Lua

ECDSA Sign Data and Get Raw R and S Values

See more ECC Examples

Demonstrates getting the raw R and S value of an ECDSA signature. Lua

local chilkat = require("chilkat")

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

-- To create an ECDSA signature, the data first needs to be hashed.  Then the hash
-- is signed.

local crypt = chilkat.Crypt2.new()
crypt.hash_algorithm = "SHA256"
crypt.charset = "utf-8"
crypt.encoding_mode = "base64"

-- Hash a string.
local hash1 = crypt:hash_string_enc("The quick brown fox jumps over the lazy dog")
print("hash1 = " .. hash1)

-- -----------------------------------------------------------
-- An ECDSA private key is used for signing.  The public key is for signature verification.
-- Load our ECC private key.
-- Our private key file contains this:

--     // -----BEGIN PRIVATE KEY-----
--     MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
--     72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
--     a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
--     -----END PRIVATE KEY-----

local privKey = chilkat.PrivateKey.new()
local success = privKey:load_pem_file("qa_data/ecc/secp256r1-key-pkcs8.pem")
if not success then
    print(privKey.last_error_text)
    return
end

-- Sign the hash..
local prng = chilkat.Prng.new()
local ecdsa = chilkat.Ecc.new()
local ecdsaSigBase64 = ecdsa:sign_hash_enc(hash1, "base64", privKey, prng)
if not ecdsa.last_method_success then
    print(ecdsa.last_error_text)
    return
end

-- The ECDSA signature is ASN.1 that contains a sequence of 2 large integers (r and s)
-- For example:
-- SEQUENCE (2 elem)
--   INTEGER (255 bit) 792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9
--   INTEGER (255 bit) 481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5

print("Base64 ECDSA signature = " .. ecdsaSigBase64)

-- If the raw R and S values are needed, here's how to get them:
local asn = chilkat.Asn.new()
success = asn:load_encoded(ecdsaSigBase64, "base64")
if not success then
    print(asn.last_error_text)
    return
end

-- The R and X will be in hexidecimal in the XML.
local xml = chilkat.Xml.new()
xml:load_xml(asn:asn_to_xml())
print(xml:get_xml())

-- The XML looks like this:
-- <sequence>
-- <int>792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9</int>
-- <int>481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5</int>
-- </sequence>

-- Copy raw R and S hex values into a Chilkat BinData object.
local bd = chilkat.BinData.new()
local r = xml:get_child_content("int[0]")
local s = xml:get_child_content("int[1]")
bd:append_encoded(r, "hex")
bd:append_encoded(s, "hex")

print("Number of bytes in bd: " .. bd.num_bytes)