45

A multi-signature address is an address that is associated with more than one ECDSA private key. The simplest type is an m-of-n address - it is associated with n private keys, and sending bitcoins from this address requires signatures from at least m keys. A multi-signature transaction is one that sends funds from a multi-signature address. The primary use ...


33

Warning: I've never actually worked with the Schnorr signature scheme. The following is my analysis based on reading the Wikipedia article, the ed25519 page, and some discussions between devs in #bitcoin-dev. Likely Changes Changed op code behavior: we will need an op code to check Schnorr signatures. With a hard fork, we can redefine op_checksig and ...


22

We need to distinguish the limitations for validity and standardness. The first is determined by the consensus rules (which cannot change without a hard fork). The second ones are determined by local relay and mining policies implemented in the reference client, and can change from version to version. In addition, we need to distinguish raw multisig (a ...


14

Your question seems to assume that the only goal is minimizing on-chain transaction size. Reducing size and related costs is certainly something that can be improved upon, but it's far from the only thing. The primary advantages of the Schnorr proposal are: Better privacy, by making different multisig spending policies indistinguishable on chain. When ...


12

Bitcoin version 0.6.1 doesn't have useful multisignature support yet, either in the GUI or via the RPC interface, because there is no support for partially signing a multisignature transaction. What is supported: creating a multisignature transaction (using addmultisigaddress), and sending to a multisignature address (either your own or somebody else's). ...


11

It seems some partial implementation exists. Quoting Gavin: Generate a multisig address: Gather (or generate) 3 bitcoin addresses, on whichever machines will be participating, using getnewaddress or getaccountaddress RPC commands (or copy and paste from the GUI). Get their public keys using the validateaddress RPC command 3 times. Then create a 2-of-3 ...


10

Actually, both receiving funds at and spending funds from a multi-sig address is already supported. You can find the code to do so, plus comments, by Gavin: TwoOfThree.sh


10

By reading this answer, I understand that in m-of-n multisig addresses, m and n are limited by the maximum size allowed by the P2SH redeemScript (i.e. 520 bytes). That's correct. Even though the OP_CHECKMULTISIG script opcode supports more keys, more than 15 public keys simply don't fit in a P2SH redeemscript, so that becomes the limiting factor. However,...


9

According to the glossary the possible prefixes for bitcoin addresses are 1,3 or 5: I'm quoting here: Address Bitcoin address is a Base58Check representation of a Hash160 of a public key with a version byte 0x00 which maps to a prefix "1". Typically represented as text (ex. 1CBtcGivXmHQ8ZqdPgeMfcpQNJrqTrSAcG) or as a QR code. A variant ...


9

There are two basic templates for using multisig for "escrow", 2-of-2 and 2-of-3. In both cases, you can currently use bitcoin-qt's raw transaction API to create the addresses and transactions. In 2-of-2 you do the following: Create a multisig address which requires signatures from both the buyer and seller. The buyer sends funds to this address. Seller ...


9

Yes you can do public key recovery with EC Schnorr. Consider R = kG, [r = R.x, s = k + H(r, m)d], Q = dG verify: sG = ?R + H(r, m)Q recovery: sG = kG + H(r, m) dG = R + H(r, m)Q so Q = 1 / H(r, m) * (sG - R). (And to compute R from r if R is point-compressed, R = (r,f(r)) R' = (r,-f(r)) and try both R and R' by checking if the signature is valid with ...


8

There are some m-of-n transactions in the blockchain (blockchain.info - block explorer) but they have only been recently added to the standard transaction types. However the reason why they are probably not in wide spread use yet is there is no gui based client that can construct one. My Wallet will be able to construct them soon, I don't know how much ...


7

TxID is just a SHA256 hash of binary transation data, so it changes upon any modification of transaction. Therefore, one cannot include verification of TxID in the script in same transaction (if I correctly understood what you want to achieve).


7

Enjoy! "Bitcoin Faucet Hacked" How a future version of the Faucet will work to prevent a similar incident: http://gavintech.blogspot.com/2012/03/bitcoin-faucet-hacked.html "BIP 16 / 17 in layman's terms" http://bitcointalk.org/index.php?topic=61125.0 "The Truth behind BIP 16 and 17" http://bitcoinmedia.com/the-truth-behind-bip-16-and-17/


7

You do not need private keys at all to generate multisig m-of-n address! You do need public keys. Yes, three for m-of-3 and eleven for 5-of-11 (for example)


6

No. A "multisig address" is really a hash of a redeem script encoded as a P2SH address. Redeem scripts can't be nested, which means you can't include one redeem script inside another redeem script, so it is impossible to implement the feature you describe under current Bitcoin consensus rules.


6

OP_CHECKMULTISIG contains a bug which consumes one extra element from the stack. Due to this, an additional OP_FALSE (0x00) is pushed for multisig scripts to make the script evaluation valid.


5

Almost all nodes on the network will not relay multisignature transactions because they are not "standard," and almost all miners will not include them in the blocks that they create (for the same reason). The notion of a "standard" transaction was implemented after Bitcoin started getting popular and had to deal with various denial-of-service attacks that ...


5

The core developers are listed on the main Bitcoin page, while everyone that contributed code are listed on the About page. Probably the most up-to-date info on what is happening with the code would be on the GitHub repo.


5

This is the new issue, the one that's causing all the trouble. You basically have two choices: Don't spend any of your own outputs until you're quite confident they're fully confirmed. For example, you could wait for three confirmations. Be prepared to deal with this problem by monitoring your outstanding transaction chains and re-issuing any orphaned ...


5

If anything, I believe the ability to buy insurance on cryptocurrency investments would speed up adoption by making it less risky to traditional investors. Simply having insurance available doesn't mandate that everyone buy it; we'd all still have the choice whether we opt-in or not. Traditional investments tend to have insurance policies on the insurance ...


5

OP_IF consumes a number from the top of the stack. The OP_IF will evaluate to true if the number is not 0, and to false if the number is 0. H/T for this answer by David Schwartz, and to Pieter Wuille for getting me on the right track.


5

Yes or no, depending on your definition. You are right that the expected time to forge a 2-of-2 multisignature is twice that of a single signature, because you obviously need to use your forger algorithm twice. However, in practice such constant factors are ignored when describing security levels. For example, typically ed25519 and secp256k1 are placed in ...


4

This is the latest info I have seen from Ben who runs blockchain.info. Question: The escrow function seems to be gone. Will it return? https://blockchain.info/wallet/escrow? Ben: The escrow feature was removed because not enough people were using it. I think maybe it was just too confusing/not well documented enough. I did not see any info on if/...


4

Electrum allows to escrow transaction but requires you to use the command line interface. I found this gist explaining how to do it.


4

1 and 3 are currently the only defined prefixes for an base58 encoded address. 1 is most common and denotes a simple "pay-to-PubKey" transaction. This transaction shows an actual recipient address. 3 indicates a "pay-to-script-hash" address that contains a hash (one way fingerprint) of a script that can be used for multiple things including address ...


4

They stay in the block chain, just as normal transactions do. Let's look at normal transactions first: When someone (A) sends bitcoins to another person (B), B is not involved in the process at all. A just publishes a transaction in the so called block chain stating that only B is allowed to claim the coins. Not before B wants to spend them, he has to prove ...


4

While multi-signature transactions with a trusted party (e.g Kickstarter Inc.) would work, their disadvantage is requiring said trusted party... The bitcoin wiki describes a different method that doesn't require any third party: Each backer creates a transaction with the amount to be pledged (this is an immediate step and required since the method doesn't ...


4

from 0-of-0 upto 20-of-20 https://blockchain.info/tx/970b435253b69cde8207b3245d7723bb24861fd7ab3cfe361f45ae8de085ac52 is 0-of-0 p2sh redeemption https://blockchain.info/tx/da738e29f64e90ae46dcc3e6b4154041d6324abbe7919e722d486a4a3148b7dc if 20-of-20 bare multisig redeemption https://blockchain.info/tx/...


4

My understanding is that one needs the private keys of Adres1 and Adres2 to be able to spend from MultiSigAddress. Is this correct? Yes that is correct What if one of the addresses belonged to someone else? How could I use the funds on MultiSigAddres using Bitcoin Core in that case? You will need the private key for both addresses (public keys) in order ...


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