To verify the XML signature on a SAML metadata aggregate, you need an authentic copy of the metadata signing certificate, that is, the certificate that contains the public key corresponding to the private InCommon metadata signing key. The certificate must be obtained securely since all subsequent operations depend on it.
To bootstrap your trusted metadata process, you MUST check the integrity of the metadata signing certificate fetched over the network. It is not sufficient to request the certificate via a TLS-protected HTTP connection, which is why the sample procedure shown below does not rely on TLS.
You may check the integrity of the downloaded certificate in a variety of ways. For example, on a GNU/Linux system, you could use
openssl to check the integrity of the metadata signing certificate as follows:
# get the metadata signing certificate on md.incommon.org # and display the HTTP response header $ CERT_PATH=/path/to/inc-md-cert.pem $ /usr/bin/curl --silent --dump-header /dev/tty http://md.incommon.org/certs/inc-md-cert.pem > $CERT_PATH HTTP/1.1 200 OK Date: Thu, 19 Dec 2013 14:01:00 GMT Server: Apache Last-Modified: Wed, 18 Dec 2013 21:08:31 GMT ETag: "150037-4fd-4edd5727611c0" Accept-Ranges: bytes Content-Length: 1277 Connection: close Content-Type: text/plain; charset=UTF-8 # compute the SHA-1 and SHA-256 fingerprints of the metadata signing certificate $ /bin/cat $CERT_PATH | /usr/bin/openssl x509 -sha1 -in $CERT_PATH -noout -fingerprint SHA1 Fingerprint=7D:B4:BB:28:D3:D5:C8:52:E0:80:B3:62:43:2A:AF:34:B2:A6:0E:DD $ /bin/cat $CERT_PATH | /usr/bin/openssl x509 -sha256 -in $CERT_PATH -noout -fingerprint SHA256 Fingerprint=2F:9D:9A:A1:FE:D1:92:F0:64:A8:C6:31:5D:39:FA:CF:1E:08:84:0D:27:21:F3:31:B1:70:A5:2B:88:81:9F:5B