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SHA-1, SHA-2 and SHA-3 functions written in pure Lua and optimized for speed.


Just copy sha2.lua to Lua modules' folder.


This module provides functions to calculate SHA digest.
This is a pure-Lua module, compatible with Lua 5.1, Lua 5.2, Lua 5.3, Lua 5.4.0 (alpha), LuaJIT 2.0/2.1 and Fengari.

Main feature of this module: it was heavily optimized for speed.
For every Lua version the module contains particular implementation branch to get benefits from version-specific features.

Supported hashes:

MD5            -- sha.md5(message)
SHA-1          -- sha.sha1(message)
-- SHA2
SHA-224        -- sha.sha224(message)
SHA-256        -- sha.sha256(message)
SHA-384        -- sha.sha384(message)
SHA-512        -- sha.sha512(message)
SHA-512/224    -- sha.sha512_224(message)
SHA-512/256    -- sha.sha512_256(message)
-- SHA3
SHA3-224       -- sha.sha3_224(message)
SHA3-256       -- sha.sha3_256(message)
SHA3-384       -- sha.sha3_384(message)
SHA3-512       -- sha.sha3_512(message)
SHAKE128       -- sha.shake128(digest_size_in_bytes, message)
SHAKE256       -- sha.shake256(digest_size_in_bytes, message)
-- HMAC (applicable to any hash-function from this module except SHAKE)
HMAC           -- sha.hmac(sha.any_hash_func, key, message)


Input data should be provided as a binary string: either as a whole string or as a sequence of substrings (chunk-by-chunk loading).
Result (SHA digest) is returned in hexadecimal representation (as a string of lowercase hex digits).

Simplest usage example:

local sha = require("sha2")
local your_hash = sha.sha256("your string")
-- assert(your_hash == "d14d691dac70eada14d9f23ef80091bca1c75cf77cf1cd5cf2d04180ca0d9911")

See file "sha2_test.lua" for more examples.


  • Q: Does this module calculate SHA really fast?
  • A:
    Probably, this is the fastest pure Lua implementation of SHA you can find.
    For example, on x64 Lua 5.3 this module calculates SHA256 twice as fast as the implementation published at
    This module has best performance on every Lua version because it contains several version-specific implementation branches:
    • branch for Lua 5.1 (emulating bitwise operators using look-up table)
    • branch for Lua 5.2 (using bit32 library), suitable also for Lua 5.1 with external bit library
    • branch for Lua 5.3 / 5.4 (using native 64-bit bitwise operators)
    • branch for Lua 5.3 / 5.4 (using native 32-bit bitwise operators) for Lua built with LUA_INT_TYPE=LUA_INT_INT
    • branch for LuaJIT without FFI library (if you're working in a sandboxed environment with FFI disabled)
    • branch for LuaJIT x86 without FFI library (LuaJIT x86 has oddity because of lack of x86 CPU registers)
    • branch for LuaJIT 2.0 with FFI library (bit.* functions work only with 32-bit values)
    • branch for LuaJIT 2.1 with FFI library (bit.* functions can work with int64_t cdata)

  • Q: How to get SHA digest as binary string instead of hexadecimal representation?
  • A:
    Use function sha.hex2bin() to convert hexadecimal to binary:
local sha = require("sha2")
local binary_hash = sha.hex2bin(sha.sha256("your string"))
-- assert(binary_hash == "\209Mi\29\172p\234\218\20\217\242>\248\0\145\188\161\199\\\247|\241\205\\\242\208A\128\202\r\153\17")

  • Q: How to get SHA digest as base64 string?
  • A:
    There are functions sha.bin2base64() and sha.base642bin() for converting between binary and base64:
local sha = require("sha2")
local binary_hash = sha.hex2bin(sha.sha256("your string"))
local base64_hash = sha.bin2base64(binary_hash)
-- assert(base64_hash == "0U1pHaxw6toU2fI++ACRvKHHXPd88c1c8tBBgMoNmRE=")

  • Q: How to calculate SHA digest of long data stream?
  • A:
local sha = require("sha2")
local append = sha.sha256()  -- if the "message" argument is omitted then "append" function is returned
append(" st")                -- you should pass all parts of your long message to the "append" function (chunk-by-chunk)
local your_hash = append()   -- and finally ask for the result (by invoking the "append" function without argument)
-- assert(your_hash == "d14d691dac70eada14d9f23ef80091bca1c75cf77cf1cd5cf2d04180ca0d9911")

  • Q: How to calculate HMAC-SHA1, HMAC-SHA256, etc. ?
  • A:
-- Calculating HMAC-SHA1
local sha = require("sha2")
local your_hmac = sha.hmac(sha.sha1, "your key", "your message")
-- assert(your_hmac == "317d0dfd868a5c06c9444ac1328aa3e2bfd29fb2")

The same in chunk-by-chunk mode (for long messages):

local sha = require("sha2")
local append = sha.hmac(sha.sha1, "your key")
append(" mess")
local your_hmac = append()
-- assert(your_hmac == "317d0dfd868a5c06c9444ac1328aa3e2bfd29fb2")

  • Q: Can SHAKE128/SHAKE256 be used to generate digest of infinite length ?
  • A:
    For example, you can convert your password into infinite stream of pseudo-random bytes.
    Set digest_size_in_bytes to -1 and obtain the function get_next_part(part_size_in_bytes).
    Invoke this function repeatedly to get consecutive parts of the infinite digest.
local sha = require("sha2")
local get_next_part_of_digest = sha.shake128(-1, "The quick brown fox jumps over the lazy dog")
assert(get_next_part_of_digest(5) == "f4202e3c58") -- 5 bytes in hexadecimal representation
assert(get_next_part_of_digest()  == "52")         -- size=1 is assumed when omitted
assert(get_next_part_of_digest(0) == "")           -- size=0 is a valid size
assert(get_next_part_of_digest(4) == "f9182a04")   -- and so on to the infinity...
-- Note: you can use sha.hex2bin() to convert these hexadecimal parts to binary strings
-- By definition, the result of SHAKE with finite "digest_size_in_bytes" is just a finite prefix of "infinite digest":
assert(sha.shake128(4, "The quick brown fox jumps over the lazy dog")) == "f4202e3c")

For SHAKE, it's possible to combine "chunk-by-chunk" input mode with "chunk-by-chunk" output mode:

local sha = require("sha2")
local append_input_message = sha.shake128(-1)
append_input_message("The quick brown fox")
append_input_message(" jumps over")
append_input_message(" the lazy dog")
local get_next_part_of_digest = append_input_message()  -- input stream is terminated, now we can start receiving the output stream
assert(get_next_part_of_digest(5) == "f4202e3c58")
assert(get_next_part_of_digest(5) == "52f9182a04")      -- and so on...

  • Q: Why does this module called "sha2.lua" despite of having implemented all SHA functions: SHA1, SHA2 and SHA3 ?
  • A:
    Yes, the notation local digest = require("sha2").sha3_512(message) looks strange :-)
    The first release of this module contained only SHA2 functions, hence the name sha2.lua.
    But I can't rename the module due to backward-compatibility I've promised to keep forever (Was it a silly promise?)


This module will always keep backward-compatibility.
If your program works successfully with some previous version of sha2.lua, it will also work with the latest version.

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