NUT-XX - Mint Remote signer standard

[lescuer97]

This is a standard for Mints to be able to communicate with a remote signer for cryptographic operations as well as keyset information.

Their is also a standard way for signers to derive their keysets from their master key.

The goal of this nut is to better isolate the private keys of the mint and standardize the communications between the signer and mint.

Implementations:

• Nutshell
• CDK bring signatory up to date with the remote signer spec cdk#1257
• Nutmix Add signatory derivation directly to nutmix lescuer97/nutmix#216

[lescuer97]

I still need to add test vectors for the key derivation

[lescuer97]

@crodas I added the final_expiry to be optional

[crodas]

I will apply the changes we discussed in CDK this week, specially whatever is in here and dropping the redundant amount field.

[crodas]

@lescuer97 I think cashubtc/cdk#1179 was the thing we discussed, is there anything else missing? /cc @thesimplekid

[vnprc]

There are a number of gaps and vulnerabilities in the deterministic derivation path function that are addressed in this proposed NUT spec: #292

Namely, leading and trailing whitespace, capitalization differences, and functionally equivalent unicode character sequences can cause visually identical currency units to hash to different derivation paths. Also, the lack of a reserved range for currently hard coded currency unit derivation paths could lead to backwards incompatible derivation path conflicts. These properties could be exploited by attackers using specially crafted currency unit strings.

If y'all would like to review PR 292 I think it would be complementary to this spec proposal and they could potentially go at the same time.

[lescuer97]

@thesimplekid @vnprc added some features form this #292 pr. should have the details that we discussed

[lescuer97]

@callebtc

[lescuer97]

demo showing the spec with 3 signers:

remote_signer_demo_compresed_free_convert.mp4

[aaronmcdaid]

When you say 'index' here, do you mean 'unit reference'? This is essentially the first mention of 'index' in this doc, and I don't know what it is.

(I see many others have commented already. Apologies in advance if I now ask a few questions that have already been answered 😀)

[lescuer97]

hi! it just talks about the actual index number that is going to be used later on the derivation path

[lescuer97]

hi! it just talks about the actual index number that is going to be used later on the derivation path.

Should probably use better naming