![]() If you want to validate historical signatures from the blockchain then either openssl or the code in contrib is sufficient. (You may need to use the signature normalize call if you want to match consensus acceptance instead of standardness acceptance). If you want to accept all transactions and only transactions that Bitcoin would accept, libsecp256k1 alone is what you want. It isn't clear to me from your question what your goal is. With some protocols that require parties to store signed transactions, that might be relevant.Īs this is historical behavior of python-bitcoinlib, I am inclined to just document this in the README.md as a 'gotcha', and leave it as it is now.īut maybe there is some other potential problems that could arise out of this issue, that may be more serious, and the first or second options described above should be considered ? What I can see is that when someone uses python-bitcointx or python-bitcoinlib to verify inputs in some transaction, and these inputs contain signatures that is accepted by openssl, but not by bitcoind, they might be convinced that tx is valid, but will have unpleasant surprise when they try to broadcast it. My question is: what may be the implications of this choice ? This means I cannot drop openssl dependency. Python-bitcoinlib was using openssl to decode, too, so I went with the later approach - decode/encode/decode. The problem with this approach (in addition to this decode/encode cycle) is that it will allow some format violations that bitcoind won't allow, because ecdsa_signature_parse_der_lax() only allows an arbitrary subset of violations allowed by openssl. encode-with-openssl then creates valid encoding, and decode-with-libsecp256k1 is happy. This way all encoding violations that openssl allows are also allowed by first decode-with-openssl. do a cycle of decode-with-openssl / encode-with-openssl / decode-with-libsecp256k1.It will also make verification slower to some degree, because more operations will be done in python, vs calling C functions. Porting this function correctly will require to invest some time. I would like to avoid this, to reduce the size of the code (reduce the surface where bug may be introduced). ![]() re-implement ecdsa_signature_parse_der_lax() in python.In some environments this may be inconvenient. This is not desireable, because it adds requirement to have C compiler to build the python package. get ecdsa_signature_parse_der_lax() function from libsecp256k1/contrib, add it to python-bitcointx repository, compile at python package build time, install with a package.openssl dependency will stay because of verify_nonstrict(). To be able to verify non-strict-encoded signatures with libsecp256k1, I see 3 options:ĮDIT: I might just implement two verification methods, strict and non-strict, and then use them in tests. It is expected for bitcoin-focused library to be able to verify signatures that bitcoind will also verify. This function is not compiled in a normal compilation cycle of libsecp256k1. Libsecp256k1 function secp256k1_ecdsa_signature_parse_der() only allows strictly valid DER-encoded signatures.īitcoind uses ecdsa_signature_parse_der_lax() function, copied from libsecp256k1's contrib/ directory. I want to be able to remove dependency on openssl in the future, and use only libsecp256k1 in python-bitcointx, but there is a problem that I noticed when I re-wrote CECKey.verify() method: In the python-bitcoinlib code (that python-bitcointx is a derivative of), openssl functions were used for signature verification. I have recently changed verification code in python-bitcointx to use libsecp256k1 library.
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