ec: fix point decoding for other curves
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2 changed files with 18 additions and 2 deletions
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@ -8,7 +8,6 @@ var BigInteger = require('bigi')
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// constants
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var TWO = BigInteger.valueOf(2)
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var THREE = BigInteger.valueOf(3)
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var SEVEN = BigInteger.valueOf(7)
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function ECFieldElementFp(q,x) {
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this.x = x;
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@ -340,6 +339,8 @@ ECPointFp.decodeFrom = function (curve, buffer) {
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assert(type === 0x02 || type === 0x03, 'Invalid sequence tag')
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var isYEven = (type === 0x02)
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var a = curve.getA().toBigInteger()
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var b = curve.getB().toBigInteger()
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var p = curve.getQ()
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// We precalculate (p + 1) / 4 where p is the field order
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@ -348,7 +349,7 @@ ECPointFp.decodeFrom = function (curve, buffer) {
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}
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// Convert x to point
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var alpha = x.pow(3).add(SEVEN).mod(p)
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var alpha = x.pow(3).add(a.multiply(x)).add(b).mod(p)
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var beta = alpha.modPow(curve.P_OVER_FOUR, p)
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// If beta is even, but y isn't, or vice versa, then convert it,
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15
test/ec.js
15
test/ec.js
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@ -64,6 +64,21 @@ describe('ec', function() {
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})
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})
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})
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it('supports other curves', function() {
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var f = fixtures.valid.ECPointFp[1]
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var ecparams2 = sec('secp256r1')
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var curve = ecparams2.getCurve()
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var D = BigInteger.ONE
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var Q = ecparams2.getG().multiply(D)
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var buffer = Q.getEncoded(true)
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var decoded = ECPointFp.decodeFrom(curve, buffer)
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assert(Q.equals(decoded.Q))
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assert(decoded.compressed, true)
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})
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})
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})
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})
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