steps to reproduce:
  openssl genrsa -F4 -out key.pem 4096
  futility vbutil_key --pack key.vbprivk --key key.pem --algorithm 8

before commit f7559e4b4652134b1e15de3ce31ee50a3de00f69 (futility: Use vboot 2.0 APIs for public keys), this command would work silently.  starting with that commit, it incorrectly prints the warning:
  vb2_read_packed_keyb() - wrong key size 3243 for algorithm 8

algorithm 8 is supposed to be RSA4096 SHA512, so i don't see why it's complaining.