OP CHECKSIG

OP_CHECKSIG is an opcode that verifies an ECDSA signature. It takes two inputs from the stack, a public key (on top of the stack) and an ECDSA signature in its DER_CANONISED format concatenated with sighash flags. It outputs true or false on the stack based on whether the signature check passes or fails.

Parameters

In addition to the stack parameters, OP_CHECKSIG needs to have

How it works

In short, OP_CHECKSIG calls a function called "sighash" which produces a hash value of the serialised transaction. (For legacy sighash algorithm, please click here.) The hash value is the message on which the signature is verified. The signature and the public key involved in the verification are obtained from the stack.

In detail,

Check the stack size is not less than 2.
the public key and the signature are popped as the top 2 items of the stack.
Check the signature encoding is of the correct format [<DER signature><hashtype>]. An example: 47304402205a2b556c71ee1c12d8e0b460c3446aeca0e3ee71b7bc11c6ddd3da8beeec99c60220783a1f0c0158674df8904022ec30fab5154c4fc4c7e8467086f0204cc8e16cbb01, where 47 indicates number of bytes in hex (71 in decimal) of the signature including 1 byte of sighash flag at the end, the next 46 bytes (70 in decimal) are the ECDSA signature (r,s), the last byte is the sighash flag "ALL".
Check the public key encoding is of the correct format. Both compressed public key and uncompressed public key can be acceptable. An example: 210220798b9772a8ae06d13027e6f501d09ea07f6dfc4b7afc3db3a6d6c57bf24239, where 21 indicates the number of bytes in hex of the public key, 02 indicates this is a compressed public and the y-coordinate is an even number, the rest is the value of the x-coordinate of the public key. Note that if the second byte is 04, then it indicates that the public key is given in its uncompressed form.

Return values

OP_CHECKSIG will push true to the stack if the check passed, false otherwise. OP_CHECKSIGVERIFY leaves nothing on the stack but will cause the script validation to fail immediately if the check does not pass.

References

https://github.com/bitcoin-sv/bitcoin-sv/blob/master/src/script/interpreter.cpp

See SIGHASH flags for more detail on the effect of combinations of flags.

Attribution

This content is based on content sourced from https://en.bitcoin.it/wiki/OP_CHECKSIG under Creative Commons Attribution 3.0. Although it may have been extensively revised and updated we acknowledge the original authors.

声明：

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比特币(BSV)知识库：脚本-OP_CHECKSIG