move stuff back from nostr package to top level.

because otherwise the path must be specified as github.com/fiatjaf/go-nostr/nostr, which is annoying.

keys.go

@@ -0,0 +1,39 @@
+package nostr
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"io"
+	"math/big"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr"
+)
+
+func GeneratePrivateKey() string {
+	params := btcec.S256().Params()
+	one := new(big.Int).SetInt64(1)
+
+	b := make([]byte, params.BitSize/8+8)
+	_, err := io.ReadFull(rand.Reader, b)
+	if err != nil {
+		return ""
+	}
+
+	k := new(big.Int).SetBytes(b)
+	n := new(big.Int).Sub(params.N, one)
+	k.Mod(k, n)
+	k.Add(k, one)
+
+	return hex.EncodeToString(k.Bytes())
+}
+
+func GetPublicKey(sk string) (string, error) {
+	b, err := hex.DecodeString(sk)
+	if err != nil {
+		return "", err
+	}
+
+	_, pk := btcec.PrivKeyFromBytes(b)
+	return hex.EncodeToString(schnorr.SerializePubKey(pk)), nil
+}