io.github.binaryfoo.decoders.apdu.ReadRecordAPDUDecoder.kt Maven / Gradle / Ivy

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Some decoders for the data used in EMV credit card transactions.

There is a newer version: 0.1.8

package io.github.binaryfoo.decoders.apdu

import io.github.binaryfoo.DecodedData
import io.github.binaryfoo.decoders.DecodeSession
import kotlin.text.substring

/**
 * Read a record (bucket of bits) from the card's file system. The record is identified by the pair (SFI, record number).
 *
 * SFI = short file indicator. "Short" in that it's only meaningful to the card's file system when combined with an application id (provided by the terminal selecting the app).
 * In this language each file has multiple records. Hence the record id. File names in a typical desktop OS are somewhat more helpful to people but since we're dealing with a
 * machine to machine conversation here numbers make sense.
 */
class ReadRecordAPDUDecoder : CommandAPDUDecoder {
    override fun getCommand(): APDUCommand {
        return APDUCommand.ReadRecord
    }

    override fun decode(input: String, startIndexInBytes: Int, session: DecodeSession): DecodedData {
        val recordNumber = Integer.parseInt(input.substring(4, 6), 16)
        val referenceControlParameter = Integer.parseInt(input.substring(6, 8), 16)
        val sfi = (referenceControlParameter and 0x000000f8) shr 3
        return DecodedData(null, "C-APDU: Read Record", "SFI $sfi record $recordNumber", startIndexInBytes, startIndexInBytes + 5)
    }
}