[xrpsdgmj] Dor Yeshorim cryptography

Accomplish the effect of Dor Yeshorim (genetic screening against two carriers of a recessive trait) without a trusted third party, using cryptography instead.  My first thought is homomorphic encryption.

Some features of the threat model: Avoid being able to distinguish between homozygous negative and heterozygous.  Avoid an adversary being able to match against more than one person without your permission.