fun signData(inputStr: String): String {
    val privateKeyEntry = getPrivateKey()

    val s = Signature.getInstance(SIGNATURE_SHA256withRSA)
    s.initSign(privateKeyEntry.privateKey)

    s.update(inputStr.toByteArray())
    val signatureBytes = s.sign()

    val signatureString = Base64.encodeToString(signatureBytes, Base64.DEFAULT)
    return signatureString
}