White-box cryptography methods are designed to safeguard cryptographic algorithms from key retrieval. They are mainly employed as cost-effective alternatives to token-based security in DRM-like applications. 


What Is White-box Cryptography, and How Does It Work?

When working with security systems, a significant problem is protecting embedded "sensitive" (secret, confidential, or private) data. The conventional approach is to encrypt the data. However, the legitimate user must also get access to the decryption key, which must be secured. This is made much more difficult with a software-only solution that runs on an untrusted host. 

White-box cryptography is used to safeguard against the disclosure of secret keys during software implementation. In this scenario, it is believed that the attacker (either a "legal" user or malicious software) will also have access to the execution environment. This is in contrast to the more conventional security paradigm. The attacker is simply granted black-box access to the cryptographic method under consideration (i.e., inputs/outputs).

To use white-box cryptography to protect software, we presume the attacker has full access to the system. This includes the following:
  • Possession of an executable binary
  • Execution memory access
  • Interception of CPU calls

To effectively conceal the keys in this situation, the procedures below must be followed, assuming we are white-boxing a block cipher:


Partial Evaluation: When we execute an operation, the white-box modifies it according to the key. For instance, during the replacement stage of a block cipher, it would modify the lookup table to make it key-dependent. Take note that anybody who sees this table may deduce the key.

Tabularize: Convert all other processes to utilize lookup tables as well. This is feasible because lookup tables may be used to describe any function.

Delinearization and Randomization: It builds an encrypted chain of lookup tables that performs identically to the original chain but conceals the key. It now has an obfuscated algorithm utilizing this new chain.


Is the White-box Concept Realistic?

For encryption systems, the classic (i.e., black-box) threat models are the chosen-plaintext attack (CPA) and the chosen-ciphertext attack (CCA). The adversary selects plaintexts and is provided with the corresponding ciphertexts in the CPA model; in the CCA model, the adversary selects ciphertexts and is provided with the corresponding plaintexts. 

The attacker may access the same resources as in the black-box model, plus complete control of the encryption/decryption software in the white-box threat model. The adversary’s objective is to obtain the key. One may question whether such a situation makes sense, given that an opponent managing the encryption/decryption program can use it to encrypt or decrypt any material without requiring the adversary to extract the keys. 

We observe that a white-box approach may be advantageous since it compels users to interact with the program in question. Additional security measures may be employed simultaneously. If an opponent has the decryption key, the data may be decrypted and utilized on any host with any software. An across-the-board breach would result, causing severe damage.


What Level of Security Do White-box Solutions Provide?
There is no such thing as an entirely s ecure system. A system is considered safe when the opponent’s objective and the resources available to the adversary (e.g., oracle decrypting selected ciphertexts — CCA model) are established. It is considerably more difficult to characterize an attacker’s resources in the white-box environment since they are practically limitless. The best we can aspire for is to avert all known relevant dangers effectively. Security is mainly reliant on implementation: it is pointless to employ robust cryptographic methods if implemented incorrectly. Additionally, white-box implementations are more vulnerable to known assaults; they are particularly vulnerable to fault attacks.


What Are the Advantages and Disadvantages?
Without addressing security concerns, we outline the benefits of white-box alternatives over hardware-based solutions below.


Advantages

  • They are economical: they are simple to distribute and install.
  • Readily renewable: if a security vulnerability is identified, remote software updates may be performed.

Disadvantages

  • Orders of magnitude: slower and more resource-intensive (e.g., processing power, memory, etc.).
  • Severely restricted to symmetric-key: no white-box implementation of public-key methods is currently known.

Where Is White-box Cryptography Used?
Numerous systems that store and process confidential information benefit from white-box cryptography. It is a critical component of some industries’ security policies. The following are a few instances of specific uses.


Contactless Payments/NFC
Recent mobile payment applications use near field communication (NFC) systems to convert commonly accessible smartphones into contactless transaction terminals. These are game-changers for businesses, especially those with limited resources to invest in specialized point-of-sale systems. However, security is paramount. According to the Payment Card Industry Security Standards Council (PCI SSC), white-box cryptography is the best technique for versatile data security in such applications.


Medical Sector
Data from medical devices is encrypted and transmitted using compact encryption. Additionally, to ensure the data’s integrity, it may be signed. In general, a key is secure both inside the confines of a medical device and on cloud servers. The weakest link is the software or applications running on smartphones or PC. White-box cryptography secures the decryption and verification keys, preventing the theft or tampering of medical data.


OTT Streaming Platforms
The proliferation of over-the-top video streaming services has posed a similar challenge to those charged with safeguarding video content from hackers while still ensuring accessibility and a pleasant viewing experience for paying customers. White-box cryptography applies to both applications used to distribute content by OTT video providers.

White-box cryptography is an integral part of any vulnerability management strategy. This method allows the performance of cryptographic operations without exposing any sensitive data. Without this, hackers may easily steal encrypted data from the executable architecture, memory, or during execution.