Dervice Key from Seed in Kotlin

deriveKey.kt

//    blake2b(n || seed, dkLen = 32)
fun deriveKeyFromSeed(seed: String, index: Int) : String {
    val param = Blake2b.Param().setDigestLength(32)
    val blake2b = Blake2b.Digest.newInstance(param)

    val indexBytes = hexStringToByteArray(String.format("%08x", index))

    blake2b.update(hexStringToByteArray(seed))
    blake2b.update(indexBytes)
    val output = blake2b.digest()

    return byteArrayToHex(output)
}

fun byteArrayToHex(a: ByteArray): String {
    val sb = StringBuilder(a.size * 2)
    for (b in a)
        sb.append(String.format("%02x", b))
    return sb.toString()
}

fun hexStringToByteArray(s: String): ByteArray {
    val len = s.length
    val data = ByteArray(len / 2)
    var i = 0
    while (i < len) {
        data[i / 2] = ((Character.digit(s[i], 16) shl 4) + Character.digit(s[i + 1], 16)).toByte()
        i += 2
    }
    return data
}