io.github.binaryfoo.decoders.SignedStaticApplicationDataDecoder.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

import io.github.binaryfoo.decoders.annotator.SignedDataDecoder
import io.github.binaryfoo.EmvTags
import io.github.binaryfoo.DecodedData
import io.github.binaryfoo.findAllForTag
import io.github.binaryfoo.findTlvForTag
import kotlin.collections.listOf

/**
 * EMV 4.3 Book 2, Table 7: Format of Data Recovered from Signed Static Application Data
 *
 * Static data auth means CA (scheme) -> Issuer -> data. Chip has no RSA hardware. No replay attack prevention.
 */
class SignedStaticApplicationDataDecoder : SignedDataDecoder {

    override fun decodeSignedData(session: DecodeSession, decoded: List) {
        val issuerPublicKeyCertificate = session.issuerPublicKeyCertificate
        val signedStaticData = decoded.findTlvForTag(EmvTags.SIGNED_STATIC_APPLICATION_DATA)
        if (signedStaticData != null && issuerPublicKeyCertificate != null) {
            for (decodedSSD in decoded.findAllForTag(EmvTags.SIGNED_STATIC_APPLICATION_DATA)) {
                recoverSignedData(signedStaticData, decodedSSD, issuerPublicKeyCertificate, ::decodeSignedStaticData)
            }
        }
    }
}

fun decodeSignedStaticData(recovered: ByteArray, startIndexInBytes: Int): List {
    return listOf(
            DecodedData.byteRange("Header", recovered, 0, 1, startIndexInBytes),
            DecodedData.byteRange("Format", recovered, 1, 1, startIndexInBytes),
            DecodedData.byteRange("Hash Algorithm", recovered, 2, 1, startIndexInBytes),
            DecodedData.byteRange("Data Auth Code", recovered, 3, 2, startIndexInBytes),
            DecodedData.byteRange("Hash", recovered, recovered.size-21, 20, startIndexInBytes),
            DecodedData.byteRange("Trailer", recovered, recovered.size-1, 1, startIndexInBytes)
    )
}