Go

ECDSA Sign and Verify

See more ECC Examples

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

    success := false

    // 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()