How Create 64 byte public and 32 byte private key Using ECDH encryption swift?

Question

I have to protect my lock from MITM (i.e man in the middle attack). For that i have to integrate ECDH encryption. I have no knowledge related to this. Please help me how do i create 64 bytes public and 32 byte private key. below are the code i'm trying

var publicKeySec, privateKeySec: SecKey?
let keyattribute = [
    kSecAttrKeyType as String: kSecAttrKeyTypeEC,
    kSecAttrKeySizeInBits as String : 256
    ] as CFDictionary

SecKeyGeneratePair(keyattribute, &publicKeySec, &privateKeySec)


var error:Unmanaged<CFError>?
if let publicCfdata = SecKeyCopyExternalRepresentation(publicKeySec!, &error) {
    let data:Data = publicCfdata as Data
    print(data)
    let b64Key = data.base64EncodedString()
    print(b64Key)
}

if let privateCfdata = SecKeyCopyExternalRepresentation(privateKeySec!, &error) {
    let data:Data = privateCfdata as Data
    print(data)
    let b64Key = data.base64EncodedString()
    print(b64Key)
}

Please help me. Thanks in advance.