sign metafeed/announce message

[cryptix]

currently type:metafeed/announce is not signed by the metafeed

[cryptix]

How about this?

const ssbKeys = require('ssb-keys')
const ssbUri = require('ssb-uri2')

// make two keypairs for the two feeds
const keyMeta = ssbKeys.generate()
const keyMain = ssbKeys.generate()

// convert the metafeed keypair into an URI
const metaUri = ssbUri.compose({
  type: 'feed', format: 'bendybutt-v1',
  data: keyMeta.public.replace('.ed25519','')
})

// craft the announce message
const announce = {
  type: 'metafeed/announce',
  metafeed: metaUri,
  tangles: {
    metafeed: {
      root: null,
      previous: null
    }
  }
}

// sign the announce message
const signedAnnounce = ssbKeys.signObj(keyMeta, announce)
console.log("signed content")
console.log(signedAnnounce)

// to verify we need to plug the data from the metafeed uri
let metafeedParts = ssbUri.decompose(signedAnnounce.metafeed)
let pubKey = metafeedParts.data + '.ed25519'
const ok = ssbKeys.verifyObj(pubKey, signedAnnounce)
console.log(`verified? ${ok}`)

// now we would db.publich(signedAnnounce)
// which would properly create a ssb message and sign it with keyMain
const signedMessage = ssbKeys.signObj(keyMain, {
  author: keyMain.id,
  sequence: 42,
  content: signedAnnounce
})
console.log("signed message")
console.log(signedMessage)

signed content
{
  type: 'metafeed/announce',
  metafeed: 'ssb:feed/bendybutt-v1/xShZwxnJ3NHOSxyfLOkRXPOJ6yvjmGICHmLI5wsdve8=',
  tangles: { metafeed: { root: null, previous: null } },
  signature: '4L/pkSxP6e4km2MwjgC1dGXMTNIiyDN3Y+bRTlHLIQralWgDttb1jtl02jlVTCbK3d6gHDWw3CQNicpmr7ATAA==.sig.ed25519'
}
verified? true
signed message
{
  author: '@e57mRlF81l8MgakYShgdykeeibrzejbOjhdiT182R9o=.ed25519',
  sequence: 42,
  content: {
    type: 'metafeed/announce',
    metafeed: 'ssb:feed/bendybutt-v1/xShZwxnJ3NHOSxyfLOkRXPOJ6yvjmGICHmLI5wsdve8=',
    tangles: { metafeed: [Object] },
    signature: '4L/pkSxP6e4km2MwjgC1dGXMTNIiyDN3Y+bRTlHLIQralWgDttb1jtl02jlVTCbK3d6gHDWw3CQNicpmr7ATAA==.sig.ed25519'
  },
  signature: '+ixGcWkdUT8w5aduPS70b0qjPelssJK1NOtYsT1OcbppBaRzbiSHiWmHYS6h9L9EF+BJRUw2RYp02bhgmWMOCw==.sig.ed25519'
}

This is basically what https://github.com/ssbc/ssb-peer-invites did to proof control over the guest keypair.

cc @staltz @arj03

[staltz]

Sure that works, in my opinion. @arj03 I can make a PR to ssb-meta-feeds if you concur.

[arj03]

Looks good, much easier to understand from the example code :)

[staltz]

Oh and I can also patch the spec too.

[cryptix]

Sorry but I just realized this is insufficient.

We need to add the main/subfeed and check that that equals the (outer) author of the message to protect against replays on other feeds.

[staltz]

Suggestions for the field name? content.subfeed? content.main?

[arj03]

Ah yes, nice spotting

[arj03]

My vote is for main, but not super tied to that decision

[staltz]

It's nice if it were always the same everywhere, i.e. content.metafeed and content.subfeed on bendy butt messages and also content.metafeed and content.subfeed on main feed messages. Principle of least WTFs.

[cryptix]

My vote is for main

I must say that main is really not a good term when looking forward to a world with multiple apps and content feeds. :-X

I vote for subfeed for consistency, too.

[arj03]

subfeed it is then :)

[staltz]

Implemented in JS https://github.com/ssb-ngi-pointer/ssb-meta-feeds/pull/46