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 correctly and reject the connection if the server identity can't be confirmed - but only if Certification Authorities (CAs) have been configured. As of 1.7.3, Mercurial will warn if CAs haven't been configured.
The new "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.
2.1. Debian/Ubuntu
On Debian and Ubuntu you can use this global configuration:
[web] cacerts = /etc/ssl/certs/ca-certificates.crt
2.2. Fedora/RHEL
On Fedora and RHEL you can use this global configuration:
[web] cacerts = /etc/pki/tls/certs/ca-bundle.crt
2.3. Mac OS X before 10.6
You can generate the file you need by opening Keychain Access (from /Applications/Utilities), going to the System Roots keychain, selecting everything and then choosing Export Items... from the File menu. Make sure the File Format is set to Privacy Enhanced Mail (.pem), then save it to your Desktop as Certificates. Next, in Terminal enter
sudo cp ~/Desktop/Certificates.pem /etc/hg-ca-roots.pem
then configure Mercurial as follows:
[web] cacerts = /etc/hg-ca-roots.pem
Note that because the vendor supplied set of CA root certificates on Mac OS X is in the system keychain, you may wish to repeat these steps after installing software updates if they include changes to the root certificate list.
2.4. Mac OS X 10.6 and higher
On Mac OS X 10.6 and higher, OpenSSL (which is what Python and therefore Mercurial use to implement their SSL support) will look in the system keychain. Unfortunately, the SSL code in the Python core doesn't allow for this situation---it always expects you to specify a certificate bundle, and if one is specified if must contain at least one certificate. A simple way to deal with this problem is to enter (in Terminal)
openssl req -new -x509 -extensions v3_ca -keyout /dev/null -out dummycert.pem -days 3650
to generate a dummy certificate (the contents don't matter, so you can just hit return at all of the prompts), then
sudo cp dummycert.pem /etc/hg-dummy-cert.pem
and set your configuration as follows:
[web] cacerts = /etc/hg-dummy-cert.pem
Don't download a dummy certificate someone on the Internet has created to solve this problem unless you're certain that they're trustworthy; if they kept the private key, they would be able to sign certificates that Mercurial would trust. Better just to enter the commands above.
2.5. Windows
The Windows installer for Mercurial 1.7.3 (and corresponding TortoiseHg installers) are now safe by default. They now check the validity of the identity of the server you connect to with the root certificates.
The Windows installers for Mercurial 1.7.3 (and corresponding TortoiseHg installers) contain a cacert.pem and by default configure web.cacerts in hgrc.d\paths.rc . Note that per the default settings installed, connect to repositories with self-signed certificates fail with 1.7.3. You need to adjust the default configuration for that case.
2.6. Other platforms
If your platform doesn't provide a usable CA list, you can download a cacert file from http://curl.haxx.se/docs/caextract.html or some other trusted source.
2.7. Self-signed certificates
You might want to tweak your cacert file, for example 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.
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 you have to view the certificate at the top of the Certification Path and "Copy to File" as "Base-64 encoded X.509 (.CER)". Several such files can be concatenated into one cacerts file.
Note: Self-signed certificates generated by IIS7 might not work with !OpenSSL/Python as used by Mercurial. They do apparently have different opinions on what a valid CA certificate should contain. Instead, use openssl to create your server certificate and your CA certificate.
The content of a single PEM encoded certificate can be seen with
openssl x509 -in server.pem -text
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.
In your local repository add the following to your .hg/hgrc:
[web] cacerts = /path/to/server.pem
Note: This requires Mercurial 1.7.3 or later.
4. Manually bypassing security checks on self-signed certificates
![/!\](/moin-static/modernized/img/alert.png "/!\"){kind=small}
This is obviously insecure.
Sometimes it may be expedient to disable security checks, for instance when dealing with hosts with self-signed certificates. This can be done by disabling the CA certificate configuration on the command line:
hg push --config web.cacerts= https://self-signed-host/repo
5. HTTP proxy support
Mercurial does not currently verify certificates for HTTPS connections made with CONNECT through HTTP proxies.
6. SMTP TLS certificates
Mercurial does not currently verify TLS certificates for SMTP.