move decryption and identity stuff to their own packages

pkg/decrypt/decrypt.go

@@ -0,0 +1,32 @@
+package decrypt
+
+import (
+	"bytes"
+	"io"
+	"os"
+
+	"filippo.io/age"
+)
+
+// Decrypt decrypts bytes from filename
+func Decrypt(filename string, identities ...age.Identity) ([]byte, error) {
+	var (
+		f   *os.File
+		r   io.Reader
+		err error
+		out = &bytes.Buffer{}
+	)
+	if f, err = os.Open(filename); err != nil {
+		return nil, err
+	}
+
+	if r, err = age.Decrypt(f, identities...); err != nil {
+		return nil, err
+	}
+
+	if _, err := io.Copy(out, r); err != nil {
+		return nil, err
+	}
+
+	return out.Bytes(), nil
+}