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ec: fix point decoding for other curves

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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

5
src/ec.js
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@ -8,7 +8,6 @@ var BigInteger = require('bigi')
// constants
var TWO = BigInteger.valueOf(2)
var THREE = BigInteger.valueOf(3)
var SEVEN = BigInteger.valueOf(7)
function ECFieldElementFp(q,x) {
this.x = x;
@ -340,6 +339,8 @@ ECPointFp.decodeFrom = function (curve, buffer) {
assert(type === 0x02 || type === 0x03, 'Invalid sequence tag')
var isYEven = (type === 0x02)
var a = curve.getA().toBigInteger()
var b = curve.getB().toBigInteger()
var p = curve.getQ()
// We precalculate (p + 1) / 4 where p is the field order
@ -348,7 +349,7 @@ ECPointFp.decodeFrom = function (curve, buffer) {
}
// 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)
// If beta is even, but y isn't, or vice versa, then convert it,