使用椭圆曲线Diffie-Hellman和辅助因子密钥生成对称密钥

I am new to ECDH and wanted to generate the a secret key in Java. I wanted to use Elliptic curve Diffie-Hellman with cofactor key derivation. I'm using the P-256 curve for the elliptic curve operations. I'm planning to use the resulting secret as the symmetric key for my block cipher.I am new to ECDH and wanted to generate the a s