From 6db3f7564c903c90e078ad5e494a50943f618ff6 Mon Sep 17 00:00:00 2001
From: Andrew Ayer <andrew@sslmate.com>
Date: Mon, 16 May 2016 11:32:48 -0700
Subject: [PATCH] Add function to reconstruct pre-cert TBS from cert TBS

---
 precerts.go | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/precerts.go b/precerts.go
index 9741e7c..d3c7b38 100644
--- a/precerts.go
+++ b/precerts.go
@@ -22,6 +22,7 @@ func bitStringEqual (a, b *asn1.BitString) bool {
 
 var (
 	oidExtensionAuthorityKeyId	= []int{2, 5, 29, 35}
+	oidExtensionSCT			= []int{1, 3, 6, 1, 4, 1, 11129, 2, 4, 2}
 	oidExtensionCTPoison		= []int{1, 3, 6, 1, 4, 1, 11129, 2, 4, 3}
 )
 func ValidatePrecert (precertBytes []byte, tbsBytes []byte) error {
@@ -115,3 +116,27 @@ func ValidatePrecert (precertBytes []byte, tbsBytes []byte) error {
 
 	return nil
 }
+func ReconstructPrecertTBS (tbs *TBSCertificate) (*TBSCertificate, error) {
+	precertTBS := TBSCertificate{
+		Version:		tbs.Version,
+		SerialNumber:		tbs.SerialNumber,
+		SignatureAlgorithm:	tbs.SignatureAlgorithm,
+		Issuer:			tbs.Issuer,
+		Validity:		tbs.Validity,
+		Subject:		tbs.Subject,
+		PublicKey:		tbs.PublicKey,
+		UniqueId:		tbs.UniqueId,
+		SubjectUniqueId:	tbs.SubjectUniqueId,
+		Extensions:		make([]Extension, 0, len(tbs.Extensions)),
+	}
+
+	for _, ext := range tbs.Extensions {
+		if !ext.Id.Equal(oidExtensionSCT) {
+			precertTBS.Extensions = append(precertTBS.Extensions, ext)
+		}
+	}
+
+	var err error
+	precertTBS.Raw, err = asn1.Marshal(precertTBS)
+	return &precertTBS, err
+}