Swift

ECDSA Sign Data and Get Raw R and S Values

See more ECC Examples

Demonstrates getting the raw R and S value of an ECDSA signature. Swift

func chilkatTest() {
    var success: Bool = false

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

    // To create an ECDSA signature, the data first needs to be hashed.  Then the hash
    // is signed.

    let crypt = CkoCrypt2()!
    crypt.hashAlgorithm = "SHA256"
    crypt.charset = "utf-8"
    crypt.encodingMode = "base64"

    // Hash a string.
    var hash1: String? = crypt.hashStringENC(str: "The quick brown fox jumps over the lazy dog")
    print("hash1 = \(hash1!)")

    // -----------------------------------------------------------
    // An ECDSA private key is used for signing.  The public key is for signature verification.
    // Load our ECC private key.
    // Our private key file contains this:

    // 	// -----BEGIN PRIVATE KEY-----
    // 	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
    // 	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
    // 	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
    // 	-----END PRIVATE KEY-----

    let privKey = CkoPrivateKey()!
    success = privKey.loadPemFile(path: "qa_data/ecc/secp256r1-key-pkcs8.pem")
    if success != true {
        print("\(privKey.lastErrorText!)")
        return
    }

    // Sign the hash..
    let prng = CkoPrng()!
    let ecdsa = CkoEcc()!
    var ecdsaSigBase64: String? = ecdsa.signHashENC(encodedHash: hash1, encoding: "base64", privkey: privKey, prng: prng)
    if ecdsa.lastMethodSuccess != true {
        print("\(ecdsa.lastErrorText!)")
        return
    }

    // The ECDSA signature is ASN.1 that contains a sequence of 2 large integers (r and s)
    // For example:
    // SEQUENCE (2 elem)
    //   INTEGER (255 bit) 792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9
    //   INTEGER (255 bit) 481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5

    print("Base64 ECDSA signature = \(ecdsaSigBase64!)")

    // If the raw R and S values are needed, here's how to get them:
    let asn = CkoAsn()!
    success = asn.loadEncoded(asnContent: ecdsaSigBase64, encoding: "base64")
    if success == false {
        print("\(asn.lastErrorText!)")
        return
    }

    // The R and X will be in hexidecimal in the XML.
    let xml = CkoXml()!
    xml.load(xmlData: asn.asnToXml())
    print("\(xml.getXml()!)")

    // The XML looks like this:
    // <sequence>
    // <int>792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9</int>
    // <int>481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5</int>
    // </sequence>

    // Copy raw R and S hex values into a Chilkat BinData object.
    let bd = CkoBinData()!
    var r: String? = xml.getChildContent(tagPath: "int[0]")
    var s: String? = xml.getChildContent(tagPath: "int[1]")
    bd.appendEncoded(encData: r, encoding: "hex")
    bd.appendEncoded(encData: s, encoding: "hex")

    print("Number of bytes in bd: \(bd.numBytes.intValue)")

}