first commit

internal/dm/encrypt.go

@@ -0,0 +1,87 @@
+package dm
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	gn "github.com/nbd-wtf/go-nostr"
+	"github.com/nbd-wtf/go-nostr/keyer"
+	"github.com/nbd-wtf/go-nostr/nip04"
+	"github.com/nbd-wtf/go-nostr/nip59"
+)
+
+var ErrUnsupportedKind = errors.New("unsupported DM kind")
+
+// BuildEvent builds the kind-4 or kind-1059 event(s) for a DM.
+// For kind 1059 it returns the gift wrap addressed to the recipient.
+// For kind 4 it returns a single signed event.
+func BuildEvent(kind int, senderSk, recipientHex, content string) ([]gn.Event, error) {
+	switch kind {
+	case 4:
+		return buildNip04(senderSk, recipientHex, content)
+	case 1059:
+		return buildNip17(senderSk, recipientHex, content)
+	default:
+		return nil, fmt.Errorf("%w: %d", ErrUnsupportedKind, kind)
+	}
+}
+
+func buildNip04(sk, recipient, content string) ([]gn.Event, error) {
+	shared, err := nip04.ComputeSharedSecret(recipient, sk)
+	if err != nil {
+		return nil, fmt.Errorf("nip04 shared: %w", err)
+	}
+	enc, err := nip04.Encrypt(content, shared)
+	if err != nil {
+		return nil, fmt.Errorf("nip04 encrypt: %w", err)
+	}
+	pk, err := gn.GetPublicKey(sk)
+	if err != nil {
+		return nil, err
+	}
+	ev := gn.Event{
+		PubKey:    pk,
+		CreatedAt: gn.Now(),
+		Kind:      4,
+		Tags:      gn.Tags{{"p", recipient}},
+		Content:   enc,
+	}
+	if err := ev.Sign(sk); err != nil {
+		return nil, fmt.Errorf("sign: %w", err)
+	}
+	return []gn.Event{ev}, nil
+}
+
+func buildNip17(sk, recipient, content string) ([]gn.Event, error) {
+	ks, err := keyer.NewPlainKeySigner(sk)
+	if err != nil {
+		return nil, fmt.Errorf("keyer: %w", err)
+	}
+	ctx := context.Background()
+	ourPubkey, err := ks.GetPublicKey(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	rumor := gn.Event{
+		Kind:      gn.KindDirectMessage,
+		Content:   content,
+		Tags:      gn.Tags{{"p", recipient}},
+		CreatedAt: gn.Now(),
+		PubKey:    ourPubkey,
+	}
+	rumor.ID = rumor.GetID()
+
+	wrap, err := nip59.GiftWrap(
+		rumor,
+		recipient,
+		func(s string) (string, error) { return ks.Encrypt(ctx, s, recipient) },
+		func(e *gn.Event) error { return ks.SignEvent(ctx, e) },
+		nil,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("nip17 giftwrap: %w", err)
+	}
+	return []gn.Event{wrap}, nil
+}