  Quantum Key Distribution is a key distribution method that uses the qubits to
safely distribute one-time use encryption keys between two or more authorised
participants in a way that ensures the identification of any eavesdropper. In
this paper, we have done a comparison between the BB84 and B92 protocols and
BBM92 and E91 entanglement based protocols for satellite based uplink and
downlink in low Earth orbit. The expressions for the quantum bit error rate and
the keyrate are given for all four protocols. The results indicate that, when
compared to the B92 protocol, the BB84 protocol guarantees the distribution of
a higher secure keyrate for a specific distance. Similarly, it is observed that
BBM92 ensures higher keyrate in comparison with E91 protocol.
