SecureVault

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private val masterKey: MasterKey by lazy {
    MasterKey.Builder(context)
        .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
        .build()
}

/**
 * Encrypts a file and saves it to the secret storage directory
 */
fun encryptFile(sourceFile: File, destinationDir: File, fileName: String): File? {
    return try {
        if (!destinationDir.exists()) {
            destinationDir.mkdirs()
        }

        val encryptedFile = File(destinationDir, "$fileName.enc")

        // Create encrypted file using Android Security library
        val androidEncryptedFile = EncryptedFile.Builder(
            context,
            encryptedFile,
            masterKey,
            EncryptedFile.FileEncryptionScheme.AES256_GCM_HKDF_4KB
        ).build()

        // Copy source file content to encrypted file
        sourceFile.inputStream().use { input ->
            androidEncryptedFile.openFileOutput().use { output ->
                input.copyTo(output)
            }
        }
        // …