(Visual FoxPro) ECDSA Sign and Verify

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

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loPrivKey
LOCAL lnSuccess
LOCAL loBd
LOCAL loCrypt
LOCAL lcHashStr
LOCAL loEcdsa
LOCAL loPrng
LOCAL lcSig
LOCAL loAsn
LOCAL loXml
LOCAL r
LOCAL s
LOCAL loPubKey
LOCAL loEcc2
LOCAL lnResult
LOCAL loXml2
LOCAL loAsn2
LOCAL lcEncodedSig

* 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('Chilkat_9_5_0.PrivateKey')
lnSuccess = loPrivKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret")
IF (lnSuccess = 0) THEN
    ? loPrivKey.LastErrorText
    RELEASE loPrivKey
    CANCEL
ENDIF

* Sign the SHA256 hash of some data.
loBd = CreateObject('Chilkat_9_5_0.BinData')
lnSuccess = loBd.LoadFile("qa_data/hamlet.xml")
IF (lnSuccess = 0) THEN
    ? "Failed to load file to be hashed."
    RELEASE loPrivKey
    RELEASE loBd
    CANCEL
ENDIF

loCrypt = CreateObject('Chilkat_9_5_0.Crypt2')
loCrypt.HashAlgorithm = "sha256"
loCrypt.EncodingMode = "base64"
lcHashStr = loCrypt.HashBdENC(loBd)

loEcdsa = CreateObject('Chilkat_9_5_0.Ecc')
loPrng = CreateObject('Chilkat_9_5_0.Prng')
* 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('Chilkat_9_5_0.Asn')
loAsn.LoadEncoded(lcSig,"base64")
loXml = CreateObject('Chilkat_9_5_0.Xml')
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('Chilkat_9_5_0.PublicKey')
lnSuccess = loPubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem")
IF (lnSuccess = 0) THEN
    ? loPubKey.LastErrorText
    RELEASE loPrivKey
    RELEASE loBd
    RELEASE loCrypt
    RELEASE loEcdsa
    RELEASE loPrng
    RELEASE loAsn
    RELEASE loXml
    RELEASE loPubKey
    CANCEL
ENDIF

* We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
loEcc2 = CreateObject('Chilkat_9_5_0.Ecc')
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
    CANCEL
ENDIF

? "Verified!"

* Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
loXml2 = CreateObject('Chilkat_9_5_0.Xml')
loXml2.Tag = "sequence"
loXml2.NewChild2("int",r)
loXml2.NewChild2("int",s)

loAsn2 = CreateObject('Chilkat_9_5_0.Asn')
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