.TH AUTHSRV 6
.SH NAME
-authsrv, p9any, p9sk1, p9sk2 \- authentication protocols
+authsrv, p9any, p9sk1, dp9ik \- authentication protocols
.SH DESCRIPTION
This manual page describes
the protocols used to authorize connections, confirm the identities
holds for each public machine, such as a CPU server or
file server, the name of the authentication server that machine uses.
.PP
-Each machine contains three values important to authentication; a 56-bit DES
-key, a 28-byte authentication ID, and a 48-byte authentication domain name.
+Each machine contains four values important to authentication; a 56-bit DES
+key, a 128-bit AES key, a 28-byte authentication ID, and a 48-byte authentication
+domain name.
The ID is a user name and identifies who is currently responsible for the
kernel running on that machine.
The domain name identifies the machines across which the ID is valid.
.I passtokey
(see
.IR authsrv (2))
-into a 56-bit DES key and saved in memory.
+into a 56-bit DES and 128-bit AES keys and saved in memory.
The authentication domain is set to the null string.
If possible,
.I factotum
a nonce key created for a ticket
.RB ( key )
.TP
-.IR K { m }
+.I K{m}
message
.I m
encrypted with key
client's desired ID on server
.RB ( uid ,
.BR suid )
+.TP
+.I YAc
+client → AS DH public key
+.TP
+.I YBc
+AS → client DH public key
+.TP
+.I YAs
+server → AS DH public key
+.TP
+.I YBs
+AS → server DH public key
+.TP
+.I RNc
+client's 32-byte random string
+.TP
+.I RNs
+server's 32-byte random string
.PD
.PP
The parenthesized names are the ones used in the
.IR AuthChap ,
.IR AuthMSchap ,
.IR AuthCram ,
+.IR AuthVNC ,
and
-.IR AuthVNC
+.IR AuthPAK
.RB ( type )
are defined in
.BR <authsrv.h> ,
.PP
The protocol to obtain a ticket pair is:
.TP
-.IR C \(-> A
+.I C→A:
.IR AuthTreq ,
.IR IDs ,
.IR DN ,
.IR CHs ,
.IR IDc ,
.IR IDr
-.sp -\n(PDu
.TP
-.IR A \(-> C
+.I A→C:
.IR AuthOK ,
.IR Kc { AuthTc ,
.IR CHs ,
allows a client and server to authenticate each other.
The protocol is:
.TP
-.IR C \(-> S
+.I C→S:
.I CHc
.br
The client starts by sending a random challenge to the server.
.TP
-.IR S \(-> C
+.I S→C:
.IR AuthTreq ,
.IR IDs ,
.IR DN ,
id and authentication domain along with its own
random challenge.
.TP
-.IR C \(-> S
+.I C→S:
.IR Ks { AuthTs ,
.IR CHs ,
.IR IDc ,
.IR CHs
in the authenticator avoids replay attacks.)
.TP
-.IR S \(-> C
+.I S→C:
.IR Kn { AuthAs ,
.IR CHc }
.br
.I Kn
and therefore
.I Ks .
-.PD
.PP
-.I P9sk2
-is an older variant of
+The 64-bit shared secret
+.I Kn
+is used as the session secret.
+.SS "Password authenticated key exchange"
+Initially, the server and client keys
+.I Ks
+and
+.I Kc
+where equivalent to the password derived 56-bit DES keys, which
+made the encrypted tickets subject to offline dictionary attacks
+and provided too small a key space against brute force attacks
+on current hardware.
+.PP
+The
+.I AuthPAK
+protocol is used to establish new 256-bit random keys with the
+AS for
+.I Ks
+and
+.I Kc
+before each ticket request on the connection.
+.PP
+The protocol is based on SPAKE2EE, where a hash of the user's secret
+is used to encypt the public keys of a Elliptic-Curve Diffie-Hellman
+key exchange. The user's
+.I ID
+and 128-bit AES key is hashed and mapped (using Elligator2)
+into two curve points
+.I PM
+and
+.IR PN ,
+called the
+.IR pakhash .
+Both sides generate a random number
+.IR xa / xb
+and make the public keys
+.IR YA / YB
+as:
+.IR YA = xa*G+PM ,
+.IR YB = xb*G+PN .
+After the public keys have been exchanged, each side calculates the
+shared secret as:
+.IR Z = xa*(YB-PN) = xb*(YA-PM) .
+The shared secret
+.I Z
+is then hashed with the transmitted public keys
+.IR YA | YB
+producing the 256-bit
+.IR pakkey .
+.PP
+The
+.I pakkey
+is then used in place of
+.I Ks
+and
+.I Kc
+to authenticate and encrypt tickets from the AS using
+Chacha20/Poly1305 AEAD for the next following
+request made on the connection.
+.PP
+The protocol (for
+.IR AuthTreq )
+to establish keys
+.I Ks
+and
+.I Kc
+with the AS for
+.I IDs
+and
+.I IDc
+is:
+.TP
+.I C→A:
+.IR AuthPAK ,
+.IR IDs ,
+.IR DN ,
+.IR CHs ,
+.IR IDc ,
+.IR IDr ,
+.IR YAs ,
+.I YAc
+.TP
+.I A→C:
+.IR AuthOK ,
+.IR YBs ,
+.I YBc
+.PP
+The protocol (for
+.IR AuthApop ,
+.IR AuthChap ...)
+to establish a single server key
+.I Ks
+for
+.IR IDs :
+.TP
+.I C→A:
+.IR AuthPAK ,
+.IR \- ,
+.IR DN ,
+.IR CHs ,
+.IR IDs ,
+.IR IDc ,
+.I YAs
+.TP
+.I A→C:
+.IR AuthOK ,
+.I YBs
+.PP
+The protocol (for
+.IR AuthPass )
+to establish a single client key
+.I Kc
+for
+.IR IDc :
+.TP
+.I C→A:
+.IR AuthPAK ,
+.IR \- ,
+.IR \- ,
+.IR CHc ,
+.IR \- ,
+.IR IDc ,
+.I YAc
+.TP
+.I A→C:
+.IR AuthOK ,
+.I YBc
+.SS "Dp9ik"
+The
+.I dp9ik
+protocol is an extended version of
.I p9sk1
-used only when connecting to pre-9P2000 remote
-execution services.
-It omits the first message and last
-messages and therefore does not
-authenticate the server to the client.
+that adds the random strings
+.I RNc
+and
+.I RNs
+in the
+.I authenticator
+messages for the session key derivation and uses the
+password authenticated key exchange as described above
+to derive the ticket encryption keys
+.I Ks
+and
+.IR Kc :
+.TP
+.I C→S:
+.I CHc
+.br
+The client starts by sending a random challenge to the server.
+.TP
+.I S→C:
+.IR AuthPAK ,
+.IR IDs ,
+.IR DN ,
+.IR CHs ,
+.IR \- ,
+.IR \- ,
+.IR YAs
+.br
+The server generates a new public key
+.I YAs
+and replies with a
+.I AuthPAK
+request giving its
+.I IDs
+and authentication domain
+.I DNs
+along with its own random challenge
+.I CHs
+and its public key
+.IR YAs .
+.TP
+.I C→S:
+.IR YBs ,
+.IR Ks { AuthTs ,
+.IR CHs ,
+.IR IDc ,
+.IR IDr ,
+.IR Kn },
+.IR Kn { AuthAc ,
+.IR CHs ,
+.IR RNc }
+.br
+The client generates its own public key
+.I YAc
+and adds it along with
+.I IDc
+and
+.I IDr
+to the
+.I AuthPAK
+request and obtains the public keys
+.I YBs
+and
+.I YBc
+from the AS response. At this point, client and AS
+have completed ther authenticated key exchange and
+derive
+.I Kc
+as described above.
+Then the client requests a ticket pair using the same
+message but with
+.I AuthPAK
+type changed to
+.IR AuthTreq .
+It decrypts his ticket with
+.I Kc
+extracting the shared secret
+.IR Kn .
+The client relays the server's
+.I YBs
+and ticket along with an
+.IR authenticator ,
+the
+.I AuthAc
+message.
+The server finishes his authenticated key exchange
+using
+.I YBs
+and derives
+.I Ks
+to decrypt his ticket to extract the shared secret
+.IR Kn .
+When the decryption of the clients authenticator using
+.I Kn
+is successfull then this proves to the server that the
+client knows
+.I Kn
+and is therefore allowed to authenticate as
+.IR IDr .
+The random string
+.I RNc
+is used in the derivation of the session secret.
+.TP
+.I S→C:
+.IR Kn { AuthAs ,
+.IR CHc ,
+.IR RNs }
+.br
+The server replies with its own authenticator,
+proving to the client that it also knows
+.I Kn
+and contributes its random string
+.IR RNs
+for the session secret.
+.PP
+The 2048-bit session secret is derived with HKDF-SHA256 hashing the
+concatenated random strings
+.IR RNc | RNs
+with the the shared secret key
+.IR Kn .
.SS "P9any
.I P9any
is the standard Plan 9 authentication protocol.
.PP
The negotiation protocol is:
.TP
-.IR S \(-> C
+.I S→C:
.B v.2
.IB proto@authdom
.IB proto@authdom
.I ...
-.sp -\n(PDu
.TP
-.IR C \(-> S
+.I C→S:
.I proto
.I dom
-.sp -\n(PDu
.TP
-.IR S \(-> C
+.I S→C:
.B OK
.PP
Each message is a NUL-terminated UTF string.
and
.IR attach (5)).
Other services, such as
-.IR cpu (1)
+.IR cpu (1),
+.IR exportfs (4)
and
-.IR exportfs (4),
+.IR tlssrv (8)
run
.I p9any
-over the network and then
-use
-.I Kn
-to derive an
+over the network and then use the session secret to derive an
.IR ssl (3)
+or
+.IR tls (3)
key to encrypt the rest of their communications.
.SS "Password Change
Users connect directly to the AS
to change their passwords.
The protocol is:
.TP
-.IR C \(-> A
+.I C→A:
.IR AuthPass ,
-.IR IDc ,
-.IR DN ,
+.IR \- ,
+.IR \- ,
.IR CHc ,
-.IR IDc ,
+.IR \- ,
.IR IDc
.br
The client sends a password change ticket request.
.TP
-.IR A \(-> C
+.I A→C:
.IR Kc { AuthTp ,
.IR CHc ,
.IR IDc ,
encrypted with the client's key
.IR Kc
.TP
-.IR C \(-> A
+.I C→A:
.IR Kn { AuthPass ,
.IR old ,
.IR new ,
.IR secret ,
the password used for non-Plan 9 authentications.
.TP
-.IR A \(-> C
+.I A→C:
.I AuthOK
or
.IR AuthErr ,
.I AuthErr
message may be substituted.
.de Ok
-.sp -\n(PDu
.TP
-.IR A \(-> S
+.I A→S:
.IR AuthOK ,
-.IR Ks { \\$1 ,
-.IR IDs ,
-.IR DN ,
+.IR Ks { AuthTs ,
.IR CHs ,
-.IR IDs ,
+.IR IDc ,
.IR IDc ,
.IR Kn },
-.IR Kn { AuthTs ,
+.IR Kn { AuthAc ,
.IR CHs }
..
.PP
.TP
-.IR S \(-> A
+.I S→A:
.IR AuthChal ,
-.IR IDs ,
+.IR \- ,
.IR DN ,
.IR CHs ,
.IR IDs ,
.IR IDc
-.sp -\n(PDu
.TP
-.IR A \(-> S
+.I A→S:
.IR AuthOK ,
.IR challenge
-.sp -\n(PDu
.TP
-.IR S \(-> A
+.I S→A:
.IR response
-.Ok AuthChal
+.Ok
.IP
This protocol allows the use of
handheld authenticators such as SecureNet
keys and SecureID tokens
in programs such as
-.IR ssh (1)
+.I telnetd
and
.I ftpd
(see
Users not listed are assumed to have the
same id in both places.
.TP
-.IR S \(-> A
-AuthApop ,
-.IR IDs ,
+.I S→A:
+.IR AuthApop ,
+.IR \- ,
.IR DN ,
.IR CHs ,
-.IR \- ,
+.IR IDs ,
.IR \-
-.sp -\n(PDu
.TP
-.IR A \(-> S
+.I A→S:
.IR AuthOKvar ,
.IR challenge
-.sp -\n(PDu
.TP
-.IR S \(-> A
-AuthApop ,
-.IR IDs ,
+.I S→A:
+.IR AuthApop ,
+.IR \- ,
.IR DN ,
.IR CHs ,
-.IR IDc ,
+.IR IDs ,
.IR IDc ;
hexadecimal MD5 checksum
-.Ok AuthApop
+.Ok
.IP
This protocol implements APOP authentication
(see
in
.IR sechash (2)).
.TP
-.IR S \(-> A
+.I S→A:
.IR AuthChap ,
-.IR IDs ,
+.IR \- ,
.IR DN ,
.IR CHs ,
-.IR \- ,
+.IR IDs ,
.IR \-
-.sp -\n(PDu
.TP
-.IR A \(-> S
+.I A→S:
.I challenge
-.sp -\n(PDu
.TP
-.IR S \(-> A
+.I S→A:
.IR pktid ,
.IR IDc ,
.IR response
-.Ok AuthChap
+.Ok
.IP
This protocol implements CHAP authentication
(see
in
.BR <authsrv.h> .
.TP
-.IR S \(-> A
+.I S→A:
.IR AuthMSchap ,
-.IR IDs ,
+.IR \- ,
.IR DN ,
.IR CHs ,
-.IR \- ,
+.IR IDs ,
.IR \-
-.sp -\n(PDu
.TP
-.IR A \(-> S
+.I A→S:
.I challenge
-.sp -\n(PDu
.TP
-.IR S \(-> A
+.I S→A:
.IR IDc ,
.IR lm-response ,
.IR nt-response
-.Ok AuthMschap
+.Ok
.IP
This protocol implements Microsoft's MS-CHAP
authentication
in
.BR <authsrv.h> .
.TP
-.IR S \(-> A
+.I S→A:
.IR AuthVNC ,
-.IR IDs ,
+.IR \- ,
.IR DN ,
.IR CHs ,
.IR IDs ,
.IR IDc
-.sp -\n(PDu
.TP
-.IR A \(-> S
+.I A→S:
.IR AuthOKvar ,
.I challenge
-.sp -\n(PDu
.TP
-.IR S \(-> A
+.I S→A:
.I response
.Ok
.IP
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