From 9ab61d6884a9ac26592723523ed2521c79c47a1a Mon Sep 17 00:00:00 2001
From: Rasmus Dahlberg <rasmus.dahlberg@kau.se>
Date: Tue, 3 Nov 2020 13:17:11 +0100
Subject: fixed signature verification and client get-sth

---
 client/verify.go | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 client/verify.go

(limited to 'client/verify.go')

diff --git a/client/verify.go b/client/verify.go
new file mode 100644
index 0000000..cd2023b
--- /dev/null
+++ b/client/verify.go
@@ -0,0 +1,55 @@
+package client
+
+import (
+	"fmt"
+
+	"crypto"
+	"crypto/ed25519"
+	"crypto/tls"
+
+	"github.com/system-transparency/stfe"
+)
+
+// TODO: fix so that publicKey is already passed as crypto.PublicKey
+//k, err := x509.ParsePKIXPublicKey(publicKey)
+//if err != nil {
+//	return fmt.Errorf("failed parsing public key: %v", err)
+//}
+
+func VerifySignedDebugInfoV1(sdi *stfe.StItem, scheme tls.SignatureScheme, key crypto.PublicKey, message []byte) error {
+	if err := supportedScheme(scheme, key); err != nil {
+		return err
+	}
+	if !ed25519.Verify(key.(ed25519.PublicKey), message, sdi.SignedDebugInfoV1.Signature) {
+		return fmt.Errorf("bad signature")
+	}
+	return nil
+}
+
+// VerifySignedTreeHeadV1 verifies an STH signature
+func VerifySignedTreeHeadV1(sth *stfe.StItem, scheme tls.SignatureScheme, key crypto.PublicKey) error {
+	serialized, err := sth.SignedTreeHeadV1.TreeHead.Marshal()
+	if err != nil {
+		return fmt.Errorf("failed marshaling tree head: %v", err)
+	}
+	if err := supportedScheme(scheme, key); err != nil {
+		return err
+	}
+
+	if !ed25519.Verify(key.(ed25519.PublicKey), serialized, sth.SignedTreeHeadV1.Signature) {
+		return fmt.Errorf("bad signature")
+	}
+	return nil
+}
+
+// supportedScheme checks whether the client library supports the log's
+// signature scheme and public key type
+func supportedScheme(scheme tls.SignatureScheme, key crypto.PublicKey) error {
+	if _, ok := key.(ed25519.PublicKey); ok && scheme == tls.Ed25519 {
+		return nil
+	}
+	switch t := key.(type) {
+	default:
+		return fmt.Errorf("unsupported scheme(%v) and key(%v)", scheme, t)
+	}
+}
-- 
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