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Double Blind Passwords a.k.a. Horcruxing

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Re: Double Blind Passwords a.k.a. Horcruxing

#21

Post by GekkePrutser »

I do't really agree with the long passphrase thing.. I leave my passwords at 12 characters max (and 8 for less important sites)

Reason: You still have to type it sometimes. Like on a device you don't have the password manager on. That makes it really annoying. And because it's only used on one site it doesn't really matter how long it is. If a hacker gets hold of the password file they already own that site anyway. Doesn't really matter whether they can bruteforce the hash. It won't give them more access than they already have.

I do agree with the horcrux thing though.. Really important passwords I only store on paper and I already add a memorised thing to them. But be aware it's not perfect either. A compromised endpoint could have a keylogger installed. Totally passwordless with Fido2 for example would be even better.

Re: Double Blind Passwords a.k.a. Horcruxing

#22

Post by GekkePrutser »

vinay_ys wrote: post #11

It is much better to use a password manager than trying to remember poorly crafted passwords in your head. But also really/truly remember not to really put all your eggs in one proverbial basket. Password managers are not without dangers: 1. If you forget your master password or secret key (you need both to setup a new device), you are screwed. 2. If the password manager cloud sync service (like 1password) decides to…

A lot of these are easily mitigated by running your own password manager. They're just general drawbacks of running stuff in the cloud.

Others are mitigated by good opsec and backup strategies.

Re: Double Blind Passwords a.k.a. Horcruxing

#23

Post by CGamesPlay »

vinay_ys wrote: post #11

It is much better to use a password manager than trying to remember poorly crafted passwords in your head. But also really/truly remember not to really put all your eggs in one proverbial basket. Password managers are not without dangers: 1. If you forget your master password or secret key (you need both to setup a new device), you are screwed. 2. If the password manager cloud sync service (like 1password) decides to…

I somewhat recently made my personal disaster recovery plan, and the password manager features prominently into it. If I lose all of my electronic devices in a sudden accident, how can I recover my online life? To address your questions specifically:

1. I used Shamir's secret sharing to send out a copy of my secret key to a few loved ones. The master password is in my memory only. If I forget the master password, I lose.

2. I use 1Password, and they say they make accounts read-only once you stop paying. If they did actively delete my account, my devices have a local copy. If I lose my devices and they delete my account at the same time, I lose.

3. I don't know what you're imagining, but you need the data, secret key, and master password to have this be a concern.

4. This has nothing to do with my threat model, I'm afraid. I can't imagine a world in which knowing my IP address leads to decrypting my password vault.

5. I am and this is correct. If there's a vulnerability in the cryptography used by 1Password, I lose. As you said, if there's a trojan update, I lose.

6. This is the same as 1 and 2.

All things considered, as a regular person who is concerned about protection from thieves and not especially concerned about being a target of governments, I am OK with these risks.

Re: Double Blind Passwords a.k.a. Horcruxing

#24

Post by kennywinker »

deanclatworthy wrote: post #20

Is there any reason why something like bitwarden couldn't prompt you with an in-browser prompt() dialog for your horcrux right before you enter your password and append it the one they auto-inject into the form?

I immediately thought of this. There’s no way I’m using this technique if it’s not automated at least a little

Re: Double Blind Passwords a.k.a. Horcruxing

#25

Post by nhumrich »

GekkePrutser wrote: post #21

I do't really agree with the long passphrase thing.. I leave my passwords at 12 characters max (and 8 for less important sites) Reason: You still have to type it sometimes. Like on a device you don't have the password manager on. That makes it really annoying. And because it's only used on one site it doesn't really matter how long it is. If a hacker gets hold of the password file they already own that site anyway. D…

> won't give him access to more then he already has.

That is very incorrect. A lot of hash leaks happen when an attacker can read data. but he can't necessarily edit it or even make sense of it. Also, the attacker usually does a quick download, then _sells_ the data. So, imagine your Twitter password was leaked. The original attacker a) likely doesn't have write access, and 2, is just going to sell the password hashes. The real worry is the buyer, who buys the hashes, to log in as you and do anything.

This is how youvebeenpwned works. He actually finds leaks of hashes on the dark web.

Re: Double Blind Passwords a.k.a. Horcruxing

#26

Post by btilly »

war1025 wrote: post #10
emmanueloga_ wrote: post #7

This is a cool/useful idea. I thought the article was gonna be about "Shamir's Secret Sharing" [1], "where a secret is divided into parts, giving each participant its own unique part. To reconstruct the original secret, a minimum number of parts is required.". Sounds horcruxy to me :-p. I learnt about it from the PIM book [2]. 1: https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing 2: https://pimbook.org/

I thought that algorithm was crazy magic when I first heard of it. The method behind it is pretty fascinating. A nth degree polynomial is uniquely identified by n+1 points. So the algorithm interprets your secret to a binary numeric value, sets that as the value at x=0 (i.e. the constant term of the polynomial), picks random coefficients for all the polynomial degrees, then computes coordinate pairs for however many…

There is some added math bit that gets added on top to make the polynomial less easy to guess, but the concept remains the same.

The added math bit is that you calculate the polynomials modulo some prime number.

That means that you're doing integer arithmetic, but with even one missing point you've gained no information about the secret. (As long as your points were actually generated with good randomness that is...)

Re: Double Blind Passwords a.k.a. Horcruxing

#27

Post by kennywinker »

some_furry wrote: post #18

This won't work very well if the site you're logging into uses bcrypt, and the value you store in your password manager is >= 72 characters. https://paragonie.com/blog/2016/02/how-safely-store-password...

If a site is using bcrypt and it allows users to set passwords longer than 72 chars, the operator of the site is the problem not the use of a password manager + in-my-head-secret

Re: Double Blind Passwords a.k.a. Horcruxing

#28

Post by Thorrez »

If there's generic malware that's targeting your password manager, then yes this provides protection against that. But it doesn't provide protection against a targeted attack, because the malware can just keylog your horcrux.

Another weakness that doesn't require a keylogger, is the attacker might be able to find some stolen database of a website that stored passwords in plaintext, then deduce your horcrux from the difference between what was in your password manager and what was in the database. And if the site did hash passwords, the attacker can try cracking the horcrux. The 5-character example horcrux probably wouldn't be too hard. The article somewhat covers this by saying only use the horcrux on important sites. This is good, but it still has weaknesses because an important site can still get its database stolen, and some people also want to protect less important sites.

And if no password databases are available, the attacker can create a website and ask you to join it under the hope you'll reuse your horcrux on the attacker's site. I've actually had an attacker contact me personally (that is, actually chatting with me live) and ask me to sign up for his forum under the hope that I would reuse my valuable account's password on the forum.

Re: Double Blind Passwords a.k.a. Horcruxing

#30

Post by Hackbraten »

Thorrez wrote: post #28

If there's generic malware that's targeting your password manager, then yes this provides protection against that. But it doesn't provide protection against a targeted attack, because the malware can just keylog your horcrux. Another weakness that doesn't require a keylogger, is the attacker might be able to find some stolen database of a website that stored passwords in plaintext, then deduce your horcrux from the d…

> I've actually had an attacker contact me personally (that is, actually chatting with me live) and ask me to sign up for his forum under the hope that I would reuse my valuable account's password on the forum.

How did you eventually find out their true motivation?

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