Lua

ECDSA Sign and Verify

See more ECC Examples

Demonstrates how to create an ECDSA signature on the SHA256 hash of some data, and then verify. Lua

local chilkat = require("chilkat")

-- This example assumes the Chilkat API to have been previously unlocked.
-- See Global Unlock Sample for sample code.

-- First load an ECDSA private key to be used for signing.
local privKey = chilkat.PrivateKey.new()
local success = privKey:load_encrypted_pem_file("qa_data/ecc/secp256r1-key-pkcs8-secret.pem", "secret")
if not success then
    print(privKey.last_error_text)
    return
end

-- Sign the SHA256 hash of some data.
local bd = chilkat.BinData.new()
success = bd:load_file("qa_data/hamlet.xml")
if not success then
    print("Failed to load file to be hashed.")
    return
end

local crypt = chilkat.Crypt2.new()
crypt.hash_algorithm = "sha256"
crypt.encoding_mode = "base64"
local hashStr = crypt:hash_bd_enc(bd)

local ecdsa = chilkat.Ecc.new()
local prng = chilkat.Prng.new()
-- Returns ASN.1 signature as a base64 string.
local sig = ecdsa:sign_hash_enc(hashStr, "base64", privKey, prng)
print("sig = " .. sig)

-- The signature is in ASN.1 format (which may be described as the "encoded DSS signature").
-- SEQUENCE (2 elem)
--   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
--   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...

-- If you wish, you can get the r and s components of the signature like this:
local asn = chilkat.Asn.new()
asn:load_encoded(sig, "base64")
local xml = chilkat.Xml.new()
xml:load_xml(asn:asn_to_xml())

print(xml:get_xml())

-- We now have this:
-- <?xml version="1.0" encoding="utf-8"?>
-- <sequence>
--     <int>6650D422D86BA4A228B5617604E59052591B9B2C32EF324C44D09EF67E5F0060</int>
--     <int>0CFD9F6AC85042FC70F672C141BA6B2A4CAFBB906C3D907BCCC1BED62B28326F</int>
-- </sequence>

-- Get the "r" and "s" as hex strings
local r = xml:get_child_content_by_index(0)
local s = xml:get_child_content_by_index(1)

print("r = " .. r)
print("s = " .. s)

-- --------------------------------------------------------------------
-- Now verify against the hash of the original data.

-- Get the corresponding public key.
local pubKey = chilkat.PublicKey.new()
success = pubKey:load_from_file("qa_data/ecc/secp256r1-pub.pem")
if not success then
    print(pubKey.last_error_text)
    return
end

-- We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
local ecc2 = chilkat.Ecc.new()
local result = ecc2:verify_hash_enc(hashStr, sig, "base64", pubKey)
if result ~= 1 then
    print(ecc2.last_error_text)
    return
end

print("Verified!")

-- Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
local xml2 = chilkat.Xml.new()
xml2.tag = "sequence"
xml2:new_child2("int", r)
xml2:new_child2("int", s)

local asn2 = chilkat.Asn.new()
asn2:load_asn_xml(xml2:get_xml())
local encodedSig = asn2:get_encoded_der("base64")
print("encoded DSS signature: " .. encodedSig)

-- You can go to https://lapo.it/asn1js/  and copy/paste the base64 encodedSig into the online tool, then press the "decode" button.
-- You will see the ASN.1 such as this:

-- SEQUENCE (2 elem)
--   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
--   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...