security: add missing license headers, more documentation

pdf/core/crypt.go

@@ -17,14 +17,20 @@ import (
 	crypto "github.com/unidoc/unidoc/pdf/core/security/crypt"
 )
 
+// Version represents a version of a PDF standard.
 type Version struct {
 	Major int
 	Minor int
 }
 
+// EncryptInfo contains an information generated by the document encrypter.
 type EncryptInfo struct {
+	// Version is minimal PDF version that supports specified encryption algorithm.
 	Version
-	Encrypt  *PdfObjectDictionary
+	// Encrypt is an encryption dictionary that contains all necessary parameters.
+	// It should be stored in all copies of the document trailer.
+	Encrypt *PdfObjectDictionary
+	// ID0 and ID1 are IDs used in the trailer. Older algorithms such as RC4 uses them for encryption.
 	ID0, ID1 string
 }
 
@@ -57,7 +63,7 @@ func PdfCryptNewEncrypt(cf crypto.Filter, userPass, ownerPass []byte, perm secur
 		crypter.streamFilter = defaultFilter
 		crypter.stringFilter = defaultFilter
 	}
-	ed := crypter.newEncyptDict()
+	ed := crypter.newEncryptDict()
 
 	// Prepare the ID object for the trailer.
 	hashcode := md5.Sum([]byte(time.Now().Format(time.RFC850)))
@@ -244,7 +250,7 @@ func decodeCryptFilter(cf *crypto.FilterDict, d *PdfObjectDictionary) error {
 	return nil
 }
 
-func (crypt *PdfCrypt) newEncyptDict() *PdfObjectDictionary {
+func (crypt *PdfCrypt) newEncryptDict() *PdfObjectDictionary {
 	// Generate the encryption dictionary.
 	ed := MakeDict()
 	ed.Set("Filter", MakeName("Standard"))

pdf/core/security/auth.go

@@ -1,9 +1,16 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
 package security
 
 // AuthEvent is an event type that triggers authentication.
 type AuthEvent string
 
 const (
-	EventDocOpen = AuthEvent("DocOpen") // document open
-	EventEFOpen  = AuthEvent("EFOpen")  // embedded file open
+	// EventDocOpen is an event triggered when opening the document.
+	EventDocOpen = AuthEvent("DocOpen")
+	// EventEFOpen is an event triggered when accessing an embedded file.
+	EventEFOpen = AuthEvent("EFOpen")
 )

pdf/core/security/crypt/filter_aesv2.go

@@ -1,3 +1,8 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
 package crypt
 
 import "fmt"
@@ -22,28 +27,35 @@ func newFilterAESV2(d FilterDict) (Filter, error) {
 	return filterAESV2{}, nil
 }
 
+var _ Filter = filterAESV2{}
+
 // filterAESV2 is an AES-based filter (128 bit key, PDF 1.6)
 type filterAESV2 struct {
 	filterAES
 }
 
+// PDFVersion implements Filter interface.
 func (filterAESV2) PDFVersion() [2]int {
 	return [2]int{1, 5}
 }
 
+// HandlerVersion implements Filter interface.
 func (filterAESV2) HandlerVersion() (V, R int) {
 	V, R = 4, 4
 	return
 }
 
+// Name implements Filter interface.
 func (filterAESV2) Name() string {
 	return "AESV2"
 }
 
+// KeyLength implements Filter interface.
 func (filterAESV2) KeyLength() int {
 	return 128 / 8
 }
 
+// MakeKey implements Filter interface.
 func (filterAESV2) MakeKey(objNum, genNum uint32, ekey []byte) ([]byte, error) {
 	return makeKeyV2(objNum, genNum, ekey, true)
 }

pdf/core/security/crypt/filter_aesv3.go

@@ -1,3 +1,8 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
 package crypt
 
 import (
@@ -146,28 +151,35 @@ func (filterAES) DecryptBytes(buf []byte, okey []byte) ([]byte, error) {
 	return buf, nil
 }
 
+var _ Filter = filterAESV3{}
+
 // filterAESV3 is an AES-based filter (256 bit key, PDF 2.0)
 type filterAESV3 struct {
 	filterAES
 }
 
+// PDFVersion implements Filter interface.
 func (filterAESV3) PDFVersion() [2]int {
 	return [2]int{2, 0}
 }
 
+// HandlerVersion implements Filter interface.
 func (filterAESV3) HandlerVersion() (V, R int) {
 	V, R = 5, 6
 	return
 }
 
+// Name implements Filter interface.
 func (filterAESV3) Name() string {
 	return "AESV3"
 }
 
+// KeyLength implements Filter interface.
 func (filterAESV3) KeyLength() int {
 	return 256 / 8
 }
 
+// MakeKey implements Filter interface.
 func (filterAESV3) MakeKey(_, _ uint32, ekey []byte) ([]byte, error) {
-	return ekey, nil
+	return ekey, nil // document encryption key == object encryption key
 }

pdf/core/security/crypt/filter_v2.go

@@ -1,3 +1,8 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
 package crypt
 
 import (
@@ -21,6 +26,7 @@ func NewFilterV2(length int) Filter {
 	return f
 }
 
+// newFilterV2 creates a RC4-based filter from a Filter dictionary.
 func newFilterV2(d FilterDict) (Filter, error) {
 	if d.Length%8 != 0 {
 		return nil, fmt.Errorf("Crypt filter length not multiple of 8 (%d)", d.Length)
@@ -74,32 +80,40 @@ func makeKeyV2(objNum, genNum uint32, ekey []byte, isAES bool) ([]byte, error) {
 	return hashb, nil
 }
 
+var _ Filter = filterV2{}
+
 // filterV2 is a RC4-based filter
 type filterV2 struct {
 	length int
 }
 
+// PDFVersion implements Filter interface.
 func (f filterV2) PDFVersion() [2]int {
 	return [2]int{} // TODO(dennwc): unspecified; check what it should be
 }
 
+// HandlerVersion implements Filter interface.
 func (f filterV2) HandlerVersion() (V, R int) {
 	V, R = 2, 3
 	return
 }
 
+// Name implements Filter interface.
 func (filterV2) Name() string {
 	return "V2"
 }
 
+// KeyLength implements Filter interface.
 func (f filterV2) KeyLength() int {
 	return f.length
 }
 
+// MakeKey implements Filter interface.
 func (f filterV2) MakeKey(objNum, genNum uint32, ekey []byte) ([]byte, error) {
 	return makeKeyV2(objNum, genNum, ekey, false)
 }
 
+// EncryptBytes implements Filter interface.
 func (filterV2) EncryptBytes(buf []byte, okey []byte) ([]byte, error) {
 	// Standard RC4 algorithm.
 	ciph, err := rc4.NewCipher(okey)
@@ -112,6 +126,7 @@ func (filterV2) EncryptBytes(buf []byte, okey []byte) ([]byte, error) {
 	return buf, nil
 }
 
+// DecryptBytes implements Filter interface.
 func (filterV2) DecryptBytes(buf []byte, okey []byte) ([]byte, error) {
 	// Standard RC4 algorithm.
 	ciph, err := rc4.NewCipher(okey)

pdf/core/security/crypt/filters.go

@@ -1,3 +1,8 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
 package crypt
 
 import (
@@ -13,6 +18,27 @@ var (
 // filterFunc is used to construct crypt filters from CryptFilter dictionary
 type filterFunc func(d FilterDict) (Filter, error)
 
+// Filter is a common interface for crypt filter methods.
+type Filter interface {
+	// Name returns a name of the filter that should be used in CFM field of Encrypt dictionary.
+	Name() string
+	// KeyLength returns a length of the encryption key in bytes.
+	KeyLength() int
+	// PDFVersion reports the minimal version of PDF document that introduced this filter.
+	PDFVersion() [2]int
+	// HandlerVersion reports V and R parameters that should be used for this filter.
+	HandlerVersion() (V, R int)
+	// MakeKey generates a object encryption key based on file encryption key and object numbers.
+	// Used only for legacy filters - AESV3 doesn't change the key for each object.
+	MakeKey(objNum, genNum uint32, fkey []byte) ([]byte, error)
+	// EncryptBytes encrypts a buffer using object encryption key, as returned by MakeKey.
+	// Implementation may reuse a buffer and encrypt data in-place.
+	EncryptBytes(p []byte, okey []byte) ([]byte, error)
+	// DecryptBytes decrypts a buffer using object encryption key, as returned by MakeKey.
+	// Implementation may reuse a buffer and decrypt data in-place.
+	DecryptBytes(p []byte, okey []byte) ([]byte, error)
+}
+
 // NewFilter creates CryptFilter from a corresponding dictionary.
 func NewFilter(d FilterDict) (Filter, error) {
 	fnc, err := getFilter(d.CFM)
@@ -56,27 +82,6 @@ func getFilter(name string) (filterFunc, error) {
 	return f, nil
 }
 
-// Filter is a common interface for crypt filter methods.
-type Filter interface {
-	// Name returns a name of the filter that should be used in CFM field of Encrypt dictionary.
-	Name() string
-	// KeyLength returns a length of the encryption key in bytes.
-	KeyLength() int
-	// PDFVersion reports the minimal version of PDF document that introduced this filter.
-	PDFVersion() [2]int
-	// HandlerVersion reports V and R parameters that should be used for this filter.
-	HandlerVersion() (V, R int)
-	// MakeKey generates a object encryption key based on file encryption key and object numbers.
-	// Used only for legacy filters - AESV3 doesn't change the key for each object.
-	MakeKey(objNum, genNum uint32, fkey []byte) ([]byte, error)
-	// EncryptBytes encrypts a buffer using object encryption key, as returned by MakeKey.
-	// Implementation may reuse a buffer and encrypt data in-place.
-	EncryptBytes(p []byte, okey []byte) ([]byte, error)
-	// DecryptBytes decrypts a buffer using object encryption key, as returned by MakeKey.
-	// Implementation may reuse a buffer and decrypt data in-place.
-	DecryptBytes(p []byte, okey []byte) ([]byte, error)
-}
-
 type filterIdentity struct{}
 
 func (filterIdentity) PDFVersion() [2]int {

pdf/core/security/permissions.go

@@ -1,3 +1,8 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
 package security
 
 import "math"
@@ -9,17 +14,22 @@ const (
 	// PermOwner grants all permissions.
 	PermOwner = Permissions(math.MaxUint32)
 
-	PermPrinting        = Permissions(1 << 2) // bit 3
-	PermModify          = Permissions(1 << 3) // bit 4
-	PermExtractGraphics = Permissions(1 << 4) // bit 5
-	PermAnnotate        = Permissions(1 << 5) // bit 6
+	// PermPrinting allows printing the document with a low quality.
+	PermPrinting = Permissions(1 << 2)
+	// PermModify allows to modify the document.
+	PermModify = Permissions(1 << 3)
+	// PermExtractGraphics allows to extract graphics from the document.
+	PermExtractGraphics = Permissions(1 << 4)
+	// PermAnnotate allows annotating the document.
+	PermAnnotate = Permissions(1 << 5)
 	// PermFillForms allow form filling, if annotation is disabled?  If annotation enabled, is not looked at.
-	PermFillForms         = Permissions(1 << 8) // bit 9
-	PermDisabilityExtract = Permissions(1 << 9) // bit 10 // TODO: not clear what this means!
+	PermFillForms = Permissions(1 << 8)
+	// PermDisabilityExtract allows to extract graphics in accessibility mode.
+	PermDisabilityExtract = Permissions(1 << 9)
 	// PermRotateInsert allows rotating, editing page order.
-	PermRotateInsert = Permissions(1 << 10) // bit 11
+	PermRotateInsert = Permissions(1 << 10)
 	// PermFullPrintQuality limits print quality (lowres), assuming Printing bit is set.
-	PermFullPrintQuality = Permissions(1 << 11) // bit 12
+	PermFullPrintQuality = Permissions(1 << 11)
 )
 
 // Allowed checks if a set of permissions can be granted.

pdf/core/security/standard_r4.go

@@ -26,6 +26,10 @@ func NewHandlerR4(id0 string, length int) StdHandler {
 	return stdHandlerR4{ID0: id0, Length: length}
 }
 
+// stdHandlerR4 is a standard security handler for R<=4.
+// It uses RC4 and MD5 to generate encryption parameters.
+// This legacy handler also requires Length parameter from
+// Encrypt dictionary and ID0 from the trailer.
 type stdHandlerR4 struct {
 	Length int
 	ID0    string
@@ -260,7 +264,7 @@ func (sh stdHandlerR4) alg6(d *StdEncryptDict, upass []byte) ([]byte, error) {
 }
 
 // alg7 authenticates the owner password and returns the document encryption key.
-//// It returns an nil key in case authentication failed.
+// It returns an nil key in case authentication failed.
 func (sh stdHandlerR4) alg7(d *StdEncryptDict, opass []byte) ([]byte, error) {
 	encKey := sh.alg3Key(d.R, opass)
 
@@ -298,6 +302,8 @@ func (sh stdHandlerR4) alg7(d *StdEncryptDict, opass []byte) ([]byte, error) {
 	return ekey, nil
 }
 
+// GenerateParams generates and sets O and U parameters for the encryption dictionary.
+// It expects R, P and EncryptMetadata fields to be set.
 func (sh stdHandlerR4) GenerateParams(d *StdEncryptDict, opass, upass []byte) ([]byte, error) {
 	// Make the O and U objects.
 	O, err := sh.alg3(d.R, upass, opass)
@@ -320,6 +326,7 @@ func (sh stdHandlerR4) GenerateParams(d *StdEncryptDict, opass, upass []byte) ([
 	return ekey, nil
 }
 
+// Authenticate implements StdHandler interface.
 func (sh stdHandlerR4) Authenticate(d *StdEncryptDict, pass []byte) ([]byte, Permissions, error) {
 	// Try owner password.
 	// May not be necessary if only want to get all contents.

pdf/core/security/standard_r6.go

@@ -27,6 +27,7 @@ func NewHandlerR6() StdHandler {
 }
 
 // stdHandlerR6 is an implementation of standard security handler with R=5 and R=6.
+// Both revisions are expected to be used with AES encryption filters.
 type stdHandlerR6 struct{}
 
 // alg2a retrieves the encryption key from an encrypted document (R >= 5).
@@ -115,10 +116,10 @@ func (sh stdHandlerR6) alg2a(d *StdEncryptDict, pass []byte) ([]byte, Permission
 	return fkey, perm, nil
 }
 
-// alg2b_R5 computes a hash for R=5, used in a deprecated extension.
+// alg2bR5 computes a hash for R=5, used in a deprecated extension.
 // It's used the same way as a hash described in Algorithm 2.B, but it doesn't use the original password
 // and the user key to calculate the hash.
-func alg2b_R5(data []byte) []byte {
+func alg2bR5(data []byte) []byte {
 	h := sha256.New()
 	h.Write(data)
 	return h.Sum(nil)
@@ -216,7 +217,7 @@ func alg2b(data, pwd, userKey []byte) []byte {
 // alg2b computes a hash for R=5 and R=6.
 func (sh stdHandlerR6) alg2b(R int, data, pwd, userKey []byte) []byte {
 	if R == 5 {
-		return alg2b_R5(data)
+		return alg2bR5(data)
 	}
 	return alg2b(data, pwd, userKey)
 }
@@ -422,9 +423,10 @@ func (sh stdHandlerR6) alg13(d *StdEncryptDict, fkey []byte) error {
 	return nil
 }
 
-// generateR6 is the algorithm opposite to alg2a (R>=5).
+// GenerateParams is the algorithm opposite to alg2a (R>=5).
 // It generates U,O,UE,OE,Perms fields using AESv3 encryption.
 // There is no algorithm number assigned to this function in the spec.
+// It expects R, P and EncryptMetadata fields to be set.
 func (sh stdHandlerR6) GenerateParams(d *StdEncryptDict, opass, upass []byte) ([]byte, error) {
 	ekey := make([]byte, 32)
 	if _, err := io.ReadFull(rand.Reader, ekey); err != nil {
@@ -461,6 +463,7 @@ func (sh stdHandlerR6) GenerateParams(d *StdEncryptDict, opass, upass []byte) ([
 	return ekey, nil
 }
 
+// Authenticate implements StdHandler interface.
 func (sh stdHandlerR6) Authenticate(d *StdEncryptDict, pass []byte) ([]byte, Permissions, error) {
 	return sh.alg2a(d, pass)
 }

pdf/core/security/standard_r6_test.go

@@ -1,3 +1,8 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
 package security
 
 import (

pdf/model/writer.go

@@ -17,12 +17,11 @@ import (
 	"io"
 	"strings"
 
-	"github.com/unidoc/unidoc/pdf/core/security/crypt"
-
 	"github.com/unidoc/unidoc/common"
 	"github.com/unidoc/unidoc/common/license"
 	. "github.com/unidoc/unidoc/pdf/core"
 	"github.com/unidoc/unidoc/pdf/core/security"
+	"github.com/unidoc/unidoc/pdf/core/security/crypt"
 	"github.com/unidoc/unidoc/pdf/model/fonts"
 )