sbool getAuthorOfSignedJava_debug;

static S getAuthorOfSignedJava(S signed) {
  try {
    L<S> lines = toLines(signed);
    S authorLine = lines.get(lines.size()-2);
    S sigLine = lines.get(lines.size()-1);
    S text = fromLines(lines.subList(0, lines.size()-1));
    S author = dropPrefixMandatory("// -", authorLine);
    if (!isComputerID(author)) fail("Not a computer ID: " + author);
    S publicKey = getPublicKeyOfComputer(author);
    if (publicKey == null)
      fail("Computer " + author + " has to publish a public key.");
    S sig = dropPrefixMandatory("// sig: ", sigLine);
    if (PKI.verifySignature(PKI.publicKeyFromString(publicKey), PKI.signatureFromString(sig), toUtf8(text)))
      ret author;
    else
      ret null;
  } catch (RuntimeException e) {
    ret null;
  }
}

Began life as a copy of #1001567