is there any separate thread explaining STB UART port open to communicate with CPU to get K1 key and also what steps and hardware/software I may need to give it a try.That’s impossible. The respond from Class D3 ins54 from smartcard is encrypted and it needs long process to decrypt it (Take a look at oscam source code). Even you have got the response from Class D3 ins54 decrypted, the CW from class D3 ins54 still encrypted with 3DES Key.
The process that turns encrypted CW to decrypted CW with 3DES Key happens inside the STB, hence this is the reason why people are anxious to establish a communication with the STB through UART port.