Visual FoxPro

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. Visual FoxPro

LOCAL lnSuccess
LOCAL loPrivKey
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

lnSuccess = 0

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

loEcdsa = CreateObject('Chilkat.Ecc')
loPrng = CreateObject('Chilkat.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.Asn')
loAsn.LoadEncoded(lcSig,"base64")
loXml = CreateObject('Chilkat.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.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.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.Xml')
loXml2.Tag = "sequence"
loXml2.NewChild2("int",r)
loXml2.NewChild2("int",s)

loAsn2 = CreateObject('Chilkat.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