3 ms·

1. A "good" key safe for the forseeable future would have around 256 effective security bits. To get a key that strong, your password would have to be (speaking

1. A "good" key safe for the forseeable future would have around 256 effective security bits. To get a key that strong, your password would have to be (speaking VERY generously here) 40 characters long and truly random. 2. When using real password authentication, connecting to a compromised server results in a disclosure of your password. When using challenge-response authentication, it does not. Note that correctly-configured OpenSSH uses challenge-response even for password-based methods. Incorrectly configured SSH will send passwords over the wire.

jwilk 8y ago
> Incorrectly configured SSH will send passwords over the wire. What do you mean?
- pests 8y ago
  Real password based vs challenge response. With real password when you type your password into the ssh password prompt it then sends that password to the server. Challenge response is a method in which you usually encrypt or hash random server provided data. You send the hash. The server knows your password and can hash the data with it too. The hashes are compared not the password. In this method the password never leaves your machine. Replay attacks are prevented due to the server sending different data for you to hash on different login attempts.
  - e12e 8y ago
    Note also that requiring a password for sudo might have some issues, as the password is sent over the ssh connection as you type. I'm not sure what the state of the art is wrt counting and guessing characters - or if mossh makes the problem worse - or helps. For the general idea, see: http://www.securiteam.com/securitynews/5KP0O0A3PU.html http://www.securiteam.com/securitynews/5KP0O0A3PU.html Does anyone know of recent work on passively attacking interactive ssh in order to guess what's being typed? I could see machine learning helping here, given the ability to observe enough sessions to form a training set...
    - e12e 8y ago
      Of course, with Pam for sudo authentication you could use otp, u2f with or in place of a password.

jwilk 8y ago

> Incorrectly configured SSH will send passwords over the wire. What do you mean?

pests 8y ago
Real password based vs challenge response. With real password when you type your password into the ssh password prompt it then sends that password to the server. Challenge response is a method in which you usually encrypt or hash random server provided data. You send the hash. The server knows your password and can hash the data with it too. The hashes are compared not the password. In this method the password never leaves your machine. Replay attacks are prevented due to the server sending different data for you to hash on different login attempts.
- e12e 8y ago
  Note also that requiring a password for sudo might have some issues, as the password is sent over the ssh connection as you type. I'm not sure what the state of the art is wrt counting and guessing characters - or if mossh makes the problem worse - or helps. For the general idea, see: http://www.securiteam.com/securitynews/5KP0O0A3PU.html http://www.securiteam.com/securitynews/5KP0O0A3PU.html Does anyone know of recent work on passively attacking interactive ssh in order to guess what's being typed? I could see machine learning helping here, given the ability to observe enough sessions to form a training set...
  - e12e 8y ago
    Of course, with Pam for sudo authentication you could use otp, u2f with or in place of a password.