On 2012-02-16 04:18, Adrian Klaver wrote:
> When you alter the role name you are told the password has been cleared. It
> would be fairly easy to wrap the rename and the setting of the password in a
> transaction.
But this shouldn't be necessary. I don't get why the salt has to be
linked with the role name. This problem would be a non-issue with a
random salt.
> Encrypting Passwords Across A Network
> The MD5 authentication method double-encrypts the password on the client before
> sending it to the server. It first MD5-encrypts it based on the user name, and
> then encrypts it based on a random salt sent by the server when the database
> connection was made. It is this double-encrypted value that is sent over the
> network to the server. Double-encryption not only prevents the password from
> being discovered, it also prevents another connection from using the same
> encrypted password to connect to the database server at a later time.
I must be missing something here... the *client* applies the salt,
because he knows it, and then sends the salted hash? Then what's the
point of using a salt at all?
The second "encryption" layer just protects the communication channel,
and has nothing to do with what I'm concerned with. It's redundant if a
secure channel already exists (SSL or TLS or whatever). But I have to
admit that I didn't read the source for this part, so I may indeed be
missing something.
> Encrypting Data Across A Network
> SSL connections encrypt all data sent across the network: the password, the
> queries, and the data returned. The pg_hba.conf file allows administrators to
> specify which hosts can use non-encrypted connections (host) and which require
> SSL-encrypted connections (hostssl). Also, clients can specify that they connect
> to servers only via SSL. Stunnel or SSH can also be used to encrypt
> transmissions.
Just so. But this still leaves the question why the hashing/salting in
PG works differently than just about anywhere else. The client isn't
supposed to know or care about the salt. Normally, salting is a purely
server-side protection against attackers who would generate lookup
tables for common password hashes, in the hope of getting their hands on
a list of actual password hashes. If the salt is as predictable as a
user/role name, it's nowhere near good enough to protect against such an
attack. At best, it might increase the size of the lookup tables by 2 or
3 orders of magnitude, which is no challenge at all with a good word
list ("backup", "dba", "slony", "postgres", "master", ...). Compare this
to a 4-byte random salt.
regards,
stefan
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