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The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
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package org.bouncycastle.jcajce.spec;

import java.security.PrivateKey;
import java.security.spec.AlgorithmParameterSpec;

import org.bouncycastle.asn1.nist.NISTObjectIdentifiers;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.asn1.x9.X9ObjectIdentifiers;
import org.bouncycastle.util.Arrays;

public class KEMExtractSpec
    extends KEMKDFSpec
    implements AlgorithmParameterSpec
{
    private static final byte[] EMPTY_OTHER_INFO = new byte[0];
    private static AlgorithmIdentifier DefKdf = new AlgorithmIdentifier(X9ObjectIdentifiers.id_kdf_kdf3, new AlgorithmIdentifier(NISTObjectIdentifiers.id_sha256));

    /**
     * Builder class for creating a KEMExtractSpec.
     */
    public static final class Builder
    {
        private final PrivateKey privateKey;
        private final byte[] encapsulation;
        private final String algorithmName;
        private final int keySizeInBits;

        private AlgorithmIdentifier kdfAlgorithm;
        private byte[] otherInfo;

        /**
         * Basic builder.
         *
         * @param privateKey       the private key to use for the secret extraction.
         * @param encapsulation    the encapsulation to process.
         * @param keyAlgorithmName the algorithm name for the secret key we want to generate.
         * @param keySizeInBits    the size of the wrapping key we want to produce in bits.
         */
        public Builder(PrivateKey privateKey, byte[] encapsulation, String keyAlgorithmName, int keySizeInBits)
        {
            this.privateKey = privateKey;
            this.encapsulation = Arrays.clone(encapsulation);
            this.algorithmName = keyAlgorithmName;
            this.keySizeInBits = keySizeInBits;
            this.kdfAlgorithm = new AlgorithmIdentifier(X9ObjectIdentifiers.id_kdf_kdf3, new AlgorithmIdentifier(NISTObjectIdentifiers.id_sha256));
            this.otherInfo = EMPTY_OTHER_INFO;
        }

        /**
         * Use the shared secret directly for key wrap generation.
         *
         * @return the current Builder instance.
         */
        public Builder withNoKdf()
        {
            this.kdfAlgorithm = null;

            return this;
        }

        /**
         * Set the KDF algorithm and digest algorithm for wrap key generation. The default KDF is X9.44 KDF-3, also
         * known as the NIST concatenation KDF.
         *
         * @param kdfAlgorithm the KDF algorithm to apply.
         * @return the current Builder instance.
         */
        public Builder withKdfAlgorithm(AlgorithmIdentifier kdfAlgorithm)
        {
            this.kdfAlgorithm = kdfAlgorithm;

            return this;
        }

        /**
         * Set the OtherInfo to use with the KDF. The default OtherInfo is a zero length byte[].
         *
         * @param otherInfo the other info to use.
         * @return the current Builder instance.
         */
        public Builder withOtherInfo(byte[] otherInfo)
        {
            this.otherInfo = (otherInfo == null) ? EMPTY_OTHER_INFO : Arrays.clone(otherInfo);

            return this;
        }

        /**
         * Build the new parameter spec.
         *
         * @return a new parameter spec configured according to the builder state.
         */
        public KEMExtractSpec build()
        {
            return new KEMExtractSpec(privateKey, encapsulation, algorithmName, keySizeInBits, kdfAlgorithm, otherInfo);
        }
    }

    private final PrivateKey privateKey;
    private final byte[] encapsulation;

    private KEMExtractSpec(PrivateKey privateKey, byte[] encapsulation, String keyAlgorithmName, int keySizeInBits, AlgorithmIdentifier kdfAlgorithm, byte[] otherInfo)
    {
        super(kdfAlgorithm, otherInfo, keyAlgorithmName, keySizeInBits);

        this.privateKey = privateKey;
        this.encapsulation = Arrays.clone(encapsulation);
    }

    public KEMExtractSpec(PrivateKey privateKey, byte[] encapsulation, String keyAlgorithmName)
    {
        this(privateKey, encapsulation, keyAlgorithmName, 256);
    }

    public KEMExtractSpec(PrivateKey privateKey, byte[] encapsulation, String keyAlgorithmName, int keySizeInBits)
    {
        this(privateKey, encapsulation, keyAlgorithmName, keySizeInBits, DefKdf, EMPTY_OTHER_INFO);
    }

    public byte[] getEncapsulation()
    {
        return Arrays.clone(encapsulation);
    }

    public PrivateKey getPrivateKey()
    {
        return privateKey;
    }
}