Non-PKI Methods for Public Key Distribution Authors: Mohammad Peyavian, Allen Rogins ky and Nevenko Zunic Source: Computers & Security, Vol.23, pp. 97-103, 2004. Adviser: Min-Shiang Hwang Speaker: Chun-Ta Li Date: 2004/10/28
Jan 12, 2016
Non-PKI Methods for Public Key Distribution
Authors: Mohammad Peyavian, Allen Roginsky and Nevenko ZunicSource: Computers & Security, Vol.23, pp.97-103, 2004.Adviser: Min-Shiang HwangSpeaker: Chun-Ta LiDate: 2004/10/28
Outline
• Introduction
• The first proposed scheme
• The second proposed scheme
• The third proposed scheme
• Conclusions
• Comments
Introduction
CA
Server
Client
1
23
2
1
3
• The X.509 PKI requires a huge and expensive infrastructure with complex operations.
Archived public key distribution without CA
Archived public key distribution without CA
Introduction (cont.)
• ID: client’s user id -- not a secret value
• PKc: initial public component of the client’s public key pair
• SKc: initial secret component of the client’s public key pair
• PKs: initial public component of the server’s public key pair
• SKs: initial secret component of the server’s public key pair
• EPK(B): data B encrypted with an asymmetric public key PK.
• ESK(B): data B signed by an asymmetric secret key SK.
The first proposed scheme
Client Server(1) generates (ID, PW)
(2) sends (ID, PW) to client
(3) sends ID, PKc, H(ID, PKc, PW) to server
(4) sends ID, PKs, H(ID, PKs, PW) to server
// PW used only once for authenticating the flows from the client and server
• Public key distribution
The first proposed scheme (cont.)
• The first scheme can be added to the top of current SSL implementations (PW-based authentication).– PWc: client generates a password– Client sends PWc to the server (e.g. on-line banking)
Client Server
(2) sends ID, ePKs(PWc), eSKc(H(ID, PWc)) to server
(1) generates PWc
The first proposed scheme (cont.)
Client Server
(1) sends ID, “SKc compromised”, eSKc(H(ID, “SKc compromised”) to server
• Public key change if client’s SKc is compromised
• The client and server do not do any further exchange
• Until the client generates and sends a new public key to server
• The sending of a new public key is done as “Public key distribution”
// If server public key is compromised, contrariwise
The first proposed scheme (cont.)
Client Server
(1) sends ID, new_PKc, eSKc(H(ID, new_PKc) to server
• Regular client public key change (periodically)
• Both the client and server start using the new client’s public key
• They won’t accept any message with the old public key
// If server generates a new public key, contrariwise
The second proposed scheme
– P: prime modulus for Diffie-Hellman algorithm
– Rc: generates random number from the client
– Rs: generates random number from the server
– D: Diffie-Hellman public key
– S: symmetric secret key derived from Diffie-Hellman algorithm
• Given that the client and server share an ID and PW– One-sided: Only the client needs to get the server’s public key (PKs).
– Two-sided: Both client and sever need to exchange public keys.
The second proposed scheme (cont.)
Client Server• Public key exchange protocol
(1) generates P, Rc and computes public key Dc Dc
= PWRc mod P
(2) sends ID, Dc, P to server
(3) computes public key Ds Ds = PWRs mod P
(4) computes symmetric secret key S S = DcRs mod P = PWRcRs mod P
(5) sends ID, [PKs], Ds, H(ID, Dc, P, [PKs], Ds, S) to client
(6) computes symmetric secret key S S = DsRc mod P = PWRcRs mod P
(7) verifies H(ID, Dc, P, [PKs], Ds, S) using the S value that is derived
(8) sends ID, [PKc], H(ID, PKs, Ds, [PKc], new_PW, S), [eS(new_PW)] to server
The second proposed scheme (cont.)
Client Server
(1) sends ID, “SKc compromised”, eSKc (H(ID, “SKc compromised”) to server
• Public key change if client secret key is compromised
• The client and server do not do any further exchange
• Until the client generates and sends a new public key to server
• The sending of a new public key is done as “Public key distribution”
// If server public key is compromised, contrariwise
The second proposed scheme (cont.)
Client Server
(1) sends ID, new_PKc, eS (H(ID, new_PKc) to server
• Regular client public key change (periodically)
• Both the client and server start using the new client’s public key
• They won’t accept any message with the old public key
// If server generates a new public key, contrariwise
The third proposed scheme
• Public key exchange protocol– Given that the client and server share an ID and PW
Client Server(1) sends ID, PKc, H(ID, PKc, PW, Rc) to server
(2) sends ID, PKs, H(ID, PKs, PW, Rs) to server
(3) sends ID, ePKs(Rc) to server
(4) sends ID, ePKc(Rs) to server
// PW used only once for authenticating the flows from the client and server
The third proposed scheme (cont.)
• The third scheme can be added to the top of current SSL implementations (PW-based authentication).– PWc: client generates a password– Client sends PWc to the server (e.g. on-line banking)
Client Server
(2) sends ID, ePKs(PWc, Rc), eSKc(H(ID, PWc, Rc)) to server
(1) generates PWc
Conclusions
• The proposed scheme can distribute the public key without CA.
• This paper is to present alternative simpler solutions to the X.509 PKI to save storage, bandwidth and to reduce the complexity of the operations.
Comments
• How to send the PKs and PKc to the client and the server in secure? (The first scheme)– Attacker can masquerade server and client to send the wr
ong PKs` (pair of SKs`) and wrong PKc` (pair of SKc`)– Attacker will require the PKc– Attacker will require the PWc , because of the client enc
rypt it by using the wrong PKs`
Comments (cont.)• Man-in-the-middle attack (The second scheme)
– Public key exchange protocol
Client Attacker Server(1) generates P, Rc and computes public key Dc Dc
= PWRc mod P
(2) sends ID, Dc`, P to server
(3) computes public key Ds Ds = PWRs mod P
(4) computes symmetric secret key S` S` = Dc`Rs mod P = PWRcRtRs mod P
(5) sends ID, [PKs], Ds`, H(ID, Dc, P, [PKs], Ds`, S`) to client
(6) computes symmetric secret key S S` = Ds`Rc mod P = PWRsRtRc mod P (7) verifies H(ID, Dc, P, [PKs], Ds`, S
`) using the S` value that is derived
(8) sends ID, [PKc], H(ID, PKs, Ds, [PKc], new_PW`, S`), [eS`(new_PW`)] to server
Dc` = DcRt = PWRcRt mod P
Ds` = DsRt = PWRsRt mod P
Comments (cont.)
• How to send the PKs and PKc to the client and the server in secure? (The third scheme)– Attacker can masquerade server and client to send the wr
ong PKs` (pair of SKs`) and wrong PKc` (pair of SKc`)– Attacker will require the PKc– Attacker will require the PWc , because of the client enc
rypt it by using the wrong PKs`
Thanks for your attention
Cryptanalysis of the first proposed scheme
Client Attacker Server(1) generates (ID, PW)
(2) sends (ID, PW) to client
(3`) sends ID, PKc`, H(ID, PKc`, PW) to server
(4`) sends ID, PKs`, H(ID, PKs`, PW) to server
// PW used only once for authenticating the flows from the client and server
• Public key distribution
(3) sends ID, PKc, H(ID, PKc, PW) to server
(4) sends ID, PKs, H(ID, PKs, PW) to server
Cryptanalysis of the first proposed scheme (cont.)
• The first scheme can be added to the top of current SSL implementations (PW-based authentication).– PWc`: attacker generates a password– Attacker sends PWc` to the server
Client Server
(2`) sends ID, ePKs(PWc`), eSKc`(H(ID, PWc`)) to server
(1) generates PWc without change
(2) sends ID, ePKs(PWc), eSKc(H(ID, PWc)) to server
Cryptanalysis of the third proposed scheme
• Public key exchange protocol– Given that the client and server share an ID and PW
Client Attacker Server
(1`) sends ID, PKc`, H(ID, PKc`, PW, Rc`) to server
(2`) sends ID, PKs`, H(ID, PKs`, PW, Rs`) to server
(3`) sends ID, ePKs(Rc`) to server
(4`) sends ID, ePKc(Rs`) to server
// PW used only once for authenticating the flows from the client and server
(1) sends ID, PKc, H(ID, PKc, PW, Rc) to server
(2) sends ID, PKs, H(ID, PKs, PW, Rs) to server
(3) sends ID, ePKs(Rc) to server
(4) sends ID, ePKc(Rs) to server
Cryptanalysis of the third proposed scheme (cont.)
• The third scheme can be added to the top of current SSL implementations (PW-based authentication).– PWc`: attacker generates a password– Attacker sends PWc` to the server
Client Attacker Server
(2`) sends ID, ePKs(PWc`, Rc`), eSKc`(H(ID, PWc`, Rc`)) to server
(1) generates PWc
(2) sends ID, ePKs(PWc, Rc), eSKc(H(ID, PWc, Rc)) to server
without change