1 files changed, 76 insertions, 0 deletions
diff --git a/pkg/types/tree_head.go b/pkg/types/tree_head.go
new file mode 100644
index 0000000..0f1efee
--- /dev/null
+++ b/pkg/types/tree_head.go
@@ -0,0 +1,76 @@
+package types
+
+import (
+	"crypto"
+	"crypto/ed25519"
+	"encoding/binary"
+	"fmt"
+	"io"
+
+	"git.sigsum.org/sigsum-lib-go/pkg/ascii"
+)
+
+type TreeHead struct {
+	Timestamp uint64 `ascii:"timestamp"`
+	TreeSize  uint64 `ascii:"tree_size"`
+	RootHash  Hash   `ascii:"root_hash"`
+}
+
+type SignedTreeHead struct {
+	TreeHead
+	Signature Signature `ascii:"signature"`
+}
+
+type CosignedTreeHead struct {
+	SignedTreeHead
+	Cosignature []Signature `ascii:"cosignature"`
+	KeyHash     []Hash      `ascii:"key_hash"`
+}
+
+func (th *TreeHead) ToBinary(keyHash *Hash) []byte {
+	b := make([]byte, 80)
+	binary.BigEndian.PutUint64(b[0:8], th.Timestamp)
+	binary.BigEndian.PutUint64(b[8:16], th.TreeSize)
+	copy(b[16:48], th.RootHash[:])
+	copy(b[48:80], keyHash[:])
+	return b
+}
+
+func (th *TreeHead) Sign(s crypto.Signer, ctx *Hash) (*SignedTreeHead, error) {
+	sig, err := s.Sign(nil, th.ToBinary(ctx), crypto.Hash(0))
+	if err != nil {
+		return nil, fmt.Errorf("types: failed signing tree head")
+	}
+
+	sth := &SignedTreeHead{
+		TreeHead: *th,
+	}
+	copy(sth.Signature[:], sig)
+	return sth, nil
+}
+
+func (sth *SignedTreeHead) ToASCII(w io.Writer) error {
+	return ascii.StdEncoding.Serialize(w, sth)
+}
+
+func (sth *SignedTreeHead) FromASCII(r io.Reader) error {
+	return ascii.StdEncoding.Deserialize(r, sth)
+}
+
+func (sth *SignedTreeHead) Verify(key *PublicKey, ctx *Hash) bool {
+	return ed25519.Verify(ed25519.PublicKey(key[:]), sth.TreeHead.ToBinary(ctx), sth.Signature[:])
+}
+
+func (cth *CosignedTreeHead) ToASCII(w io.Writer) error {
+	return ascii.StdEncoding.Serialize(w, cth)
+}
+
+func (cth *CosignedTreeHead) FromASCII(r io.Reader) error {
+	if err := ascii.StdEncoding.Deserialize(r, cth); err != nil {
+		return err
+	}
+	if len(cth.Cosignature) != len(cth.KeyHash) {
+		return fmt.Errorf("types: mismatched cosignature count")
+	}
+	return nil
+}