tink/issues/69

keyset.json

{
    "primaryKeyId": 515944260,
    "key": [{
        "keyData": {
            "typeUrl": "type.googleapis.com/google.crypto.tink.AesGcmKey",
            "keyMaterialType": "SYMMETRIC",
            "value": "EgAaEDoFupL7XJF8sddiW94aDs8="
        },
        "outputPrefixType": "TINK",
        "keyId": 515944260,
        "status": "ENABLED"
    }]
}

main.kt

import com.google.crypto.tink.Aead
import com.google.crypto.tink.CleartextKeysetHandle
import com.google.crypto.tink.Config
import com.google.crypto.tink.JsonKeysetReader
import com.google.crypto.tink.JsonKeysetWriter
import com.google.crypto.tink.KeysetHandle
import com.google.crypto.tink.aead.AeadConfig
import com.google.crypto.tink.aead.AeadFactory
import com.google.crypto.tink.aead.AeadKeyTemplates
import java.io.File
import java.io.FileOutputStream
import java.nio.charset.Charset
import java.nio.file.Files

class Crypto(keySetFile: File) {
    private val keySetHandle: KeysetHandle
    private val aead: Aead

    init {
        Config.register(AeadConfig.TINK_1_0_0)
        keySetHandle = readKeySetFile(keySetFile)
        aead = AeadFactory.getPrimitive(this.keySetHandle)
    }

    companion object Writer {
        fun writeNewKeySetFile(file: File) {
            val keySetHandle = KeysetHandle.generateNew(AeadKeyTemplates.AES128_GCM)
            CleartextKeysetHandle.write(keySetHandle, JsonKeysetWriter.withFile(file))
        }
    }

    private fun readKeySetFile(keySetFile: File): KeysetHandle {
        return CleartextKeysetHandle.read(JsonKeysetReader.withFile(keySetFile))
    }

    fun encryptFile(plaintext: ByteArray, outFile: File, associatedData: String) {
        val ciphertext: ByteArray = aead.encrypt(plaintext, associatedData.toByteArray())
        FileOutputStream(outFile).use { it.write(ciphertext) }
    }

    fun decryptFile(file: File, associatedData: String): String {
        val ciphertext: ByteArray = Files.readAllBytes(file.toPath())
        val plainText: ByteArray = aead.decrypt(ciphertext, associatedData.toByteArray())
        return plainText.toString(Charset.defaultCharset())
    }
}


fun main() {
    val file = File("testfile")
    val keysetFile = File("keyset.json")
    val crypto = Crypto(keysetFile)
    crypto.encryptFile("123".toByteArray(), file, "passphrase")
    println(crypto.decryptFile(file, "passphrase"))
}