comparison mercurial/sslutil.py @ 31290:f819aa9dbbf9

sslutil: issue warning when [hostfingerprint] is used

Mercurial 3.9 added the [hostsecurity] section, which is better
than [hostfingerprints] in every way.

One of the ways that [hostsecurity] is better is that it supports
SHA-256 and SHA-512 fingerprints, not just SHA-1 fingerprints.

The world is moving away from SHA-1 because it is borderline
secure. Mercurial should be part of that movement.

This patch adds a warning when a valid SHA-1 fingerprint from
the [hostfingerprints] section is being used. The warning informs
users to switch to [hostsecurity]. It even prints the config
option they should set. It uses the SHA-256 fingerprint because
recommending a SHA-1 fingerprint in 2017 would be ill-advised.

The warning will print itself on every connection to a server until
it is fixed. There is no way to suppress the warning. I admit this
is annoying. But given the security implications of sticking with
SHA-1, I think this is justified. If this patch is accepted,
I'll likely send a follow-up to start warning on SHA-1
certificates in [hostsecurity] as well. Then sometime down
the road, we can drop support for SHA-1 fingerprints.

Credit for this idea comes from timeless in issue 5466.

31289:718a57e95a89

    if settings['certfingerprints']:
        for hash, fingerprint in settings['certfingerprints']:
            if peerfingerprints[hash].lower() == fingerprint:
                ui.debug('%s certificate matched fingerprint %s:%s\n' %
                         (host, hash, fmtfingerprint(fingerprint)))
                return

        # Pinned fingerprint didn't match. This is a fatal error.
        if settings['legacyfingerprint']:
            section = 'hostfingerprint'

31290:f819aa9dbbf9

    if settings['certfingerprints']:
        for hash, fingerprint in settings['certfingerprints']:
            if peerfingerprints[hash].lower() == fingerprint:
                ui.debug('%s certificate matched fingerprint %s:%s\n' %
                         (host, hash, fmtfingerprint(fingerprint)))
                if settings['legacyfingerprint']:
                    ui.warn(_('(SHA-1 fingerprint for %s found in legacy '
                              '[hostfingerprints] section; '
                              'if you trust this fingerprint, set the '
                              'following config value in [hostsecurity] and '
                              'remove the old one from [hostfingerprints] '
                              'to upgrade to a more secure SHA-256 '
                              'fingerprint: '
                              '%s.fingerprints=%s)\n') % (
                                  host, host, nicefingerprint))
                return

        # Pinned fingerprint didn't match. This is a fatal error.
        if settings['legacyfingerprint']:
            section = 'hostfingerprint'