move nostr-sdk repository into here because why not?

keyring/plain.go

@@ -0,0 +1,44 @@
+package keyring
+
+import (
+	"context"
+
+	"github.com/nbd-wtf/go-nostr"
+	"github.com/nbd-wtf/go-nostr/nip44"
+)
+
+// Keysigner is a signer that holds the private key in memory and can do all the operations instantly and easily.
+type KeySigner struct {
+	sk string
+	pk string
+
+	conversationKeys map[string][32]byte
+}
+
+func (ks KeySigner) SignEvent(ctx context.Context, evt *nostr.Event) error { return evt.Sign(ks.sk) }
+func (ks KeySigner) GetPublicKey(ctx context.Context) string               { return ks.pk }
+
+func (ks KeySigner) Encrypt(ctx context.Context, plaintext string, recipient string) (c64 string, err error) {
+	ck, ok := ks.conversationKeys[recipient]
+	if !ok {
+		ck, err = nip44.GenerateConversationKey(recipient, ks.sk)
+		if err != nil {
+			return "", err
+		}
+		ks.conversationKeys[recipient] = ck
+	}
+	return nip44.Encrypt(plaintext, ck)
+}
+
+func (ks KeySigner) Decrypt(ctx context.Context, base64ciphertext string, sender string) (plaintext string, err error) {
+	ck, ok := ks.conversationKeys[sender]
+	if !ok {
+		var err error
+		ck, err = nip44.GenerateConversationKey(sender, ks.sk)
+		if err != nil {
+			return "", err
+		}
+		ks.conversationKeys[sender] = ck
+	}
+	return nip44.Encrypt(plaintext, ck)
+}