KeyStoreException：尝试解密时签名/MAC 验证失败

Question

我正在尝试创建一个简单的 Kotlin 对象，该对象通过在保存内容之前加密内容来包装对应用程序共享首选项的访问。

加密似乎工作正常，但是当我尝试解密时，我得到一个 javax.crypto.AEADBadTagException，它从“android.security.KeyStoreException：签名/MAC 验证失败”触发。

我已尝试调试以查看根本问题是什么，但我找不到任何东西。没有搜索给我任何线索，我似乎遵循了一些指南，但没有成功。

private val context: Context?
    get() = this.application?.applicationContext
private var application: Application? = null

private val transformation = "AES/GCM/NoPadding"
private val androidKeyStore = "AndroidKeyStore"
private val ivPrefix = "_iv"
private val keyStore by lazy { this.createKeyStore() }

private fun createKeyStore(): KeyStore {
    val keyStore = KeyStore.getInstance(this.androidKeyStore)
    keyStore.load(null)
    return keyStore
}

private fun createSecretKey(alias: String): SecretKey {
    val keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, this.androidKeyStore)

    keyGenerator.init(
        KeyGenParameterSpec.Builder(alias, KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT)
            .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
            .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
            .build()
    )

    return keyGenerator.generateKey()
}

private fun getSecretKey(alias: String): SecretKey {
    return if (this.keyStore.containsAlias(alias)) {
        (this.keyStore.getEntry(alias, null) as KeyStore.SecretKeyEntry).secretKey
    } else {
        this.createSecretKey(alias)
    }
}

private fun removeSecretKey(alias: String) {
    this.keyStore.deleteEntry(alias)
}

private fun encryptText(alias: String, textToEncrypt: String): String {
    val cipher = Cipher.getInstance(this.transformation)
    cipher.init(Cipher.ENCRYPT_MODE, getSecretKey(alias))

    val ivString = Base64.encodeToString(cipher.iv, Base64.DEFAULT)
    this.storeInSharedPrefs(alias + this.ivPrefix, ivString)

    val byteArray = cipher.doFinal(textToEncrypt.toByteArray(charset("UTF-8")))
    return String(byteArray)
}

private fun decryptText(alias: String, textToDecrypt: String): String? {
    val ivString = this.retrieveFromSharedPrefs(alias + this.ivPrefix) ?: return null

    val iv = Base64.decode(ivString, Base64.DEFAULT)
    val spec = GCMParameterSpec(iv.count() * 8, iv)
    val cipher = Cipher.getInstance(this.transformation)
    cipher.init(Cipher.DECRYPT_MODE, getSecretKey(alias), spec)

    try {
        val byteArray = cipher.doFinal(textToDecrypt.toByteArray(charset("UTF-8")))
        return String(byteArray)
    } catch (e: Exception) {
        e.printStackTrace()
        return null
    }
}

private fun storeInSharedPrefs(key: String, value: String) {
    this.context?.let {
        PreferenceManager.getDefaultSharedPreferences(it).edit()?.putString(key, value)?.apply()
    }
}

private fun retrieveFromSharedPrefs(key: String): String? {
    val validContext = this.context ?: return null
    return PreferenceManager.getDefaultSharedPreferences(validContext).getString(key, null)
}

谁能指出我正确的方向？

Answer 1

我有类似的问题。都是关于android:allowBackup="true"

问题：

卸载应用程序然后重新安装时会出现此问题。 KeyStore 将在卸载时被清除，但首选项不会被删除，因此最终会尝试使用新密钥解密，从而引发异常。

解决方案：

尝试禁用 android:allowBackup

<application android:allowBackup="false" ... >

Answer 2

我在密码加密“AES/GCM/NoPadding”上遇到了相同的异常/问题“android.security.KeyStoreException：签名/MAC 验证失败”。

就我而言，帮助解决此问题的方法是首先创建一个字节数组持有者，其大小通过调用 Cipher.getOutputSize(int inputLen) 获得，然后调用 doFinal 重载 Cipher.doFinal(byte[] input, int inputOffset, int inputLen, byte[] output, int outputOffset) 以在字节数组持有者中设置密文.

    private var iv: ByteArray? = null

    fun doEncryptionOperation() {
        val keyStore = KeyStore.getInstance(PROVIDER_ANDROID_KEYSTORE).apply {
            load(null)
        }
        // Assumption: key with alias 'secret_key' has already been stored
        val entry = keyStore.getEntry("secret_key", null)
        val secretKeyEntry = entry as KeyStore.SecretKeyEntry
        val key secretKeyEntry.secretKey

        val plainText = "Sample plain text"
        val cipherText = encryptSymmetric(key, plainText.toByteArray())
        val decrypted = decryptSymmetric(key, cipherText)

        val decryptedStr = String(decrypted)
        val same = decryptedStr == plainText
        Log.d("SampleTag", "Is plaintext same from decrypted text? $same")
    }

    fun encryptSymmetric(key: SecretKey, plainText: ByteArray): ByteArray? {
        val cipher = Cipher.getInstance("AES/GCM/NoPadding")
        cipher.init(Cipher.ENCRYPT_MODE, key)
        iv = cipher.iv
        val len = plainText.size
        val outLen = cipher.getOutputSize(len) // get expected cipher output size
        val result = ByteArray(outLen) // create byte array with outLen
        cipher.doFinal(plainText, 0, len, result,0) // doFinal passing plaintext data and result array
        return result
    }

    fun decryptSymmetric(key: SecretKey, cipherText: ByteArray): ByteArray? {
        val cipher = Cipher.getInstance("AES/GCM/NoPadding")
        val tagLen = 128 // default GCM tag length
        cipher.init(Cipher.DECRYPT_MODE, key, GCMParameterSpec(tagLen,iv))
        cipher.update(input.data)
        val result = cipher.doFinal()
        return result
    }

另外，使用 AEAD 时，不要忘记在 ENCRYPT_MODE 中调用 Cipher.updateAAD()，并在 DECRYPT_MODE 中设置相同的 AEAD 标签。否则，您将遇到相同的 javax.crypto.AEADBadTagException。

Answer 3

当您将身份验证标签长度从 iv.count() 更改为 128 时，它将起作用。