LÖVE

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local function newBlock(head, payload)
	local time = os.date()
	local blockData = (head and head.hash or '') .. time .. payload
	local block = {
		time = time,
		payload = payload,
		hash = love.data.hash('sha256', blockData),
	}
	if head then head.next = block end
	return block
end

local function verifyBlock(block, prev)
	local blockData = (prev and prev.hash or '') .. block.time .. block.payload
	return love.data.hash('sha256', blockData) == block.hash
end

local function verify(head)
	local prev
	while head do
		print(head.time, head.payload, love.data.encode('string', 'hex', head.hash))
		if not verifyBlock(head, prev) then return false end
		prev, head = head, head.next
	end
	return true
end

local chain = newBlock(nil, 'GENESIS BLOCK')
local head = newBlock(chain, 'second block')
head = newBlock(head, 'and a third one')
print("Chain is valid: ", verify(chain) and 'yes' or 'nope')

-- change second block
chain.next.payload = 'block modified!'
-- the basic idea is that a valid hash for the modified block in the middle of the chain is practically impossible to compute
-- because all previous hashes contribute to all subsequent block's hashes
chain.next.hash = love.data.hash('sha256', chain.hash .. chain.next.time .. chain.next.payload)
print("Chain is valid: ", verify(chain) and 'yes' or 'nope')