(Go) ECDSA Sign and Verify

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

Chilkat Go Downloads Go Package for Windows, MacOS, Linux, Alpine Linux, Solaris

    // 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 := chilkat.NewPrivateKey()
    success := privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret")
    if success == false {
        fmt.Println(privKey.LastErrorText())
        privKey.DisposePrivateKey()
        return
    }

    // Sign the SHA256 hash of some data.
    bd := chilkat.NewBinData()
    success = bd.LoadFile("qa_data/hamlet.xml")
    if success == false {
        fmt.Println("Failed to load file to be hashed.")
        privKey.DisposePrivateKey()
        bd.DisposeBinData()
        return
    }

    crypt := chilkat.NewCrypt2()
    crypt.SetHashAlgorithm("sha256")
    crypt.SetEncodingMode("base64")
    hashStr := crypt.HashBdENC(bd)

    ecdsa := chilkat.NewEcc()
    prng := chilkat.NewPrng()
    // Returns ASN.1 signature as a base64 string.
    sig := ecdsa.SignHashENC(*hashStr,"base64",privKey,prng)
    fmt.Println("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 := chilkat.NewAsn()
    asn.LoadEncoded(*sig,"base64")
    xml := chilkat.NewXml()
    xml.LoadXml(*asn.AsnToXml())

    fmt.Println(*xml.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 := xml.GetChildContentByIndex(0)
    s := xml.GetChildContentByIndex(1)

    fmt.Println("r = ", *r)
    fmt.Println("s = ", *s)

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

    // Get the corresponding public key.
    pubKey := chilkat.NewPublicKey()
    success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem")
    if success == false {
        fmt.Println(pubKey.LastErrorText())
        privKey.DisposePrivateKey()
        bd.DisposeBinData()
        crypt.DisposeCrypt2()
        ecdsa.DisposeEcc()
        prng.DisposePrng()
        asn.DisposeAsn()
        xml.DisposeXml()
        pubKey.DisposePublicKey()
        return
    }

    // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    ecc2 := chilkat.NewEcc()
    result := ecc2.VerifyHashENC(*hashStr,*sig,"base64",pubKey)
    if result != 1 {
        fmt.Println(ecc2.LastErrorText())
        privKey.DisposePrivateKey()
        bd.DisposeBinData()
        crypt.DisposeCrypt2()
        ecdsa.DisposeEcc()
        prng.DisposePrng()
        asn.DisposeAsn()
        xml.DisposeXml()
        pubKey.DisposePublicKey()
        ecc2.DisposeEcc()
        return
    }

    fmt.Println("Verified!")

    // Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
    xml2 := chilkat.NewXml()
    xml2.SetTag("sequence")
    xml2.NewChild2("int",*r)
    xml2.NewChild2("int",*s)

    asn2 := chilkat.NewAsn()
    asn2.LoadAsnXml(*xml2.GetXml())
    encodedSig := asn2.GetEncodedDer("base64")
    fmt.Println("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...

    privKey.DisposePrivateKey()
    bd.DisposeBinData()
    crypt.DisposeCrypt2()
    ecdsa.DisposeEcc()
    prng.DisposePrng()
    asn.DisposeAsn()
    xml.DisposeXml()
    pubKey.DisposePublicKey()
    ecc2.DisposeEcc()
    xml2.DisposeXml()
    asn2.DisposeAsn()