use of the term "verifier" with SCRAM

On 14/08/2019 08:59, Peter Eisentraut wrote:

I'm confused by how the code uses the term "verifier" in relation to SCRAM.

ISTM that the code uses the term as meaning whatever is or would be
stored in pg_auth.rolpassword.

I don't see this usage supported in the RFCs. In RFC 5802,

verifier = "v=" base64
;; base-64 encoded ServerSignature.

where

ServerSignature := HMAC(ServerKey, AuthMessage)
ServerKey := HMAC(SaltedPassword, "Server Key")
AuthMessage := client-first-message-bare + "," +
server-first-message + "," +
client-final-message-without-proof

whereas what is stored in rolpassword is

SCRAM-SHA-256$<iterations>:<salt>$<storedkey>:<serverkey>

where

StoredKey := H(ClientKey)
ClientKey := HMAC(SaltedPassword, "Client Key")

So while these are all related, I don't think it's accurate to call what
is in rolpassword a SCRAM "verifier".

Huh, you're right.

RFC 5803 is titled "Lightweight Directory Access Protocol (LDAP) Schema
for Storing Salted Challenge Response Authentication Mechanism (SCRAM)
Secrets". Following that, I think calling the contents of rolpassword a
"secret" or a "stored secret" would be better.

RFC 5802 uses the term "Authentication information". See section "2.1
Terminology":

o Authentication information: Information used to verify an identity
claimed by a SCRAM client. The authentication information for a
SCRAM identity consists of salt, iteration count, "StoredKey" and
"ServerKey" (as defined in the algorithm overview) for each
supported cryptographic hash function.

But I agree that "secret", as used in RFC5803 is better.

- Heikki

On 2019-08-14 10:41, Heikki Linnakangas wrote:

RFC 5803 is titled "Lightweight Directory Access Protocol (LDAP) Schema
for Storing Salted Challenge Response Authentication Mechanism (SCRAM)
Secrets". Following that, I think calling the contents of rolpassword a
"secret" or a "stored secret" would be better.

But I agree that "secret", as used in RFC5803 is better.

Here is my proposed patch to adjust this.

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

On Thu, Oct 10, 2019 at 09:08:37AM +0200, Peter Eisentraut wrote:

Here is my proposed patch to adjust this.

Looks fine to me reading through. I think that you are right to not
change the descriptions in build_server_final_message(), as that's
described similarly in RFC 5802. By renaming scram_build_verifier()
to scram_build_secret() you are going to break one of my in-house
extensions. I am using it to register for a user SCRAM veri^D^D^D^D
secrets with custom iteration and salt length :)
--
Michael

On 2019-10-10 10:03, Michael Paquier wrote:

On Thu, Oct 10, 2019 at 09:08:37AM +0200, Peter Eisentraut wrote:

Here is my proposed patch to adjust this.

Looks fine to me reading through. I think that you are right to not
change the descriptions in build_server_final_message(), as that's
described similarly in RFC 5802.

committed

By renaming scram_build_verifier()
to scram_build_secret() you are going to break one of my in-house
extensions. I am using it to register for a user SCRAM veri^D^D^D^D
secrets with custom iteration and salt length :)

OK, that should be easy to work around with an #ifdef or two.

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services