fixed get-entries output and client-side verification

6 files changed, 95 insertions, 29 deletions

diff --git a/client/client.go b/client/client.go
index 43386b0..a7f8abb 100644
--- a/client/client.go
+++ b/client/client.go
@@ -193,6 +193,13 @@ func (c *Client) GetProofByHash(ctx context.Context, treeSize uint64, rootHash,
 	return item, nil
 }
 
+// GetEntries fetches a range of entries from the log, verifying that they are
+// of type checksum_v1 and signed by a valid certificate chain in the appendix.
+// Fewer entries may be returned if too large range, in which case the end is
+// truncated. Safe to use without a client chain and corresponding private key.
+//
+// Note that a certificate chain is considered valid if it is chained correctly.
+// In other words, the caller may want to check whether the anchor is trusted.
 func (c *Client) GetEntries(ctx context.Context, start, end uint64) ([]*stfe.GetEntryResponse, error) {
 	req, err := http.NewRequest("GET", c.protocol()+c.Log.BaseUrl+"/get-entries", nil)
 	if err != nil {
@@ -209,7 +216,22 @@ func (c *Client) GetEntries(ctx context.Context, start, end uint64) ([]*stfe.Get
 	if err := c.doRequest(ctx, req, &rsp); err != nil {
 		return nil, err
 	}
-	// TODO: verify signature over leaf data
+	for _, entry := range rsp {
+		var item stfe.StItem
+		if err := item.Unmarshal(entry.Item); err != nil {
+			return nil, fmt.Errorf("unmarshal failed: %v (%v)", err, entry)
+		}
+		if item.Format != stfe.StFormatChecksumV1 {
+			return nil, fmt.Errorf("bad StFormat: %v (%v)", err, entry)
+		}
+		if chain, err := x509util.ParseDerChainToList(entry.Chain); err != nil {
+			return nil, fmt.Errorf("bad certificate chain: %v (%v)", err, entry)
+		} else if err := x509util.VerifyChain(chain); err != nil {
+			return nil, fmt.Errorf("invalid certificate chain: %v (%v)", err, entry)
+		} else if err := VerifyChecksumV1(&item, chain[0].PublicKey, entry.Signature, tls.SignatureScheme(entry.SignatureScheme)); err != nil {
+			return nil, fmt.Errorf("invalid signature: %v (%v)", err, entry)
+		}
+	}
 	return rsp, nil
 }
 
diff --git a/client/get-entries/main.go b/client/get-entries/main.go
index 6a45707..511d53d 100644
--- a/client/get-entries/main.go
+++ b/client/get-entries/main.go
@@ -22,39 +22,47 @@ var (
 func main() {
 	flag.Parse()
 
-	client, err := client.NewClientFromPath(*logId, "", "", *operators, &http.Client{}, true)
-	if err != nil {
+	if client, err := client.NewClientFromPath(*logId, "", "", *operators, &http.Client{}, true); err != nil {
+		glog.Fatal(err)
+	} else if items, err := getRange(client, *start, *end); err != nil {
+		glog.Fatal(err)
+	} else if err := printRange(items); err != nil {
 		glog.Fatal(err)
 	}
 
-	items := make([]*stfe.StItem, 0, *end-*start+1)
-	i := *start
+	glog.Flush()
+}
+
+func getRange(client *client.Client, start, end uint64) ([]*stfe.StItem, error) {
+	items := make([]*stfe.StItem, 0, end-start+1)
 	for len(items) != cap(items) {
-		rsps, err := client.GetEntries(context.Background(), i, *end)
+		rsps, err := client.GetEntries(context.Background(), start, end)
 		if err != nil {
-			glog.Fatal(err)
+			return nil, fmt.Errorf("fetching entries failed: %v", err)
 		}
 
 		for _, rsp := range rsps {
 			var item stfe.StItem
-			if err := item.Unmarshal(rsp.Leaf); err != nil {
-				glog.Fatalf("bad StItem: unmarshal failed: %v", err)
+			if err := item.Unmarshal(rsp.Item); err != nil {
+				return nil, fmt.Errorf("expected valid StItem but unmarshal failed: %v", err)
 			} else if item.Format != stfe.StFormatChecksumV1 {
-				glog.Fatalf("bad StFormat: %v", item.Format)
+				return nil, fmt.Errorf("expected checksum_v1 but got: %v", item.Format)
 			}
 			items = append(items, &item)
 		}
-		i += uint64(len(rsps))
+		start += uint64(len(rsps))
 	}
+	return items, nil
+}
 
+func printRange(items []*stfe.StItem) error {
 	for i, item := range items {
-		glog.V(2).Infof("Index(%d): %s", *start+uint64(i), item)
+		glog.V(3).Infof("Index(%d): %s", *start+uint64(i), item)
 		str, err := item.MarshalB64()
 		if err != nil {
-			glog.Fatalf("bad StItem: marshal failed: %v", err)
+			glog.Fatalf("expected valid StItem but marshal failed: %v", err)
 		}
 		fmt.Printf("Index(%d): %s\n", *start+uint64(i), str)
 	}
-
-	glog.Flush()
+	return nil
 }
diff --git a/client/verify.go b/client/verify.go
index 8d64211..d9c18bf 100644
--- a/client/verify.go
+++ b/client/verify.go
@@ -12,6 +12,7 @@ import (
 	"github.com/system-transparency/stfe"
 )
 
+// VerifySignedDebugInfoV1 verifies an SDI signature
 func VerifySignedDebugInfoV1(sdi *stfe.StItem, scheme tls.SignatureScheme, key crypto.PublicKey, message []byte) error {
 	if err := supportedScheme(scheme, key); err != nil {
 		return err
@@ -31,13 +32,27 @@ func VerifySignedTreeHeadV1(sth *stfe.StItem, scheme tls.SignatureScheme, key cr
 	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
 }
 
+// VerifyChecksumV1 verifies a checksum signature
+func VerifyChecksumV1(checksum *stfe.StItem, key crypto.PublicKey, signature []byte, scheme tls.SignatureScheme) error {
+	serialized, err := checksum.Marshal()
+	if err != nil {
+		return fmt.Errorf("failed marshaling StItem: %v", err)
+	}
+	if err := supportedScheme(scheme, key); err != nil {
+		return err
+	}
+	if !ed25519.Verify(key.(ed25519.PublicKey), serialized, signature) {
+		return fmt.Errorf("bad signature")
+	}
+	return nil
+}
+
 // VerifyConsistencyProofV1 verifies that a consistency proof is valid without
 // checking any sth signature
 func VerifyConsistencyProofV1(proof, first, second *stfe.StItem) error {
diff --git a/markup/api.md b/markup/api.md
index 45c6deb..8a4f527 100644
--- a/markup/api.md
+++ b/markup/api.md
@@ -161,8 +161,10 @@ Input:
 Output:
 - an array of objects, each consisting of
 	- leaf: `StItem` that corresponds to the leaf's type.
-	- signature: signature that covers the retrieved item using the log's
-	configured signature algorithm.
+	- signature: signature that covers the retrieved item using the below
+	signature scheme.
+	- signature_scheme: one that the log accepts, see supported signature
+	schemes and how they are represeneted in the log's parameters.
 	- chain: an array of base-64 encoded certificates, where the first
 	corresponds to the signing certificate and the final one a trust anchor.
 
diff --git a/reqres.go b/reqres.go
index a5464ea..5013d95 100644
--- a/reqres.go
+++ b/reqres.go
@@ -39,13 +39,9 @@ type GetConsistencyProofRequest struct {
 	Second int64 `json:"second"` // size of the newer Merkle tree
 }
 
-// GetEntryResponse is an assembled log entry and its associated appendix
-// TODO: fix GetEntryResponse and update doc: should have signature scheme
-type GetEntryResponse struct {
-	Leaf      []byte   `json:"leaf"`      // tls-serialized StItem
-	Signature []byte   `json:"signature"` // Serialized signature using the log's signature scheme
-	Chain     [][]byte `json:"chain"`     // der-encoded certificates
-}
+// GetEntryResponse is an assembled log entry and its associated appendix.  It
+// is identical to the add-entry request that the log once accepted.
+type GetEntryResponse AddEntryRequest
 
 // newAddEntryRequest parses and sanitizes the JSON-encoded add-entry
 // parameters from an incoming HTTP post.  The serialized leaf value and
@@ -158,7 +154,7 @@ func (lp *LogParameters) newGetEntryResponse(leaf, appendix []byte) (*GetEntryRe
 	for _, c := range app.Chain {
 		chain = append(chain, c.Data)
 	}
-	return &GetEntryResponse{leaf, app.Signature, chain}, nil
+	return &GetEntryResponse{leaf, app.Signature, app.SignatureScheme, chain}, nil
 }
 
 // newGetEntriesResponse assembles a get-entries response
diff --git a/x509util/x509util.go b/x509util/x509util.go
index b33b4e9..b300ef3 100644
--- a/x509util/x509util.go
+++ b/x509util/x509util.go
@@ -108,9 +108,9 @@ func ParseChain(rest []byte) ([]*x509.Certificate, error) {
 	return chain, nil
 }
 
-// ParseDerChain parses a list of base64 DER-encoded X.509 certificates, such
-// that the first (zero-index) string is interpretted as an end-entity
-// certificate and the remaining ones as the an intermediate CertPool.
+// ParseDerChain parses a list of DER-encoded X.509 certificates, such that the
+// first (zero-index) string is interpretted as an end-entity certificate and
+// the remaining ones as the an intermediate CertPool.
 func ParseDerChain(chain [][]byte) (*x509.Certificate, *x509.CertPool, error) {
 	var certificate *x509.Certificate
 	intermediatePool := x509.NewCertPool()
@@ -132,3 +132,26 @@ func ParseDerChain(chain [][]byte) (*x509.Certificate, *x509.CertPool, error) {
 	return certificate, intermediatePool, nil
 }
 
+// ParseDerChainToList parses a list of DER-encoded certificates
+func ParseDerChainToList(chain [][]byte) ([]*x509.Certificate, error) {
+	ret := make([]*x509.Certificate, 0, len(chain))
+	for _, der := range chain {
+		c, err := x509.ParseCertificate(der)
+		if err != nil {
+			return nil, fmt.Errorf("certificate decoding failed: %v", err)
+		}
+		ret = append(ret, c)
+	}
+	return ret, nil
+}
+
+// VerifyChain checks whether the listed certificates are chained such
+// that the first is signed by the second, the second by the third, etc.
+func VerifyChain(chain []*x509.Certificate) error {
+	for i := 0; i < len(chain)-1; i++ {
+		if err := chain[i].CheckSignatureFrom(chain[i+1]); err != nil {
+			return err
+		}
+	}
+	return nil
+}