ZTP_verification_1.pv

(* FIDO FDO - version 1.1 *)

free ch:channel. 			(* Public channel *)
free ch_dev_man:channel [private].	(* Private channel between the Device and the Manufacturer*)
const P:bitstring.

type pkey.
type skey.
type result.

(* Asymmetric signature *)
fun pk(skey):pkey.
fun ok():result.
fun sign(bitstring, skey):bitstring.
reduc forall m:bitstring, sk:skey; checksign(sign(m, sk), m, pk(sk)) = ok().

(* Symmetric encryption *)
fun senc(bitstring, bitstring):bitstring.
reduc forall m:bitstring, shk:bitstring; sdec(senc(m, shk), shk) = m.

(* Hash function *)
fun hash(bitstring):bitstring.

(* Key derivation function *)
fun KDF(bitstring):bitstring.

(* HMAC *)
fun hmac(bitstring, bitstring):bitstring.

(* Scalar multiplication *)
fun pmult(bitstring, bitstring):bitstring.
fun plus(bitstring, bitstring):bitstring.
reduc forall R:bitstring, y:bitstring;
	emverify(R, pmult(R,y), pmult(P,y)) = ok().

(* AACKA ephimeral credentials *)
fun cre(bitstring):bitstring.
fun exp(bitstring, bitstring):bitstring.
equation forall x:bitstring, y:bitstring, B:bitstring;
	exp(exp(cre(B), x), y) = exp(exp(cre(B), y), x).

(* EVENTS *)
event EndProtocol().
event EndManufacturer().
event EndOwner().
event EndRendezvousServer().
event EndDevice().
event Test().
event OwnerValidOVDevCredentialsReceived(bitstring).
event ManufacturerValidOVDevCredentialsSent(bitstring).
event OwnerValidOVReceived(bitstring).
event ManufacturerValidOVSent(bitstring).
event RendezvousServerEndTO0(bitstring).
event OwnerInitTO0(bitstring).
event RendezvousServerEndTO1(bitstring).
event DeviceInitTO1(bitstring).
event RendezvousServerInitTO1(bitstring).
event DeviceEndTO1(bitstring).
event DeviceInitTO2(bitstring).
event FogNodeEndTO2(bitstring).

(* QUERIES *)

(* Secrey of the symmetric key shared between device and fog node - result. TRUE, the property holds *)
free squery:bitstring [private].
query attacker(squery).

(* Strong secrey of the symmetric key shared between device and fog node - result: TRUE, the property holds *)
noninterf squery.

(* Offline guessing attacks - result: TRUE, the property holds *)
weaksecret squery.

(* Phase -1: The Owner reeives the OV from the Manufacturer *)
(* Authentication of the Manufacturer OVCredentials: only the Manufacturer can have created valid CL-credentials - RESULT: true *)
query OVDevCredentials:bitstring; 
	event(OwnerValidOVDevCredentialsReceived(OVDevCredentials)) ==> event(ManufacturerValidOVDevCredentialsSent(OVDevCredentials)).
(* Injective version - RESULT: false, OV can be changed while maintaining the same credentials (see below) *)
query OVDevCredentials:bitstring; 
	inj-event(OwnerValidOVDevCredentialsReceived(OVDevCredentials)) ==> inj-event(ManufacturerValidOVDevCredentialsSent(OVDevCredentials)).
(* Authentication of the Manufacturer: OV - RESULT: false, OV can be changed during the transit, Owner needs pkman to check integrity *)
query OV:bitstring; event(OwnerValidOVReceived(OV)) ==> event(ManufacturerValidOVSent(OV)).
	
(* TO0 protocol *)
(* Authentication of the Owner to the Server - RESULT: true *)
query m:bitstring; event(RendezvousServerEndTO0(m)) ==> event(OwnerInitTO0(m)).
(* The protocol does not provide mechanisms to verify authentication of the Server to the Owner *)

(* TO1 protocol *)
(* Authentication of the Device to the Server - RESULT: false, there is no device authentication to the server in TO1, device simply sends its guid *)
query guid:bitstring; event(RendezvousServerEndTO1(guid)) ==> event(DeviceInitTO1(guid)).
(* Authentication of the Server to the Device - RESULT: false, the attacker can intercept the message from Owner-Server and send this message to the Device *)
query m:bitstring; event(DeviceEndTO1(m)) ==> event(RendezvousServerInitTO1(m)).
(* Authentication of the Owner to the Device: only a valid Owner can have computed a valid kenc and kmac. The device checks also proof of possession of OV
   RESULT: true *)
query m:bitstring; inj-event(DeviceEndTO1(m)) ==> inj-event(OwnerInitTO0(m)).

(* TO2 protocol *)
(* Authentication of the Device to the FogNode - RESULT: true *)
query m:bitstring; event(FogNodeEndTO2(m)) ==> event(DeviceInitTO2(m)).


query event(EndProtocol()).




let Device(spkman:pkey) =

	(* DI PROTOCOL *)

	(* Receive CL-credentials and f (private key) from the Manufacturer *)
	in(ch_dev_man, m:bitstring);
	let (clcre:bitstring, OVHeader:bitstring, f:bitstring) = m in
	let (guid:bitstring, iprendezvous:bitstring, pkman:pkey, hashDevCertChain:bitstring) = OVHeader in

	(* Compute hash of the OVHeader *)
	let hashOVHeader = hash(OVHeader) in

	(* T01 protocol *)

	(* Message for the Rendezvous server *)
	let mtoserver = (iprendezvous, guid) in

	event DeviceInitTO1(guid);
	out(ch, mtoserver);

	in(ch, mserver:bitstring);
	
	let (mowner:bitstring, signature:bitstring) = mserver in
	let (guid'':bitstring, U':bitstring, OV':bitstring, tag':bitstring, encblob':bitstring) = mowner in
	
	(* Validate OV' *)
	let (OVHeader':bitstring, OVDevCertChain':bitstring, OVEntry':bitstring) = OV' in
	let (guid':bitstring, iprendezvous':bitstring, pkman':pkey, hashDevCertChain':bitstring) = OVHeader' in
	let (OVEntryPayload':bitstring, signman':bitstring) = OVEntry' in
	let (pkown':pkey, hashHeader':bitstring) = OVEntryPayload' in 

	(* Check hash OVHeader *)
	if hashOVHeader = hash(OVHeader') then		(* OVHeader matches the original one, so also guid, iprendezvous, pkman, hashDevCertChain *)
	(* Check hash on DevCertChain *)
	if hashDevCertChain = hash(OVDevCertChain') then
	(* Check signature in the last entry *)
	if checksign(signman', OVEntryPayload', pkman') = ok() then
	(* Check if pkman in the OVHeader is correct *)
	if pkman = pkman' then

	(* Received a correct OV *)
	
	(* Verify the signature on mowner *)
	if checksign(signature, mowner, pkown') = ok() then

	(* Finish AACKA *)
	let Z = exp(U', f) in
	
	let kenc = KDF(Z) in
	let kmac = KDF(KDF(Z)) in

	(* Extract blob *)
	let blob = sdec(encblob', kenc) in
	(* Verify tag *)
	if tag' = hmac(blob, kmac) then

	event DeviceEndTO1(mowner);

	(* TO2 protocol *)

	(* Open blob *)
	let (ipfognode:bitstring, kfogdevice:bitstring) = blob in

	let mfognode = (guid, ipfognode, senc(squery, kfogdevice)) in

	event DeviceInitTO2(mfognode);

	out(ch, mfognode);

	event EndDevice()
	.


let Manufacturer(skman:skey, guid:bitstring, iprendezvous:bitstring, pkown:pkey, x:bitstring, y:bitstring) =

	(* DI PROTOCOL *)
	
	(* Create Device CL-credentials *)
	new r:bitstring;
	new f:bitstring;

	(* Generate randomized credentials *)
	let R = pmult(P, r) in
	let S = pmult(R, y) in
	let T = pmult(plus(R, exp(cre(pmult(pmult(P, r), y)), f)), x) in
	let W = exp(cre(pmult(pmult(P, r), y)), f) in

	let clcre = (R, S, T, W) in

	(* Create Ownership Voucher *)
	let OVDevCertChain = clcre in
	let OVHeader = (guid, iprendezvous, pk(skman), hash(OVDevCertChain)) in
	let OVEntryPayload = (pkown, hash(OVHeader)) in
	let OVEntry = (OVEntryPayload, sign(OVEntryPayload, skman)) in
	let OV = (OVHeader, OVDevCertChain, OVEntry) in

	(* Send CL-credentials, OVHeader and f (private seed) to the Device *)
	(* We assume the DI protocol happens in a safe environment (e.g., manufacturing house) *)
	out(ch_dev_man,  (clcre, OVHeader, f));

	(* Send OV to the Owner *)
	event ManufacturerValidOVDevCredentialsSent(OVDevCertChain);
	event ManufacturerValidOVSent(OV);
	out(ch, OV);

	event EndManufacturer()
	.
	


let Owner(kfog:bitstring, skown:skey, ipfognode:bitstring, X:bitstring, Y:bitstring) = 
	
	(* Receive OV from the Manufacturer *)
	in(ch, OV:bitstring);

	(* Validate OV *)
	let (OVHeader:bitstring, OVDevCertChain:bitstring, OVEntry:bitstring) = OV in
	let (R:bitstring, S:bitstring, T:bitstring, W:bitstring) = OVDevCertChain in

	(* Check bilinear pairings *)
	(* Verify h(R, Y) == h(S,P) *)
	if emverify(R, S, Y) = ok() then
	
	(* Verify h(R+W, X) = h(T, P) *)
	if emverify(plus(R, W), T, X) = ok() then 

	(* CL-Credentials are valid (only Manufacturer can have computed them becuase it is the only one that knows x and y) *)

	(* Ownership Voucher internal verification *)
	let (guid:bitstring, iprendezvous:bitstring, pkman:pkey, hashDevCertChain:bitstring) = OVHeader in
	let (OVEntryPayload:bitstring, signature:bitstring) = OVEntry in
	let (pkown:pkey, hashHeader:bitstring) = OVEntryPayload in 

	(* Check hash hashDevCertChain *)
	if hashDevCertChain = hash(OVDevCertChain) then
	(* Check correct Owner pk in the last Entry *)
	if pkown = pk(skown) then
	(* Check hash hashHeader in the Entry *)
	if hashHeader = hash(OVHeader) then
	(* Check signature in the last Entry *)
	if checksign(signature, OVEntryPayload, pkman) = ok() then
	
	event OwnerValidOVDevCredentialsReceived(OVDevCertChain);
	event OwnerValidOVReceived(OV);
	
	(* NOTE: here we don't check if the pkman is the correct key, it will be done by the Rendezvous Server *)

	(* Finish AACKA *)
	new secOwner:bitstring;
	let Z = exp(W, secOwner) in
	let U = exp(cre(S), secOwner) in

	let kenc = KDF(Z) in
	let kmac = KDF(KDF(Z)) in	
	let kfogdevice = KDF((kfog, guid)) in

	let blob = (ipfognode, kfogdevice) in
	let encblob = senc(blob, kenc) in
	let tag = hmac(blob, kmac) in

	(* TO0 protocol *)

	(* Message for the Rendezvous Server *)
	let mserver = (guid, U, OV, tag, encblob) in
	let signmserver = sign(mserver, skown) in

	event OwnerInitTO0(mserver);
	out(ch, (iprendezvous, mserver, signmserver));

	event EndOwner()
	.


let FogNode(kfog:bitstring, ip:bitstring) = 

	(* TO2 protocol *)
	
	(* Fog node waitinf for a message from the device *)
	in(ch, mdevice:bitstring);

	let (guid:bitstring, ipfognode:bitstring, encm:bitstring) = mdevice in
	
	(* Check correct IP *)
	if ipfognode = ip then
	
	(* Compute kfogdevice *)
	let kfogdevice = KDF((kfog, guid)) in

	let squery' = sdec(encm, kfogdevice) in

	if squery' = squery then

	event FogNodeEndTO2(mdevice);

	(* END PROTOCOL *)
	event EndProtocol()
	.


let RendezvousServer(ip:bitstring, pkman:pkey) =
	
	(* TO0 protocol *)
	(* Receive the message from the Owner *)
	in(ch, mowner:bitstring);

	let (iprendezvous:bitstring, m:bitstring, signature:bitstring) = mowner in
	let (guid:bitstring, U:bitstring, OV:bitstring, tag:bitstring, encblob:bitstring) = m in

	(* Check IP server is correct *)
	if iprendezvous = ip then
	let (OVHeader:bitstring, OVDevCertChain:bitstring, OVEntry:bitstring) = OV in
	let (OVEntryPayload:bitstring, signman:bitstring) = OVEntry in
	let (pkown:pkey, hashHeader:bitstring) = OVEntryPayload in
	let (guid':bitstring, iprendezvous':bitstring, pkman':pkey, hashDevCertChain':bitstring) = OVHeader in

	(* Extract the pkown and verify signature on the message *)
	if checksign(signature, m, pkown) = ok() then
	if guid = guid' then
	if iprendezvous' = iprendezvous then

	(* Ownership Voucher internal verification *)
	(* Check hash on DevCertChain *)
	if hashDevCertChain' = hash(OVDevCertChain) then
	(* Check hash on OVHeader *)
	if hashHeader = hash(OVHeader) then
	(* Check signature in the last entry *)
	if checksign(signman, OVEntryPayload, pkman') = ok() then
	(* Check if pkman in the OVHeader is correct *)
	(* NOTE: We assume pkman is trusted by the Rendezvous Server *)
	if pkman = pkman' then
		
	(* The Owner is the correct "owner" of the OV *)
	(* Save the correspondance -> guid, OV, tag, encblob *)
	event RendezvousServerEndTO0(m);

	(* TO1 protocol *)
	(* Rendezvous server waiting for a connection from Device *)
	in(ch, mdevice:bitstring);

	let (iprendezvous'':bitstring, guid'':bitstring) = mdevice in

	event RendezvousServerInitTO1(m);
	
	(* TODO: the device should authenticate to the server *)

	if iprendezvous'' = ip then
	if guid'' = guid then
	
	event RendezvousServerEndTO1(guid'');
	out(ch, (m, signature));
	
	event EndRendezvousServer()
	.
	
		

process

	(* Device guid *)
	new guid:bitstring;
	
	(* AACKA SETUP *)
	new x:bitstring;
	new y:bitstring;
	let X = pmult(P, x) in
	let Y = pmult(P, y) in

	(* Rendezvous Server IP address *)
	new iprendezvous:bitstring;

	(* Fog Node IP address *)
	new ipfognode:bitstring;

	(* Owner key pair *)
	new skown:skey;
	let pkown = pk(skown) in

	(* Manufacturer key pair *)				(* We assume the manufacturer is trusted by the Rendezvous Server *)
	new skman:skey;						(* Otherwise we can add a CA*)
	let pkman = pk(skman) in

	(* Kfog shared between the Owner and FogNode *)
	new kfog:bitstring;
	
	
	Device(pkman) | Manufacturer(skman, guid, iprendezvous, pkown, x, y) | !Owner(kfog, skown, ipfognode, X, Y) 
		| !FogNode(kfog, ipfognode) | !RendezvousServer(iprendezvous, pkman)