move decryption and identity stuff to their own packages

pkg/identity/identity.go

@@ -0,0 +1,43 @@
+package identity
+
+import (
+	"io/fs"
+	"os"
+
+	"filippo.io/age"
+)
+
+// NewIdentity generates a new Age identity
+func NewIdentity() (*age.X25519Identity, error) {
+	id, err := age.GenerateX25519Identity()
+	if err != nil {
+		return nil, err
+	}
+
+	return id, nil
+}
+
+// ReadIdentityFromFile reads the identity from the supplied filename
+func ReadIdentityFromFile(filename string) (*age.X25519Identity, error) {
+	bytes, err := os.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+
+	id, err := age.ParseX25519Identity(string(bytes))
+	if err != nil {
+		return nil, err
+	}
+
+	return id, nil
+}
+
+// WriteIdentityToFile writes the supplied identity to the supplied filename
+func WriteIdentityToFile(id *age.X25519Identity, filename string) error {
+	err := os.WriteFile(filename, []byte(id.String()), fs.FileMode(0600))
+	if err != nil {
+		return err
+	}
+
+	return nil
+}