Lianja

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. Lianja

llSuccess = .F.

// 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.
loPrivKey = createobject("CkPrivateKey")
llSuccess = loPrivKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret")
if (llSuccess = .F.) then
    ? loPrivKey.LastErrorText
    release loPrivKey
    return
endif

// Sign the SHA256 hash of some data.
loBd = createobject("CkBinData")
llSuccess = loBd.LoadFile("qa_data/hamlet.xml")
if (llSuccess = .F.) then
    ? "Failed to load file to be hashed."
    release loPrivKey
    release loBd
    return
endif

loCrypt = createobject("CkCrypt2")
loCrypt.HashAlgorithm = "sha256"
loCrypt.EncodingMode = "base64"
lcHashStr = loCrypt.HashBdENC(loBd)

loEcdsa = createobject("CkEcc")
loPrng = createobject("CkPrng")
// Returns ASN.1 signature as a base64 string.
lcSig = loEcdsa.SignHashENC(lcHashStr,"base64",loPrivKey,loPrng)
? "sig = " + lcSig

// 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:
loAsn = createobject("CkAsn")
loAsn.LoadEncoded(lcSig,"base64")
loXml = createobject("CkXml")
loXml.LoadXml(loAsn.AsnToXml())

? loXml.GetXml()

// 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
r = loXml.GetChildContentByIndex(0)
s = loXml.GetChildContentByIndex(1)

? "r = " + r
? "s = " + s

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

// Get the corresponding public key.
loPubKey = createobject("CkPublicKey")
llSuccess = loPubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem")
if (llSuccess = .F.) then
    ? loPubKey.LastErrorText
    release loPrivKey
    release loBd
    release loCrypt
    release loEcdsa
    release loPrng
    release loAsn
    release loXml
    release loPubKey
    return
endif

// We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
loEcc2 = createobject("CkEcc")
lnResult = loEcc2.VerifyHashENC(lcHashStr,lcSig,"base64",loPubKey)
if (lnResult <> 1) then
    ? loEcc2.LastErrorText
    release loPrivKey
    release loBd
    release loCrypt
    release loEcdsa
    release loPrng
    release loAsn
    release loXml
    release loPubKey
    release loEcc2
    return
endif

? "Verified!"

// Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
loXml2 = createobject("CkXml")
loXml2.Tag = "sequence"
loXml2.NewChild2("int",r)
loXml2.NewChild2("int",s)

loAsn2 = createobject("CkAsn")
loAsn2.LoadAsnXml(loXml2.GetXml())
lcEncodedSig = loAsn2.GetEncodedDer("base64")
? "encoded DSS signature: " + lcEncodedSig

// 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...


release loPrivKey
release loBd
release loCrypt
release loEcdsa
release loPrng
release loAsn
release loXml
release loPubKey
release loEcc2
release loXml2
release loAsn2