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Although to be resistant to common Internet attacks, network coding should be accompanied with homomorphic signatures.

The Tangled Web. The web is the biggest kludge ever: a chaotic patchwork of technologies with security added as an afterthought. Understanding the details and motivation behind each security feature is no small feat whatsoever, an effort that can only be carried out by someone, like the author, well battled on exploiting them through the years. Reviewing the entire browser security model through its history it’s the only way to get a full understanding of how things have come to be the way they are, and this is the definitive guide to understand how complexity quickly builds up in security front when it’s not been planned since the beginning.

But in the last decade, the greater emphasis on models, formalization and the building of provable secure protocols transformed the discipline in a transcendental way: however, many of these results are yet to be implemented. Next, some of the most interesting constructions, that only appear on the academic literature and are not yet published in textbooks:

• Identity Based Encryption: public cryptography reduced the problem of information security “to that of key distribution” (Martin Hellman) and IBE schemes are the next step forward, because they enable the use of any string as the public key. This way, the recipient’s email address could be used as the public key, even if he didn’t requested a certificate for it, removing the need to pre-deploy a Public Key Infrastructure and their cumbersome costs. Later variants even allow for the use of biometric identities with the introduction of a margin of error in the definition of the public key, or for the efficient revocation of certificates.
• Attribute-Based Encryption: embedding a Role-Based Access Control model in public key cryptography, so every private key gets associated with a set of attributes representing its capabilities and every ciphertext could only be decrypted by those users complying with a prefixed set of attributes (vg. only “NATO officials” with an authorization level of “Cosmic Top Secret” are able to decrypt an important document). Later variants develop advanced features, like doing without a centralized authority.
• Predicate Encryption: generalizes and extends the previous IBE and ABE schemes, allowing for the encryption of the attributes and the decryption policy itself, and for far more granular policies.
• Signcryption: as the name implies, performs the encryption and signing at the same time, with lesser storage and computational costs than if the operations were individually carried out.
• Post-quantum cryptography: after Shor’s algorithm for efficiently integer factoring, new public key encryption algorithms are required, resistant to cryptanalytic methods enabled by quantum computation, like NTRU.
• Proofs of retrievability, ownership and work: a must in the cloud computing world, they respectively allow checking the integrity of remotely storaged files, without the need to keep a local backup of them; and storing only one copy of the same encrypted file (both proofs can be joined in just one proof of storage); or to proof that a costly computation has been carried out, a very useful primitive to fight spam and the basis of Bitcoin.
• Zero-Knowledge Protocols: This fascinating idea, initially contradictory, has become a fundamental building block of modern cryptography as the basic primitive for authentication and secure computation, among others. They allow proving the truth of a statement to another party, without revealing anything but the truthfulness of said statement, or in other words, to proof that the solution to a problem has been found, but without having to show the result to prove it.
• Commitment schemes: one party commits to a value, but keeps it hidden with the option to reveal it later. Intimately related to the previously described zero-knowledge protocols, they also are a fundamental primitive for more complicated protocols, in practice and in formal proofs.
• Private Information Retrieval: this family of protocols enables to privately query a database with very little overhead, without revealing to the server the exact information that is being search for. For example, a modern implementation of PIR-enabled MapReduce only introduces an overhead of 11%.
• Threshold cryptography: a set of modifications to common encryption schemes to share keys within a group, so at least a set of parties over a threshold are needed to decrypt the secrets. Their equivalents for signing schemes are ring signatures or group signatures.

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Another, and less strategic viewpoint, considers the answer of the correct place for a given functionality (exact processor ring, kernel/user mode and/or if it should be a library provided by the OS) a matter of custom and efficiency: for example, the need to get rid of the latency from user-mode calls to the kernel has always pushed more functionality into it, together with satisfying the demand of a basic security model. But these are just examples of the multiple balances that have to be struck, and what’s really interesting is to search for the non-obvious trade-offs and how they have given rise to different cultures of computing. Consider the case of the graphical interface and the window system: in the Unix tradition, a minimalistic approach was taken in that most of it is taken out of the kernel and even relegated to third parties (X Foundation), but the Windows tradition opted for the opposing approach, so it includes the Windows Manager and the GDI framework in kernel space; the consequences are long and lasting, even disastrous in the security space,  like how any X client can dump the content of an arbitrary window, including the ones it did not create. Also note that the precise breakdown of the barrier of user and kernel mode varies over time: traditional kernel-mode components are being moved into user-mode processes, like the User-Mode Scheduling for threads and the User Mode Driver Framework. But at the end, the truth is that the forces shaping the design of operating software tend to be more of economic than technical nature, as exemplified in the discussions collected in the following paper:

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