From e4ad73eef8db436df0122a4d742d62c2ea9a346f Mon Sep 17 00:00:00 2001
From: oleksandrsarapulovgl
 <82441124+oleksandrsarapulovgl@users.noreply.github.com>
Date: Mon, 14 Feb 2022 11:41:50 +0200
Subject: [PATCH] Certificate revocation (#73)

---
 decoder/build.gradle                          |  2 +-
 .../dgca/verifier/app/decoder/Extensions.kt   | 85 +++++++++++++++----
 2 files changed, 70 insertions(+), 17 deletions(-)

diff --git a/decoder/build.gradle b/decoder/build.gradle
index c4f55f0..638ee9e 100644
--- a/decoder/build.gradle
+++ b/decoder/build.gradle
@@ -7,7 +7,7 @@ android {
     compileSdkVersion 30
 
     defaultConfig {
-        minSdkVersion 21
+        minSdkVersion 23
         targetSdkVersion 30
         versionCode 1
         versionName "1.0.0"
diff --git a/decoder/src/main/java/dgca/verifier/app/decoder/Extensions.kt b/decoder/src/main/java/dgca/verifier/app/decoder/Extensions.kt
index a6bc187..c7962a5 100644
--- a/decoder/src/main/java/dgca/verifier/app/decoder/Extensions.kt
+++ b/decoder/src/main/java/dgca/verifier/app/decoder/Extensions.kt
@@ -22,18 +22,24 @@
 
 package dgca.verifier.app.decoder
 
+import android.security.keystore.KeyGenParameterSpec
+import android.security.keystore.KeyProperties
 import android.util.Base64
 import com.upokecenter.cbor.CBORObject
 import dgca.verifier.app.decoder.model.KeyPairData
 import java.io.ByteArrayInputStream
-import java.security.KeyPairGenerator
-import java.security.MessageDigest
+import java.security.*
 import java.security.cert.CertificateFactory
 import java.security.cert.X509Certificate
+import java.security.spec.ECGenParameterSpec
 
 const val ECDSA_256 = -7
 const val RSA_PSS_256 = -37
 
+const val ANDROID_KEYSTORE_PROVIDER = "AndroidKeyStore"
+const val SHA_256_WITH_ECDSA = "SHA256withECDSA"
+const val SHA_256_WITH_RSA = "SHA256WithRSA"
+
 fun ByteArray.toBase64(): String = Base64.encodeToString(this, Base64.NO_WRAP)
 
 fun ByteArray.toHexString(): String = joinToString("") { "%02x".format(it) }
@@ -44,6 +50,8 @@ fun String.hexToByteArray(): ByteArray = chunked(2)
 
 fun String.fromBase64(): ByteArray = Base64.decode(this, Base64.NO_WRAP)
 
+fun String.toBase64(): String = Base64.encodeToString(this.toByteArray(), Base64.NO_WRAP)
+
 fun String.base64ToX509Certificate(): X509Certificate? {
     val decoded = Base64.decode(this, Base64.NO_WRAP)
     val inputStream = ByteArrayInputStream(decoded)
@@ -57,23 +65,68 @@ fun ByteArray.toHash(): String {
         .toBase64()
 }
 
-fun ByteArray.generateKeyPair(): KeyPairData? {
+private fun provideEcKeyPairData(alias: String): KeyPairData {
+    val keyPairGen = KeyPairGenerator.getInstance(KeyProperties.KEY_ALGORITHM_EC, ANDROID_KEYSTORE_PROVIDER)
+    val keyPairGeneratorSpec = KeyGenParameterSpec.Builder(
+        alias,
+        KeyProperties.PURPOSE_SIGN or KeyProperties.PURPOSE_VERIFY
+    )
+        .setAlgorithmParameterSpec(ECGenParameterSpec("secp256r1"))
+        .setDigests(
+            KeyProperties.DIGEST_SHA256,
+            KeyProperties.DIGEST_SHA384,
+            KeyProperties.DIGEST_SHA512
+        )
+        .setKeySize(256)
+        .build()
+    keyPairGen.initialize(keyPairGeneratorSpec)
+    return KeyPairData(SHA_256_WITH_ECDSA, keyPairGen.generateKeyPair())
+}
+
+private fun provideRsaKeyPairData(alias: String): KeyPairData {
+    val keyPairGen = KeyPairGenerator.getInstance(KeyProperties.KEY_ALGORITHM_RSA, ANDROID_KEYSTORE_PROVIDER)
+    val keyGenParameterSpec = KeyGenParameterSpec.Builder(
+        alias,
+        KeyProperties.PURPOSE_SIGN or KeyProperties.PURPOSE_VERIFY
+    )
+        .setDigests(KeyProperties.DIGEST_SHA256, KeyProperties.DIGEST_SHA512)
+        .setKeySize(2048)
+        .setSignaturePaddings(KeyProperties.SIGNATURE_PADDING_RSA_PKCS1)
+        .build()
+
+    keyPairGen.initialize(keyGenParameterSpec)
+    return KeyPairData(SHA_256_WITH_RSA, keyPairGen.generateKeyPair())
+}
+
+fun ByteArray.generateKeyPairFor(alias: String): KeyPairData? {
     val messageObject = CBORObject.DecodeFromBytes(this)
     val protectedHeader = messageObject[0].GetByteString()
 
     // get algorithm from header
-    when (CBORObject.DecodeFromBytes(protectedHeader).get(1).AsInt32Value()) {
-        ECDSA_256 -> {
-            val keyPairGen = KeyPairGenerator.getInstance("EC")
-            keyPairGen.initialize(256)
-            return KeyPairData("SHA256withECDSA", keyPairGen.generateKeyPair())
-        }
-        RSA_PSS_256 -> {
-            val keyPairGen = KeyPairGenerator.getInstance("RSA")
-            keyPairGen.initialize(2048)
-            return KeyPairData("SHA256WithRSA", keyPairGen.generateKeyPair())
-        }
+    return when (CBORObject.DecodeFromBytes(protectedHeader).get(1).AsInt32Value()) {
+        ECDSA_256 -> provideEcKeyPairData(alias)
+        RSA_PSS_256 -> provideRsaKeyPairData(alias)
+        else -> null
+    }
+}
+
+fun getKeyPairFor(alias: String): KeyPairData {
+    val ks: KeyStore = KeyStore.getInstance(ANDROID_KEYSTORE_PROVIDER)
+    ks.load(null)
+    val entry: KeyStore.Entry = ks.getEntry(alias, null)
+    val privateKey: PrivateKey = (entry as KeyStore.PrivateKeyEntry).privateKey
+    val publicKey: PublicKey = ks.getCertificate(alias).publicKey
+    val keyPair = KeyPair(publicKey, privateKey)
+    val algo = when (privateKey.algorithm) {
+        KeyProperties.KEY_ALGORITHM_EC -> SHA_256_WITH_ECDSA
+        KeyProperties.KEY_ALGORITHM_RSA -> SHA_256_WITH_RSA
+        else -> throw IllegalArgumentException()
     }
+    return KeyPairData(algo, keyPair)
+}
 
-    return null
-}
\ No newline at end of file
+fun deleteKeyPairFor(alias: String) {
+    val ks: KeyStore = KeyStore.getInstance(ANDROID_KEYSTORE_PROVIDER)
+    ks.load(null)
+    ks.deleteEntry(alias)
+}