Example:

python MakeSignedAttributes.py attr.priv attr.cert 1:2:http://blabla.com/foo.xml 2:2:http://blabla.com/bar.xml

mp4encrypt --method MARLIN-IPMP-ACBC --key 1:000102030405060708090a0b0c0d0e0f:0000000000000000 --property 1:SignedAttributes:00000058736e6761000000287275726c000000000102687474703a2f2f626c61626c612e636f6d2f666f6f2e786d6c00000000287275726c000000000202687474703a2f2f626c61626c612e636f6d2f6261722e786d6c000000005061736967000000000000000198a38798e283e5e7d3bf253603fe184707ee9e2e51afd6f22cf3ca815f98806fd791c117a4d88196865d35b89db55b0dfcd73e96526d62ea1a2327b3e4c96f7600000012636572740000000068656c6c6f0a  --property 1:ContentId:urn:marlin:organization:foo:1234 foo.mp4 foo.mln