From 9ca4b300faeb27f186f81a5002f1c61a1dfd7656 Mon Sep 17 00:00:00 2001
From: Keith Fong <keith.fong@transferwise.com>
Date: Tue, 8 Sep 2026 12:13:10 +0800
Subject: [PATCH] SEC-1151 enforce KEK bundle completeness

Reject AES and TripleDES key merges until every declared component has been imported. Add collision-shaped regression coverage for both key types.\n\nCo-Authored-By: Claude <noreply@anthropic.com>
---
 kek/kek_bundle.go      |  8 ++++++++
 kek/kek_bundle_test.go | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/kek/kek_bundle.go b/kek/kek_bundle.go
index 4efb043..d1308dc 100644
--- a/kek/kek_bundle.go
+++ b/kek/kek_bundle.go
@@ -103,6 +103,10 @@ func (b *Bundle) Merge() (des.Cipher, error) {
 
 // MergeTripleDESKey tries to build the result TripleDES key from all the imported components
 func (b *Bundle) MergeTripleDESKey() (des.Cipher, error) {
+	if !b.IsComplete() {
+		return des.Cipher{}, fmt.Errorf("incomplete KEK bundle: expected %d components but got %d", b.Size, len(b.Components))
+	}
+
 	kekBytes := make([]byte, 24)
 	for _, component := range b.Components {
 		kekBytes, _ = xor.XORBytes(kekBytes, component)
@@ -121,6 +125,10 @@ func (b *Bundle) MergeTripleDESKey() (des.Cipher, error) {
 
 // MergeAESKey tries to build the result AES key from all the imported components
 func (b *Bundle) MergeAESKey() (aes.Cipher, error) {
+	if !b.IsComplete() {
+		return aes.Cipher{}, fmt.Errorf("incomplete KEK bundle: expected %d components but got %d", b.Size, len(b.Components))
+	}
+
 	var keyLen int
 	for _, component := range b.Components {
 		if keyLen == 0 {
diff --git a/kek/kek_bundle_test.go b/kek/kek_bundle_test.go
index f974c35..f99b0e7 100644
--- a/kek/kek_bundle_test.go
+++ b/kek/kek_bundle_test.go
@@ -118,6 +118,23 @@ func TestMergeResultKeySuccess(t *testing.T) {
 	}
 }
 
+func TestMergeTripleDESKeyRejectsIncompleteBundleWithMatchingCheckValue(t *testing.T) {
+	kek := New("visa", 1, 3, "DD1375")
+
+	err := kek.AddComponent(1, "E38FD6D9EF85A892F2FBFDD083A407AE", "DD1375")
+	if err != nil {
+		t.Fatalf("adding component failed with %v", err)
+	}
+
+	_, err = kek.MergeTripleDESKey()
+	if err == nil {
+		t.Fatal("should have failed if the bundle is incomplete")
+	}
+	if err.Error() != "incomplete KEK bundle: expected 3 components but got 1" {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 // AES KEK tests
 
 func TestAESAddComponentInvalidValue(t *testing.T) {
@@ -174,6 +191,23 @@ func TestAESMergeAESKeySuccess(t *testing.T) {
 	}
 }
 
+func TestMergeAESKeyRejectsIncompleteBundleWithMatchingCheckValue(t *testing.T) {
+	kek := NewWithKeyType("aes-kek", 1, 3, "B1DD24", KeyTypeAES)
+
+	err := kek.AddComponent(1, "574953452d504f430000000000546263", "B1DD24")
+	if err != nil {
+		t.Fatalf("adding component failed with %v", err)
+	}
+
+	_, err = kek.MergeAESKey()
+	if err == nil {
+		t.Fatal("should have failed if the bundle is incomplete")
+	}
+	if err.Error() != "incomplete KEK bundle: expected 3 components but got 1" {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 func TestAESMergeAESKeyCheckValueNotTally(t *testing.T) {
 	kek := NewWithKeyType("aes-kek", 1, 3, "FFFFFF", KeyTypeAES)