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BIP: 13
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Title: Address Format for pay-to-script-hash
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Author: Gavin Andresen <gavinandresen@gmail.com>
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Status: Final
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Type: Standards Track
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Created: 2011-10-18
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--------------------------------------------------
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[[abstract]]
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Abstract
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~~~~~~~~
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This BIP describes a new type of Bitcoin address to support arbitrarily
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complex transactions. Complexity in this context is defined as what
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information is needed by the recipient to respend the received coins, in
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contrast to needing a single ECDSA private key as in current
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implementations of Bitcoin.
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In essence, an address encoded under this proposal represents the
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encoded hash of a script, rather than the encoded hash of an ECDSA
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public key.
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[[motivation]]
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Motivation
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~~~~~~~~~~
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Enable "end-to-end" secure wallets and payments to fund escrow
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transactions or other complex transactions. Enable third-party wallet
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security services.
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[[specification]]
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Specification
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~~~~~~~~~~~~~
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The new bitcoin address type is constructed in the same manner as
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existing bitcoin addresses (see link:Base58Check encoding[Base58Check
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encoding]):
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` base58-encode: [one-byte version][20-byte hash][4-byte checksum]`
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Version byte is 5 for a main-network address, 196 for a testnet address.
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The 20-byte hash is the hash of the script that will be used to redeem
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the coins. And the 4-byte checksum is the first four bytes of the double
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SHA256 hash of the version and hash.
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[[rationale]]
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Rationale
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~~~~~~~~~
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One criticism is that bitcoin addresses should be deprecated in favor of
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a more user-friendly mechanism for payments, and that this will just
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encourage continued use of a poorly designed mechanism.
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Another criticism is that bitcoin addresses are inherently insecure
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because there is no identity information tied to them; if you only have
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a bitcoin address, how can you be certain that you're paying who or what
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you think you're paying?
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Furthermore, truncating SHA256 is not an optimal checksum; there are
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much better error-detecting algorithms. If we are introducing a new form
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of Bitcoin address, then perhaps a better algorithm should be used.
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This is one piece of the simplest path to a more secure bitcoin
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infrastructure. It is not intended to solve all of bitcoin's usability
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or security issues, but to be an incremental improvement over what
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exists today. A future BIP or BIPs should propose more user-friendly
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mechanisms for making payments, or for verifying that you're sending a
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payment to the Free Software Foundation and not Joe Random Hacker.
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Assuming that typing in bitcoin addresses manually will become
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increasingly rare in the future, and given that the existing checksum
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method for bitcoin addresses seems to work "well enough" in practice and
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has already been implemented multiple times, the Author believes no
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change to the checksum algorithm is necessary.
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The leading version bytes are chosen so that, after base58 encoding, the
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leading character is consistent: for the main network, byte 5 becomes
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the character '3'. For the testnet, byte 196 is encoded into '2'.
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[[backwards-compatibility]]
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Backwards Compatibility
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~~~~~~~~~~~~~~~~~~~~~~~
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This proposal is not backwards compatible, but it fails gracefully-- if
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an older implementation is given one of these new bitcoin addresses, it
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will report the address as invalid and will refuse to create a
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transaction.
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[[reference-implementation]]
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Reference Implementation
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~~~~~~~~~~~~~~~~~~~~~~~~
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See base58.cpp1/base58.h at https://github.com/bitcoin/bitcoin/src
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[[see-also]]
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See Also
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~~~~~~~~
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* link:bip-0012.mediawiki[BIP 12: OP_EVAL, the original P2SH design]
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* link:bip-0016.mediawiki[BIP 16: Pay to Script Hash (aka "/P2SH/")]
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* link:bip-0017.mediawiki[BIP 17: OP_CHECKHASHVERIFY, another P2SH
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design]
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