If you are a member of IMS you may get more help there than here. But let's see if I can help.
For reference, here is what moodle passes back in its provider.
716c919df5a065dd7a3fc5702544d33a:::115:::249:::{"data":{"instanceid":"3","userid":"249","launchid":180548532},"hash":"290ab06bcf0ed944243b530718bdad0d33277884842e3f304cfb95c56c91b752"}Here is what the test tool provider passes back.
716c919df5a065dd7a3fc5702544d33a:::S3294476:::29123:::dyJ86SiwwA9
Here is the documentation, although you might have already found it http://www.imsglobal.org/specs/ltiv1p1/implementation-guide#toc-17