Java code for retrieve Public key from Certificate
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     KeyStore inputKeyStore = KeyStore.getInstance(Constents.PFX_TYPE);
            FileInputStream fis = new FileInputStream(keyStoreFile);
            char[] nPassword = password.toCharArray();
            inputKeyStore.load(fis, nPassword);
            Enumeration enumeration = inputKeyStore.aliases();
            String keyAlias = null;
            while (enumeration.hasMoreElements()) {
                keyAlias = (String) enumeration.nextElement();
            }
            X509Certificate certificate = (X509Certificate) inputKeyStore
                    .getCertificate(keyAlias);           
            publicKey = certificate.getPublicKey(); 

And Encrypt Code using Public Key of certificate.
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            Cipher cipher = Cipher.getInstance(xform); //xform:RSA/ECB/PKCS1Padding
            cipher.init(Cipher.ENCRYPT_MODE, publicKey );         
            return cipher.doFinal(Data.getEncoded());

C# compatible Code
===================

Include Namespace of Bouncy Castle Dll.

This DLL is freely available from this link http://www.bouncycastle.org/csharp/

using Org.BouncyCastle.Pkcs;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.X509;
using Org.BouncyCastle.Crypto.Encodings;
using Org.BouncyCastle.Crypto.Engines;

               //Create file stream object to read certificate
                FileStream keyStream = new FileStream(strCertificatePath, FileMode.Open, FileAccess.Read);

                //Read certificate using BouncyCastle component
                Pkcs12Store inputKeyStore = new Pkcs12Store(keyStream, strCertificatePassword.ToCharArray());
                
                //Close File stream
                keyStream.Close();

                string keyAlias = null;

                //Read Key from Alieases  
                foreach (string n in inputKeyStore.Aliases)
                {
                    if (inputKeyStore.IsKeyEntry(n))
                    {
                        keyAlias = n;
                        break;
                    }
                }

                if (keyAlias == null)
                    throw new NotImplementedException("Alias");

                //Read certificate into 509 format
                X509Certificate certificate = (X509Certificate)inputKeyStore.GetCertificate(keyAlias).Certificate;

                //Retrieve public key of certificate
                AsymmetricKeyParameter publicKey = certificate.GetPublicKey();
                #endregion

                 //Encrypting (aesKey is a byte array containing an AES key): RSA/ECB/PKCS1Padding
                IAsymmetricBlockCipher cipher = new Pkcs1Encoding(new RsaEngine());
                cipher.Init(true, publicKey);
                byte[] encodedKey = cipher.ProcessBlock(SecretKey, 0, SecretKey.Length);