| 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.ECPoint; |
| |
| /** |
| * P1363 7.2.2 ECSVDP-DHC |
| * |
| * ECSVDP-DHC is Elliptic Curve Secret Value Derivation Primitive, |
| * Diffie-Hellman version with cofactor multiplication. It is based on |
| * the work of [DH76], [Mil86], [Kob87], [LMQ98] and [Kal98a]. 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 does not assume the |
| * validity of the input public key (see also Section 7.2.1). |
| * <p> |
| * Note: As stated P1363 compatibility mode with ECDH can be preset, and |
| * in this case the implementation doesn't have a ECDH compatibility mode |
| * (if you want that just use ECDHBasicAgreement and note they both implement |
| * BasicAgreement!). |
| */ |
| public class ECDHCBasicAgreement |
| implements BasicAgreement |
| { |
| 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("ECDHC public key has wrong domain parameters"); |
| } |
| |
| BigInteger hd = params.getH().multiply(key.getD()).mod(params.getN()); |
| |
| // Always perform calculations on the exact curve specified by our private key's parameters |
| ECPoint pubPoint = ECAlgorithms.cleanPoint(params.getCurve(), pub.getQ()); |
| if (pubPoint.isInfinity()) |
| { |
| throw new IllegalStateException("Infinity is not a valid public key for ECDHC"); |
| } |
| |
| ECPoint P = pubPoint.multiply(hd).normalize(); |
| |
| if (P.isInfinity()) |
| { |
| throw new IllegalStateException("Infinity is not a valid agreement value for ECDHC"); |
| } |
| |
| return P.getAffineXCoord().toBigInteger(); |
| } |
| } |