app: restructure and start building p15 output

pkg/pkcs15/keyid.go

@@ -0,0 +1,35 @@
+package pkcs15
+
+import (
+	"apc-p15-tool/pkg/tools/asn1obj"
+	"crypto/sha1"
+	"math/big"
+)
+
+// keyId returns the keyId for the overall key object
+func (p15 *pkcs15KeyCert) keyId() []byte {
+	// Create Object to hash
+	hashObj := asn1obj.Sequence([][]byte{
+		asn1obj.Sequence([][]byte{
+			// Key is RSA
+			asn1obj.ObjectIdentifier(asn1obj.OIDrsaEncryptionPKCS1),
+			asn1obj.Null(),
+		}),
+		// BIT STRING of rsa key public key
+		asn1obj.BitString(
+			asn1obj.Sequence([][]byte{
+				asn1obj.Integer(p15.key.N),
+				asn1obj.Integer((big.NewInt(int64(p15.key.E)))),
+			}),
+		),
+	})
+
+	// SHA-1 Hash
+	hasher := sha1.New()
+	_, err := hasher.Write(hashObj)
+	if err != nil {
+		panic(err)
+	}
+
+	return hasher.Sum(nil)
+}