app: restructure and start building p15 output

pkg/tools/asn1obj/bitstring.go

@@ -0,0 +1,27 @@
+package asn1obj
+
+import (
+	"encoding/asn1"
+	"math/bits"
+)
+
+// BitString returns a BIT STRING of the content
+func BitString(content []byte) []byte {
+	bs := asn1.BitString{
+		Bytes: content,
+	}
+
+	// drop trailing 0s by removing them from overall length
+	if len(content) > 0 {
+		trailing0s := bits.TrailingZeros8(content[len(content)-1])
+		bs.BitLength = 8*len(content) - trailing0s
+	}
+
+	// should never error
+	asn1result, err := asn1.Marshal(bs)
+	if err != nil {
+		panic(err)
+	}
+
+	return asn1result
+}