(DataFlex) 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

Use ChilkatAx-win32.pkg

Procedure Test
    Variant vPrivKey
    Handle hoPrivKey
    Boolean iSuccess
    Variant vBd
    Handle hoBd
    Handle hoCrypt
    String sHashStr
    Handle hoEcdsa
    Variant vPrng
    Handle hoPrng
    String sSig
    Handle hoAsn
    Handle hoXml
    String r
    String s
    Variant vPubKey
    Handle hoPubKey
    Handle hoEcc2
    Integer iResult
    Handle hoXml2
2    Handle hoAsn2
    String sEncodedSig
    String sTemp1

    // 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.
    Get Create (RefClass(cComChilkatPrivateKey)) To hoPrivKey
    If (Not(IsComObjectCreated(hoPrivKey))) Begin
        Send CreateComObject of hoPrivKey
    End
    Get ComLoadEncryptedPemFile Of hoPrivKey "qa_data/ecc/secp256r1-key-pkcs8-secret.pem" "secret" To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoPrivKey To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Sign the SHA256 hash of some data.
    Get Create (RefClass(cComChilkatBinData)) To hoBd
    If (Not(IsComObjectCreated(hoBd))) Begin
        Send CreateComObject of hoBd
    End
    Get ComLoadFile Of hoBd "qa_data/hamlet.xml" To iSuccess
    If (iSuccess = False) Begin
        Showln "Failed to load file to be hashed."
        Procedure_Return
    End

    Get Create (RefClass(cComChilkatCrypt2)) To hoCrypt
    If (Not(IsComObjectCreated(hoCrypt))) Begin
        Send CreateComObject of hoCrypt
    End
    Set ComHashAlgorithm Of hoCrypt To "sha256"
    Set ComEncodingMode Of hoCrypt To "base64"
    Get pvComObject of hoBd to vBd
    Get ComHashBdENC Of hoCrypt vBd To sHashStr

    Get Create (RefClass(cComChilkatEcc)) To hoEcdsa
    If (Not(IsComObjectCreated(hoEcdsa))) Begin
        Send CreateComObject of hoEcdsa
    End
    Get Create (RefClass(cComChilkatPrng)) To hoPrng
    If (Not(IsComObjectCreated(hoPrng))) Begin
        Send CreateComObject of hoPrng
    End
    // Returns ASN.1 signature as a base64 string.
    Get pvComObject of hoPrivKey to vPrivKey
    Get pvComObject of hoPrng to vPrng
    Get ComSignHashENC Of hoEcdsa sHashStr "base64" vPrivKey vPrng To sSig
    Showln "sig = " sSig

    // 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:
    Get Create (RefClass(cComChilkatAsn)) To hoAsn
    If (Not(IsComObjectCreated(hoAsn))) Begin
        Send CreateComObject of hoAsn
    End
    Get ComLoadEncoded Of hoAsn sSig "base64" To iSuccess
    Get Create (RefClass(cComChilkatXml)) To hoXml
    If (Not(IsComObjectCreated(hoXml))) Begin
        Send CreateComObject of hoXml
    End
    Get ComAsnToXml Of hoAsn To sTemp1
    Get ComLoadXml Of hoXml sTemp1 To iSuccess

    Get ComGetXml Of hoXml To sTemp1
    Showln sTemp1

    // 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
    Get ComGetChildContentByIndex Of hoXml 0 To r
    Get ComGetChildContentByIndex Of hoXml 1 To s

    Showln "r = " r
    Showln "s = " s

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

    // Get the corresponding public key.
    Get Create (RefClass(cComChilkatPublicKey)) To hoPubKey
    If (Not(IsComObjectCreated(hoPubKey))) Begin
        Send CreateComObject of hoPubKey
    End
    Get ComLoadFromFile Of hoPubKey "qa_data/ecc/secp256r1-pub.pem" To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoPubKey To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    Get Create (RefClass(cComChilkatEcc)) To hoEcc2
    If (Not(IsComObjectCreated(hoEcc2))) Begin
        Send CreateComObject of hoEcc2
    End
    Get pvComObject of hoPubKey to vPubKey
    Get ComVerifyHashENC Of hoEcc2 sHashStr sSig "base64" vPubKey To iResult
    If (iResult <> 1) Begin
        Get ComLastErrorText Of hoEcc2 To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln "Verified!"

    // Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
    Get Create (RefClass(cComChilkatXml)) To hoXml2
    If (Not(IsComObjectCreated(hoXml2))) Begin
        Send CreateComObject of hoXml2
    End
    Set ComTag Of hoXml2 To "sequence"
    Send ComNewChild2 To hoXml2 "int" r
    Send ComNewChild2 To hoXml2 "int" s

    Get Create (RefClass(cComChilkatAsn)) To hoAsn2
    If (Not(IsComObjectCreated(hoAsn2))) Begin
        Send CreateComObject of hoAsn2
    End
    Get ComGetXml Of hoXml2 To sTemp1
    Get ComLoadAsnXml Of hoAsn2 sTemp1 To iSuccess
    Get ComGetEncodedDer Of hoAsn2 "base64" To sEncodedSig
    Showln "encoded DSS signature: " sEncodedSig

    // 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...


End_Procedure