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ec: decodeFrom now uses Buffers and handles errors

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This commit is contained in:
Daniel Cousens 2014-05-17 00:39:30 +10:00
parent a3f691bf7c
commit 24371425f9
3 changed files with 50 additions and 49 deletions
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60
src/ec.js
View file

@ -2,6 +2,7 @@
// Ported loosely from BouncyCastle's Java EC code
// Only Fp curves implemented for now
var assert = require('assert')
var BigInteger = require('bigi')
function ECFieldElementFp(q,x) {
@ -326,34 +327,43 @@ ECPointFp.prototype.getEncoded = function(compressed) {
return buffer
}
ECPointFp.decodeFrom = function (curve, enc) {
var type = enc[0];
var dataLen = enc.length-1;
var SEVEN = BigInteger.valueOf(7)
// Extract x and y as byte arrays
if (type == 4) {
var xBa = enc.slice(1, 1 + dataLen/2),
yBa = enc.slice(1 + dataLen/2, 1 + dataLen),
x = BigInteger.fromBuffer(xBa),
y = BigInteger.fromBuffer(yBa);
}
else {
var xBa = enc.slice(1),
x = BigInteger.fromBuffer(xBa),
p = curve.getQ(),
xCubedPlus7 = x.multiply(x).multiply(x).add(new BigInteger('7')).mod(p),
pPlus1Over4 = p.add(new BigInteger('1'))
.divide(new BigInteger('4')),
y = xCubedPlus7.modPow(pPlus1Over4,p);
if (y.mod(new BigInteger('2')).toString() != ''+(type % 2)) {
y = p.subtract(y)
}
ECPointFp.decodeFrom = function (curve, buffer) {
var type = buffer.readUInt8(0)
var compressed = type !== 0x04
var x = BigInteger.fromBuffer(buffer.slice(1, 33))
var y
if (compressed) {
assert.equal(buffer.length, 33, 'Invalid sequence length')
assert(type === 0x02 || type === 0x03, 'Invalid sequence tag')
var isYEven = type === 0x03
var p = curve.getQ()
// We precalculate (p + 1) / 4 where p is the field order
var P_OVER_FOUR = p.add(BigInteger.ONE).shiftRight(2)
// Convert x to point
var alpha = x.square().multiply(x).add(SEVEN).mod(p)
var beta = alpha.modPow(P_OVER_FOUR, p)
y = (beta.isEven() ? !isYEven : isYEven) ? beta : p.subtract(beta)
} else {
assert.equal(buffer.length, 65, 'Invalid sequence length')
y = BigInteger.fromBuffer(buffer.slice(33))
}
return new ECPointFp(curve,
curve.fromBigInteger(x),
curve.fromBigInteger(y));
};
var Q = new ECPointFp(curve, curve.fromBigInteger(x), curve.fromBigInteger(y))
return {
Q: Q,
compressed: compressed
}
}
ECPointFp.prototype.add2D = function (b) {
if(this.isInfinity()) return b;

10
src/ecpubkey.js
View file

@ -21,14 +21,8 @@ function ECPubKey(Q, compressed) {
// Static constructors
ECPubKey.fromBuffer = function(buffer) {
var type = buffer.readUInt8(0)
assert(type >= 0x02 || type <= 0x04, 'Invalid public key')
var compressed = (type !== 0x04)
assert.strictEqual(buffer.length, compressed ? 33 : 65, 'Invalid public key')
var Q = ECPointFp.decodeFrom(ecparams.getCurve(), buffer)
return new ECPubKey(Q, compressed)
var decode = ECPointFp.decodeFrom(ecparams.getCurve(), buffer)
return new ECPubKey(decode.Q, decode.compressed)
}
ECPubKey.fromHex = function(hex) {

29
test/ec.js
View file

@ -48,25 +48,22 @@ describe('ec', function() {
var buffer = new Buffer(f.hex, 'hex')
var decoded = ECPointFp.decodeFrom(curve, buffer)
assert.equal(decoded.getX().toBigInteger().toString(), f.x)
assert.equal(decoded.getY().toBigInteger().toString(), f.y)
// TODO
// assert.equal(decoded.compressed, f.compressed)
assert.equal(decoded.Q.getX().toBigInteger().toString(), f.x)
assert.equal(decoded.Q.getY().toBigInteger().toString(), f.y)
assert.equal(decoded.compressed, f.compressed)
})
})
// FIXME
// fixtures.invalid.ECPointFp.forEach(function(f) {
// it('throws on ' + f.description, function() {
// var curve = ecparams.getCurve()
// var buffer = new Buffer(f.hex, 'hex')
//
// assert.throws(function() {
// ECPointFp.decodeFrom(curve, buffer)
// })
// })
// })
fixtures.invalid.ECPointFp.forEach(function(f) {
it('throws on ' + f.description, function() {
var curve = ecparams.getCurve()
var buffer = new Buffer(f.hex, 'hex')
assert.throws(function() {
ECPointFp.decodeFrom(curve, buffer)
})
})
})
})
})
})