SSL/TLS and MITM attacks
A case study in Network SecurityBy Lars Nybom & Alexander Wall
SSL/TLS – Background
● SSL/TLS – Secure Socket Layer/Transport Layer Security (rfc 2246)
SSL/TLS – Background
● SSL/TLS – Secure Socket Layer/Transport Layer Security (rfc 2246)
● Originally developed by Netscape.
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.
SSL/TLS – How does it work?
Based on public key cryptography and certificate authority.
SSL/TLS - Components
● Tree structure where Certificate Authorities (CA) is nodes and Servers leafs.
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.
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.
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.
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.
MITM
● Man-In-The-Middle attack is virtually transparent to the victim.
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.
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.
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.
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.
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 ”https://...” (i.e. Facebook, Gmail and Hotmail)
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 ”https://...” (i.e. Facebook, Gmail and Hotmail)
● SSLStrip rewrites all HTTPS addresses as HTTP addresses and then saves traffic content.
SSLStrip – How does it look?
SSLStrip – How does it look?
Countermeasures
● Before logging on webpage make sure that address in address bar begins with ”https://...”. If it doesn't, retype it so it does. (This only helps against SSLStrip, not SSLSniff.)
Countermeasures
● Before logging on webpage make sure that address in address bar begins with ”https://...”. If it doesn't, retype it so it does. (This only helps against SSLStrip, not SSLSniff.)
● If the address begins with ”https://...” make sure that the certificate doesn't look fishy.
Countermeasures
SSL/TLS and MITM attacks
The End
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