In `gpg/g10/armor.c`, I found:
> /* No CRC at all is legal ("MAY") */
But with current implementation, it actually requires a character `=` after base64 encoded data.
It's good to support no CRC checksum at all (I mean, with no `=`) in ASCII armored data.
In the specification, it says:
> The checksum with its leading equal sign MAY appear on the first line after the base64 encoded data.
My interpretation is that the checksum (`=` plus three characters) is optional.