http://www.bouncycastle.org/java.html: The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.5 to JDK 1.8. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.cms;

import org.bouncycastle.asn1.ASN1OctetString;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;

public interface KeyAgreeRecipient
    extends Recipient
{
    RecipientOperator getRecipientOperator(AlgorithmIdentifier keyEncAlg, AlgorithmIdentifier contentEncryptionAlgorithm, SubjectPublicKeyInfo senderPublicKey, ASN1OctetString userKeyingMaterial, byte[] encryptedContentKey)
        throws CMSException;

    AlgorithmIdentifier getPrivateKeyAlgorithmIdentifier();
}