Go

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. Go

    success := false

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

    crypt := chilkat.NewCrypt2()

    crypt.SetEncodingMode("hex")
    crypt.SetHashAlgorithm("sha-1")

    hashStr := crypt.HashFileENC("qa_data/hamlet.xml")
    fmt.Println("hash to sign: ", hashSthashStr)

    dsa := chilkat.NewDsa()

    var pemPrivateKey *string = new(string)
    pemPrivateKey = dsa.LoadText("qa_data/dsa/dsaPrivKey2.pem")
    success = dsa.FromPem(*pemPrivateKey)
    if success == false {
        fmt.Println(dsa.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        return
    }

    // Load the hash to be signed into the DSA object:
    success = dsa.SetEncodedHash("hex",hashSthashStr)
    if success == false {
        fmt.Println(dsa.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        return
    }

    // Sign the hash.
    success = dsa.SignHash()
    if success == false {
        fmt.Println(dsa.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        return
    }

    // Get the ASN.1 signature.
    asnSig := dsa.GetEncodedSignature("base64")
    fmt.Println("Signature: ", *asnSig)

    // Examine the details of the ASN.1 signature.
    // We want to get the r,s values as hex strings..
    asn := chilkat.NewAsn()
    success = asn.LoadEncoded(*asnSig,"base64")
    if success == false {
        fmt.Println(asn.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        asn.DisposeAsn()
        return
    }

    // Get the ASN.1 as XML.
    xml := chilkat.NewXml()
    success = xml.LoadXml(*asn.AsnToXml())
    fmt.Println("Signature as XML: ")
    fmt.Println(*xml.GetXml())

    // 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
    r := "2C187F3AB6E47A66497B86CE97BB39E2133810F5"
    s := "588E53D3F7B69636B48FD7175E99A3961BD7D775"

    // Build the XML that will be converted to ASN.1
    xml.Clear()
    xml.SetTag("sequence")
    xml.NewChild2("int",r)
    xml.NewChild2("int",s)

    // Convert the XML to ASN.1
    success = asn.LoadAsnXml(*xml.GetXml())

    // Emit the signature as DER encoded ASN.1 (base64)
    asnSig = asn.GetEncodedDer("base64")

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

    dsa2 := chilkat.NewDsa()

    // Load the DSA public key to be used for verification:
    var pemPublicKey *string = new(string)
    pemPublicKey = dsa2.LoadText("qa_data/dsa/dsaPubKey2.pem")
    success = dsa2.FromPublicPem(*pemPublicKey)
    if success == false {
        fmt.Println(dsa2.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        asn.DisposeAsn()
        xml.DisposeXml()
        dsa2.DisposeDsa()
        return
    }

    // Load the hash to be verified.
    success = dsa2.SetEncodedHash("hex",hashSthashStr)
    if success == false {
        fmt.Println(dsa2.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        asn.DisposeAsn()
        xml.DisposeXml()
        dsa2.DisposeDsa()
        return
    }

    // Load the ASN.1 signature:
    success = dsa2.SetEncodedSignature("base64",*asnSig)
    if success == false {
        fmt.Println(dsa2.LastErrorText())
        crypt.DisposeCrypt2()
        dsa.DisposeDsa()
        asn.DisposeAsn()
        xml.DisposeXml()
        dsa2.DisposeDsa()
        return
    }

    // Verify:
    success = dsa2.Verify()
    if success == false {
        fmt.Println(dsa2.LastErrorText())
    } else {
        fmt.Println("DSA Signature Verified!")
    }


    crypt.DisposeCrypt2()
    dsa.DisposeDsa()
    asn.DisposeAsn()
    xml.DisposeXml()
    dsa2.DisposeDsa()