1 SSL server requirements
2 -----------------------
4 This document is meant for Internet service providers as a check-list. If
5 fetchmail refers you to it, mail this file to the support address for the
6 server that caused the reference.
8 In order to let any mail client (not just fetchmail) verify server certificates
9 properly, so that users can be sure their connection is not eavesdropped, there
10 are several requirements that need to be fulfilled.
12 1. Match certificate and DNS names:
14 The server certificate's "common name" or "subject alternative name" must
15 match the name by which clients are connecting. Avoid the use of wildmats if
16 possible, not all clients support them (fetchmail does).
18 This may sound trivial, but for load balancing and failover setups, it may
21 2. Provide the *full* certificate chain
23 Many SSL documents tell you to install the server certificate, silently
24 assuming that it were directly signed by a trusted root certification
27 If your server certificate is not directly signed by the root certification
28 authority (root CA), then you are using intermediate CA. In this case, you
29 *MUST* (as per the TLS standard) provide *ALL* intermediate certificates.
31 If you fail to provide intermediate certificates, clients can only connect
32 if the end user overrides/disables security warnings in his/her software,
33 and this disables the detection of eavesdroppers.
35 The intermediate CA certificates must be issued after the server's
36 certificate in proper order, that is:
37 first the intermediate CA cert that signed the servers' certificate, then
38 the intermedate CA cert that signed the previous intermediate CA, and all
39 the way back to the root CA cert (which you should omit).
41 You can optionally add the root CA certificate, but this is redundant, as
42 the client needs to have that installed anyways (see 3 below) in its store
43 of trusted root certification authorities in order to verify certificates
44 that this root CA has signed.
46 For software that does not offer "chain certificate" options, but that
47 supports reading certificates in PEM format, it is usually sufficient to
48 concatenate all the certs in proper order (again, from server to root).
50 3. Provide the *root* CA's certificate separately.
52 Provide the root CA's certificate in a place where your end users will
53 quickly and easily find it, or provide a link to it. Depending on which mail
54 software your clients use, it may not be pre-installed, and users require
55 this root CA to verify your SSL server certificate, and possibly
56 intermediate certificates.
58 This is particularly important if you're using local self-signed
59 certificates, as these are never preinstalled into end-users clients.
61 Your technical support team should have the finger prints of this root CA
62 readily available at least in MD5 and SHA1 formats and offer to clients and
63 be ready to answer client questions as to the fingerprints (for
64 verification) and installation in commonly used clients.