GnuPG signature

Making a signature of the document to your friend
gpg --output document.sig --sign doc

Making a detached signature of the document to your friend
gpg --output document.sig --detach-sig document 

Making a clearsign of an ascii file
gpg --clearsign document.txt

GnuPG web-of-trust
Signature trust
Local owner trust (unknown, none, marginal, full)

[img]