another newbie question about elliptic HOT 9 CLOSED

@mrose17 Looking into it...

I could tell for sure that your public key thing is the same up to the curve modulus. For some reason curve25519 package does not mod it before returning to you.

Also curve25519 C module seems to amend the public key before using it, but it seems that even when uncommenting section in your example - it still differs.

from elliptic.

I wonder if it could be that Adam is using http://elligator.cr.yp.to/poster.pdf in his donna code.

from elliptic.

Ok, figured it out :) It does everything in reverse!

var elliptic   = require('./lib/elliptic.js')
  , ec         = new elliptic.ec('curve25519')
  , mysecret   = new Buffer('00843b75caa5bdb940f740b7d9262e2ae9937c946dca7b0d18617ff5a1a33f46', 'hex')
  , rev = new Buffer(32);


 mysecret[0] &= 248
 mysecret[31] &= 127
 mysecret[31] |= 64
for (var i = 0; i < 32; i++)
  rev[i] = mysecret[32 - i - 1];

var mykey      = ec.keyFromPrivate(rev)
  , yourpublic = new Buffer('97b22cf64c25ae2db61d07618ff291086feff2ae8779e57be59e988c33916b0f', 'hex')
  , yourkey    = ec.keyFromPublic(yourpublic)
  , shared     = mykey.derive(yourkey.getPublic())

console.log('               my private key ='+mykey.getPrivate('hex') + '\n')

console.log('    old pkg says my public key='+'200b85ac0e08d3fd0a0be90436765119037d30b7bff56f07cfab51ec1691837f')
// !!!!!!!!
// This one is reversed!
// !!!!!!!!
console.log('    new pkg says my public key='+mykey.getPublic('hex') + '\n')

console.log('  old pkg says your public key='+yourpublic.toString('hex'))
console.log('  new pkg says your public key='+yourkey.getPublic('hex') + '\n')

console.log('old pkg says the shared secret='+'91bae78939e897c5996417c77c5e3e19f82f4143acb34ef23848d3b6cc1f9930')
console.log('new pkg says the shared secret='+shared.toString(16))

from elliptic.

Thanks for sharing, though!

from elliptic.

thanks for looking into this. very odd. i was expecting something less esoteric. ok, so basically, the trick is to know when the flip the results for transmission to the other side (my public key) or use (derived shared secret). i've updated the gist above to reflect that.

https://gist.github.com/mrose17/36a9f5ada76bfab4b8bc

sorry for the confusion!

from elliptic.

/Users/indutny/Code/indutny/elliptic/2.js:26
curve25519.makeSecretKey(C_mysecret)
           ^
TypeError: Object #<Object> has no method 'makeSecretKey'
    at Object.<anonymous> (/Users/indutny/Code/indutny/elliptic/2.js:26:12)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:929:3

from elliptic.

hmmm... just to confirm, we're talking about this package

https://github.com/thejh/node-curve25519

(or at least that's the one i'm talking about!)

from elliptic.

Yeah, it is just your gist that does not work :) May be you are using older version?

from elliptic.

sorry about that. here's what i did:

1. (temporarily) add this dependency to package.json for elliptic:

       "curve25519": "git://github.com/thejh/node-curve25519.git"
   

2. the usual npm -l install

3. ran this gist: https://gist.github.com/mrose17/36a9f5ada76bfab4b8bc

maybe there is a version mismatch, but i'm not sure how i did that...

from elliptic.