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  1. Choose one of three Metadata Aggregates
  2. Download Obtain an authentic copy of the Metadata Signing CertificateDeploy and configure an automated metadata refresh process:
  3. Install and configure your recommended Metadata Client Software:
    1. Refresh metadata at least daily (but more often if possible)
    2. Validate the expiration date on downloaded metadata
    3. Verify the XML signature on downloaded metadata
  4. Adjust your outbound firewall rules (if necessary)

Refresh Interval

Deployments are strongly encouraged to refresh metadata at least daily. If your metadata client supports HTTP Conditional GET, configure the client to refresh metadata every hour. This strategy provides the best protection in the event of a key compromise.

Validity Check

Federation metadata has an expiration date, much like an X.509 certificate. It is important that expired metadata not be accepted, otherwise an attacker would be able to substitute expired metadata in conjunction with metadata refresh. In particular, a metadata file should not be accepted if any of the following conditions are true:

  1. If the metadata file does not have a validUntil XML attribute on the root element.
  2. If the validUntil date on the root element is expired.
  3. If the validUntil date on the root element is too far into the future.

A metadata refresh process should check each of the above conditions before accepting the metadata. Alternatively, if your SAML implementation is known to ignore/reject expired metadata (a basic correctness requirement), it may be sufficient to ensure that a validUntil attribute exists and its date value is not unexpectedly far into the future.

Warning
titleValidate the expiration date on InCommon metadata!

Verifying the signature on a SAML metadata file does not validate the presence or value of an expiration date. The only way to validate the expiration date is to parse the XML.

Signature Verification

Federation metadata is signed for integrity and authenticity. Participants are strongly encouraged to verify the XML signature on the metadata file before use; failure to do so will seriously compromise the security of your SAML deployment.

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The InCommon Federation is based on the Explicit Key Trust Model, one of several possible metadata trust models. To bootstrap the trust fabric of the Federation, participants download and configure an authentic copy of the Metadata Signing Certificate into their metadata refresh process. The certificate must be obtained securely since all subsequent operations depend on it.

Once the certificate file is locally installed, you can use it to verify the signature on the metadata file. For example, you could use the XmlSecTool (or some similar 3rd-party tool) to verify the signature:

Code Block
languagebash
$ MD_LOCATION=http://md.incommon.org/InCommon/InCommon-metadata.xml
$ MD_PATH=/pathtmp/to/InCommon-metadata.xml
$ /usr/bin/curl --silent http://md.incommon.org/InCommon/InCommon-metadata.xml$MD_LOCATION > $MD_PATH
$ ./xmlsectool.sh --verifySignature --signatureRequired \
    --certificate $CERT$MD_CERT_PATH --inFile $MD_PATH
INFO  XmlSecTool - Reading XML document from file '/tmp/InCommon-metadata.xml'
INFO  XmlSecTool - XML document parsed and is well-formed.
INFO  XmlSecTool - XML document signature verified.

You may also want to schema validate the metadata:

Code Block
languagebash

$ ./xmlsectool.sh --validateSchema \
    --schemaDirectory $SCHEMA_DIR --inFile $MD_PATH
INFO  XmlSecTool - Reading XML document from file '/tmp/InCommon-metadata.xml'
INFO  XmlSecTool - XML document parsed and is well-formed.
INFO  XmlSecTool - XML document is schema valid

For convenience, we provide a set of (suitably modified) schema files that permit offline schema validation.

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Federation metadata has an expiration date, much like an X.509 certificate. It is important that expired metadata not be accepted, otherwise an attacker would be able to substitute expired metadata in conjunction with metadata refresh. In particular, a metadata file should not be accepted if any of the following conditions are true:

  1. If the metadata file does not have a validUntil attribute on the root element.
  2. If the validUntil attribute on the root element is expired.
  3. If the validUntil attribute on the root element is too far into the future.

A metadata reload process should check each of the above conditions before accepting the metadata; alternatively if your SAML implementation is known to ignore/reject expired metadata (a basic correctness requirement), it may be sufficient to ensure that a validUntil attribute exists and is not unexpectedly far into the future.

Warning
titleVerify the expiration date independently!

Verifying the signature on a SAML metadata file does not verify the presence or value of an expiration date. The only way to verify the expiration date is to parse the XML.

Anchor
firewall-config
firewall-config

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