Founder's Addresses and private keys

General
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Lazy question so I don’t have to go figure it out on my own:
Were the founder’s reward addresses generated by the same rules and cryptography as any other t-address?

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The simple answer is yes. They are hard-coded into the protocol specification and you can see them all on page 45 here https://raw.githubusercontent.com/zcash/zips/master/protocol/protocol.pdf. There are 48 of them and they are multi-sig transparent addresses (as indicated by the t3 prefix) and change once per month. There is some more info here: Proposal to create a Zcash Ecosystem Fund directly funded by the Founder's Reward - #12 by daira

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I didn’t realize this was even part of bitcoin core. neat!

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They were generated as 2-of-3 multisig addresses using custom software; there’s nothing special about them other than being multisig.

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I’ll continue my string of lazy requests:

Would zcashco be willing to publish (at least in part?) the software used for generating 2 of 3, or if implemented, m of n multisig script addresses? If yes, the same for signing transactions?

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Or If using the tools in libbitcoin-explorer would allow me the same capability then I guess I don’t need your tools, as long as they are compatible.

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Ah jeez there’s an RPC call spelled out in 6.3.1 AddMultiSigAddress. I’ll look into that instead. Disregard the above request

So for signing a raw transaction from a m of n multisig address would I roughly have to do this:
(pseudo code)

zcash-cli signrawtransaction UNSIGNED_RAW_TX [“$ADDR_0_PRIVATE_KEY”]
Output: PARTIALLYSIGNED_RAW_TX1
zcash-cli signrawtransaction PARTIALLYSIGNED_RAW_TX1 [“$ADDR_1_PRIVATE_KEY”]
Output: PARTIALLYSIGNED_RAW_TX2
…
zcash-cli signrawtransaction PARTIALLYSIGNED_RAW_TXm [“$ADDR_m-1_PRIVATE_KEY”]
Output: FULLYSIGNED_RAW_TX

And then broadcast with

zcash-cli sendrawtransaction FULLYSIGNED_RAW_TX

I think this is correct from what I read in the bitcoin documentation (assuming the current bitcoin documentation is close to the version forked for zcash at v0.11.x.

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I know I’m sort of having a conversation with myself here but I’m just wondering why anyone would use anything less than a multi signature address for a cold storage application. Physically separating multiple keys, generating all transactions offline and submitting them from different, anonymous nodes.

I have to imagine that the founders addresses would be using this for more reasons than just security from outside influence, but also from internal theft.

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Ahah. So maybe I do really want your custom software.

@daira
How do I create a transaction from multisig address to Z_address like was done from the first FR address in Tx
231c92d871f0578a5537fb949fc5cf9fd27f125fac4afb9e251b46d3d077e206 in block 000000003d7d6af1badc4c25323092f4580ab571b0293dfa8ee57c9633c86b61

As far as I can see from the documentation I can’t spend the amounts in a multisig address with Z_sendmany unless I have imported m private keys into the client. I think that would defeat the security of keeping private keys private and only signing transactions. Is there a way to use a signed transaction as an input to Z-sendmany?