Chapter 6: Security of higher layers. (network security)

Transcription

1 Chapter 6: Security of higher layers (network security)

2 Outline TLS SET

3 1. TLS History of TLS SSL = Secure Socket Layer defined by Netscape normalized as TLS TLS = Transport Layer Security between TCP and the application use: HTTP, FTP, SMTP, telnet,... TLS = SSL v3.1

4 Services of TLS Security services authentication of the server (using certificates) confidentiality (symmetrical cryptography, key generated at the session creation) integrity (HMAC) optional client authentication non-replay (using a sequence number)

5 Services of TLS Other services transparency of higher protocols spontaneity: transparent connection to a new server, without prior knowledge

6 Sub-protocols of SSL Sub-protocols of SSL handshake: in charge of the negociation change cypher: in charge of changing the encryption algorithm alert: in charge of notification in case of alarms record: in charge of encryption

7 Mechanism Mechanism client sends a Hello with available encryption algorithms serveur sends a Hello with the chosen encryption algorithm, a certificate and a public key client verifies the certificate client sends a symmetrical key, encrypted with the public key of the server server retrieves the symmetrical key communication using the symmetrical key

8 SSL vs IPSec Advantages SSL does not require a modification of the TCP/IP stack SSL supports NAT SSL can go through firewalls and proxys easily

9 SSL vs SSH SSH = Secure Shell port 22 can be used to redirect a communication through a secured tunnel asymmetrical cryptography used by SCP and SFTP, or to create VPNs Drawbacks of SSH no authentication verification of public keys is external

10 SSL vs SSH Differences SSL is text-oriented, SSH is file-oriented SSL negociates and encrypts, SSH allow a distant access and a distant file transfer SSL is based on PKI, SSH allows several authentication schemes

11 SSL and VPN SSL is not adapted to VPNs SSL uses a port for each application Solution: webify any protocol (FTP,...) is translated into a web textformat Solution: MTLS = Multiplexing TLS creation of a secure session establishment of several secure sessions using a request/response protocol

12 Drawbacks of SSL Drawbacks only one authentication, at the beginning of the session certificates are not required for the client there is no signature after the initial handshake

13 Test tool for SSL OpenSSL openssl s_client -connect server:443 ssldump

14 2. SET SET = Secure Electronic Transaction defined by Visa and Mastercard in 1997 security protocols for online transactions using bank cards

15 Architecture Autorité de certification (CA) Card holder (CH) Internet Payment gateway (P) Financial network Merchant (M)

16 Services Services of SET autentication and identification of entities confidentiality of payment orders integrity (hash) non repudiation Mechanism signed messages (hash + sender private key) symmetrical key deduced from a random value, transmitted using the destination public key messages encrypted using the symmetrical key

17 Dual signature principle Objective Alice wants to send M1 to Bob and M2 to Carole Bob should not see M2 Carole should not see M1 Bob and Carole have to be sure that the messages are not modified

18 Dual signature principle Mechanism Alice sends to Bob: M1 + H(M2) + S Bob verifies that enc(h(h(m1)+h(m2)), K_pub(Alice)) = S Alice sends to Carole: M2 + H(M1) + S Carole verifies it too Bob and Carole can ensure that H(M1) and H(M2) correspond to M1 and M2

19 Phases and protocol Phases registration to the CA transaction request payment authorization payment

20 Registration SET requires that CH is registered to the CA SET requires that M is registered to the CA

21 Transaction Algorithm CH sends a request to M M sends the request authorization to P P sends authorization to M M sends response to CH (later) M sends request to P P sends response to M

22 Transaction Algorithm CH generates OI (order information) to M, without bank card number CH generates PI (payment information) to P, without details on the articles bought CH sends to M: OI + H(OI) + enc(pi, K_pub(CA)) + H(PI) + enc(h(oi)+h(pi), K_priv_CH) M sends to P: H(OI) + enc(pi, K_pub(CA)) + H(PI) + enc(h(oi)+h(pi), K_priv_CH) M receives from P a payment vouch or an error

23 Transaction Goal M knows only OI, H(OI), H(PI) M can verify the signature P knows only H(OI), PI et H(PI) P can verify the signature dual signature principle

24 Compensation Payment vouch is used (and required) for the compensation

25 Drawbacks Drawbacks certificates can be hard to check large cryptographic computations

26 Conclusion SSL and TLS are secured they do not provide non-repudiation they are not suitable to online transactions the client authentication is not mandatory SET is a secure online payment protocol