ec: fix point decoding for other curves

This commit is contained in:
Daniel Cousens 2014-05-17 14:10:32 +10:00
parent 5ec9504ed6
commit a17a5b23d9
2 changed files with 18 additions and 2 deletions

View file

@ -8,7 +8,6 @@ var BigInteger = require('bigi')
// constants // constants
var TWO = BigInteger.valueOf(2) var TWO = BigInteger.valueOf(2)
var THREE = BigInteger.valueOf(3) var THREE = BigInteger.valueOf(3)
var SEVEN = BigInteger.valueOf(7)
function ECFieldElementFp(q,x) { function ECFieldElementFp(q,x) {
this.x = x; this.x = x;
@ -340,6 +339,8 @@ ECPointFp.decodeFrom = function (curve, buffer) {
assert(type === 0x02 || type === 0x03, 'Invalid sequence tag') assert(type === 0x02 || type === 0x03, 'Invalid sequence tag')
var isYEven = (type === 0x02) var isYEven = (type === 0x02)
var a = curve.getA().toBigInteger()
var b = curve.getB().toBigInteger()
var p = curve.getQ() var p = curve.getQ()
// We precalculate (p + 1) / 4 where p is the field order // We precalculate (p + 1) / 4 where p is the field order
@ -348,7 +349,7 @@ ECPointFp.decodeFrom = function (curve, buffer) {
} }
// Convert x to point // Convert x to point
var alpha = x.pow(3).add(SEVEN).mod(p) var alpha = x.pow(3).add(a.multiply(x)).add(b).mod(p)
var beta = alpha.modPow(curve.P_OVER_FOUR, p) var beta = alpha.modPow(curve.P_OVER_FOUR, p)
// If beta is even, but y isn't, or vice versa, then convert it, // If beta is even, but y isn't, or vice versa, then convert it,

View file

@ -64,6 +64,21 @@ describe('ec', function() {
}) })
}) })
}) })
it('supports other curves', function() {
var f = fixtures.valid.ECPointFp[1]
var ecparams2 = sec('secp256r1')
var curve = ecparams2.getCurve()
var D = BigInteger.ONE
var Q = ecparams2.getG().multiply(D)
var buffer = Q.getEncoded(true)
var decoded = ECPointFp.decodeFrom(curve, buffer)
assert(Q.equals(decoded.Q))
assert(decoded.compressed, true)
})
}) })
}) })
}) })