CA Certificates
About Mercurial's handling of SSL certificates for https urls.
Contents
1. Changes in Mercurial 1.7.x
Mercurial has improved its HTTPS support in the 1.7.x series. When connecting to an HTTPS server, it will now verify the server's certificate. Connections to a server with the wrong identity will be rejected. As of 1.7.3, Mercurial will warn if it doesn't know how to verify it because no Certification Authorities (CAs) have been configured.
The "certificate not verified" warning does not mean that you are less secure than before. It just informs you of how insecure you have always been.
You should fix your setup so you get the security you might expect from SSL and don't get any warnings; otherwise you might just as well stop using HTTPS.
2. Configuration of HTTPS certificate authorities
Most operating systems maintain a set of root certificates that you might decide to trust. Note that any of these authorities can approve any server identity, and any of them will thus be able to spoof any server identity.
On Debian and Ubuntu you can use this global configuration:
[web] cacerts = /etc/ssl/certs/ca-certificates.crt
On Fedora and RHEL you can use this global configuration:
[web] cacerts = /etc/pki/tls/certs/ca-bundle.crt
If your platform doesn't provide a usable CA list, you can download a cacert file from http://curl.haxx.se/docs/caextract.html .
The Windows installers for Mercurial 1.7.3 (and corresponding TortoiseHg installers) contain a cacert.pem and will by default configure web.cacerts in hgrc.d\paths.rc and will thus prevent connecting to repositories with self-signed certificates.
You might want to tweak your cacert file, for examply by removing CAs you don't trust or by adding your own internal or self-signed CAs. Only one cacerts file can be specified at any time, so you might want to override web.cacerts in your user or repository configuration.
3. Per-repository configuration
If you want to control more explicitly who can impersonate which servers you will authenticate to and pull from you can explicitly configure the trusted CAs for each local clone.
The root CA certificate for a server can for example be retrieved with Firefox. Browse to https://server/repo and verify that this is the repository you trust, click the lock symbol in the lower right corner, View Certificate, Details, select the certificate at the top of the Certificate Hierarchy, Export, "X.509 Certificate (PEM)" and save somewhere for example as server.pem. With other browsers on Windows (XP) you have to view the certificate at the top of the Certification Path and "Copy to File" as "Base-64 encoded X.509 (.CER)".
In your local repository edit .hg/hgrc and add
[web] cacerts = /path/to/server.pem
Note: This requires Mercurial 1.7.3 or later.
4. Packaging
Packagers are encouraged to integrate as good as possible with the platforms existing PKI, for example by distributing a hgrc.d/cacert.rc with configuration of web.cacerts. If the platform doesn't have a suitable CA list you might want to distribute your own - for example the one from cURL/Mozilla.
Note however that that using a pre-configured cacert list by default will cause a regression for those who connect to servers with self-signed certificates. It should thus not be introduced in a bugfix release but wait for a major update, depending on how your update strategy is.
5. SMTP TLS certificates
Mercurial does not currently verify TLS certificates for SMTP.