Swift

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. Swift

func chilkatTest() {
    var success: Bool = 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.
    let privKey = CkoPrivateKey()!
    success = privKey.loadEncryptedPemFile(path: "qa_data/ecc/secp256r1-key-pkcs8-secret.pem", password: "secret")
    if success == false {
        print("\(privKey.lastErrorText!)")
        return
    }

    // Sign the SHA256 hash of some data.
    let bd = CkoBinData()!
    success = bd.loadFile(path: "qa_data/hamlet.xml")
    if success == false {
        print("Failed to load file to be hashed.")
        return
    }

    let crypt = CkoCrypt2()!
    crypt.hashAlgorithm = "sha256"
    crypt.encodingMode = "base64"
    var hashStr: String? = crypt.hashBdENC(bd: bd)

    let ecdsa = CkoEcc()!
    let prng = CkoPrng()!
    // Returns ASN.1 signature as a base64 string.
    var sig: String? = ecdsa.signHashENC(encodedHash: hashStr, encoding: "base64", privkey: privKey, prng: prng)
    print("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:
    let asn = CkoAsn()!
    asn.loadEncoded(asnContent: sig, encoding: "base64")
    let xml = CkoXml()!
    xml.load(xmlData: asn.asnToXml())

    print("\(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
    var r: String? = xml.getChildContent(byIndex: 0)
    var s: String? = xml.getChildContent(byIndex: 1)

    print("r = \(r!)")
    print("s = \(s!)")

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

    // Get the corresponding public key.
    let pubKey = CkoPublicKey()!
    success = pubKey.load(fromFile: "qa_data/ecc/secp256r1-pub.pem")
    if success == false {
        print("\(pubKey.lastErrorText!)")
        return
    }

    // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    let ecc2 = CkoEcc()!
    var result: Int = ecc2.verifyHashENC(encodedHash: hashStr, encodedSig: sig, encoding: "base64", pubkey: pubKey).intValue
    if result != 1 {
        print("\(ecc2.lastErrorText!)")
        return
    }

    print("Verified!")

    // Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
    let xml2 = CkoXml()!
    xml2.tag = "sequence"
    xml2.newChild2(tagPath: "int", content: r)
    xml2.newChild2(tagPath: "int", content: s)

    let asn2 = CkoAsn()!
    asn2.loadXml(xmlStr: xml2.getXml())
    var encodedSig: String? = asn2.getEncodedDer(encoding: "base64")
    print("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...

}