* ok, if simple, case for you question, I have an open file in cold store, i have it hash, my public key (mpk), you public key (ypk) and hash from file, encrypted using our, for example ECDH (or quantum resistant analogue SIDH), e2e shared secret key (ssk) 
So what we can do? send each other data, using as address unique id, which also store sending direction, compare: 
SHA256( mpk, ypk, ssk ) - from me to you
SHA256( ypk, mpk, ssk ) - from you to me
we are write to ledger transaction with address hash, and IPNS address on sent content using encrypted hash with local IPv6 for current global broadcast domain, Yggdrasil, Dock DB or just public IPv6 address, or local or public domain.
So, in the header of encrypted file, or even in that DPKI transaction can be present hash from open data, for guarantee, that this is exactly sent data