What is trust?
When seriously evaluating a security solution, we need to be clear about our end goals. By formalizing the concept of password security concretely, we gain the ability to test solutions and evaluate their real benefit in concrete fact.
All trust is by necessity limited. There are no guarantees. What it means “to trust a solution” therefore requires an objective awareness of what the solution’s security parameters are and whether those parameters are compatible with our security needs.
What this article sets out to accomplish is to explore the security parameters involved in different approaches to password authentication in an effort to clearly identify the objective weaknesses present in the solution as well as the ancillary risk that adoption requires us to incur. This will allow us to select the strategy that best aligns with our needs and ability to assume risk.
To determine a solution’s viability, we need to evaluate its performance in several distinct categories. It’s important to think beyond claims such as security, encryption or entropy, and consider the full scope of consequences that adoption brings.
In this article, we will be testing solutions against to the following categories.
- What limitations are we placing on the password’s entropy?
- What do we need in order to create passwords this way?
- What dependencies do we incur for continued use of this password?
- What paths exist for an unauthorized party to obtain this password?
We will rate our findings on a scale from safe to problematic, where:
- A safe rating represents a finding that we do not expect should give rise to concern in terms of impact on the viability of using this strategy for securing our accounts.
- A notice rating represents a finding that warrants care in order to ensure the implementation accommodates for what might otherwise become a cause for concern that could impact the security of our account.
- A severe rating indicates a finding that compromises the strategy’s ability to yield trustworthy account security with no viable solutions for mitigating the weakness.
In this context, entropy is defined as the size of the space that an attacker would need to search in order to successfully guess the password that was created.
A low entropy means fewer guesses are required in order to make a successful guess against the password. This unlocks the ability to brute-force the password, ie. defeat the solution’s security with no need for finding and exploiting any inherent weaknesses.
The way in which low entropy is exploited is by making attempts against the password and checking whether those attempts were successful.
Even when we consider the incredibly limited space of a 4-digit PIN, an attacker attempting a brute-force strategy against the PIN’s entropy would still need to search a space of 10,000 possibilities.
Nearly all password-protected assets are engineered specifically to minimize
the ability for attackers to make random attempts against the password.
If an attacker is only permitted an attempt every 10 seconds, the time it takes to search a space of 10,000 candidates tops out at 100,000 seconds, or over 27 hours. Increase the delay to 1 hour after the first 5 failed attempts and the attack now tops out at 35,982,050 seconds, surpassing a year.
If an attacker is only permitted a total of 5 attempts before being locked out, a brute-force strategy that needs to search a space of 10,000 candidates has no realistic chances of success.
Consequently, any attack against a password that seeks to successfully exploit its entropy requires access to a method of testing the password by the thousands per second.
Unfortunately, we do live in a world where such a tool exists: password leaks. The websites that hold our accounts need some way of testing whether we have provided the correct password. They can do this either by storing your password directly in their database, or by storing a one-way cryptographic hash of the password. When the website’s database is infiltrated and its contents stolen, attackers can now use what’s in the database to make an attempt against your account at this website.
When websites leak clear-text password databases, ie. databases where your password was stored as-is, it’s unfortunately game-over for you. An attacker can now simply find your exact password in the leak and impersonate you with it.
When websites store one-way hashes of passwords, ie. the recommended way of storing shared secrets, an attacker can only see a “fingerprint” of your password. They have a “clue” about what your password might be, and will need to try looking at a bunch of passwords to see which one has the same fingerprints as your password in this leak has. This is where brute-forcing your password’s entropy comes in. An attacker will run the website’s chosen hash function against a random guess. This will give them a similar fingerprint for their guess. If the result matches what they find in the leak, they know they’ve made a correct guess and what your original password was.
There are different types of hash functions that websites use to protect our accounts. The main feature of a good hash function in this context must be that it is expensive: ie. it takes a lot of resources to run the hash function. This may seem counter-intuitive: wouldn’t a website want their account login code to be cheap, so that many thousands of customers can log in quickly and easily? Why, yes, but keep in mind that an attacker would need to use the same hash function as that chosen by the website, so the more expensive the chosen hash function is for a website, the more expensive it will be for an attacker to make guesses against your fingerprint in it. We arrive thus at a situation where a careful balance must be made in choosing a hash function that is expensive enough to repel attackers and yet cheap enough to allow the website to employ it at scale for its customers.
Widely adopted currently is the bare minimum recommendation of
bcryptwith a cost factor of
In the table below, we evaluate the time cost for scanning the full entropy of
our hash functions using the
Nvidia GTX 1080 Ti work horse GPU.
|Entropy||Example||Time (bcrypt-10)||Time (sha-256)|
||14.59 Seconds||0 Seconds|
||1.31 Months||0.50 Seconds|
||205.54 Years||15.41 Minutes|
||3 Million Years||5.28 Months|
||1011 Years||16,374.89 Years|
||1025 Years||1018 Years|
In conclusion, we find that:
sha-256is inadequate for password hashing and websites should not use it.
~55 bitmakes a decent minimum bar for ordinary use password entropy.
- Going much higher in entropy doesn’t really net us any realistic benefit.
One final consideration is the fact that many websites impose counter-productive password policies which force password generators to contort the types of passwords they produce away from max entropy in an effort to remain generally supported by an unpredictable range of website policies. Sacrificing some entropy to ensure wide applicability and avoid user frustration is an acceptable trade-off so long as the final entropy is still sufficiently high.
To some extent, parallelization can be used in an attempt to bring down high time costs. While this isn’t perfectly linear, one could imagine a cluster of ~20,000 GPUs might be used to bring a 16,374.89 Years estimate down to the single year range, but keep in mind that this would incur extreme expenses in terms of hardware acquisition, infrastructure and operating costs. It’s safe to say that any numbers beyond those are out of range for brute-force attempts.
Any solution that incurs a cost higher than we’re willing to pay in the very moment we need it, is a non-solution. We notice that users are very picky about their own convenience. For instance, as an employer you may require that passwords be kept in a book which is kept securely in a vault, and must always be returned immediately after use. In which case you may find that employees begin copying passwords out of the book to keep them elsewhere, violating the solution for the sake of feasibility.
We need to be realistic, therefore, and consider solutions only when their use requirements are compatible with the usage scenarios. Considering the diversity in the population as well as the unpredictability of what future situations we may find ourselves in, we should take into account that we cannot necessarily judge realistic requirements as an objective measure.
We therefore aspire to keep requirements to an absolute minimum and grant ourselves maximal flexibility in terms of future contingencies.
We should be very wary of requirements that incur:
- A lot of effort on our part.
- Actively maintained contracts with other parties.
- Loss of control, such as proprietary solutions with no recourse.
Going beyond requirements, it’s also important to evaluate to what extent we’re outsourcing our security to other parties where trust is always going to be limited.
Wherever we involve other parties, it’s important to acknowledge honestly the position of power in which we’d be placing them and moderate our trust level accordingly.
Involving dependent parties is a slightly insidious process in our current society where we’ve been conditioned to accept that in a contractual engagement, parties who claim to be security vendors can certainly be trusted to act with integrity and flawless operation.
Dependencies may be incurred in the sense that we become dependent on the cooperation of another party in order to gain access to our own accounts. They may also be incurred in the sense that we’ve put them in a position of power where if their intentions became misaligned or operations became compromised, they could easily gain access to our complete online identity.
In times of stability, we tend to put faith in the system of law and order, contracts and policy. But the reality is that tides shift and if we want to future-proof our operations, it’s imperative that we seek to minimize our dependencies on and trust in external entities.
We spoke of entropy and brute-force attacks and got a clear picture of what it might take for an attacker to seek to guess our password through searching the space of its entropy. In doing so, we understood that sufficiently high-entropy passwords are quite robust against brute force attempts.
As an attacker, knowing that brute-force may be off the table, the next strategy is to seek out what solution you’re employing to manage your passwords. It’s therefore important that we become cognisant of the different pathways that exist in our chosen solution for compromising our passwords.
A 120 bit entropy password may be resilient to millions of years of brute-forcing, but if an attacker can download it off of your computer tomorrow, that hasn’t helped much.
Vulnerabilities can come from all sorts of angles. The best way to discover them is to put yourself in the role of an attacker and seek out the best strategy you can come up with for attacking your own assets.
With a clear picture of the security parameters and a framework for trust in mind, let’s begin our evaluation: what are the different ways in which we can create and manage our passwords and what are the consequences they incur?
We’ll test the following password creation strategies:
- User Memorized
- We create a password we’re likely to be able to recall.
- User Stored
- We think of a new and maximally arbitrary password.
- User Algorithm
- We use a personal algorithm for translating a website into an associated password.
- Software Memorized
- Using software, we compose a random password or passphrase that is memorable.
- Software Stored
- Using software, we create a maximally arbitrary password.
- Software Algorithm
- Using software, we derive a name into an associated password.
Below, we’ll explore each of these strategies in some detail to check them against our security parameters. The following table summarizes those findings:
From an overview of the different approaches to password security, we can draw some conclusions:
- User generated passwords tend to be critically weak in entropy.
- User-based solutions come with unsustainable requirements.
- User-based solutions suffer from critical vulnerability pathways.
- Computing high-entropy memorable passwords works well, but only in limited quantities.
- Storing high-entropy passwords is robust, but demands questionable dependencies.
- Deriving high-entropy passwords algorithmically incurs minimal trade-offs if done right.
In the absence of any tools and prior experience, this strategy is often what first comes to us when confronted with a need to secure our online presence.
Confronted with a request for a password, we do our best to answer to what appears to be the question asked of us: “please tell me a secret word that I can recognize you by in the future”. We think of what might be such a word, cognisant of the fact that we will need to be able to recall it in the future.
- Constrained by past experiences, often non-exclusive knowledge
- Human creativity biases away from uniformly random
- Creative energy
- Reliable expansive memory
- Low entropy facilitates searching the domain space
- Knowledge of personal information may further narrow the domain space
- Partial or complete password re-use is a fast track to compromise
When we learn of the realities around account insecurity and the impact it may have, hopefully indirectly and not first-hand, we often find the next step toward taking account security seriously involves the realization that our passwords need to be both unique for each site and also sufficiently random so as to make successful guesses against the token we’ve chosen less likely. We may adopt this strategy selectively, such as only for our most valued accounts.
We think really hard and try to come up with a token that appears as far away as anything guessable might appear. We do now realize that this isn’t something we can continue to try to remember, especially after doing this for four or five accounts, and seek out solutions for persisting our more secure passwords.
- Human creativity biases away from uniformly random
- Creative energy
- A method for persistence and recollection
- Bias impacts the size of the domain space
- Our persistence method and its usage can lead to complete compromise
Having gone from a solution where we created and remembered our own passwords to one where it had now become impossible to log into our accounts without the support of a tool, often one we don’t have exclusive control over.
Instinctively some people chose a different path, intentionally seeking to find a middle ground between being able to have hundreds of unique passwords and not needing to surrender our ownership and control. The end result tends to be a home crafted algorithm of some sort where we translate the name of the site into a unique password for it.
- Human crafted algorithms are deceptively low entropy
- Mentally solving the algorithm
- We need to remember the algorithm
- Biased output leads to critically low entropy
- The algorithm is susceptible to reverse engineering
banana colored duckling,
totally physical shoulder,
want timely plastic butterfly
A less common solution attempts to combine the benefits of personal ownership with the cheap and unbiased ability for software to generate high entropy tokens. In this strategy, a program can be used to generate what will often be a sentence based on a very large word list, with sufficient grammatical coherence to allow our memories to easily store and recollect the sentence on demand.
The size of the original word list combined with the length of these passphrases is often quite successful at generating high entropy passwords. Interestingly, people are in fact very capable of remembering arbitrary or nonsensical sentences since the mind naturally tends to weave a story around them that aids in recollection.
- Incompatible with many website password policies
- Remembering passphrases is quite manageable in limited quantities only
- Any application with a sufficiently diverse dictionary
- Sufficiently high entropy to make searching the space infeasible
Industry standard solutions appear to have settled on generating tokens based on a secure random device generating maximally unbiased output within a predefined character class or template. The result is a high-entropy password that’s very robust against direct attacks.
The main downside being that these solutions are fully dependent on stateful storage of the resulting passwords, though not to worry - these industry solutions come with an answer to this as well: just marry the product and they will store it for you in their proprietary vault or remote data-centres.
- High entropy may be tweaked to maximally fit the website’s password policies
- Access to your password vault and a working app that can read it
- Proprietary data storage
- Remote data storage
- Sufficiently high entropy to make searching the space infeasible
- Data storage may be captured
zowp quy roxzuyu qim,
A rare approach in the industry involves seeking to combine the benefits of high-entropy software generated tokens with the control and ownership benefits of incurring minimal dependencies while remaining maximally applicable.
A one-way algorithm can be used to derive a password from the website’s name. The output can be rendered user-specific by seeding the algorithm with a user token such as their own name. The output can also be made secret by seeding the algorithm with a user provided secret, something the user would then need to either store or remember themselves.
- Password policy compatible output templates can maintain high entropy
- Access to the algorithm
- Software capable of evaluating the algorithm
- Algorithms might be reversed if not well designed
With a good understanding of the general categories of password solutions out there, let’s take a closer look at some products that are available on the market to help us address this problem and how we might evaluate their proposals.
We’ll test these products against the same metrics to find the concrete results
of how their implementation resolves against the security parameters you may
want to consider.
Hover over each finding for details.
You may not find it wholly surprising that an article on spectre.app finds the Spectre solution to be least problematic - that said, we hope we’ve given you sufficient context to draw consider the relevant problems for yourself and draw your own conclusions.
Feel free to drop by our community with your questions and your thoughts. We’d love to have your voice added to the conversation and together work toward a future where we’re empowered as individuals to control our own digital privacy and security.