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Passwords that can be decrypted reliably are isomorphic to passwords stored in plaintext. That is very undesirable. Even assuming they are encrypted with a st

Passwords that can be decrypted reliably are isomorphic to passwords stored in plaintext. That is very undesirable. Even assuming they are encrypted with a strong key, anyone with access to the decryption key and the database can trivially recover any password stored by such a system. Password hashes are not isomorphic to plaintext passwords, because there can be collisions. That means there is no function to reliably take the stored passwords and turn them back into plaintext passwords; therefore, while reversing some/most passwords through complex iterative functions (e.g. brute force) is possible, the amount of work (particularly for bcrypt, pbkdf2, or other many-round hash+salt schemes) on average is many, many orders of magnitude greater than applying a decryption key. For good passwords, the amount of work is not quite unbounded, but might as well be. It's true that plaintext passwords and singly-hashed md5 passwords are both quite bad, but at least with the md5 hash nobody can (I think?) currently crack a 32 character random string since there are no rainbow tables for such long passwords. (Assuming the password is vetted for common weaknesses, since "random" alone does not guarantee anything. "aaaaaaaa" is a random 8 char password, after all.) Functions that attempt to reverse non-isomorphic mappings end up being complex and, even in the case of rainbow tables for (unsalted) md5, are much slower than not having to recover the unencrypted password at all, or having some master key that decrypts all passwords.

tptacek 15y ago
When we're talking about passwords stored "encrypted" on customer-exposed applications, I agree. When we're talking about passwords "vaulted" in non-exposed systems used for customer support, I have a harder time getting upset about it. I don't like systems that work this way, but I see the support/security tradeoff and it's a valid one. It is likely but not certain that the site in question here did not go through the trouble of setting up a non-exposed secure password vault system for customer support people to use under supervision. Probably they do just store passwords in a column somewhere. But you don't know for sure whether they do. Nobody needs rainbow tables to crack passwords. http://codahale.com/how-to-safely-store-a-password/ http://codahale.com/how-to-safely-store-a-password/
- elithrar 15y ago
  > When we're talking about passwords "vaulted" in non-exposed systems used for customer support, I have a harder time getting upset about it. I don't like systems that work this way, but I see the support/security tradeoff and it's a valid one. Worth also knowing is that many ISP's store your password using reversible encryption, because if a customer calls up wanting to know their password, it doesn't have to be regenerated. Which can save a lot of time re-configuring modem PPP credentials with your average Joe.
  - sdkmvx 15y ago
    If a customer calls up wanting to know their password, I would bet that they are configuring a new modem and that's why the need it. If their modem knows the password, why do they need to know it?
    - trafficlight 15y ago
      Email, ftp access, ssh access. There are lots of other reasons for needing to know a password.
      - lurker19 15y ago
        I think elithrar was talking about the layer-2 modem password, not the layer-7 application user credentials.
        rmc 15y ago
        What makes you think they are different?
  - dfox 15y ago
    ISPs providing any kind of authenticated PPP store your password in cleartext, because PPP authentication does not work without storing cleartext passwords.
baddox 15y ago
> Passwords that can be decrypted reliably are isomorphic to passwords stored in plaintext. This is absolutely correct, and I feel some readers may not exactly understand it. It would be one thing if only you had the key to decrypt the password (as is the case for example when you sync your browser data in Google Chrome). When the same people have access to both your encrypted password and the key to decrypt it, your password is only as secure as your confidence in the company's policies and employees' integrity. Also, as a side note I should mention that even if Newegg was securely storing your encrypted password and key, they forfeit that when they email it to you in plaintext.
- overcyn 15y ago
  > your password is only as secure as your confidence in the company's policies and employees' integrity. Thats always the case. Encrypted password or not. There's nothing stopping them from getting your password the next time you log in.
  - baddox 15y ago
    That's certainly true, although such an act would essentially constitute willful deceit at a company policy level, which is much worse than what I was hinting at. The hypothetical situation I was hinting at was something like an unruly employee being able to circumvent the company's process due to lax enforcement, even if the company's process itself was reasonable.

tptacek 15y ago

When we're talking about passwords stored "encrypted" on customer-exposed applications, I agree. When we're talking about passwords "vaulted" in non-exposed systems used for customer support, I have a harder time getting upset about it. I don't like systems that work this way, but I see the support/security tradeoff and it's a valid one. It is likely but not certain that the site in question here did not go through the trouble of setting up a non-exposed secure password vault system for customer support people to use under supervision. Probably they do just store passwords in a column somewhere. But you don't know for sure whether they do. Nobody needs rainbow tables to crack passwords. http://codahale.com/how-to-safely-store-a-password/ http://codahale.com/how-to-safely-store-a-password/

elithrar 15y ago
> When we're talking about passwords "vaulted" in non-exposed systems used for customer support, I have a harder time getting upset about it. I don't like systems that work this way, but I see the support/security tradeoff and it's a valid one. Worth also knowing is that many ISP's store your password using reversible encryption, because if a customer calls up wanting to know their password, it doesn't have to be regenerated. Which can save a lot of time re-configuring modem PPP credentials with your average Joe.
- sdkmvx 15y ago
  If a customer calls up wanting to know their password, I would bet that they are configuring a new modem and that's why the need it. If their modem knows the password, why do they need to know it?
  - trafficlight 15y ago
    Email, ftp access, ssh access. There are lots of other reasons for needing to know a password.
    - lurker19 15y ago
      I think elithrar was talking about the layer-2 modem password, not the layer-7 application user credentials.
      - rmc 15y ago
        What makes you think they are different?
- dfox 15y ago
  ISPs providing any kind of authenticated PPP store your password in cleartext, because PPP authentication does not work without storing cleartext passwords.

baddox 15y ago

> Passwords that can be decrypted reliably are isomorphic to passwords stored in plaintext. This is absolutely correct, and I feel some readers may not exactly understand it. It would be one thing if only you had the key to decrypt the password (as is the case for example when you sync your browser data in Google Chrome). When the same people have access to both your encrypted password and the key to decrypt it, your password is only as secure as your confidence in the company's policies and employees' integrity. Also, as a side note I should mention that even if Newegg was securely storing your encrypted password and key, they forfeit that when they email it to you in plaintext.

overcyn 15y ago
> your password is only as secure as your confidence in the company's policies and employees' integrity. Thats always the case. Encrypted password or not. There's nothing stopping them from getting your password the next time you log in.
- baddox 15y ago
  That's certainly true, although such an act would essentially constitute willful deceit at a company policy level, which is much worse than what I was hinting at. The hypothetical situation I was hinting at was something like an unruly employee being able to circumvent the company's process due to lax enforcement, even if the company's process itself was reasonable.