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SSL certificate errors
CKAN uses .NET/Mono's standard WebClient for all downloads (with CURL as a fallback on some platforms). For HTTPS URLs, WebClient needs to be able to verify a host's SSL certificate using trusted certificates on your local system. This is also what a browser does for the same URLs, and it's why you sometimes see a "security warning" about an expired certificate.
Modern operating systems have built-in certificate stores, but Mono also has its own certificate store, which may or may not be automatically synchronized with the system certificate store, which may or may not include certificates that trust all of the download hosts.
You may see the following errors when CKAN attempts to download a file if its host's certificate cannot be verified:
Oh no! Our download failed with a certificate error!
Error: TrustFailure (The authentication or decryption has failed.)
Error: TrustFailure (Ssl error:1000007d:SSL routines:OPENSSL_internal:CERTIFICATE_VERIFY_FAILED)
Unhandled Exception:
System.Net.WebException: Error: SendFailure (Error writing headers) --->
System.Net.WebException: Error writing headers --->
System.IO.IOException: The authentication or decryption has failed.
Occasionally, these errors may happen because a download host is using an expired certificate. This has happened with SpaceDock a few times. If this is what's happening, then you should also see an error in your browser when visiting the download site. In these cases all you can do is wait for the host to fix the problem; typically it only takes a few days or less.
More often, these errors happen because your Mono certificate store is missing certificates. Fortunately, this is a problem that you can solve.
As of February 2018, TLS errors can also occur for any GitHub download, including operations internal to CKAN such as registry updates. This is because GitHub now requires TLS 1.2, and making .NET or Mono use TLS 1.2 can be a challenge.
On September 30, 2021 a significant Let's Encrypt certificate expired. This causes certificate verification failures for some clients, affecting some mod hosts but not others. Fortunately a workaround was found for systems which still include the expired certificate in their OS certificate store.
Certificate errors can also be caused by general corruption of your Mono installation. At least one user had a stray /usr/local/bin/mono executable from version 3.10.0 that was running instead of the more recent binary at /usr/bin/mono. Check mono --version to make sure you are running at least Mono 5.
To resolve these errors, Mono's certificate store must be updated to trust the affected download hosts, which entails adding the right certificates to your local Mono configuration. There are multiple tools available to do this, but any of them might work as long as the right certificates are added.
CKAN 1.24.0 includes changes specifically to enable TLS 1.2. No previous version of CKAN can access GitHub URLs anymore as of February 2018.
As of February 2018, your Mono installation must support TLS 1.2 to access GitHub URLs. Mono 5.0 is recommended for this.
Ubuntu:
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
# Note "stable-xenial" -- set to your distro
echo "deb http://download.mono-project.com/repo/debian stable-xenial main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
sudo apt-get update
sudo apt-get dist-upgrade
The cert-sync command was added in Mono 3.12.0 (release date: 13 Jan 2015). It imports certificates from your OS certificate store into the Mono SSL certificate store. This should happen automatically when installing Mono, but can also be done manually; see the Mono release note instructions for details on using cert-sync.
Debian/Ubuntu:
sudo apt install ca-certificates-mono
sudo cert-sync /etc/ssl/certs/ca-certificates.crt
Fedora:
sudo cert-sync /etc/pki/tls/certs/ca-bundle.crt
cert-sync --user /etc/pki/tls/cert.pem
Arch:
sudo cert-sync /etc/ssl/certs/ca-certificates.crt
The older mozroots command downloads and imports Mozilla's trusted root certificates into Mono. This variant of the command will prompt the user before removing any trusted certificate:
mozroots --import --ask-remove
If you get "Couldn't retrieve the file using the supplied information." as an error then try:
wget -q 'http://mxr.mozilla.org/seamonkey/source/security/nss/lib/ckfw/builtins/certdata.txt?raw=1' -O "/tmp/certdata.txt"
mozroots --import --ask-remove --file /tmp/certdata.txt
If your OS certificate store still includes the expired Let's Encrypt DST Root CA X3 certificate you may continue to experience certificate verification failures for some mod hosts (e.g.: SpaceDock) and not others (e.g.: Github). This can continue even after updating the Mono SSL certificate store as detailed above.
As a workaround this certificate can be manually removed from your OS certificate store. After the expired certificate has been removed from your OS certificate store, importing into the Mono SSL certificate store with cert-sync or mozroots as detailed above should resolve the certificate verification failures.
Contact us on the KSP forum or on our Discord server