It is very important to understand the semantics used with signature verification. Checking a signature is not as simple as it may sound and so the operation is a bit complicated. In most cases it is required to look at several status lines. Here is a table of all cases a signed message may have:
This does mean that the signature has been successfully verified, the
certificates are all sane. However there are two subcases with
important information: One of the certificates may have expired or a
signature of a message itself as expired. It is a sound practise to
consider such a signature still as valid but additional information
should be displayed. Depending on the subcase
gpgsm will issue
these status codes:
Note, that this case is currently not implemented.
This means that the signature verification failed (this is an indication
of af a transfer error, a program error or tampering with the message).
gpgsm issues one of these status codes sequences:
For some reason the signature could not be verified, i.e. it cannot be decided whether the signature is valid or invalid. A common reason for this is a missing certificate.