Re: [Cfrg] Interest in an "Ed25519-HD" standard?
Phillip Hallam-Baker <phill@hallambaker.com> Wed, 22 March 2017 21:53 UTC
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From: Phillip Hallam-Baker <phill@hallambaker.com>
Date: Wed, 22 Mar 2017 17:53:34 -0400
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To: Tony Arcieri <bascule@gmail.com>
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Subject: Re: [Cfrg] Interest in an "Ed25519-HD" standard?
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On Wed, Mar 22, 2017 at 4:47 PM, Tony Arcieri <bascule@gmail.com> wrote: > On Tue, Mar 21, 2017 at 9:00 PM, Phillip Hallam-Baker < > phill@hallambaker.com> wrote: > >> You can do hierarchical key derivation in Montgomery without the need for >> an add. >> >> Say your master key is x. To generate a key for site 'example.com' we >> take >> >> xs = (x + H('example.com')) mod q >> >> Where q is the sub group order. >> >> In fact that isn't really using any EC relevant operation at all. Perhaps >> I am not understanding the full requirements for the scheme. >> > > One of the goals of the scheme is unlinkability: given a set of candidate > keys, some of which are children of the same parent key, and others > randomly generated, an attacker should not be able to do better than chance > in determining which keys in the candidate set have the same parents. > > For example, Tor hidden services will be identified by constantly rotating > "epoch keys". To find the "epoch key" for a given hidden service, a user in > possession of the parent public key derives a child key offline from the > parent key. However, it'd be undesirable for someone not in possession of > the parent key to be able to link the child epoch keys together and > enumerate hidden services without knowledge of their parent public keys. > > In your scheme, given z=H("example.com"), and a parent key xG, the > derived child key would be (x+z)G. To recover the original parent public > key, you can simply subtract out zG and recover xG. To prevent this from > happening we need to use an operation which is not easily reversible, hence > multiplication > > That is the case if you disclose x.G. But why would you do that? You could also do: xs = ( H(x + 'example.com')) mod q Which is more robust.
- [Cfrg] Interest in an "Ed25519-HD" standard? Tony Arcieri
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Aaron Zauner
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Phillip Hallam-Baker
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Phillip Hallam-Baker
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Dmitry Khovratovich
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Phillip Hallam-Baker
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Tony Arcieri
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Nadim Kobeissi
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Tony Arcieri
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Taylor R Campbell
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Phillip Hallam-Baker
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Tony Arcieri
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Phillip Hallam-Baker
- Re: [Cfrg] Interest in an "Ed25519-HD" standard? Tony Arcieri
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