(PureBasic) ECDSA Sign and Verify

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

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkAsn.pb"
IncludeFile "CkBinData.pb"
IncludeFile "CkEcc.pb"
IncludeFile "CkPrivateKey.pb"
IncludeFile "CkPrng.pb"
IncludeFile "CkXml.pb"
IncludeFile "CkCrypt2.pb"
IncludeFile "CkPublicKey.pb"

Procedure ChilkatExample()

    ; 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.
    privKey.i = CkPrivateKey::ckCreate()
    If privKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkPrivateKey::ckLoadEncryptedPemFile(privKey,"qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret")
    If success = 0
        Debug CkPrivateKey::ckLastErrorText(privKey)
        CkPrivateKey::ckDispose(privKey)
        ProcedureReturn
    EndIf

    ; Sign the SHA256 hash of some data.
    bd.i = CkBinData::ckCreate()
    If bd.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkBinData::ckLoadFile(bd,"qa_data/hamlet.xml")
    If success = 0
        Debug "Failed to load file to be hashed."
        CkPrivateKey::ckDispose(privKey)
        CkBinData::ckDispose(bd)
        ProcedureReturn
    EndIf

    crypt.i = CkCrypt2::ckCreate()
    If crypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkCrypt2::setCkHashAlgorithm(crypt, "sha256")
    CkCrypt2::setCkEncodingMode(crypt, "base64")
    hashStr.s = CkCrypt2::ckHashBdENC(crypt,bd)

    ecdsa.i = CkEcc::ckCreate()
    If ecdsa.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    prng.i = CkPrng::ckCreate()
    If prng.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Returns ASN.1 signature as a base64 string.
    sig.s = CkEcc::ckSignHashENC(ecdsa,hashStr,"base64",privKey,prng)
    Debug "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:
    asn.i = CkAsn::ckCreate()
    If asn.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkAsn::ckLoadEncoded(asn,sig,"base64")
    xml.i = CkXml::ckCreate()
    If xml.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkXml::ckLoadXml(xml,CkAsn::ckAsnToXml(asn))

    Debug CkXml::ckGetXml(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
    r.s = CkXml::ckGetChildContentByIndex(xml,0)
    s.s = CkXml::ckGetChildContentByIndex(xml,1)

    Debug "r = " + r
    Debug "s = " + s

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

    ; Get the corresponding public key.
    pubKey.i = CkPublicKey::ckCreate()
    If pubKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPublicKey::ckLoadFromFile(pubKey,"qa_data/ecc/secp256r1-pub.pem")
    If success = 0
        Debug CkPublicKey::ckLastErrorText(pubKey)
        CkPrivateKey::ckDispose(privKey)
        CkBinData::ckDispose(bd)
        CkCrypt2::ckDispose(crypt)
        CkEcc::ckDispose(ecdsa)
        CkPrng::ckDispose(prng)
        CkAsn::ckDispose(asn)
        CkXml::ckDispose(xml)
        CkPublicKey::ckDispose(pubKey)
        ProcedureReturn
    EndIf

    ; We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    ecc2.i = CkEcc::ckCreate()
    If ecc2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    result.i = CkEcc::ckVerifyHashENC(ecc2,hashStr,sig,"base64",pubKey)
    If result <> 1
        Debug CkEcc::ckLastErrorText(ecc2)
        CkPrivateKey::ckDispose(privKey)
        CkBinData::ckDispose(bd)
        CkCrypt2::ckDispose(crypt)
        CkEcc::ckDispose(ecdsa)
        CkPrng::ckDispose(prng)
        CkAsn::ckDispose(asn)
        CkXml::ckDispose(xml)
        CkPublicKey::ckDispose(pubKey)
        CkEcc::ckDispose(ecc2)
        ProcedureReturn
    EndIf

    Debug "Verified!"

    ; Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
    xml2.i = CkXml::ckCreate()
    If xml2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkXml::setCkTag(xml2, "sequence")
    CkXml::ckNewChild2(xml2,"int",r)
    CkXml::ckNewChild2(xml2,"int",s)

    asn2.i = CkAsn::ckCreate()
    If asn2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkAsn::ckLoadAsnXml(asn2,CkXml::ckGetXml(xml2))
    encodedSig.s = CkAsn::ckGetEncodedDer(asn2,"base64")
    Debug "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...


    CkPrivateKey::ckDispose(privKey)
    CkBinData::ckDispose(bd)
    CkCrypt2::ckDispose(crypt)
    CkEcc::ckDispose(ecdsa)
    CkPrng::ckDispose(prng)
    CkAsn::ckDispose(asn)
    CkXml::ckDispose(xml)
    CkPublicKey::ckDispose(pubKey)
    CkEcc::ckDispose(ecc2)
    CkXml::ckDispose(xml2)
    CkAsn::ckDispose(asn2)


    ProcedureReturn
EndProcedure