Allow vector values for π and s

[ymarcus93]

From the paper on p.10:

Escrowed Users may identify Perpetrators using one or more diverse credentials such as social media URLs, phone numbers, or email addresses. In our system, we insist on the use of such (relatively) unambiguous identifiers. To allow for this diversity of credentials, π and s are not scalars. Instead, they are vectors of values π ⃗ and s ⃗, where each component in these vectors corresponds to a particular predetermined type of identifying credential. We say that two records are a match if the vectors π ⃗ and π2 ⃗ match on at least one component.