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## 2 Help For Users

From the user’s perspective, there’s nothing to the GnuTLS integration. It Just Works for any Emacs Lisp code that uses `open-protocol-stream` or `open-network-stream` (see Network Connections in The Emacs Lisp Reference Manual). The two functions are equivalent, the first one being an alias of the second.

There’s one way to find out if GnuTLS is available, by calling `gnutls-available-p`. This is a little bit trickier on the W32 (Windows) platform, but if you have the GnuTLS DLLs (available from http://sourceforge.net/projects/ezwinports/files/ thanks to Eli Zaretskii) in the same directory as Emacs, you should be OK.

Function: gnutls-available-p

  This function returns `t` if GnuTLS is available in this instance of Emacs.

Oh, but sometimes things go wrong. Budgets aren’t balanced, television ads lie, and even TLS and SSL connections can fail to work properly. Well, there’s something to be done in the last case.

Variable: gnutls-log-level

  The `gnutls-log-level` variable sets the log level. 1 is verbose. 2 is very verbose. 5 is crazy. Crazy! Set it to 1 or 2 and look in the `*Messages*` buffer for the debugging information.

Variable: gnutls-algorithm-priority

  The `gnutls-algorithm-priority` variable sets the GnuTLS priority string. This is global, not per host name (although `gnutls-negotiate` supports a priority string per connection so it could be done if needed). The priority string syntax is in the GnuTLS documentation.

Variable: gnutls-trustfiles

  The `gnutls-trustfiles` variable is a list of trustfiles (certificates for the issuing authorities). This is global, not per host name (although `gnutls-negotiate` supports a trustfile per connection so it could be done if needed). The trustfiles can be in PEM or DER format and examples can be found in most Unix distributions. By default the following locations are tried in this order: `/etc/ssl/certs/ca-certificates.crt` for Debian, Ubuntu, Gentoo and Arch Linux; `/etc/pki/tls/certs/ca-bundle.crt` for Fedora and RHEL; `/etc/ssl/ca-bundle.pem` for Suse; `/usr/ssl/certs/ca-bundle.crt` for Cygwin; `/usr/local/share/certs/ca-root-nss.crt` for FreeBSD. You can easily customize `gnutls-trustfiles` to be something else, but let us know if you do, so we can make the change to benefit the other users of that platform.

Variable: gnutls-verify-error

  The `gnutls-verify-error` variable allows you to verify SSL/TLS server certificates for all connections or by host name. It defaults to `nil` for now but will likely be changed to `t` later, meaning that all certificates will be verified.

  There are two checks available currently, that the certificate has been issued by a trusted authority as defined by `gnutls-trustfiles`, and that the hostname matches the certificate. `t` enables both checks, but you can enable them individually as well with `:trustfiles` and `:hostname` instead.

  Because of the low-level interactions with the GnuTLS library, there is no way currently to ask if a certificate can be accepted. You have to look in the `*Messages*` buffer.

Variable: gnutls-min-prime-bits

  The `gnutls-min-prime-bits` variable is a pretty exotic customization for cases where you want to refuse handshakes with keys under a specific size. If you don’t know for sure that you need it, you don’t. Leave it `nil`.

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