DataFlex

DSA R,S Signature Values

See more DSA Examples

Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature. DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoCrypt
    String sHashStr
    Handle hoDsa
    String sPemPrivateKey
    String sAsnSig
    Handle hoAsn
    Handle hoXml
    String r
    String s
2    Handle hoDsa2
    String sPemPublicKey
    String sTemp1

    Move False To iSuccess

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    Get Create (RefClass(cComChilkatCrypt2)) To hoCrypt
    If (Not(IsComObjectCreated(hoCrypt))) Begin
        Send CreateComObject of hoCrypt
    End

    Set ComEncodingMode Of hoCrypt To "hex"
    Set ComHashAlgorithm Of hoCrypt To "sha-1"

    Get ComHashFileENC Of hoCrypt "qa_data/hamlet.xml" To sHashStr
    Showln "hash to sign: " sHashStr

    Get Create (RefClass(cComChilkatDsa)) To hoDsa
    If (Not(IsComObjectCreated(hoDsa))) Begin
        Send CreateComObject of hoDsa
    End

    Get ComLoadText Of hoDsa "qa_data/dsa/dsaPrivKey2.pem" To sPemPrivateKey
    Get ComFromPem Of hoDsa sPemPrivateKey To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoDsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Load the hash to be signed into the DSA object:
    Get ComSetEncodedHash Of hoDsa "hex" sHashStr To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoDsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Sign the hash.
    Get ComSignHash Of hoDsa To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoDsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Get the ASN.1 signature.
    Get ComGetEncodedSignature Of hoDsa "base64" To sAsnSig
    Showln "Signature: " sAsnSig

    // Examine the details of the ASN.1 signature.
    // We want to get the r,s values as hex strings..
    Get Create (RefClass(cComChilkatAsn)) To hoAsn
    If (Not(IsComObjectCreated(hoAsn))) Begin
        Send CreateComObject of hoAsn
    End
    Get ComLoadEncoded Of hoAsn sAsnSig "base64" To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoAsn To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Get the ASN.1 as XML.
    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
    Showln "Signature as XML: "
    Get ComGetXml Of hoXml To sTemp1
    Showln sTemp1

    // Sample XML shown here.
    // The r and s values are the two hex strings in the XML.

    // <?xml version="1.0" encoding="utf-8"?>
    // <sequence>
    //     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
    //     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
    // </sequence>

    // Pretend we're starting with r,s
    Move "2C187F3AB6E47A66497B86CE97BB39E2133810F5" To r
    Move "588E53D3F7B69636B48FD7175E99A3961BD7D775" To s

    // Build the XML that will be converted to ASN.1
    Send ComClear To hoXml
    Set ComTag Of hoXml To "sequence"
    Send ComNewChild2 To hoXml "int" r
    Send ComNewChild2 To hoXml "int" s

    // Convert the XML to ASN.1
    Get ComGetXml Of hoXml To sTemp1
    Get ComLoadAsnXml Of hoAsn sTemp1 To iSuccess

    // Emit the signature as DER encoded ASN.1 (base64)
    Get ComGetEncodedDer Of hoAsn "base64" To sAsnSig

    // --------------------------------------------------------------------
    // Verify the signature using the asnSig we built from the r,s values
    // --------------------------------------------------------------------

    Get Create (RefClass(cComChilkatDsa)) To hoDsa2
    If (Not(IsComObjectCreated(hoDsa2))) Begin
        Send CreateComObject of hoDsa2
    End

    // Load the DSA public key to be used for verification:

    Get ComLoadText Of hoDsa2 "qa_data/dsa/dsaPubKey2.pem" To sPemPublicKey
    Get ComFromPublicPem Of hoDsa2 sPemPublicKey To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoDsa2 To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Load the hash to be verified.
    Get ComSetEncodedHash Of hoDsa2 "hex" sHashStr To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoDsa2 To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Load the ASN.1 signature:
    Get ComSetEncodedSignature Of hoDsa2 "base64" sAsnSig To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoDsa2 To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Verify:
    Get ComVerify Of hoDsa2 To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoDsa2 To sTemp1
        Showln sTemp1
    End
    Else Begin
        Showln "DSA Signature Verified!"
    End



End_Procedure