## Security considerations

The following is a list of security features that I hope to add eventually, in approximately the order in which I expect to add them.

* Request logging, obviously.
* Disallow all Tauri APIs except for `invoke` and `emit`. The sole job of the frontend should be to collect user interaction. Everything else should be mediated through the backend.
* Maximally-restrictive CSP - not sure if Tauri does this by default. Also not sure whether it will interfere with IPC to set a zero-access CSP.
* Allow user to specify a role to assume, so that role can be given narrower permissions. Allow falling back to the root credentials in the event that broader permissions are required. (Unsure about this one, is there a good way to make it low-friction?)
* To defend against the possibility that an attacker could replace, say, the `aws` executable with a malicious one that snarfs your credentials and then passes the command on to the real one, maybe track the path (and maybe even the hash) of the executable, and raise a warning if this is the first time we've seen that one? Using the hash would be safer, but would also introduce a lot of false positives, since every time the application gets updated it would trigger. On the other hand, users should presumably know when they've updated things, so maybe it would be ok. On the _other_ other hand, if somebody doesn't use `aws` very often then it might be weeks or months in between updating it and actually using the updated executable, in which case they probably won't remember that this is the first time they've used it since updating.  
Another possible approach is to _watch_ the files in question, and alert the user whenever any of them changes. Presumably the user will know whether this change is expected or not.
* Downgrade privileges after launching. In particular, if possible, disallow any kind of outgoing network access (obviously we have to bind the listening socket, but maybe we can filter that down to _just_ the ability to bind that particular address/port) and filesystem access outside of state db. I think this is doable on Linux, although it may involve high levels of `seccomp` grossness. No idea whether it's possible on Windows. Probably possible on MacOS although it may require lengths to which I am currently unwilling to go (e.g. pay for a certificate from Apple or something.)
* "Panic button" - if a potential attack is detected (e.g. the user denies a request but Creddy discovers the request has already succeeded somehow), offer a one-click option to lock out the current IAM user. (Sadly, you can't revoke session tokens, so this is the only way to limit a potential compromise). Not sure how feasible this is, session credentials may be limited with regard to what kind of IAM operations they can carry out.)
* Some kind of Yubikey or other HST integration. (Optional, since not everyone will have a HST.) This comes in two flavors:
    1. (Probably doable) Store the encryption key for the passphrase on the HST, and ask the HST to decrypt the passphrase instead of asking the user to enter it. This has the advantage of being a) lower-friction, since the user doesn't have to type in the passphrase, and b) more secure, since the application code never sees the encryption key.
    2. (Less doable) Store the actual AWS secret key on the HST, and then ask the HST to just sign the whole `GetSessionToken` request. This requires that the HST support the exact signing algorithm required by AWS, which a) it probably doesn't, and b) is subject to change anyway. So this is probably not doable, but it's worth at least double-checking, since it would provide the maximum theoretical level of security. (That is, after initial setup, the application would never again see the long-lived AWS secret key.)


## Threat model

Who exactly are we defending against and why?

The basic idea behind Creddy is that it provides "gap coverage" between two wildly different security boundaries: 1) the older, user-based model, where all code executing as a given user is assumed to have the same level of trust, and 2) the newer, application-based model (most clearly seen on mobile devices) where that bondary instead exists around each _application_. 

The unfortunate reality is that desktop environments are unlikely to adopt the latter model any time soon, if ever. This is primarily due to friction: Per-application security is a nightmare to manage. The only reason it works at all on mobile devices is because most mobile apps eschew the local device in favor of cloud-backed services where they can, e.g. for file storage. Arguably, the higher-friction trust model of mobile environments is in part _why_ mobile apps tend to be cloud-first.

Regardless, we live in a world where it's difficult to run untrusted code without giving it an inordinate level of access to the machine on which it runs. Creddy attempts to prevent that access from including your AWS credentials. The threat model is thus "untrusted code running under your user". This is especially likely to occur in the form of a supply-chain attack, where the compromised code is not your own but rather a dependency, or a dependency of a dependency, etc.

## Particular attacks

There are lots of ways that I can imagine someone might try to circumvent Creddy's protection. Most of them require that the attacker be targeting Creddy in particular, rather than just "AWS credentials generally". In addition, most of them are "noisy" - that is, there's a good chance that the attack will alert the user to the fact that they are being attacked. This is generally something attackers try to avoid, since an easily-detected attack is likely to be shut down before it can spread very far.

### Tricking Creddy into allowing a request that it shouldn't

If an attacker is able to compromise Creddy's frontend, e.g. via a JS library that Creddy relies on, they could forge "request accepted" responses and cause the backend to hand out credentials to an unauthorized client. Most likely, the user would immediately be alerted to the fact that Something Is Up because as soon as the request came in, Creddy would pop up requesting permission. When the user (presumably) denied the request, Creddy would discover that the request had already been approved - we could make this a high-alert situation because it would be unlikely to happen unless something fishy were going on. Additionally, the request and (hopefully) what executable made it would be logged.

### Tricking the user into allowing a request they didn't intend to

If an attacker can edit the user's .bashrc or similar, they could theoretically insert a function or pre-command hook that wraps, say, the `aws` command, and dump the credentials before continuing on with the user's command. This would most likely alert the user because either a) the attacker is hijacking the original `aws` command and thus it doesn't do what the user told it to, or b) the user's original `aws` command proceeds as normal after the malicious one, and the user is alerted by the second request where there should only have been one.

A similar but more-difficult-to-detect attack would be replacing the `aws` executable, or any other executable that is always expected to ask for AWS credentials, with a malicious wrapper that snarfs the credentials before passing them through to the original command. Creddy could defend against this to a certain extent by storing the hash of the executable, as discussed above.

### Pretending to be the user

Most desktop environments don't prevent applications from simulating user-input events such as mouse clicks and keypresses. An attacker could issue a credentials request, then immediately simulate whatever hotkey or mouse click Creddy normally interprets as "confirm this request". To mitigate this Creddy could implement a minimum time for which it _must_ be on screen before dismissal. The attacker could try to wait for the machine to be unattended before executing this attack, but this is chancy and could still result in detection. The request would still be logged in any case.

### Twiddling with Creddy's persistent state

The solutions to or mitigations for a lot of these attacks rely on Creddy being able to assume that its local database hasn't been tampered with. Unfortunately, given that our threat model is "other code running as the same user", this isn't a safe assumption.
