# Gavin Andresen
# 2012-03-03 17:24:22
# https://bitcointalk.org/index.php?topic=67105.msg781681#msg781681

If you're using multisig to secure your wallet, then I think backup could be "free" ; all the involved multisig keys could be derived predictably from singlesig keys that you'll already need to backup. Disaster recovery from a lost wallet would mean importing all the backed up singlesig keys, then deriving (say) the first 1000 multisig ScriptSigs that would have been derived from those keys and scanning the blockchain for transactions involving those (and, hand-wave, hand-wave, doing something smart to derive more than 1000 in case it looks like more than 1000 were used).  (or, in other words: what kjj said) @p{par}

If you're using multisig for escrow involving other people... then the escrow transaction has to be recorded and backed up, including all the keys involved.  In that case I'm pretty sure you'll want to record and backup other information about the escrow@p{--} like "100 BTC escrow to my cousin Bob; release them if he's still not smoking on June 1." @p{par}

Backup should be part of the user experience design for the escrow function; for example, I think a lot of escrows will an associated date, so the client should store the escrow transaction id AND the public keys involved in the escrow AND a "remind me to do something on June 1" AND (maybe) a link to my Address Book entry for Bob so I can call him on June 1. For me, I think the best way to backup that kind of escrow information would be for the client to send me an email containing all of that stuff in a standardized mini-file-format; I'll let gmail archive it and that would be my emergency backup. @p{par}

So, emergency recovery of a lost wallet would then be: @p{par}

1. Recover all private keys from paper backup (or whatever the singlesig backup solution is). @p{brk}
2. Re-import all escrows that involve other people from email archive. @p{par}

 @p{brk}
RE: Bytecoin and "OR BACKUP_KEY" :  In either the OP_EVAL or the BIP16 case you need a new type of 'standard' transaction (and bitcoin address) to make that work.