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Replace weak crypto implementation (#158)
Replace crypto implementation with stronger key generation method.
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35 changes: 35 additions & 0 deletions
35
line-sdk/src/main/java/com/linecorp/android/security/encryption/CipherData.kt
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,35 @@ | ||
| package com.linecorp.android.security.encryption | ||
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| import android.util.Base64 | ||
|
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| class CipherData( | ||
| val encryptedData: ByteArray, | ||
| val initialVector: ByteArray, | ||
| val hmacValue: ByteArray, | ||
| ) { | ||
| fun encodeToBase64String(): String = | ||
| listOf(encryptedData, initialVector, hmacValue) | ||
| .joinToString(SEPARATOR) { it.encodeBase64() } | ||
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| companion object { | ||
| private const val SEPARATOR = ";" | ||
| private const val SIZE_DATA_TYPES = 3 | ||
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| fun decodeFromBase64String(cipherDataBase64String: String): CipherData { | ||
| val parts = cipherDataBase64String.split(SEPARATOR) | ||
| require(parts.size == SIZE_DATA_TYPES) { | ||
| "Failed to split encrypted text `$cipherDataBase64String`" | ||
| } | ||
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| return CipherData( | ||
| encryptedData = parts[0].decodeBase64(), | ||
| initialVector = parts[1].decodeBase64(), | ||
| hmacValue = parts[2].decodeBase64() | ||
| ) | ||
| } | ||
| } | ||
| } | ||
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| private fun ByteArray.encodeBase64(): String = Base64.encodeToString(this, Base64.NO_WRAP) | ||
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| private fun String.decodeBase64(): ByteArray = Base64.decode(this, Base64.NO_WRAP) |
187 changes: 187 additions & 0 deletions
187
line-sdk/src/main/java/com/linecorp/android/security/encryption/StringAesCipher.kt
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,187 @@ | ||
| package com.linecorp.android.security.encryption | ||
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| import android.content.Context | ||
| import android.security.keystore.KeyGenParameterSpec | ||
| import android.security.keystore.KeyProperties | ||
| import android.security.keystore.KeyProperties.PURPOSE_DECRYPT | ||
| import android.security.keystore.KeyProperties.PURPOSE_ENCRYPT | ||
| import android.security.keystore.KeyProperties.PURPOSE_SIGN | ||
| import android.security.keystore.KeyProperties.PURPOSE_VERIFY | ||
| import java.security.KeyStore | ||
| import java.security.MessageDigest | ||
| import javax.crypto.Cipher | ||
| import javax.crypto.KeyGenerator | ||
| import javax.crypto.Mac | ||
| import javax.crypto.SecretKey | ||
| import javax.crypto.spec.IvParameterSpec | ||
|
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| /** | ||
| * AES cipher by AndroidKeyStore | ||
| */ | ||
| class StringAesCipher : StringCipher { | ||
| private val keyStore: KeyStore by lazy { | ||
| KeyStore.getInstance(ANDROID_KEY_STORE).also { | ||
| it.load(null) | ||
| } | ||
| } | ||
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| private lateinit var hmac: Mac | ||
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| override fun initialize(context: Context) { | ||
| if (::hmac.isInitialized) { | ||
| return | ||
| } | ||
|
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| synchronized(this) { | ||
| getAesSecretKey() | ||
| val integrityKey = getIntegrityKey() | ||
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| hmac = Mac.getInstance(KeyProperties.KEY_ALGORITHM_HMAC_SHA256).apply { | ||
| init(integrityKey) | ||
| } | ||
| } | ||
| } | ||
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| override fun encrypt(context: Context, plainText: String): String { | ||
| synchronized(this) { | ||
| initialize(context) | ||
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| try { | ||
| val secretKey = getAesSecretKey() | ||
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| val cipher = Cipher.getInstance(TRANSFORMATION_FORMAT).apply { | ||
| init(Cipher.ENCRYPT_MODE, secretKey) | ||
| } | ||
| val encryptedData: ByteArray = cipher.doFinal(plainText.toByteArray()) | ||
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| return CipherData( | ||
| encryptedData = encryptedData, | ||
| initialVector = cipher.iv, | ||
| hmacValue = hmac.calculateHmacValue(encryptedData, cipher.iv) | ||
| ).encodeToBase64String() | ||
| } catch (e: Exception) { | ||
| throw EncryptionException("Failed to encrypt", e) | ||
| } | ||
| } | ||
| } | ||
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| override fun decrypt(context: Context, cipherText: String): String { | ||
| synchronized(this) { | ||
| try { | ||
| val secretKey = getAesSecretKey() | ||
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| val cipherData = CipherData.decodeFromBase64String(cipherText) | ||
|
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| cipherData.verifyHmacValue(hmac) | ||
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| val ivSpec = IvParameterSpec(cipherData.initialVector) | ||
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| return Cipher.getInstance(TRANSFORMATION_FORMAT) | ||
| .apply { init(Cipher.DECRYPT_MODE, secretKey, ivSpec) } | ||
| .run { doFinal(cipherData.encryptedData) } | ||
| .let { | ||
| String(it) | ||
| } | ||
| } catch (e: Exception) { | ||
| throw EncryptionException("Failed to decrypt", e) | ||
| } | ||
| } | ||
| } | ||
|
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| private fun getAesSecretKey(): SecretKey { | ||
| return if (keyStore.containsAlias(AES_KEY_ALIAS)) { | ||
| val secretKeyEntry = | ||
| keyStore.getEntry(AES_KEY_ALIAS, null) as KeyStore.SecretKeyEntry | ||
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| secretKeyEntry.secretKey | ||
| } else { | ||
| createAesKey() | ||
| } | ||
| } | ||
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| private fun getIntegrityKey(): SecretKey { | ||
| return if (keyStore.containsAlias(INTEGRITY_KEY_ALIAS)) { | ||
| val secretKeyEntry = | ||
| keyStore.getEntry(INTEGRITY_KEY_ALIAS, null) as KeyStore.SecretKeyEntry | ||
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| secretKeyEntry.secretKey | ||
| } else { | ||
| createIntegrityKey() | ||
| } | ||
| } | ||
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| /** | ||
| * Create a new AES key in the Android KeyStore. This key will be used for | ||
| * encrypting and decrypting data. The key is generated with a size of 256 bits, | ||
| * using the CBC block mode and PKCS7 padding. | ||
| */ | ||
| private fun createAesKey(): SecretKey { | ||
| val keyGenerator = KeyGenerator | ||
| .getInstance(KeyProperties.KEY_ALGORITHM_AES, ANDROID_KEY_STORE) | ||
| val keyGenParameterSpec = KeyGenParameterSpec.Builder( | ||
| AES_KEY_ALIAS, | ||
| PURPOSE_ENCRYPT or PURPOSE_DECRYPT | ||
| ) | ||
| .setKeySize(KEY_SIZE_IN_BIT) | ||
| .setBlockModes(KeyProperties.BLOCK_MODE_CBC) | ||
| .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_PKCS7) | ||
| .build() | ||
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| keyGenerator.run { | ||
| init(keyGenParameterSpec) | ||
| return generateKey() | ||
| } | ||
| } | ||
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| private fun createIntegrityKey(): SecretKey { | ||
| val keyGenerator = KeyGenerator | ||
| .getInstance(KeyProperties.KEY_ALGORITHM_HMAC_SHA256, ANDROID_KEY_STORE) | ||
| val keyGenParameterSpec = KeyGenParameterSpec.Builder( | ||
| INTEGRITY_KEY_ALIAS, | ||
| PURPOSE_SIGN or PURPOSE_VERIFY | ||
| ) | ||
| .build() | ||
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| keyGenerator.run { | ||
| init(keyGenParameterSpec) | ||
| return generateKey() | ||
| } | ||
| } | ||
|
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| private fun Mac.calculateHmacValue( | ||
| encryptedData: ByteArray, | ||
| initialVector: ByteArray | ||
| ): ByteArray = doFinal(encryptedData + initialVector) | ||
|
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| /** | ||
| * Validate the HMAC value | ||
| * | ||
| * @throws SecurityException if the HMAC value doesn't match with [encryptedData] | ||
| */ | ||
| private fun CipherData.verifyHmacValue(mac: Mac) { | ||
| val expectedHmacValue: ByteArray = mac.calculateHmacValue( | ||
| encryptedData = encryptedData, | ||
| initialVector = initialVector | ||
| ) | ||
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| if (!MessageDigest.isEqual(expectedHmacValue, hmacValue)) { | ||
| throw SecurityException("Cipher text has been tampered with.") | ||
| } | ||
| } | ||
|
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| companion object { | ||
| private const val AES_KEY_ALIAS = | ||
| "com.linecorp.android.security.encryption.StringAesCipher" | ||
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| private const val INTEGRITY_KEY_ALIAS = | ||
| "com.linecorp.android.security.encryption.StringAesCipher.INTEGRITY_KEY" | ||
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| private const val ANDROID_KEY_STORE = "AndroidKeyStore" | ||
| private const val KEY_SIZE_IN_BIT = 256 | ||
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| private const val TRANSFORMATION_FORMAT = | ||
| KeyProperties.KEY_ALGORITHM_AES + | ||
| "/${KeyProperties.BLOCK_MODE_CBC}" + | ||
| "/${KeyProperties.ENCRYPTION_PADDING_PKCS7}" | ||
| } | ||
| } |
12 changes: 12 additions & 0 deletions
12
line-sdk/src/main/java/com/linecorp/android/security/encryption/StringCipher.kt
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,12 @@ | ||
| package com.linecorp.android.security.encryption | ||
|
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| import android.content.Context | ||
|
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| interface StringCipher { | ||
|
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| fun initialize(context: Context) | ||
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| fun encrypt(context: Context, plainText: String): String | ||
|
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| fun decrypt(context: Context, cipherText: String): String | ||
| } |
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