[EthanHeilman]

Neither backdoor nor frontdoor are well defined (backdoor does not always imply secrecy). I never heard the word "front door" until this recent push, and generally key escrow has been referred to as a backdoor despite being public knowledge.

My personal definitional taste would be:

* Backdoor - an additional way to decrypt a communication without the consent of the communicating parties.

* Secret Backdoor - a backdoor which the communicating parties are not aware of (DUAL_EC).

* Public Backdoor - a backdoor which is built into the public description the of the encryption system so that the communication parties are aware of it (lotus email backdoor).

* Frontdoor - a type of public backdoor which requires a warrant to access and whose key is controlled by a neutral (disinterested) third party. I'm not sure this is exactly what the FBI wants.

Thus, frontdoors are a very specific form of backdoors.

[AgentME]

I would have thought "front door" would mean to get the intended recipient of the message to decrypt it for you.

[AnthonyMouse]

Exactly. The front door is what the end user uses in the regular operation of the system. If there is another "door" imposed under penalty of law then it isn't the front door.

[htns]

Every user downloads and runs arbitrary code constantly, as updates. In the far future updates might come with a formal proof of their security, machine-verified on download, but for quite a few years still we will be stuck with just cryptography.

A front door would be using Microsoft's signing keys. As long as you don't leak the keys, you aren't diluting security in general. A back door would be just leaving vulnerabilities around. It's a meaningful distinction.

[AnthonyMouse]

There is a meaningful distinction between lawful imprisonment and false imprisonment; that doesn't make it accurate to call lawful imprisonment freedom.

Moreover, the ability of software vendors to push malicious updates is a security vulnerability. Just because we haven't eradicated it yet doesn't mean we should codify our inability to address it in the future, e.g. by allowing users to choose what party they trust to verify and sign updates.

[cb18]

Language is power.

I say we refrain from adopting any new silly terminology that anyone attempts to foist upon us regarding this issue.

Something is either cryptographically secure, or it isn't. A "cryptographic" method that allows access to anyone not authorized by the one doing the encryption is not cryptographically secure. And in that case, what's the point in using it or even calling it cryptography?

[harshreality]

That's some semantic gymnastics. So a "Public backdoor" is a "Frontdoor" when used by a law enforcement agency with a warrant. What about when the "neutral" third party uses the keys for some purpose without a warrant? What about when the third party is hacked? It seems confusing to refer to the same system as both a frontdoor and a backdoor.

The FBI would probably be happy with a front door. Unfortunately, a "frontdoor" means some "neutral" third party (or anyone who hacks it) then has the ability to decrypt all your communications. Furthermore, a "neutral" third party isn't necessarily that trustworthy. The saving grace of the CA system is that non-targeted attacks are likely to be detected, because the CAs don't have the certificates' private keys, and use of alternate keys is detectable, or even preventable (only in advance) with pinning.

Everyone would balk at a CA system where the CAs had all the servers' private keys. No matter how trustworthy the CA. It would be undetectable, and pinning wouldn't mitigate it. And that's exactly what the FBI wants for Google, Facebook, Microsoft, and Whatsapp communication products.

If a neutral third party holds the keys, then you have the company (1) that makes the communications products having the keys, transferring them to the neutral third party (2) and deleting them ("we promise!"), so only the third party holds them for possible eventual use by the FBI (3). That's three entities that may potentially have access to key material in the future, not to mention anyone who hacks those three entities.

[EthanHeilman]

I'm not advocating such a system and I agree with the points you make. I don't think a "frontdoor" would be effectively secure against either government abuse or key compromise. Its a bad idea. Not only that but since it is publicly known, such products would have a competitive disadvantage.