feat(identity): implement X25519 keypair generation and file storage

identity/identity.go

@@ -2,7 +2,67 @@ package identity
 
 // GetLocalKeypair retrieves the local keypair for the Noise protocol.
 // Actual implementation is pending.
-func GetLocalKeypair() {
-	// TODO: Implement keypair retrieval logic
-
+// TODO: Implement keypair retrieval logic
+import (
+	"crypto/rand"
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"golang.org/x/crypto/curve25519"
+)
+
+// Keypair holds a Noise-compatible X25519 keypair
+type Keypair struct {
+	PrivateKey [32]byte
+	PublicKey  [32]byte
+}
+
+// GenerateKeypair creates a new X25519 keypair
+func GenerateKeypair() (*Keypair, error) {
+	var priv [32]byte
+	_, err := rand.Read(priv[:])
+	if err != nil {
+		return nil, fmt.Errorf("failed to generate private key: %v", err)
+	}
+
+	pub, err := curve25519.X25519(priv[:], curve25519.Basepoint)
+	if err != nil {
+		return nil, fmt.Errorf("failed to derive public key: %v", err)
+	}
+
+	var pub32 [32]byte
+	copy(pub32[:], pub)
+
+	return &Keypair{
+		PrivateKey: priv,
+		PublicKey:  pub32,
+	}, nil
+}
+
+// SaveKeypair stores the keypair to a file as JSON
+func SaveKeypair(kp *Keypair, filepath string) error {
+	f, err := os.Create(filepath)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	return json.NewEncoder(f).Encode(kp)
+}
+
+// LoadKeypair loads a keypair from file
+func LoadKeypair(filepath string) (*Keypair, error) {
+	f, err := os.Open(filepath)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var kp Keypair
+	err = json.NewDecoder(f).Decode(&kp)
+	if err != nil {
+		return nil, err
+	}
+	return &kp, nil
 }

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"msg-sdk-go/identity"
 	"msg-sdk-go/transport"
 	"time"
 )
@@ -33,6 +34,8 @@ func testTCPTransport() {
 		fmt.Println("Error sending message:", err)
 		return
 	}
+	kp, _ := identity.GenerateKeypair()
+	fmt.Printf("Public Key: %x\n", kp.PublicKey)
 
 	// Wait a bit if you’re testing against a local echo server *need to be optimised
 	time.Sleep(1 * time.Second)