feat: ber to der convertor

internal/encoding/asn1/ber/ber.go

@@ -21,6 +21,7 @@
 // Reference:
 // - http://luca.ntop.org/Teaching/Appunti/asn1.html
 // - ISO/IEC 8825-1:2021
+// - https://learn.microsoft.com/windows/win32/seccertenroll/about-introduction-to-asn-1-syntax-and-encoding
 package ber
 
 import (
@@ -32,7 +33,7 @@ import (
 // value is the interface for an ASN.1 value node.
 type value interface {
 	// EncodeMetadata encodes the identifier and length in DER to the buffer.
-	EncodeMetadata(Writer) error
+	EncodeMetadata(writer) error
 
 	// EncodedLen returns the length in bytes of the data when encoding in DER.
 	EncodedLen() int

internal/encoding/asn1/ber/common.go

@@ -13,18 +13,17 @@
 
 package ber
 
-import (
-	"io"
-)
+import "io"
 
-// Writer is the interface that wraps the basic Write and WriteByte methods.
-type Writer interface {
+// writer is the interface that wraps the basic Write and WriteByte methods.
+type writer interface {
 	io.Writer
 	io.ByteWriter
 }
 
 // encodeLength encodes length octets in DER.
 // Reference: ISO/IEC 8825-1: 10.1
+// Reference: https://learn.microsoft.com/windows/win32/seccertenroll/about-encoded-length-and-value-bytes
 func encodeLength(w io.ByteWriter, length int) error {
 	// DER restriction: short form must be used for length less than 128
 	if length < 0x80 {
@@ -48,14 +47,16 @@ func encodeLength(w io.ByteWriter, length int) error {
 // encodedLengthSize gives the number of octets used for encoding the length
 // in DER.
 // Reference: ISO/IEC 8825-1: 10.1
+// Reference: https://learn.microsoft.com/windows/win32/seccertenroll/about-encoded-length-and-value-bytes
 func encodedLengthSize(length int) int {
 	if length < 0x80 {
 		return 1
 	}
 
 	lengthSize := 1
-	for ; length > 0; lengthSize++ {
+	for length > 0 {
 		length >>= 8
+		lengthSize++
 	}
 	return lengthSize
 }

internal/encoding/asn1/ber/constructed.go

@@ -23,7 +23,7 @@ type constructed struct {
 
 // EncodeMetadata encodes the identifier and length octets of constructed
 // to the value writer in DER.
-func (v *constructed) EncodeMetadata(w Writer) error {
+func (v *constructed) EncodeMetadata(w writer) error {
 	_, err := w.Write(v.identifier)
 	if err != nil {
 		return err

internal/encoding/asn1/ber/primitive.go

@@ -21,7 +21,7 @@ type primitive struct {
 
 // EncodeMetadata encodes the identifier and length octets of primitive to
 // the value writer in DER.
-func (v *primitive) EncodeMetadata(w Writer) error {
+func (v *primitive) EncodeMetadata(w writer) error {
 	_, err := w.Write(v.identifier)
 	if err != nil {
 		return err