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Double Blind Passwords a.k.a. Horcruxing

kaizoku.dev

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

#32
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?

I had one of the most valuable accounts in a video game, so attackers of all kinds were constantly contacting me. I was immediately suspicious of anyone who contacted me. I signed up for the forum with a password from my password manager (I like toying with attackers). I told him I signed up, and a few minutes later he said there was a problem with my account and asked if I used a password manager. I said yes. He said to sign up without it because the site doesn't support it. I tried arguing with him that that makes no sense. But arguing with someone who's lying and refuses to admit it is generally not productive, and the argument got nowhere.

His idea to make me sign up without a password manager was illogical anyways. If I use a password manager on his site, it should be obvious I use a password manager for my video game account, so me halting my password manager usage for his site wouldn't help him get my video game account.

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

#33

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/

That was my initial thought as well. I wrote about how to use Shamir's Secret Sharing (with a similar Horcrux analogy) to reset master passwords for end-to-end encrypted applications (such as password managers):

https://francoisbest.com/posts/2020/password-reset-for-e2ee-...

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

#34
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…

Oh, my... I can imagine quite a few obscene and anatomically impossible pass phrases that would be generated for that forum. However, I supposed you would still give up some knowledge/deniability in that case.

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

#35

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/

That was my initial thought as well. I wrote about how to use Shamir's Secret Sharing (with a similar Horcrux analogy) to reset master passwords for end-to-end encrypted applications (such as password managers): https://francoisbest.com/posts/2020/password-reset-for-e2ee-...

Damn good stuff!

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

#37

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 l…

How did you encode messages for (1)? Did you provide instructions? Did you keep a copy?

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

#38
You could take this a step further and make your "horcrux" a short & simple cipher code based on some attributes of the organization instead.

It takes a bit longer to construct for sites you don't log into often, but when appended to a password/passphrase, it appears to be random across each site. If multiple logins get leaked it's not immediately obvious you're are using the double-blind approach.

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

#39

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/

Is this related to that one algorithm where 3 people can find out who makes the most money without any of them knowing what the other makes, and without consulting a 4th person? That one always felt like black magic to me.

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

#40

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 l…

My least-effort solution to most of these issues is to be storing hard copies of the password to my primary email in different places and using 2FA.

Then if my password manager does get nuked or compromised, I can "restore" my accounts by using the "forgotten password" feature for most places. If I get trojaned, what are they really going to do with my accounts? The majority of things of importance are behind 2FA anyway, and I'm not a public enough figure that any of my data that isn't is of any importance anyway.

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