types: Start using sigsum-lib-go

This commit does not change the way in which the log behaves externally.
In other words, all changes are internal and involves renaming and code
restructuring.  Most notably picking up the refactored sigsum-lib-go.

1 files changed, 85 insertions, 0 deletions

diff --git a/pkg/instance/experimental.go b/pkg/instance/experimental.go
new file mode 100644
index 0000000..ab81ada
--- /dev/null
+++ b/pkg/instance/experimental.go
@@ -0,0 +1,85 @@
+package instance
+
+import (
+	"bytes"
+	"context"
+	"crypto"
+	"crypto/ed25519"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/binary"
+	"fmt"
+	"net/http"
+
+	"git.sigsum.org/sigsum-lib-go/pkg/types"
+	"github.com/golang/glog"
+)
+
+// algEd25519 identifies a checkpoint signature algorithm
+const algEd25519 byte = 1
+
+// getCheckpoint is an experimental endpoint that is not part of the official
+// Sigsum API.  Documentation can be found in the transparency-dev repo.
+func getCheckpoint(ctx context.Context, i *Instance, w http.ResponseWriter, r *http.Request) (int, error) {
+	glog.V(3).Info("handling get-checkpoint request")
+	sth, err := i.Stateman.ToSign(ctx)
+	if err != nil {
+		return http.StatusInternalServerError, err
+	}
+	if err := i.signWriteNote(w, sth); err != nil {
+		return http.StatusInternalServerError, err
+	}
+	return http.StatusOK, nil
+}
+
+// signWriteNote signs and writes a checkpoint which uses "sigsum.org:<prefix>"
+// as origin string.  Origin string is also used as ID in the note signature.
+// This means that a sigsum log's prefix (say, "glass-frog"), must be unique.
+func (i *Instance) signWriteNote(w http.ResponseWriter, sth *types.SignedTreeHead) error {
+	origin := fmt.Sprintf("sigsum.org:%s", i.Prefix)
+	msg := fmt.Sprintf("%s\n%d\n%s\n",
+		origin,
+		sth.TreeSize,
+		base64.StdEncoding.EncodeToString(sth.RootHash[:]),
+	)
+	sig, err := noteSign(i.Signer, origin, msg)
+	if err != nil {
+		return err
+	}
+
+	fmt.Fprintf(w, "%s\n\u2014 %s %s\n", msg, origin, sig)
+	return nil
+}
+
+// noteSign returns a note signature for the provided origin and message
+func noteSign(signer crypto.Signer, origin, msg string) (string, error) {
+	sig, err := signer.Sign(nil, []byte(msg), crypto.Hash(0))
+	if err != nil {
+		return "", err
+	}
+
+	var hbuf [4]byte
+	binary.BigEndian.PutUint32(hbuf[:], noteKeyHash(origin, notePubKeyEd25519(signer)))
+	sig = append(hbuf[:], sig...)
+	return base64.StdEncoding.EncodeToString(sig), nil
+}
+
+// See:
+// https://cs.opensource.google/go/x/mod/+/refs/tags/v0.5.1:sumdb/note/note.go;l=336
+func notePubKeyEd25519(signer crypto.Signer) []byte {
+	return bytes.Join([][]byte{
+		[]byte{algEd25519},
+		signer.Public().(ed25519.PublicKey),
+	}, nil)
+}
+
+// Source:
+// https://cs.opensource.google/go/x/mod/+/refs/tags/v0.5.1:sumdb/note/note.go;l=222
+func noteKeyHash(name string, key []byte) uint32 {
+	h := sha256.New()
+	h.Write([]byte(name))
+	h.Write([]byte("\n"))
+	h.Write(key)
+	sum := h.Sum(nil)
+	return binary.BigEndian.Uint32(sum)
+}