3 ms·

While that may be true, an attacker would not initially know the scheme, but with a list of passwords would instantly notice the To01n so I could argue that tha

While that may be true, an attacker would not initially know the scheme, but with a list of passwords would instantly notice the To01n so I could argue that that is in fact the weakest part of this procedure, which leaves them with the 7 letters remaining: mc ds and com - but it would not be obvious from the outset how to calculate these nor that we were even using a scheme. So assuming the shared portion of the password is compromised I assume it would be 64 bits of entropy? (I'm not overly experienced with calculating that so I assumed you did 2 x 2 ^ numberofcharacters, whereas in this case we have 6 characters, doubling the entropy.) While this may not be a massive amount, bare in mind these are temporary passwords and last only a week or two before we sign off on a project and the client has access.

jgrahamc 14y ago
Ignoring the fact that I usually go by Kerckhoff's Principle and would assume that an attacker knows the scheme. Let's imagine the situation where two passwords are compromised. 1. As you say the To01n would be static and I would assume that this would be the same in both 2. If both sites are .com then I'll spot the com in both and so I'll end up assuming there are 4 characters to attack. And they appear to be lowercase. 3. Or they are not both .com and assuming I'm not smart I think there are 7 or 8 characters to attack (all lowercase). In case #2 picking 4 characters from lowercase ASCII has an bit strength of 4.7 bits per character and so 18 bits. Very weak. In case #3 picking 8 characters from lowercase ASCII has a bit strength of 38 bits. Still weak.
- shanelja 14y ago
  Thanks for the reply, would you be able to supply a decent link or a quick explanation of how you calculate that? I'm more than happy to admit I'm wrong when I am - the scheme is to make sure all client passwords are different, though not in any way secure against an intelligent attacker - but I am keen to learn more about this, so that as with every discussion on HN, I walk away with a little more knowledge and a little less stupidity.
  - jgrahamc 14y ago
    http://en.wikipedia.org/wiki/Password_strength http://en.wikipedia.org/wiki/Password_strength

jgrahamc 14y ago

Ignoring the fact that I usually go by Kerckhoff's Principle and would assume that an attacker knows the scheme. Let's imagine the situation where two passwords are compromised. 1. As you say the To01n would be static and I would assume that this would be the same in both 2. If both sites are .com then I'll spot the com in both and so I'll end up assuming there are 4 characters to attack. And they appear to be lowercase. 3. Or they are not both .com and assuming I'm not smart I think there are 7 or 8 characters to attack (all lowercase). In case #2 picking 4 characters from lowercase ASCII has an bit strength of 4.7 bits per character and so 18 bits. Very weak. In case #3 picking 8 characters from lowercase ASCII has a bit strength of 38 bits. Still weak.

shanelja 14y ago
Thanks for the reply, would you be able to supply a decent link or a quick explanation of how you calculate that? I'm more than happy to admit I'm wrong when I am - the scheme is to make sure all client passwords are different, though not in any way secure against an intelligent attacker - but I am keen to learn more about this, so that as with every discussion on HN, I walk away with a little more knowledge and a little less stupidity.
- jgrahamc 14y ago
  http://en.wikipedia.org/wiki/Password_strength http://en.wikipedia.org/wiki/Password_strength