SSL/TLS and MITM attacks. A case study in Network Security By Lars Nybom & Alexander Wall

Transcription

1 SSL/TLS and MITM attacks A case study in Network Security By Lars Nybom & Alexander Wall

2 SSL/TLS Background SSL/TLS Secure Socket Layer/Transport Layer Security (rfc 2246)

3 SSL/TLS Background SSL/TLS Secure Socket Layer/Transport Layer Security (rfc 2246) Originally developed by Netscape.

4 SSL/TLS Background SSL/TLS Secure Socket Layer/Transport Layer Security (rfc 2246) Originally developed by Netscape. Used to deploy confidentiality, authenticity and integrity between web client and web server.

5 SSL/TLS How does it work? Based on public key cryptography and certificate authority.

6 SSL/TLS - Components Tree structure where Certificate Authorities (CA) is nodes and Servers leafs.

7 SSL/TLS - Components Tree structure where Certificate Authorities (CA) is nodes and Servers leafs. Server certificate issued by CA one level above meaning that it's signed by CA one level above.

8 SSL/TLS - Components Tree structure where Certificate Authorities (CA) is nodes and Servers leafs. Server certificate issued by CA one level above meaning that it's signed by CA one level above. If Client doesn't trust Server identity he/she uses the CA's public key to verify that the Server certificate is legit.

9 SSL/TLS - Components Tree structure where Certificate Authorities (CA) is nodes and Servers leafs. Server certificate issued by CA one level above meaning that it's signed by CA one level above. If Client doesn't trust Server identity he/she uses the CA's public key to verify that the Server certificate is legit. Root CA in top of tree trusted by everyone.

10 SSL/TLS - Problem If there's a lot of intermediate CA's between the Server and Root CA, authenticity is weak. Server CA 1 CA 2 Root CA This allowed for older form of attack SSLSniff, where a MITM generates a bogus self-signed certificate sent to Client while connecting normally to Server. New attack SSLStrip.

11 MITM Man-In-The-Middle attack is virtually transparent to the victim.

12 ARP Spoofing In order to become in the middle attacker needs to redirect the victims network traffic through his/hers computer acting like a gateway.

13 ARP Spoofing In order to become in the middle attacker needs to redirect the victims network traffic through his/hers computer acting like a gateway. Every network interface has a MAC address associated with its IP.

14 ARP Spoofing In order to become in the middle attacker needs to redirect the victims network traffic through his/hers computer acting like a gateway. Every network interface has a MAC address associated with its IP. When a computer wants to communicate with another computer within it's subnet it needs to know that computers MAC address so it sends an ARP query.

15 ARP Spoofing In a MITM attack the attacker sends out a false ARP reply telling the victim his/hers computer is the computer the victim is looking for.

16 SSLStrip Client normally connects via HTTPS (SSL/TLS) to a Server because an user tries to GET/POST information on a webpage by a link/button that begins with (i.e. Facebook, Gmail and Hotmail)

17 SSLStrip Client normally connects via HTTPS (SSL/TLS) to a Server because an user tries to GET/POST information on a webpage by a link/button that begins with (i.e. Facebook, Gmail and Hotmail) SSLStrip rewrites all HTTPS addresses as HTTP addresses and then saves traffic content.

18 SSLStrip How does it look?

19 SSLStrip How does it look?

20 Countermeasures Before logging on webpage make sure that address in address bar begins with If it doesn't, retype it so it does. (This only helps against SSLStrip, not SSLSniff.)

21 Countermeasures Before logging on webpage make sure that address in address bar begins with If it doesn't, retype it so it does. (This only helps against SSLStrip, not SSLSniff.) If the address begins with make sure that the certificate doesn't look fishy.

22 Countermeasures

23 SSL/TLS and MITM attacks The End