diff --git a/bank.lua b/bank.lua
new file mode 100644
index 0000000..11756cc
--- /dev/null
+++ b/bank.lua
@@ -0,0 +1,117 @@
+--[[
+bank.lua is the central bank server code, which runs 24/7 on a single computer
+that is globally available via wireless connectivity (ender modem). It keeps a
+persistent record of all accounts, and all transactions for accounts.
+
+This program essentially serves as a simplified REST API for ingame clients,
+like pocket computers and ATMs, for managing funds.
+]]--
+
+local USERS_DIR = "users"
+local USER_DATA_FILE = "data.json"
+local ACCOUNTS_FILE = "accounts.json"
+local TRANSACTIONS_FILE = "transactions.json"
+
+-- Basic account functions:
+
+local function validateUsername(name)
+    local i, j = string.find(name, "%a%a%a+")
+    return (
+        i == 1 and
+        j == #name and
+        j <= 12
+    )
+end
+
+local function userDir(name)
+    return fs.combine(USERS_DIR, name)
+end
+
+local function userDataFile(name)
+    return fs.combine(USERS_DIR, name, USER_DATA_FILE)
+end
+
+local function userAccountsFile(name)
+    return fs.combine(USERS_DIR, name, ACCOUNTS_FILE)
+end
+
+local function userExists(name)
+    return validateUsername(name) and fs.exists(userDir(name))
+end
+
+local function validatePassword(password)
+    return #password >= 8
+end
+
+local function randomAccountId()
+    local id = ""
+    for i = 1, 16 do
+        id = id .. tostring(math.random(1, 9))
+        if i % 4 == 0 and i < 16 then
+            id = id .. "-"
+        end
+    end
+    return id
+end
+
+local function getAccounts(name)
+    local f = io.open(userAccountsFile(name), "r")
+    local accounts = textutils.unserializeJSON(f:read("*a"))
+    f:close()
+    return accounts
+end
+
+local function saveAccounts(name, accounts)
+    local f = io.open(userAccountsFile(name), "w")
+    f:write(textutils.serializeJSON(accounts))
+    f:close()
+end
+
+local function createUser(name, password)
+    if not validateUsername(name) then return false, "Invalid username" end
+    if not validatePassword(password) then return false, "Invalid password" end
+    if userExists(name) then return false, "Username taken" end
+    local userData = {
+        password = password
+    }
+    fs.makeDir(userDir(name))
+    local dataFile = io.open(userDataFile(name), "w")
+    dataFile:write(textutils.serializeJSON(userData))
+    dataFile:close()
+    -- Add an initial account.
+    local initialAccounts = {
+        {
+            id = randomAccountId(),
+            name = "Checking",
+            balance = 0
+        },
+        {
+            id = randomAccountId(),
+            name = "Savings",
+            balance = 0
+        }
+    }
+    saveAccounts(name, initialAccounts)
+    return true
+end
+
+local function deleteUser(name)
+    if not userExists(name) then return false end
+    fs.delete(userDir(name))
+    return true
+end
+
+local function renameUser(oldName, newName)
+    if not userExists(oldName) then return false, "User doesn't exist" end
+    if userExists(newName) then return false, "New username is taken" end
+    fs.move(userDir(oldName), userDir(newName))
+    return true
+end
+
+rednet.open("modem")
+rednet.host("BANK", "central-bank")
+
+while true do
+    local remoteId, msg = rednet.receive("BANK")
+    print("Got message from " .. remoteId .. ": " .. msg)
+end