How should I approach replicating a damage remote securely?

I'm trying to make a punch script and I'm handling the OnTouched event in Localscript (this whole script is a localscript). Yes, I want to deal damage, but at the same time make the RemoteEvent secure and as server-sided as possible so exploiters cannot manipulate it. I cannot think of a way to do it, however.

			local punchConnection
			punchConnection = LeftHand.Touched:Connect(function(interacted)
				-- Punch Variables were placed in an event to randomize them more. --
				local PunchDamage_Range = math.random(4, 8) -- Randomized Range of Damages for Punch.
				local PunchCritical = math.random() -- Chance of Critical Hit if Player hits another Player in the Head.
				local interactedHumanoid = interacted:FindFirstChild('Humanoid') or interacted.Parent:FindFirstChild('Humanoid')
				if interactedHumanoid ~= nil and interactedHumanoid ~= Humanoid and not Hit and Punching then
					Hit = true
					if interacted.Name == 'Head' and PunchCritical >= 0.85 then
						-- N/A
					else
						-- Line where I want to do damage
					end
					wait(PunchCooldown)
					Hit = false
					punchConnection:Disconnect()
				end
			end)

Any ideas? If so, please help, thanks!

First of all, do NOT calculate the damage client sided. This opens up the possibility of sending any number of damage to the server for exploiters (insta kill, .etc).

Second of all, your best possibility is probably to do distance (so they cant do it from anywhere) and time (so exploiters cant rapid fire punch).

so basically first we need to define max distance, wait time and if the target actually has a humanoid!

local maxDistance = 10 --Change this to what you want (I have 10 as a generally good number)
local waitTime = 1 --Wait one second before able to hit again
local tHum = target:FindFirstChild("Humanoid")

Now theres many ways you can register the players last hit time but I like to use a table in my preference:

local lastHitTime = {} --We're going to create a dictionary for the players so its easily accessible

Now we need to go serverside.

First we need to check the target exists, work out distance then check time

To work out distance

local distance = (player.Position - target.Position).magnitude

Magnitude gives us the distance in studs between the target and the player.

we then check if its too far or not:

if distance <= maxDistance and tHum then

What we have so far:

local maxDistance = 10 --Change this to what you want (I have 10 as a generally good number)
local waitTime = 1 --Wait one second before able to hit again
local lastHitTime = {} --We're going to create a dictionary for the players so its easily accessible

game.ReplicatedStorage.RemoteEvent.OnServerEvent:Connect(function(player, target)
	local distance = (player.Position - target.Position).magnitude
	if distance <= maxDistance and tHum then
		
	end
end)

Now we need to check the last time they hit, for this we'll use roblox's tick() this tells us how many seconds have passed since the UNIX epoch

if lastHitTime[player.Name] then --If they've never hit before they won't have a last hit time
			if tick()-lastHitTime[player.Name] >= waitTime then
				tHum:TakeDamage(math.random(4, 8)) --we'll just move the math random here for ease
				lastHitTime[player.Name] = tick() --we need to update the lastHitTime
			end
		else
			tHum:TakeDamage(math.random(4, 8)) --we'll just move the math random here for ease
			lastHitTime[player.Name] = tick() --we need to update the lastHitTime
		end

And now the whole thing:

local maxDistance = 10 --Change this to what you want (I have 10 as a generally good number)
local waitTime = 1 --Wait one second before able to hit again
local lastHitTime = {} --We're going to create a dictionary for the players so its easily accessible

game.ReplicatedStorage.RemoteEvent.OnServerEvent:Connect(function(player, target)
	local distance = (player.Position - target.Position).magnitude
	local tHum = target:FindFirstChild("Humanoid")
	if distance <= maxDistance then
		if lastHitTime[player.Name] then --If they've never hit before they won't have a last hit time
			if tick()-lastHitTime[player.Name] >= waitTime then
				tHum:TakeDamage(math.random(4, 8)) --we'll just move the math random here for ease
				lastHitTime[player.Name] = tick() --we need to update the lastHitTime
			end
		else
			tHum:TakeDamage(math.random(4, 8)) --we'll just move the math random here for ease
			lastHitTime[player.Name] = tick() --we need to update the lastHitTime
		end
	end
end)

Hope this helps! feel free to contact me if you need more help!