  To achieve lightweight selective disclosure for protecting privacy of
document holders, we propose an XML format for documents that can hide
arbitrary elements using a cryptographic hash function and salts, which allows
to be partially digitally signed and efficiently verified, as well as a JSON
format that can be converted to such XML. The documents can be efficiently
proven to exist by representing multiple such structures as a Merkle tree and
storing its root in blockchain.
  We show that our proposal has advantages over known methods that represent
the document itself as a Merkle tree and partially hide it.
