| package org.bouncycastle.crypto.agreement; |
| |
| import java.math.BigInteger; |
| |
| import org.bouncycastle.crypto.BasicAgreement; |
| import org.bouncycastle.crypto.CipherParameters; |
| import org.bouncycastle.crypto.params.ECDomainParameters; |
| import org.bouncycastle.crypto.params.ECPrivateKeyParameters; |
| import org.bouncycastle.crypto.params.ECPublicKeyParameters; |
| import org.bouncycastle.math.ec.ECAlgorithms; |
| import org.bouncycastle.math.ec.ECConstants; |
| import org.bouncycastle.math.ec.ECPoint; |
| |
| /** |
| * P1363 7.2.1 ECSVDP-DH |
| * |
| * ECSVDP-DH is Elliptic Curve Secret Value Derivation Primitive, |
| * Diffie-Hellman version. It is based on the work of [DH76], [Mil86], |
| * and [Kob87]. This primitive derives a shared secret value from one |
| * party's private key and another party's public key, where both have |
| * the same set of EC domain parameters. If two parties correctly |
| * execute this primitive, they will produce the same output. This |
| * primitive can be invoked by a scheme to derive a shared secret key; |
| * specifically, it may be used with the schemes ECKAS-DH1 and |
| * DL/ECKAS-DH2. It assumes that the input keys are valid (see also |
| * Section 7.2.2). |
| */ |
| public class ECDHBasicAgreement |
| implements BasicAgreement |
| { |
| private ECPrivateKeyParameters key; |
| |
| public void init( |
| CipherParameters key) |
| { |
| this.key = (ECPrivateKeyParameters)key; |
| } |
| |
| public int getFieldSize() |
| { |
| return (key.getParameters().getCurve().getFieldSize() + 7) / 8; |
| } |
| |
| public BigInteger calculateAgreement( |
| CipherParameters pubKey) |
| { |
| ECPublicKeyParameters pub = (ECPublicKeyParameters)pubKey; |
| ECDomainParameters params = key.getParameters(); |
| if (!params.equals(pub.getParameters())) |
| { |
| throw new IllegalStateException("ECDH public key has wrong domain parameters"); |
| } |
| |
| BigInteger d = key.getD(); |
| |
| // Always perform calculations on the exact curve specified by our private key's parameters |
| ECPoint Q = ECAlgorithms.cleanPoint(params.getCurve(), pub.getQ()); |
| if (Q.isInfinity()) |
| { |
| throw new IllegalStateException("Infinity is not a valid public key for ECDH"); |
| } |
| |
| BigInteger h = params.getH(); |
| if (!h.equals(ECConstants.ONE)) |
| { |
| d = params.getHInv().multiply(d).mod(params.getN()); |
| Q = ECAlgorithms.referenceMultiply(Q, h); |
| } |
| |
| ECPoint P = Q.multiply(d).normalize(); |
| if (P.isInfinity()) |
| { |
| throw new IllegalStateException("Infinity is not a valid agreement value for ECDH"); |
| } |
| |
| return P.getAffineXCoord().toBigInteger(); |
| } |
| } |