Question about DST

[b00f]

The DST that is defined here is not compatible with the spec. It's defined like this: https://github.com/herumi/mcl/blob/41497c9cf9b38edb6d1aafbafaf2237848b0dee7/include/mcl/mapto_wb19.hpp#L556

However Spec definition recommends different DST for different schemes. Is there any reason for this?

[aguycalled]

it would help to be able to set the DST label for other schemes

[herumi]

Okay, I'll add the api.

[herumi]

FYI. "BLS_SIG_BLS12381G1_XMD:SHA-256_SSWU_ROPOP" is for Ethereum. https://pypi.org/project/py-ecc/

[aguycalled]

I'd make use of being able to set BLS_SIG_BLS12381G2_XMD:SHA-256_SSWU_RO_NUL_ and BLS_SIG_BLS12381G2_XMD:SHA-256_SSWU_RO_AUG_ as DST labels

[herumi]

I added hashAndMapToG1 and hashAndMapToG2 with DST for C++. https://github.com/herumi/mcl/commit/b3f4d607cb5f823b88de11717e4f9c387606d2bb What language do you want to use them with?

[aguycalled]

Thank you very much!

I would use it from C.

[aguycalled]

I think a function setDSTLabel(*char, size_t) which sets a global setting like setMapToMode() would be more flexible, and require less changes in other libraries like herumi/bls which use mcl for signing and verification but dont support different schemes yet.

[herumi]

I've added mclBn{G1,G2}_setDst(const char* dst, size_t dstSize) functions at https://github.com/herumi/mcl/commit/d7fe9d748ab88b342024fa2f05dc38ea773ffa00 .

[aguycalled]

👍

[b00f]

@herumi and @aguycalled Thank you so much guys for the fast implementation. I will test it soon and update you guys.

[b00f]

@herumi I looked at your change. I am going to test it with GoLang. Do you think you can update the bls-go-binary? I can update it if you don't mind. I suggest to add new methods like CoreSign and CoreVerify to accept DST as an additional parameter.

What do you think?

[herumi]

Is it enough only to add the global setting functions of DST?

[b00f]

That also should work. But I think it become a bit far from the spec. The APIs can follow the spec, for example, we can have different Sign and Verify methods for different schema. For example look here

I think now it is very risky to touch it. Better to have a global setting.

[herumi]

I updated https://github.com/herumi/bls-go-binary to support setDst.

[b00f]

I tested it, it worked as it promised. Thanks