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Firstly, you need to obtain a membership in the ilc Virtual Organization (VO), which is sponsored by DESY. This is a VO on the LCG grid. Alternately, you can become a member of the calice VO, but this will only work if your institution is actually a member of this collaboration.
Follow the workflow at https://grid-voms.desy.de:8443/vo/ilc/vomrs which will require several rounds of confirmations and emails.
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