Re: Saving and Encoding Passwords

["Robert I. Eachus" <eachus@mitre.org>]

Florian Weimer wrote:
 
> Do you need the passwords themselves, or do you want to check whether
> the password entered by the user is correct?  In the latter case, you
> should not store the password itself, but a cryptographic hash of it.
> It is considered close to impossible to recover the password from
> the hash value if the cryptographic hash function is one of the most
> commonly used and thoroughly analyzed (i.e. MD5 or SHA-1).
> 
> If your program needs the passwords themselves (for example, to
> authenticate itself with a POP mail server) and you don't want any user
> interaction, you can't get much security, because your software must
> be able to decrypt the passwords -- and so is a possible attacker.

    Hmmm... Cryptographic protocols--lots of fun!  If the idea is to
store multiple passwords for a single user in a fashion that allows the
user to enter a single password to access all acounts, the best idea
would be to use a hash of the user-entered password as a symmetric (say
3DES) key to decrypt the stored passwords.  (Of course you should
"whiten" the key by using say the SHA-1 hash of the user-entered
password as the ky.)  This way a particular user needs only to enter one
password to access multiple accounts, even if several people have access
to the stored data.

    One last point, you probably should store ALL information about the
accounts,
including the number of accounts an individual has, encoded using 3DES. 
The reason for this is that the user may not want others with access to
the same machine to know which accounts he has....
-- 

                                        Robert I. Eachus

with Standard_Disclaimer;
use  Standard_Disclaimer;
function Message (Text: in Clever_Ideas) return Better_Ideas is...