package instance import ( "bytes" "context" "crypto" "crypto/ed25519" "crypto/sha256" "encoding/base64" "encoding/binary" "fmt" "net/http" "git.sigsum.org/sigsum-go/pkg/log" "git.sigsum.org/sigsum-go/pkg/types" ) // 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) { log.Debug("handling get-checkpoint request") sth, err := i.Stateman.ToCosignTreeHead(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:" // 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) }