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ECKey: use Bouncy Castle to decompress keys. Thanks to Peter Dettman for the hint. Resolves issue 493.

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Mike Hearn 2013-12-14 14:12:52 -08:00
parent 8f48b119b7
commit f7a944983c
1 changed files with 5 additions and 14 deletions
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19
core/src/main/java/com/google/bitcoin/core/ECKey.java
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@ -28,6 +28,7 @@ import org.slf4j.LoggerFactory;
import org.spongycastle.asn1.*;
import org.spongycastle.asn1.sec.SECNamedCurves;
import org.spongycastle.asn1.x9.X9ECParameters;
import org.spongycastle.asn1.x9.X9IntegerConverter;
import org.spongycastle.crypto.AsymmetricCipherKeyPair;
import org.spongycastle.crypto.generators.ECKeyPairGenerator;
import org.spongycastle.crypto.params.*;
@ -759,20 +760,10 @@ public class ECKey implements Serializable {
/** Decompress a compressed public key (x co-ord and low-bit of y-coord). */
private static ECPoint decompressKey(BigInteger xBN, boolean yBit) {
// This code is adapted from Bouncy Castle ECCurve.Fp.decodePoint(), but it wasn't easily re-used.
ECCurve.Fp curve = (ECCurve.Fp) CURVE.getCurve();
ECFieldElement x = new ECFieldElement.Fp(curve.getQ(), xBN);
ECFieldElement alpha = x.multiply(x.square().add(curve.getA())).add(curve.getB());
ECFieldElement beta = alpha.sqrt();
// If we can't find a sqrt we haven't got a point on the curve - invalid inputs.
if (beta == null)
throw new IllegalArgumentException("Invalid point compression");
if (beta.toBigInteger().testBit(0) == yBit) {
return new ECPoint.Fp(curve, x, beta, true);
} else {
ECFieldElement.Fp y = new ECFieldElement.Fp(curve.getQ(), curve.getQ().subtract(beta.toBigInteger()));
return new ECPoint.Fp(curve, x, y, true);
}
X9IntegerConverter x9 = new X9IntegerConverter();
byte[] compEnc = x9.integerToBytes(xBN, 1 + x9.getByteLength(CURVE.getCurve()));
compEnc[0] = (byte)(yBit ? 0x03 : 0x02);
return CURVE.getCurve().decodePoint(compEnc);
}
/**