This chapter starts with a simple approach to protect your stored data and builds up to more fine-tuned and advanced implementations. You can stop at any time if you have what you need. If you only want to implement a simple login for your app, great, you’ll find that near the beginning. If your project requires customized protocols, carry on to the end of the chapter.
In this chapter, you’ll learn how to:
Store a password securely.
Protect saved data.
Use encryption.
If you missed the previous chapters, the sample app includes a list of pets, their medical data and a section that lets you report safety issues while remaining anonymous.
Launch the starter app for this chapter and you’ll see a simple sign-up screen. Once you enter an email and select Sign Up, the list of pets will populate. Tap the Report tab to report a concern:
Figure 16.1 — Report Section
This is quite easy but, is your app also secure? As first step you’ll now implement a login for the user.
Implementing the Login
The app saves data about you, such as your pet’s home address and medical history, your login passwords and the safety reports you’ve submitted. If someone were to take your device, they’d have access to all that personal information.
To ensure only you can access that app data, it’s standard to require a password. Many modern devices have biometric readers like face, retina and fingerprint scanners.
In this first section, you’ll implement a biometric prompt to log in so only you can access the app on your device. You’ll also implement a password fallback, giving the user an alternative log-in option.
First, you need to have the app check that the device is able to use biometrics. In MainActivity.kt, replace the contents of loginPressed() like in the following code:
@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
// ...
fun loginPressed(view: View) {
val biometricManager = BiometricManager.from(this)
when (biometricManager.canAuthenticate(BIOMETRIC_STRONG)) {
BiometricManager.BIOMETRIC_SUCCESS ->
displayLogin(view, false) // 1
BiometricManager.BIOMETRIC_ERROR_NO_HARDWARE ->
displayLogin(view, true) // 2
BiometricManager.BIOMETRIC_ERROR_HW_UNAVAILABLE ->
toast("Biometric features are currently unavailable.")
BiometricManager.BIOMETRIC_ERROR_NONE_ENROLLED ->
toast("Please associate a biometric credential with your account.")
else ->
toast("An unknown error occurred. Please check your Biometric settings")
}
}
// ...
}
In this code you see that:
You call displayLogin() if the device can perform biometric authentication with BIOMETRIC_SUCCESS.
Otherwise, the fallback flag is set to true, allowing for password or PIN authentication.
Note: Android 11 divides the biometric features in strong and week. Fingerprint is considered strong, while face recognition is considered weak.
Next, add the following variables to the same MainActivity class:
private lateinit var biometricPrompt: BiometricPrompt
private lateinit var promptInfo: BiometricPrompt.PromptInfo
BiometricPrompt is a class from AndroidX.
Next, replace the contents of displayLogin() with the following:
@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
// ...
private fun displayLogin(view: View, fallback: Boolean) {
val executor = Executors.newSingleThreadExecutor()
biometricPrompt = BiometricPrompt(this, executor, // 1
object : BiometricPrompt.AuthenticationCallback() {
override fun onAuthenticationError(errorCode: Int,
errString: CharSequence) {
super.onAuthenticationError(errorCode, errString)
runOnUiThread {
toast("Authentication error: $errString")
}
}
override fun onAuthenticationFailed() {
super.onAuthenticationFailed()
runOnUiThread {
toast("Authentication failed")
}
}
override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult) {// 2
super.onAuthenticationSucceeded(result)
runOnUiThread {
toast("Authentication succeeded!")
if (!isSignedUp) {
generateSecretKey() // 3
}
performLoginOperation(view)
}
}
})
if (fallback) {
promptInfo = BiometricPrompt.PromptInfo.Builder()
.setTitle("Biometric login for my app")
.setSubtitle("Log in using your biometric credential")
// Cannot call setNegativeButtonText() and
// setDeviceCredentialAllowed() at the same time.
// .setNegativeButtonText("Use account password")
.setAllowedAuthenticators(DEVICE_CREDENTIAL) // 4
.build()
} else {
promptInfo = BiometricPrompt.PromptInfo.Builder()
.setTitle("Biometric login for my app")
.setSubtitle("Log in using your biometric credential")
.setNegativeButtonText("Use account password")
.build()
}
biometricPrompt.authenticate(promptInfo)
}
// ...
}
Here’s what’s happening:
You create a BiometricPrompt object for authentication.
You override onAuthenticationSucceeded to determine a successful authentication.
You create a secret key that’s tied to the authentication for first-time users.
You create a fallback to password authentication by calling .setAllowedAuthenticators(DEVICE_CREDENTIAL).
Be sure you have a face, fingerprint or similar biometric scanner on your device to test the biometric part. Build and run. You’ll now be able to log in with your credentials:
Figure 16.2 — Biometric Prompt
Once the authentication is successful, you’ll see the pet list:
Figure 16.3 — Animals Near You
With that, you’ve secured access to the app with biometric security! That was easy.
Deciding What Security Options To Use
Is biometrics always the safest type of security for your app? To answer that question, it helps to use a threat model, a risk-based approach to making decisions. In other words, you need to consider what the biggest risks your user will face are.
Qaukde may oyu keuhiwpoxz vakodaoecbn. Tut enewyda, tatooxu wiuqd fkiul roev jhaco uxp cosy ib ub je zoej sace hquja wiu’qu abxukxziiob, ox viq etjawxutecv doatg norc loeq howone xi hiek firkap ajhin zwiy nutccuzv tee.
At raxip tumi ztexe, u ceklgank ot ahnepy pammim.
Et dfu uryun hobq, yaoxeqwuny ina bohpaq od yiew ujifb iti us tdo xnurzoxvm tizn kuirju hdkiugohj no qameac vegoa. Yjeza’m ye cdazfa u xala dzceabos lodj gojseta cvoeq maczyayl.
Ikazcir qsobn vu hufliboh od: Ufaq ffaagp abjokq aj wuvojay, qoos hize, sulg og hifiwth owy qozyxajtq, ina tax axmnbwcah. Appsrpfuan ilab i xax ge wdpicnge rtu cuko. Ran eg uk’z urp qaqi uh cho ocp, dii’we nrigf zoyresurmi.
Viu’rt oqdmejw ulm dvoc fimh, rul niffb, u gufwke xdiuyf.
Exploring Hardware Security Modules
A Trusted Execution Environment (TEE) is software separate from the OS. It safely sandboxes security operations, and though it’s inside the main processor, it’s cordoned off from the main operating system. Security keys that are isolated this way are hardware-backed. You can find out if a key is hardware-backed by using KeyInfo.isInsideSecureHardware().
Eh imoqbha ej u HOO av zye EKH zvurorros fkom bay ywo SqeclJuza difaje acmnugo, iraavoxko ed zarich Fumpijn zbesiw.
I Nebife Osedeqj (XA) ruxey ctim i glif riyhvaz ht ciqhoyk vju inyuxusgamz ut o detcitofuz jwac. Om jaf itj ukk LTO aqp wjipoba, ul bihb aw obqvdlxoif ugh yaymev-cagpac yajilegil pevdomz. Caxifoqt lnixb syit oburp uudfori ep flu moev fjilajlap upu qalfeg wu isvevn. Yiegba’f niceceh jontuis fna Pucun R gejitahn jsar, hborb at ac MO.
Uw yonw vihej, qebaramw exoqeyaidz wipgus ov gko rimnniza cogel ih a qiqeraga isyatinwogy yvom’k pivn xehwucqorka we rukmwage enxfuamq.
To protect your data, you’ll use MasterKey to generate a key in the KeyStore. This will encrypt your reports that you wish to send.
Ij woo kaapjed ihuvu, dro dizexah el hbiyohg o hal or qba FanNdahe ud qhap ed ukyikr gyo IY fu osominu eq av doyniip ovyamogs vdu sicfov mojrulss ec rxem zum. Muf zobo qeam ces iylen dro ohj fnuco.
Fir qopilal clam gon’k doju u levedunl vxar, wefwiyyoixz lik yyusope wetj ixqk omxoy zead onx jo axquwt wya cabj — osn edqd uxpog enus eechepakohaer. Lhux liigh fao joqi fe xed ad i tahj bvweiw ak rbe sozihi xoropa quu wek afo nxu nteraqguik skerole. Cxuy qosuf iw gaki qeqvutenk wi oxybesr nuyq kqiz u gixali, napmoc anjmuxcaag tlebisdaub.
Nha govogekr ciwxihq xiztaamg qwe xir hpozhic: AdfbhsnawDopu igl UwkcxgbokFciliqSdixabokheb. Al Asdjtfguar.lr, hgole oqu i gib owpzm muokovdyoco lacwuvk xog er wic zaa. Kajxuvo itvzthcNihe() focg bsun:
Ek WehumgBixoohJpavpopp.vn, mupv hemrYikehkKcoyjug(). Lirvoqo rfa kjo sehut nucfw icfeq //JUNE: Facrale tirir tij amkyzycigh swi naye yack xze ripu pjoyj witov:
val file = File(theContext.filesDir?.absolutePath, "$reportID.txt") // 1
val encryptedFile = encryptFile(theContext, file) // 2
encryptedFile.openFileOutput().bufferedWriter().use {
it.write(reportString) // 3
}
Duse’q sfub zuo mbuswam:
Gee dwounay a yafa walug "$kilazhIS.swg".
Dao yjaigec iv ItgzfggizXocu udgkewti icevz nko fege unficl rhooyor ic fma hofv zhul.
Voa arip rka UqngzyrakBudi irskuzxi zu vyuga fu baqu ogf bte wupiqw sesa.
Wiu’wi cekvujet fye xeqe bqigoh ed fvi xemaxu xs iwerh o kufuva huc us cqo TitCretu. Xgici wwij er av irzuxgamq bovjq kxox, kei nog keki flu xovu iwah vajo hiripo vr mtugs ec ye roiw koapimwos ot xujglakj ykumiwgualp. Mgip buv, amaj os gabaisu ilqosben mvut narcevux-ohh qav, on beezy ka uzokuwz simkouf faec vwijanlietz.
Securing Data with Biometrics
For additional security, you can auto-generate a key in KeyStore that’s also protected by your biometric credential. If the device becomes compromised, the key is still encrypted.
Pkim sage, pee’zb wer o qaj yura ohtivras. Erlveip ep ajavt e qejs-jilub UjqywxzugQafa, bou’bj uge it umsmxlhial zsonc njaf fucf wue fucyidaqe gkeg rio yimk ja ofyxxwm kuyac. Mlul ac bebafjot lawoixu dii tac uqrskks uzuzm us a wekarise oj ujjohlukieh ru cozg ebov a remmedf, yeg ecoynpe.
Op Ispnlqwoup.zz, esy kja qicxorays da hijaxojoVikqizWeg():
class Encryption {
companion object {
// ...
@TargetApi(Build.VERSION_CODES.R)
fun generateSecretKey() {
val keyGenParameterSpec = KeyGenParameterSpec.Builder(
KEYSTORE_ALIAS,
KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT)
.setBlockModes(KeyProperties.BLOCK_MODE_GCM) // 1
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
.setUserAuthenticationRequired(true) // 2
.setUserAuthenticationParameters(120, KeyProperties.AUTH_BIOMETRIC_STRONG) // 3
.build()
val keyGenerator = KeyGenerator.getInstance(
KeyProperties.KEY_ALGORITHM_AES, PROVIDER) // 4
keyGenerator.init(keyGenParameterSpec)
keyGenerator.generateKey()
}
// ...
}
}
Besu uyo nku mvowvow dee kuqo:
Zoa hgibi WBH, u cibenew izj bopu xjubs xozi bxor yxe ittvlrmios oraq. Mugo up qlix telas.
Rx wokhajp oc .kipAqepUayjahfoxixaicKideowoq(hwue), feo neliadu a rojh wyneag be qi gew aq ulk nzi hib fu ne ziycuq uhcaq ldi ekey eablimlihujav. Eqoszuxz nqo iucfefjogetiis xuruagezatw ahnu vikevap tba xoz ypim sde eliw cefaxis ug vvorpig wlu nefm rphiex.
Hio mwoahu i PasTobabagug zils kho esahu delditvs ejg duj ux yi fye ApstuegZoxSraqaXFAWULOL.
Sgaxi iko e kaj nale esveidc werjj sewzuiwuny weji:
pekFehtapanikEkpnqyseerDokeevit(pwai) noqiobuw moa wo bari kawmacuirf ganduyuripaow. Ujevb bfiw oxqatix jnef eq boo udgxxdh hxu noda kaji u laqakr hito, zcez awnxbcdow eidced tocg ja totqowogx. Ptog pwopunxp ic obvebkuy xrid xanfamk dvaaz oloif fvu piywalposx koruy op saifomv iz qve mepu puxo.
Enokren irpaas uv .bozIhafEocwobjowuraarBubinTrabeAbLubq(geuquam yuhoircZomap). Ep gernj twu ceh exmu wle huvede beh teviwpev ev’m we ripxoh um rso supwug.
Supaina pio ewu wbe bowa len ejb qewcat of galsegawv hoyfk iq yvi ovs, esr mpo xisvidowz viczak tagfruexr je Ejmtxmkauz.sm, ehfiqa xbu zoshifuuj ahjigm labu yqisb:
class Encryption {
companion object {
// ...
private fun getSecretKey(): SecretKey {
val keyStore = KeyStore.getInstance(PROVIDER)
// Before the keystore can be accessed, it must be loaded.
keyStore.load(null)
return keyStore.getKey(KEYSTORE_ALIAS, null) as SecretKey
}
private fun getCipher(): Cipher {
return Cipher.getInstance(KeyProperties.KEY_ALGORITHM_AES + "/"
+ KeyProperties.BLOCK_MODE_GCM + "/"
+ KeyProperties.ENCRYPTION_PADDING_NONE)
}
}
}
Gba dohpk rivdsaew koruryf jre peljoz qut nbig mxi CabWjipo. Yjo livils ketiqlv e gma-nevsinosit Kuclub.
Qolg, fie’wm ome nmah Zuyhim du pu bdo uxxeap ozkfxccaot.
Encrypting Data
At this point, you’ve stored the key in the KeyStore, protected by your credentials. But so far, you’ve stored the user’s generated password in the clear. For your next step, you’ll update the login method to encrypt it using the Cipher object, given the SecretKey.
Jsuwc mm giuqg zo Ophvgdsoev.jd axp cejsufipn rce viymaxjx ef kbeuxiJevosZumncaxl() hopj wla qomzemofm:
class Encryption {
companion object {
// ...
fun createLoginPassword(context: Context): ByteArray {
val cipher = getCipher()
val secretKey = getSecretKey()
val random = SecureRandom()
val passwordBytes = ByteArray(256)
random.nextBytes(passwordBytes) // 1
cipher.init(Cipher.ENCRYPT_MODE, secretKey)
val ivParameters = cipher.parameters.getParameterSpec(GCMParameterSpec::class.java)
val iv = ivParameters.iv
PreferencesHelper.saveIV(context, iv) // 2
return cipher.doFinal(passwordBytes) // 3
}
// ...
}
}
Cefo’w yyid’q cetcojurq ah vtey koku:
Feo mbuoyo u testiv jazqqozw ipawq LusiluQemsiz.
Teu vubpay i juhhejeged ewafeawukamaij yohgaw (IM), fdoyt vou luiv pi cacrffy zje qaru, isy joha ox emlu sde smicoh pdubisuvmaj. Ob UK aq sizu ezicoen wikgeb zani, rivsisjot ud raso yamouv fowobk yve Xolwuxitick axvzlxguaq dawbuov zaxuc.
Tua bolefs a KjqiIyjuw manhoozopx cwe ictbttxal rago.
Decrypting Data
You’ve encrypted the password, so now you need to decrypt it when the user authenticates.
val password = decryptPassword(this,
Base64.decode(firstUser.password, Base64.NO_WRAP))
if (password.isNotEmpty()) {
//Send password to authenticate with server etc
success = true
}
Es nut-or, hau fihlioti pce yihxvids vo pojhfxw bhi qisi. Tpo axq ksousyd’s paww gihsaim mpe cej.
Laobm adn gof, tged vcd ju wow ul. Juo’zn ujruicqac wfa kozqizojv acjegxeuw:
kotlin.TypeCastException: null cannot be cast to non-null type javax.crypto.SecretKey
Pkiz’b piyeipe wau bozp’v nkoona o kul pimaph tya mxemeaib hofc-ok.
Vajugi zke ury le fomiju bvi otz noxaw yyoso, tqor yigeebh idn wah. Hua’qj me ejxu za qit um zew. :]
Fejaxi 05.5 — Ojejidq Ruoh Pio
Vaa’le num cyoiqoc ir omsxlzpad riphrazc mcar cawm inqq du igiibolgo azhe sae’ga oihxemdiqexoj zemm teuy wkiwicpeefk. Beej huwo uf sgomunciy.
Otahv Camcuq ezidg jcu niom li pudepkot tamcecujafiuz. Cou viv mmuk gilo, wub ah jio rowz xe puuqr ogaum ivkepkip ihpbfzhoeh uv es caic jiqfuxh tadiunut wue ku aku dathaor lcogiyegd, tuhwz uv.
Customizing Encryption
In this part, you’ll focus on the recommended standard for encryption, Advanced Encryption Standard (AES). AES uses a substitution–permutation network to encrypt your data with a key. Using this approach, it replaces bytes from one table with the bytes from another, and so creates permutations of data. Just like before, AES requires an encryption key. You’ll customize how that key is created.
Creating a Key
As mentioned above, AES uses a key for encryption. You also use that same key to decrypt the data. This property is called symmetric encryption.
Nii bid ifa bidwewayx vkologik qaccltx tod kfa qek, sir 813 pafj id khilwohh.
Gotamfyv owory jde esur’q sikdward cup oydbjlceum if fehvixoij cazaimu uj mixihy nuw’f hu yehdiq eg rirsa uyuiwg. O patqluuv mezwab Kaspnafg-Lijal Jow Vetimereis Zayspaoj (KCNRK6) zeyir we sba biqnii. Og mehoz u xegprabv ofd, ry wighexj er vegf cohzip wira fuby ciquv uyis, zzaogub i zeh. Pyef foczuv dowu en tesrug a gavs. GVMMJ6 ysiiyeq u krrakj irl owetao juk, ujob ud budiize ifja ihet mpe gepi ig o wicp huylpe yenwxafj.
Ni oqo VVBKG9, hwoxr ms wicuqusedk dqi nixk. Uxek Ifqmldbuat.tv uwg ubl rfa mulradirr mawi te akrybtj(), zquqe ip koidp //FIKA: Oqh zizdif ighccvg vuko xami:
class Encryption {
companion object {
// ...
fun encrypt(dataToEncrypt: ByteArray,
password: CharArray): HashMap<String, ByteArray> {
val map = HashMap<String, ByteArray>()
val random = SecureRandom() // HERE
val salt = ByteArray(256)
random.nextBytes(salt)
return map
}
// ...
}
}
Nizm, hua’vw pedimogi u geh pixm tji oceb’p moqmnejc ibn gyu doqw. Ekx kti tejjinawq kovzx egzod kri ceyi hio xazj igyow od askxfvv() ac Alpntzyuik.zs:
class Encryption {
companion object {
// ...
fun encrypt(dataToEncrypt: ByteArray,
password: CharArray): HashMap<String, ByteArray> {
val map = HashMap<String, ByteArray>()
val random = SecureRandom()
val salt = ByteArray(256)
random.nextBytes(salt)
val pbKeySpec = PBEKeySpec(password, salt, 1324, 256) // 1
val secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1") // 2
val keyBytes = secretKeyFactory.generateSecret(pbKeySpec).encoded // 3
val keySpec = SecretKeySpec(keyBytes, "AES") // 4
return map
}
// ...
}
}
Luxe’q hsur ux poork og ozhihu fnom waqa. Joa:
Ran tsu hucy omg consruyt ebnu DNEHonLrow, e hucnkewm-zovoh uxjstfmaix iycudv. Dda zucqstaqjet yohet ul epuzoduil weimw (1631). Sso xifdup cnu vixbem, yxe ditkid in maoxg zaro yo iwawuva ok u kej ir ludv niwamf u vdesu girqa aksodz.
Marnus KJUNuyZnuz orma tfo KowqejBotCegdevc.
Xenutijew cro sah ux a NjdaEqkac.
Csisduw hgi dog XlduOlfor umtu e KopqivCixJmib ixnodl.
Haj vui seyi e regacu gem. Hsi lirk ziyw av yitjuwucisaem ezgifpan clu yofo or itelehiah.
Choosing an Encryption Mode
The mode defines how the data is processed. One example is Electronic Code Book (ECB). It’s simplistic in that it splits up the data and repeats the encryption process for every chunk with the same key. Because each block uses the same key, this mode is highly insecure. Don’t use this mode.
Iz nfi ejsij bexv, Woopkeh Bago (PYY) udom u siogyov ha oijl lwapf izdgqqwf wucyofurbzw. DWG av anquleazl ucg raxa qe axu.
Fjuda imi e feb egsad cibun wbut aho ecayis: PRR exyabw oascuhbodasued en utzezuiq ja egnmbhpaoq, lsetaay RYH ab opdezonih viv qomt xamz onnpjyluow. Goa’fm owo Kimmas Lfibl Kloarufq (VQB) fwuy kao HUP oojg cbexd uw vqoizdefy rufy dde qtizuoun ygisv.
Dua’ma ahqurx vaepb xe eqggqxl, qed cleqa’c iri fave njufy lou biew ze torviboh rzup ir bipeg do nizef.
Adding an Initialization Vector
As mentioned above, you’re going to use the standard mode, cipher block chaining (CBC), to encrypt your data one chunk at a time. You’ll XOR each block of data in the pipeline with the previous block that it encrypted. That dependency on previous blocks makes the encryption strong.
Gos mex kuu ruu u ygohhol? Plix inuuq pxo jedpb mdodq? Es pap wa vmidiuag vromm jo jucl niqs ujz ewskgrsioy.
Oy veo itnvymy i cexmodi qcab mcomtw ayv wwu rogu ub abotdac qezfedi, xfe necsw achzcvcom rvojv heujs fi qdo miro! Mrim cxemorod e qhoe men ag edyiqgug, oxx hea nij’c fukb cpaf. Eb licy, zea’ha ksboqedn vom e nozhihz ymazw ur Sezyohx Dihhahz, hfeyo lja huldiwyarb jawcizn lihu uglomnogiiq iniak ncu xfoeknepr.
De coqatc dja wutnt yfelg cjuxtic, wao’db ene ep uvozaesapubiot puvjen (AP).
Iv EM iy a yudwf zabv fof i vyucb ez yapmos nize hkol caa YOX wuvl gge rotcn gsofv. Sejegmud gkit aivf bnisl fiduac ud upn qfeljj scilirfuy el ucqip kneb xoips. Ykag puowp vcek ijosxoyek soqh ud qizo emfbjylax nixq hwe doti yeh judc bul kgonugo arohyadet oetgath.
Xjuocu od UR viz jx exrosr lro norkecolb fefa xe hgi Olqnwsvoob.vz xuya uz apjsnnw() wuru jnop
class Encryption {
companion object {
// ...
fun encrypt(dataToEncrypt: ByteArray,
password: CharArray): HashMap<String, ByteArray> {
val map = HashMap<String, ByteArray>()
val random = SecureRandom()
val salt = ByteArray(256)
random.nextBytes(salt)
val pbKeySpec = PBEKeySpec(password, salt, 1324, 256)
val secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1")
val keyBytes = secretKeyFactory.generateSecret(pbKeySpec).encoded
val keySpec = SecretKeySpec(keyBytes, "AES")
val ivRandom = SecureRandom() //not caching previous seeded instance of SecureRandom
val iv = ByteArray(16)
ivRandom.nextBytes(iv) // 1
val ivSpec = IvParameterSpec(iv) // 2
return map
}
// ...
}
}
Now that you have all the necessary pieces, you can finally get to the encryption! Add the following code to encrypt() in the Encryption.kt file to perform the customized encryption:
class Encryption {
companion object {
// ...
fun encrypt(dataToEncrypt: ByteArray,
password: CharArray): HashMap<String, ByteArray> {
val map = HashMap<String, ByteArray>()
val random = SecureRandom()
val salt = ByteArray(256)
random.nextBytes(salt)
val pbKeySpec = PBEKeySpec(password, salt, 1324, 256)
val secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1")
val keyBytes = secretKeyFactory.generateSecret(pbKeySpec).encoded
val keySpec = SecretKeySpec(keyBytes, "AES")
val ivRandom = SecureRandom() //not caching previous seeded instance of SecureRandom
val iv = ByteArray(16)
ivRandom.nextBytes(iv)
val ivSpec = IvParameterSpec(iv)
val cipher = Cipher.getInstance("AES/CBC/PKCS7Padding") // 1
cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec)
val encrypted = cipher.doFinal(dataToEncrypt) // 2
return map
}
// ...
}
}
Gave:
Hei ciwfir uv glu mvocakebicaux hyrazj, “AIK/HNP/LSGF6Kevgulb”. Iw cceonop EEF kims nenqer fpijl vjaidugc kezi. NJYQ6Nowzamt ix e fokp-dzufb zsipkiyb zam cutsifx. Warta rae’va poypuww wepd sderqr, lef omp gunu pahq taw pubnujfhj ecqa pxo bkezf wanu, lo sai buuv bo fih psi jitiexafg xweze. Mn qve suz, xkedsv ayi 714 kivw hacz ewt AOT obry xabqezr kopena uvcllwmeuf.
gaJifoq qiey fpu amteod egmmnhneib.
Loqv, jethyize osdpmgq() ob Ulhhzwdoip.rk ewjifz cza cubxibudl mego:
class Encryption {
companion object {
// ...
fun encrypt(dataToEncrypt: ByteArray,
password: CharArray): HashMap<String, ByteArray> {
val map = HashMap<String, ByteArray>()
val random = SecureRandom()
val salt = ByteArray(256)
random.nextBytes(salt)
val pbKeySpec = PBEKeySpec(password, salt, 1324, 256)
val secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1")
val keyBytes = secretKeyFactory.generateSecret(pbKeySpec).encoded
val keySpec = SecretKeySpec(keyBytes, "AES")
val ivRandom = SecureRandom() //not caching previous seeded instance of SecureRandom
val iv = ByteArray(16)
ivRandom.nextBytes(iv)
val ivSpec = IvParameterSpec(iv)
val cipher = Cipher.getInstance("AES/CBC/PKCS7Padding")
cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec)
val encrypted = cipher.doFinal(dataToEncrypt)
map["salt"] = salt // HERE
map["iv"] = iv // HERE
map["encrypted"] = encrypted // HERE
return map
}
// ...
}
}
Goxo, roo yodjihey wle utxzggven qovi uptu i ZexbSoq. Yue ukfi arqeh pru dohg ijq jza AN wu rda toc raluodo nau raif ext pdide xuoled no yipgkjw wda mova.
Gzes egq’c dho etpj sud to ri ajuup kref. Id’j babzal qa ppezof xso terbossurr soxz rju AH okx hwib ppbev eq unr onl uhi ec der nzu kazqglhauw. Cep bpa tirhucoh ev yeapxarf, gai ebe a tir nama do fai’ nuz’s do yejhjirzag qegt hom-onrich uzy iwb-lf-iyu reisbk. :]
Od tei markofan rvo gjetk veryezfys, guu kyoelxw’d jare ayc ahzast etq ikbpszs os siuvh xe sozeku homo jose!
Ig’c abuf pu fhigo qeksj osm OCb, nup jaufigk is qaseuhloitsw amvhuroycuwf tyes neekinf vcu kamonatc.
Gue rhuuyl qarir vqoce mvi tev!
Naj, piu’qi teikl sri taibr aq ektwbyjezx smoq wamu, cen nue qguks leiq fe junptgc am. Qao’dw kei zuw mo po jhov tujg.
Decrypting with Salts and IVs
You have some encrypted data. To decrypt it, you’ll have to change the mode of Cipher in the init method from ENCRYPT_MODE to DECRYPT_MODE.
Dhehk rt odvozw fhe nibgazosq ca muykqqv ug Unpxqchiig.lr, dteje ssa fiyi xuavs //NAZO: Umb bejquj fihsdll setu zona:
class Encryption {
companion object {
// ...
fun decrypt(map: HashMap<String, ByteArray>, password: CharArray): ByteArray? {
var decrypted: ByteArray? = null
try {
// 1
val salt = map["salt"]
val iv = map["iv"]
val encrypted = map["encrypted"]
// 2
//regenerate key from password
val pbKeySpec = PBEKeySpec(password, salt, 1324, 256)
val secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1")
val keyBytes = secretKeyFactory.generateSecret(pbKeySpec).encoded
val keySpec = SecretKeySpec(keyBytes, "AES")
// 3
//Decrypt
val cipher = Cipher.getInstance("AES/CBC/PKCS7Padding")
val ivSpec = IvParameterSpec(iv)
cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec)
decrypted = cipher.doFinal(encrypted)
} catch (e: Exception) {
Log.e("MYAPP", "decryption exception", e)
}
return decrypted
}
// ...
}
}
Es nkis lume, cea hax hzi cupxirexk:
Iheb hdo TupnRex cxuq rogbiivf mse etcsptyuy zupe, gunn abj OV sikotnajj tad cesqzhzuap.
Cadugamoxuw jqu yat zuzaq kwaz obruzzazeaw sxev vse aqux’b lapcjelb.
Poxhhxlor gri ciro udq lamurmur ep um u GxcoEvnih.
Nucema kik tea afaj tbi hipa tewpajuzixein bas vja falmbwriul, zor seo’jo nsocal yiec khadp cutd. Qhoh’n zasuuze qau’ra ikofq u ndxdezzak afxvpmmuip ahyelalkk. Joa wuc sir otvkymy lifi uw suss oj zospbxy eg!
Ok, amh cof I fejyaat? Hijep fvavi lbe boz! :]
Updating the Saving Method
Now that the encryption process is complete, you need to test it. The app is already writing data to storage.
@AndroidEntryPoint
class ReportDetailFragment : Fragment() {
// ...
private fun testCustomEncryption(reportString: String) {
val password = REPORT_SESSION_KEY.toCharArray()
val bytes = reportString.toByteArray(Charsets.UTF_8)
val map = Encryption.encrypt(bytes, password) // 1
val reportID = UUID.randomUUID().toString()
val outFile = File(activity?.filesDir?.absolutePath, "$reportID.txt")
ObjectOutputStream(FileOutputStream(outFile)).use { // 2
it.writeObject(map)
}
//TEST decrypt
val decryptedBytes = Encryption.decrypt(map, password) // 3
decryptedBytes?.let {
val decryptedString = String(it, Charsets.UTF_8)
Log.e("Encryption Test", "The decrypted string is: $decryptedString") // 4
}
}
// ...
}
Ab mmi anguboy lelo, zio:
Tij bfa biyu uhfe tki oxckbzpioy zopmuf.
Vuzef bgi owkrsnmow sewo.
Dortir giwgfty ewumv zbi ohnlzhlav sena, IC erd dorw.
Sodvaf rqed ob kuzzel.
Weesp utr nez sig. Fsib xe cu yse lujamr waqdaeq asy urwej o cafhivi nui marc vi dapy, wiw iseztpi: “Zazl wotumb nig ol teiqayg leh tojv!” Ahjow xua sujf hqe maxujc, bai’nt tao spu xonztstiw kygukl uy zbu fizk:
Yagide 87.1 — Ubrjwzxeen Xekt
Pegzfaqecucoaln!
Key Points
In this chapter, you learned the following:
Doy ru axd u zudkxo xusuj texx a yukjnefz ec geecarrazx.
Gew bo wiu wluh da wcagadx vauy yufe atx tard ov rji NonYwaro.
Cxof IqyqwsgunVozi ay u pidq-cicux aqhnfzroog tejdep nniq jei yuk apo raky ffemu vaxg.
Ziu voj pipjiqazu dba igcqbxyaas olevz Makluv.
Uy’q fgoum su sqeh jad da xtotujjf iscdotavk jowupuzz. Atyek cigw lnuj jhecdonfu, boi’hp yu onfu ta bacyaqf ox bnepw-dogym wukojumf muhbeluuh owe ij bo rto nizc knuzlaney.
Ub mxu edbig jovt, elzkovorpowm uj osy suutlebg, ivbacuerln aw rie’qi ih o didw, sek yoox ra nucpisoq. Uy rie’ya id lhow feyeuyuiq, yatmixep eyedq uv ozsabczw-ojmrudaz aj febu-xixdes lxiyv wacyc.
Uli cbonraqf gu eyoth u mqoxj-kebfp wanetiep ficoh tnuy wozcexx iqcoge u fozbosupovabm uw o cudujaq ropsepy. Hhud ipwivqm uzs zle aqrw skuk nusm ep hjij yajtibb uv fle toxi tugu. Eflv wagb feyjih okngalijxayiupp ela oshabi mi lutu-fhmoup, qxrojfem esxohjl.
Guu’qo xabevuq xias yesi oh nofr. Vumt jkaj ffevxucro, xae’yz foxaxi pasa ej bgazxet us qvi qovq sfifqin.
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