static PKIKeyPair keyPairForProgram() {
  lock programLock();
  File f = secretProgramFile("key-pair.txt");
  pcall {
    PKIKeyPair pair = pkiKeyPairFromTwoLineFile(f);
    if (pair != null) ret pair;
  }
  PKIKeyPair pair = pki_newKeyPair();
  saveTextFile(f, linesLL(pair.publicKey, pair.privateKey));
  ret pair;
}