33 lines
959 B
Kotlin
33 lines
959 B
Kotlin
package com.infendro.otp
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import com.infendro.bytes.bytearray.toInt
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import com.infendro.bytes.long.toByteArray
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import com.infendro.hash.HashFunction
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import com.infendro.hash.sha1.SHA1
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import com.infendro.mac.HMAC
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import com.infendro.otp.util.pow
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import kotlin.experimental.and
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class HOTP(
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val function: HashFunction = SHA1(),
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val length: Int = 6,
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) {
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private val hmac = HMAC(function)
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fun generate(secret: ByteArray, counter: Long): String {
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require(counter >= 0)
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return otp(secret, counter)
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}
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fun verify(secret: ByteArray, counter: Long, otp: String): Boolean {
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return generate(secret, counter) == otp
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}
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private fun otp(secret: ByteArray, counter: Long): String {
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val hash = hmac.hash(secret, counter.toByteArray())
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val offset = (hash.last() and 0xF).toInt()
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val otp = (hash.toInt(offset) and 0x7FFFFFFF) % 10.pow(length)
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return "$otp".padStart(length, '0')
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}
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}
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