33

identity.go

@@ -0,0 +1,86 @@
+package lafsession
+
+import (
+	"crypto/ed25519"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+)
+
+// Identity is a long-term Ed25519 key pair used for mutual authentication.
+type Identity struct {
+	Private ed25519.PrivateKey
+	Public  ed25519.PublicKey
+}
+
+// GenerateIdentity creates a new random identity key pair.
+func GenerateIdentity() (*Identity, error) {
+	pub, priv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		return nil, err
+	}
+	return &Identity{Private: priv, Public: pub}, nil
+}
+
+// IdentityFromSeed derives an identity from a 32-byte seed (deterministic).
+func IdentityFromSeed(seed []byte) (*Identity, error) {
+	if len(seed) != ed25519.SeedSize {
+		return nil, fmt.Errorf("lafsession: seed must be %d bytes", ed25519.SeedSize)
+	}
+	priv := ed25519.NewKeyFromSeed(seed)
+	return &Identity{Private: priv, Public: priv.Public().(ed25519.PublicKey)}, nil
+}
+
+// PublicBytes returns the 32-byte public key.
+func (id *Identity) PublicBytes() []byte {
+	return append([]byte(nil), id.Public...)
+}
+
+// Fingerprint returns a SHA-256 hex fingerprint of the public key (full 32 bytes hex).
+func (id *Identity) Fingerprint() string {
+	sum := sha256.Sum256(id.Public)
+	return hex.EncodeToString(sum[:])
+}
+
+// ShortFingerprint returns the first 20 bytes of SHA-256 as spaced hex groups (display).
+func (id *Identity) ShortFingerprint() string {
+	sum := sha256.Sum256(id.Public)
+	h := hex.EncodeToString(sum[:20])
+	out := make([]byte, 0, 24+5)
+	for i := 0; i < len(h); i += 4 {
+		if i > 0 {
+			out = append(out, ' ')
+		}
+		end := i + 4
+		if end > len(h) {
+			end = len(h)
+		}
+		out = append(out, h[i:end]...)
+	}
+	return string(out)
+}
+
+// Sign signs a transcript with the identity private key.
+func (id *Identity) Sign(msg []byte) []byte {
+	return ed25519.Sign(id.Private, msg)
+}
+
+// Verify checks a signature under this identity public key.
+func (id *Identity) Verify(msg, sig []byte) bool {
+	return ed25519.Verify(id.Public, msg, sig)
+}
+
+// VerifyPeer checks a signature under an arbitrary peer public key.
+func VerifyPeer(peerPub, msg, sig []byte) bool {
+	if len(peerPub) != ed25519.PublicKeySize {
+		return false
+	}
+	return ed25519.Verify(ed25519.PublicKey(peerPub), msg, sig)
+}
+
+// FingerprintOf returns SHA-256 hex of a raw public key.
+func FingerprintOf(pub []byte) string {
+	sum := sha256.Sum256(pub)
+	return hex.EncodeToString(sum[:])
+}