Explain the implications of non-standard end-to-end encryption protocols, highlighting potential security risks and implementation vulnerabilities.

Non-standard end-to-end encryption (E2EE) protocols are those that deviate from established, widely vetted, and peer-reviewed cryptographic standards. While the intention behind developing a custom protocol might be to improve security or add unique features, the lack of standardization often introduces significant security risks and implementation vulnerabilities. When an E2EE system uses an unproven or non-standard protocol, users are generally placing their trust in untested cryptography, which may have unforeseen consequences.

One of the most prominent risks is the increased likelihood of cryptographic flaws. Standard protocols such as TLS, Signal Protocol, and OpenPGP have undergone rigorous scrutiny from cryptographers and security researchers. This means that any vulnerabilities that are discovered will likely be fixed quickly and are widely known. Non-standard protocols, on the other hand, typically lack this level of scrutiny. They are often developed in-house by small teams who may not have sufficient expertise in cryptography, and thus can introduce serious flaws. For example, they may implement a flawed key exchange mechanism or use weak encryption algorithms, leading to attacks that may be simple to perform, and that a standard algorithm would have been immune to. Also, using non-standard methods will make it difficult to review or have an independent audit.

Another major risk is the lack of peer review. Peer review is a crucial step in developing secure cryptographic protocols. It ensures that the protocol is robust against various known attacks and that the underlying assumptions are valid. Non-standard protocols generally lack this peer review and their security relies on the judgment and skill of the developers who created it. This lack of independent validation can lead to undetected vulnerabilities and flawed design, as well as an implementation that isn't tested properly, which may mean that it will not perform as required. For example, the developers of a non-standard protocol may use an insecure method to create session keys, or incorrectly use cryptographic libraries.

There is also a higher chance of implementation vulnerabilities with non-standard protocols. Even if the protocol design is sound on paper, implementation flaws can compromise the entire system. The complexities of cryptography mean that it is easy to introduce bugs or vulnerabilities into the code which can be easy to exploit. Standard libraries are often thoroughly tested to minimize this, but these libraries may not be supported when using non-standard encryption protocols. These flaws could leave the system vulnerable to attacks such as buffer overflows or timing attacks. For example, if the developers incorrectly use a key derivation function, it can make the system prone to brute-force attacks, or cause key reuse.

Non-standard protocols often lack interoperability. This makes it difficult for different systems or applications to communicate with each other securely. Because the implementation is not public, and there is no central authority to standardize these protocols, using these protocols will often result in a lack of standardization. For example, two parties using different messaging applications with custom E2EE protocols may not be able to exchange encrypted messages. The lack of interoperability also makes it difficult for the user to switch messaging applications which further reinforces the risks of a proprietary protocol.

There is also the risk of security through obscurity. Non-standard protocols are often kept secret, with the hope that an attacker will not be able to understand the system and therefore not be able to attack it. This approach, known as security through obscurity, has been proven ineffective. If the underlying assumptions are flawed or there are vulnerabilities in the implementation, it’s only a matter of time before an attacker discovers those weaknesses. True security must be provided by well-tested, open, and peer-reviewed methods. Thus, security through obscurity will not work because a non-standard protocol will not get the scrutiny required to discover weaknesses.

Also, there is often a lack of community support and resources for non-standard protocols. Because they are often proprietary, there is a lack of documentation, tutorials, and development tools, which makes them difficult to implement securely. When using non-standard methods it is often difficult to get support or guidance for the particular method chosen, resulting in a security risk if the implementation is incorrect. A larger community, that a standard protocol enjoys, will often have a more robust base of knowledge.

Furthermore, there may also be a lack of long-term support and maintenance. Because they are proprietary, the protocol may be abandoned at some point in the future, without long-term support. If the protocol is abandoned and there are vulnerabilities, then it could result in catastrophic security compromises to users of the system. Also, the lack of ongoing security audits and updates can expose the system to new vulnerabilities as they are discovered.

In summary, non-standard E2EE protocols introduce significant security risks and implementation vulnerabilities because of the lack of standardization, peer review, and long-term support. They increase the risk of cryptographic flaws, implementation bugs, lack of interoperability, and reliance on security through obscurity. Therefore, it's always recommended to use well-established and peer-reviewed cryptographic standards for secure communication, because any custom protocol should be regarded with suspicion.