ext/ -> Implementation of TLS extensions
auth/ -> Implementation of TLS authentication methods (DHE, SRP etc.)
accelerated/ -> Implementation of cipher acceleration
Certificate support:
x509/ -> Implementation of GnuTLS X.509 certificate support (and more)
openpgp/ -> Implementation of GnuTLS openpgp support
opencdk/ -> Implementation of low level openpgp packet parsing
minitasn1 -> ASN.1 structure parsing library
Crypto backends:
nettle/ -> -> The nettle crypto back-end
gcrypt/ -> -> The libgcrypt crypto back-end