Blurry Box Encryption Scheme and Why it Matters to Industrial IoT
the domain knowledge necessary to create the program code. Neither should the hacker be able to learn the inner workings of the software. The latter is called the assumption of the inherent complexity of program code, which can be formalized as follows: Given a subset of variants, a hacker should not be able to create additional ones.
Not all programs allow for creating variants with the above-mentioned security property.
For instance, a simple program such as“ Hello World” does not have this property and cannot be protected by the Blurry Box scheme. Only programs that are sufficiently complex can be protected effectively. Note that not the whole program has to fulfill this requirement; it suffices if only a part of it is sufficiently complex. Typically, this complex part is exactly the critical part that needs to be protected. Programs that meet this requirement include video games, raster graphics editors, and feedback control systems.
In accordance with the principles of modern cryptography, the security of the Blurry Box scheme can be proven rigorously based on falsifiable assumptions. To this end, a mathematical security model was conceived that is tailored to this setting. In this model, security is not an absolute factor, but defined by comparison. More specifically, security is defined by comparing every conceivable attack on the Blurry Box scheme with the mentioned Copy-and-Paste attack. This definition is reasonable, since Copy-and-Paste attacks cannot be prevented, but become practically infeasible and therefore not a security concern. It can be proven that no attack strategy can do better than the Copy-and-Paste strategy.
Formally, this means that, for every attack strategy, there exists a Copy-and-Paste attack that retrieves the same number of variants with the same number of dongle calls. The proof is based on three assumptions:
1) The security of the encryption scheme( IND-CCA2 security) 7, 2) The security of the dongle( the key is not extractable) and 3) The assumption on the inherent complexity of the program code.
IND-CCA2 security is a well-established security notion for encryption schemes. Intuitively, an encryption scheme is IND-CCA2 secure if no adversary can gain any information about a plaintext by analyzing a corresponding ciphertext, even if he can decrypt other arbitrary ciphertexts. The encryption scheme in the Blurry Box scheme has to be IND-CCA2 secure, because a hacker – analyzing the( encrypted) program code – has access to the dongle that contains the secret key.
4.3 CORRECTNESS
The protected program has the same functionality as the original, as each mechanism preserves the functionality of the original program. This holds for variant encryption: By design, each variant yields the same values as the original function block for restricted input sets. All variants
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Katz, Jonathan, and Yehuda Lindell,“ Introduction to modern cryptography,” CRC press, 2014
- 12- June 2016