
+	M             *core.PdfObjectString
+	Location      *core.PdfObjectString
+	Reason        *core.PdfObjectString
+	ContactInfo   *core.PdfObjectString
+	R             *core.PdfObjectInteger
+	V             *core.PdfObjectInteger
+	Prop_Build    *core.PdfObjectDictionary
+	Prop_AuthTime *core.PdfObjectInteger
+	Prop_AuthType *core.PdfObjectName
+}
+
+// PdfSignatureReference represents a signature reference dictionary.
+// (Table 253 - p. 477 in PDF32000_2008).
+type PdfSignatureReference struct {
+	// Type: SigRef
+	TransformMethod *core.PdfObjectName
+	TransformParams *core.PdfObjectDictionary
+	Data            core.PdfObject
+	DigestMethod    *core.PdfObjectName
+}
+
+// NewPdfSignature returns an initialized PdfSignature.
+// TODO: Make more flexible?
+func NewPdfSignature() *PdfSignature {
+	sig := &PdfSignature{}
+	sig.container = core.MakeIndirectObject(core.MakeDict())
+
+	// FIXME/TODO: Replace with generic signature handler (provide default).
+	sig.Filter = core.MakeName("Adobe.PPKLite")
+	//sig.Type = core.MakeName("Sig")
+
+	return sig
+}
+
+// ToPdfObject implements interface PdfModel.
+func (sig *PdfSignature) ToPdfObject() core.PdfObject {
+	container := sig.container
+	dict := container.PdfObject.(*core.PdfObjectDictionary)
+
+	dict.Set("Type", core.MakeName("Sig"))
+
+	if sig.Filter != nil {
+		dict.Set("Filter", sig.Filter)
+	}
+	if sig.SubFilter != nil {
+		dict.Set("SubFilter", sig.SubFilter)
+	}
+	if sig.Contents != nil {
+		dict.Set("Contents", sig.Contents)
+	}
+	if sig.Cert != nil {
+		dict.Set("Cert", sig.Cert)
+	}
+	if sig.ByteRange != nil {
+		dict.Set("ByteRange", sig.ByteRange)
+	}
+	if sig.Reference != nil {
+		dict.Set("Reference", sig.Reference)
+	}
+	if sig.Changes != nil {
+		dict.Set("Changes", sig.Changes)
+	}
+	if sig.Name != nil {
+		dict.Set("Name", sig.Name)
+	}
+	if sig.M != nil {
+		dict.Set("M", sig.M)
+	}
+	if sig.Reason != nil {
+		dict.Set("Reason", sig.Reason)
+	}
+	if sig.ContactInfo != nil {
+		dict.Set("ContactInfo", sig.ContactInfo)
+	}
+
+	// XXX/FIXME: ByteRange and Contents need to be updated dynamically.
+	return container
+}
+
+// PdfSignatureField represents a form field that contains a digital signature.
+// (12.7.4.5 - Signature Fields p. 454 in PDF32000_2008.PDF).
+//
+// The signature form field serves two primary purposes. 1. Define the form field that will provide the
+// visual signing properties for display but may also hold information needed when the actual signing
+// takes place such as signature method. This carries information from the author of the document to the
+// software that later does signing.
+//
+// Filling in (signing) the signature field entails updating at least the V entry and usually the AP entry of the
+// associated widget annotation. (Exporting a signature field exports the T, V, AP entries)
+//
+// The annotation rectangle (Rect) in such a dictionary shall give the position of the field on its page. Signature
+// fields that are not intended to be visible shall have an annotation rectangle that has zero height and width. PDF
+// processors shall treat such signatures as not visible. PDF processors shall also treat signatures as not
+// visible if either the Hidden bit or the NoView bit of the F entry is true
+//
+// The location of a signature within a document can have a bearing on its legal meaning. For this reason,
+// signature fields shall never refer to more than one annotation.
+type PdfSignatureField struct {
+	container *core.PdfIndirectObject
+
+	V *PdfSignature
+	// Type: /Sig
+	// V: *PdfSignature...
+	Lock *core.PdfIndirectObject // Shall be an indirect reference.
+	SV   *core.PdfIndirectObject // Shall be an indirect reference.
+}
+
+// NewPdfSignatureField prepares a PdfSignatureField from a PdfSignature.
+func NewPdfSignatureField(signature *PdfSignature) *PdfSignatureField {
+	sf := &PdfSignatureField{}
+	sf.container = &core.PdfIndirectObject{}
+	sf.container.PdfObject = core.MakeDict()
+
+	sf.V = signature
+
+	return sf
+}
+
+// ToPdfObject implements interface PdfModel.
+func (sf *PdfSignatureField) ToPdfObject() core.PdfObject {
+	container := sf.container
+	dict := container.PdfObject.(*core.PdfObjectDictionary)
+
+	dict.Set("FT", core.MakeName("Sig"))
+
+	if sf.V != nil {
+		dict.Set("V", sf.V.ToPdfObject())
+	}
+	if sf.Lock != nil {
+		dict.Set("Lock", sf.Lock)
+	}
+	if sf.SV != nil {
+		dict.Set("SV", sf.SV)
+	}
+	// Other standard fields...
+
+	return container
+}
+
+// PdfSignatureFieldLock represents signature field lock dictionary.
+// (Table 233 - p. 455 in PDF32000_2008).
+type PdfSignatureFieldLock struct {
+	Type   core.PdfObject
+	Action *core.PdfObjectName
+	Fields *core.PdfObjectArray
+	P      *core.PdfObjectInteger
+}
+
+// PdfSignatureFieldSeed represents signature field seed value dictionary.
+// (Table 234 - p. 455 in PDF32000_2008).
+type PdfSignatureFieldSeed struct {
+	// Type
+	Ff               *core.PdfObjectInteger
+	Filter           *core.PdfObjectName
+	SubFilter        *core.PdfObjectArray
+	DigestMethod     *core.PdfObjectArray
+	V                *core.PdfObjectInteger
+	Cert             core.PdfObject
+	Reasons          *core.PdfObjectArray
+	MDP              *core.PdfObjectDictionary
+	TimeStamp        *core.PdfObjectDictionary
+	LegalAttestation *core.PdfObjectArray
+	AddRevInfo       *core.PdfObjectBool
+	LockDocument     *core.PdfObjectName
+	AppearanceFilter *core.PdfObjectString
+}
+
+// PdfCertificateSeed represents certificate seed value dictionary.
+// (Table 235 - p. 457 in PDF32000_2008).
+type PdfCertificateSeed struct {
+	// Type
+	Ff                            *core.PdfObjectInteger
+	Subject                       *core.PdfObjectArray
+	SignaturePolicyOID            *core.PdfObjectString
+	SignaturePolicyHashValue      *core.PdfObjectString
+	SignaturePolicyHashAlgorithm  *core.PdfObjectName
+	SignaturePolicyCommitmentType *core.PdfObjectArray
+	SubjectDN                     *core.PdfObjectArray
+	KeyUsage                      *core.PdfObjectArray
+	Issuer                        *core.PdfObjectArray
+	OID                           *core.PdfObjectArray
+	URL                           *core.PdfObjectString
+	URLType                       *core.PdfObjectName
+}
+
+// TODO: Add signature model.  PdfSignature...
+// getSignatureDictionaries returns a slice of signature dictionaries from form fields.
+func (form *PdfAcroForm) getSignatureDictionaries() []*core.PdfObjectDictionary {
+	sigdicts := []*core.PdfObjectDictionary{}
+
+	sigfields := form.getSignatureFields()
+	for _, f := range sigfields {
+		dict, has := core.GetDict(f.V)
+		if has {
+			sigdicts = append(sigdicts, dict)
+		}
+
+	}
+
+	return sigdicts
+}
+
+// getSignatureFields returns a slice of signature fields.
+func (form *PdfAcroForm) getSignatureFields() []*PdfField {
+	sigfields := []*PdfField{}
+
+	if form.Fields != nil {
+		for _, f := range *form.Fields {
+			if f.FT != nil && f.FT.String() == "Sig" {
+				sigfields = append(sigfields, f)
+			}
+		}
+	}
+
+	return sigfields
+}