I don't understand the need for "//" in the URI. The thing that follows it is usually an authority (hostname), not a name for an algorithm.

This would still be a valid URI without the unnecessary characters and without the confusion:

    ni:sha-256;UyaQV-Ev4rdLoHyJJWCi11OHfrYv9E1aGQAlMO2X_-Q

See: https://www.ietf.org/rfc/rfc2396.txt

Also: "nih" sounds like a pun :-)