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-rw-r--r--pkg/instance/experimental.go85
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)
+}