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/client.go | 31 ++++++++++++-------------------
 client/verify.go | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 19 deletions(-)
 create mode 100644 client/verify.go

(limited to 'client')

diff --git a/client/client.go b/client/client.go
index 34fa8a2..c9aaee3 100644
--- a/client/client.go
+++ b/client/client.go
@@ -92,30 +92,20 @@ func (c *Client) AddEntry(ctx context.Context, name, checksum []byte) (*stfe.StI
 		return nil, fmt.Errorf("failed creating http request: %v", err)
 	}
 	req.Header.Set("Content-Type", "application/json")
-	glog.V(2).Infof("created request: %s %s", req.Method, req.URL)
+	glog.V(2).Infof("created http request: %s %s", req.Method, req.URL)
 
-	var itemStr string
-	if err := c.doRequest(ctx, req, &itemStr); err != nil {
-		return nil, err
-	}
-	b, err := base64.StdEncoding.DecodeString(itemStr)
+	item, err := c.doRequestWithStItemResponse(ctx, req)
 	if err != nil {
-		return nil, fmt.Errorf("failed decoding base64 body: %v", err)
-	}
-	var item stfe.StItem
-	if err := item.Unmarshal(b); err != nil {
-		return nil, fmt.Errorf("failed decoding StItem: %v", err)
+		return nil, err
 	}
-	glog.V(3).Infof("got StItem: %s", item)
-
 	if item.Format != stfe.StFormatSignedDebugInfoV1 {
 		return nil, fmt.Errorf("bad StItem format: %v", item.Format)
 	}
-	if err := item.SignedDebugInfoV1.Verify(c.Log.Scheme, c.Log.PublicKey, leaf); err != nil {
+
+	if err := VerifySignedDebugInfoV1(item, c.Log.Scheme, c.Log.Key(), leaf); err != nil {
 		return nil, fmt.Errorf("bad SignedDebugInfoV1 signature: %v", err)
 	}
-	glog.V(2).Infof("add-entry request succeeded")
-	return &item, nil
+	return item, nil
 }
 
 func (c *Client) GetSth(ctx context.Context) (*stfe.StItem, error) {
@@ -123,7 +113,7 @@ func (c *Client) GetSth(ctx context.Context) (*stfe.StItem, error) {
 	if err != nil {
 		return nil, fmt.Errorf("failed creating http request: %v", err)
 	}
-	glog.V(2).Infof("created request: %s %s", req.Method, req.URL)
+	glog.V(2).Infof("created http request: %s %s", req.Method, req.URL)
 
 	item, err := c.doRequestWithStItemResponse(ctx, req)
 	if err != nil {
@@ -132,10 +122,10 @@ func (c *Client) GetSth(ctx context.Context) (*stfe.StItem, error) {
 	if item.Format != stfe.StFormatSignedTreeHeadV1 {
 		return nil, fmt.Errorf("bad StItem format: %v", item.Format)
 	}
-	if err := item.SignedTreeHeadV1.Verify(c.Log.Scheme, c.Log.PublicKey); err != nil {
+
+	if err := VerifySignedTreeHeadV1(item, c.Log.Scheme, c.Log.Key()); err != nil {
 		return nil, fmt.Errorf("bad SignedDebugInfoV1 signature: %v", err)
 	}
-	glog.V(2).Infof("get-sth request succeeded")
 	return item, nil
 }
 
@@ -187,6 +177,8 @@ func (c *Client) doRequest(ctx context.Context, req *http.Request, out interface
 	return nil
 }
 
+// doRequestWithStItemResponse sends an HTTP request and returns a decoded
+// StItem that the resulting HTTP response contained json:ed and marshaled
 func (c *Client) doRequestWithStItemResponse(ctx context.Context, req *http.Request) (*stfe.StItem, error) {
 	var itemStr string
 	if err := c.doRequest(ctx, req, &itemStr); err != nil {
@@ -200,6 +192,7 @@ func (c *Client) doRequestWithStItemResponse(ctx context.Context, req *http.Requ
 	if err := item.Unmarshal(b); err != nil {
 		return nil, fmt.Errorf("failed decoding StItem: %v", err)
 	}
+	glog.V(3).Infof("got StItem: %s", item)
 	return &item, nil
 }
 
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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