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clarified P2SH redeemScript requirements of isStandard

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Andreas M. Antonopoulos 2014-06-25 12:29:24 -04:00
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commit 81ea186efa
1 changed files with 4 additions and 2 deletions
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@ -460,7 +460,7 @@ If the redeemScript hash matches, then the unlocking script is executed on its o
===== Pay-to-Script-Hash Addresses
Another important part of the P2SH feature is the ability to encode a script hash as an address. P2SH addresses are Base58Check encodings of the 20-byte hash of a script, just like bitcoin addresses are Base58Check encodings of the 20-byte hash of a public key. P2SH addresses use the version prefix "5", which results in Base58Check encoded addresses that start with a "3". For example, Mohammed's complex script, hashed and Base58Check encoded as P2SH address becomes +39RF6JqABiHdYHkfChV6USGMe6Nsr66Gzw+. Now, Mohammed can give this "address" to his customers and they can use almost any bitcoin wallet to make a simple payment, as if it were a bitcoin address. The 3 prefix gives them a hint that this is a special type of address, one corresponding to a script instead of a public key, but otherwise it works in exactly the same way as a payment to a bitcoin address.
Another important part of the P2SH feature is the ability to encode a script hash as an address, as defined in BIP0013. P2SH addresses are Base58Check encodings of the 20-byte hash of a script, just like bitcoin addresses are Base58Check encodings of the 20-byte hash of a public key. P2SH addresses use the version prefix "5", which results in Base58Check encoded addresses that start with a "3". For example, Mohammed's complex script, hashed and Base58Check encoded as P2SH address becomes +39RF6JqABiHdYHkfChV6USGMe6Nsr66Gzw+. Now, Mohammed can give this "address" to his customers and they can use almost any bitcoin wallet to make a simple payment, as if it were a bitcoin address. The 3 prefix gives them a hint that this is a special type of address, one corresponding to a script instead of a public key, but otherwise it works in exactly the same way as a payment to a bitcoin address.
P2SH addresses hide all of the complexity, so that the person making a payment does not see the script.
@ -477,7 +477,9 @@ The Pay-to-Script-Hash feature offers the following benefits compared to the dir
===== Redeem Script and isStandard Validation
Pay-to-Script-Hash is currently limited to the standard types of bitcoin transaction scripts, by the +isStandard()+ function. That means that the redeemScript presented in the spending transaction must be one of the standard types: P2PK, P2PK or Multi-Sig, excluding OP_RETURN and P2SH itself. You cannot reference a P2SH script inside a redeemScript and you can't use an OP_RETURN inside a P2SH script. This limitation is temporary and will likely be removed in future versions of the bitcoin reference implementation, allowing the use of any valid script inside a P2SH redeemScript.
Pay-to-Script-Hash is currently limited to the standard types of bitcoin transaction scripts, by the +isStandard()+ function. That means that the redeemScript presented in the spending transaction must be one of the standard types: P2PK, P2PKH or Multi-Sig, excluding OP_RETURN and P2SH itself. You cannot reference a P2SH script inside a redeemScript and you can't use an OP_RETURN inside a P2SH redeemScript.
This limitation of redeemScript to only standard transaction scripts is temporary and will likely be removed in future versions of the bitcoin reference implementation, allowing the use of any valid script inside a P2SH redeemScript. You will still not be able to put a P2SH inside a P2SH redeemScript, because the P2SH specification is not recursive. You will still not be able to use OP_RETURN in a redeemScript because OP_RETURN cannot be redeemed by definition. But you will be able to use all the other operators to create a vast range of complex and novel scripts that can be used as redeemScripts and referenced as P2SH payment to their hash.
Note that since the redeemScript is not presented to the network until you attempt to spend a P2SH output, if you lock an output with the hash of a non-standard transaction it will be processed as valid. However, you will not be able to spend it as the spending transaction which includes the redeemScript will not be accepted, as it is non-standard. This creates a risk, as you can lock bitcoin in a P2SH which cannot be later spent. The network will accept the P2SH encumbrance even if it corresponds to a non-standard or invalid redeemScript, because the script hash gives no indication of the script it represents.