Add hs_ed25519_secret_key_parsing

1 files changed, 29 insertions, 0 deletions

diff --git a/pkg/okey/okey.go b/pkg/okey/okey.go
new file mode 100644
index 0000000..aba4f3e
--- /dev/null
+++ b/pkg/okey/okey.go
@@ -0,0 +1,29 @@
+// Package okey provides access to onion service private keys
+package okey
+
+import (
+	"crypto"
+	"fmt"
+	"os"
+
+	bed25519 "github.com/cretz/bine/torutil/ed25519"
+)
+
+// New parses the content of Tor's hs_ed25519_secret_key file by interpretting
+// bytes 32..96 as the 64-byte expanded seed.  For reference, see:
+// https://gitlab.torproject.org/tpo/core/tor/-/blob/main/src/feature/keymgt/loadkey.c#L379
+func New(b []byte) (crypto.Signer, error) {
+	if len(b) != 96 {
+		return nil, fmt.Errorf("invalid key file size: %d", len(b))
+	}
+	return bed25519.PrivateKey(b[32:96]), nil
+}
+
+// NewFromHSDir reads and parses the hs_ed25519_secret_key file in a given directory
+func NewFromHSDir(dir string) (crypto.Signer, error) {
+	b, err := os.ReadFile(dir + "/hs_ed25519_secret_key")
+	if err != nil {
+		return nil, err
+	}
+	return New(b)
+}