minicrypto.lua

Author: Mehgugs

minicrypto.lua

@@ -0,0 +1,77 @@
+minicrypto = {}
+
+local insert, concat, modf, tostring, char = table.insert, table.concat, math.modf, tostring, string.char
+
+
+local function numberToBinStr(x)
+    local ret = {}
+    while x~=1 and x~=0 do
+        insert(ret, 1, x%2)
+        x=modf(x/2)
+    end
+    insert(ret, 1, x)
+    for i = 1, 8 - #ret do 
+       insert(ret, 1, 0)
+    end
+    return concat(ret)
+end
+
+local function computeBinaryKey(str)
+    local t = {}
+    for i = #str, 1, -1 do 
+        insert(t, numberToBinStr(str:byte(i,i)))
+    end
+    return concat(t)
+end
+
+local binaryKeys = setmetatable({}, {__mode = "k"})
+
+local function binaryKey(key)
+    local v = binaryKeys[key]
+    if v == nil then
+        v = computeBinaryKey(key)
+        binaryKeys[key] = v 
+    end
+    return v
+end
+
+local function initialize_state(key)
+    local S = {}; for i = 0, 255 do S[i] = i end
+    key = binaryKey(key)
+
+    local j = 0
+    for i = 0, 255 do 
+        local idx = (i % #key) +1
+        j = (j + S[i] + tonumber(key:sub(idx, idx))) % 256
+        S[i], S[j] = S[j], S[i]
+    end
+    S.i = 0
+    S.j = 0
+    return S
+end
+
+local function encrypt_one(state, byt)
+    state.i = (state.i+1) % 256
+    state.j = (state.j + state[state.i]) % 256
+    state[state.i], state[state.j] = state[state.j], state[state.i]
+    local K = state[(state[state.i] + state[state.j]) % 256]
+    return K ~ byt
+end
+
+function minicrypto.encrypt(text, key)
+    local state = initialize_state(key)
+    local encrypted = {}
+    for i = 1, #text do 
+        encrypted[i] = ("%02X"):format(encrypt_one(state, text:byte(i,i)))
+    end
+    return concat(encrypted)
+end
+
+function minicrypto.decrypt(text, key)
+    local state = initialize_state(key)
+    local decrypted = {}
+    for i = 1, #text, 2 do 
+        insert(decrypted, char(encrypt_one(state, tonumber(text:sub(i, i+1), 16))))
+    end
+    return concat(decrypted)
+end