How to convert php function to kotlin android? - php

Question

I have a project I'm working on that uses an API for it request, but in order to preform them I need to generate the token first.
Before the API was update everything was working, after the update I don't know how to adjust my code to make it work again.
This was the code that worked before the update (Android | Kotlin):
fun hmacHash(str: String, secret: String): String {
val sha256HMAC = Mac.getInstance("HmacSHA256")
val secretKey = SecretKeySpec(secret.toByteArray(), "HmacSHA256")
sha256HMAC.init(secretKey)
return convertToHex(sha256HMAC.doFinal(str.toByteArray()))
}
fun convertToHex(data: ByteArray): String {
val buf = StringBuilder()
for (b in data) {
var halfbyte = (b.toInt() shr 4) and (0x0F.toByte()).toInt()
var two_halfs = 0
do {
buf.append(if (halfbyte in 0..9) ('0'.toInt() + halfbyte).toChar() else ('a'.toInt() + (halfbyte - 10)).toChar())
halfbyte = (b and 0x0F).toInt()
} while (two_halfs++ < 1)
}
return buf.toString()
}
Which was equivalent to this PHP code:
hash_hmac('sha256', $string, $privateKey);
But now after the update the php code looks like this:
hash_hmac('sha256', $string, hex2bin($privateKey));
And I don't know how to adjust my code to make it work with this new change.

Answer 1

From what I can deduce, the PHP code made that change because $privateKey went from being plain text to being hex-encoded. So hex2bin was needed to change it back to plain text (hex2bin changes hex-encoded text to plain text; a confusingly named function if you ask me).
Since your secret is plain text, you don't need to change anything to match. But there are other ways to improve your code. For example, converting a byte array to a hex-encoded string is much easier than that.
fun hmacHash(str: String, secret: String): String {
val sha256HMAC = Mac.getInstance("HmacSHA256")
val bytes = secret.toByteArray()
val secretKey = SecretKeySpec(bytes, "HmacSHA256")
sha256HMAC.init(secretKey)
return convertToHex(sha256HMAC.doFinal(str.toByteArray()))
}
fun convertToHex(data: ByteArray): String =
data.joinToString("") { "%02x".format(it) }