On 11/17/2014 06:20 AM, Adam Back wrote:

b) backup: the blockchain is not an efficient reliable generic backup
mechanism because its broadcast.  there are cheaper and relatively
simple ways to get end2end secure backup, the main challenge of which
is having secure keys and not forgetting them.  bitcoin already has
that covered as its a central requirement of blockchain security.  If
you want to archive your payment protocol receipts store them on some
cloud storage service or disk encrypted with related keys.  for
example tahoe-lafs is optimised for the decentralised long-term
storage kind of use.

This is my main concern in the context of stealth addresses. I intend to start a larger discussion on stealth addresses, but I wont hijack the tread.

Of course it's easy to send the necessary data out of band as opposed to OP_RETURN. The problem is if you do that the transaction cannot not be recovered from seed. We've been fairly successful in transitioning to HD wallets and avoiding the need to make regular wallet backups.

If users wishes to use stealth addresses with out of band communication, the benefits of HD would largely be lost and they would be back to making regular backups ― this time after every transaction rather than every 100.

There are only a couple options in such cases:

1) The user could send the payment to an addresses that is derived from seed, but now you're using even more storage space than you would by just using OP_RETURN.

2) The user can backup after every transaction, which nobody wants to do.

3) The user could use some form of a cloud backup service and place trust in them that their servers wont go down and lose their coins.

None of those options are really that appealing. OP_RETURN seems like the best alternative to me, at least for that use case.