Online SecurityOnline Security

Tuesday April 8, 2003Tuesday April 8, 2003

Maxence CrossleyMaxence Crossley

OutlineOutline

How do we authenticate a service?How do we authenticate a service? How do we encrypt a session?How do we encrypt a session? How do we prevent a “replay attack”?How do we prevent a “replay attack”? Another Problem: SpoofingAnother Problem: Spoofing

How do we authenticate a session?How do we authenticate a session?

Certification Authorities Certification Authorities (CAs)(CAs) VeriSignVeriSign SecureNetSecureNet Digital Signature TrustDigital Signature Trust

Distribute and store Distribute and store certificatescertificates

Public Key CryptographyPublic Key Cryptography

Server publishes public key with Certification Server publishes public key with Certification AgencyAgency

Client encrypts message with public keyClient encrypts message with public key Server decrypts message with private keyServer decrypts message with private key

Source: http://waubonsie.com/security/www.html

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Private Key CryptographyPrivate Key Cryptography

Server and Client share a secret and private keyServer and Client share a secret and private key Client encrypts message with private keyClient encrypts message with private key Server decrypts message with private keyServer decrypts message with private key

Source: http://waubonsie.com/security/www.html

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

How do we encrypt a session? How do we encrypt a session? SSLSSL

Client requests a secured fileClient requests a secured file Server sends its certificateServer sends its certificate Client checks with CA that the signature is Client checks with CA that the signature is

validvalid Client generates a unique session key and Client generates a unique session key and

sends it to serversends it to server

Source: http://waubonsie.com/security/www.html

How do we encrypt a session?How do we encrypt a session?

Source: http://waubonsie.com/security/www.html

How do we encrypt a session?How do we encrypt a session?

Source: http://waubonsie.com/security/www.html

How do we encrypt a session?How do we encrypt a session?

Source: http://waubonsie.com/security/www.html

What is a “replay attack”?What is a “replay attack”?

When an attacker uses captured authentication When an attacker uses captured authentication tokens to gain access to a user’s account while tokens to gain access to a user’s account while bypassing normal authenticationbypassing normal authentication

Sniffing a URL that has a session ID in itSniffing a URL that has a session ID in it Attacker can obtain access to users accountAttacker can obtain access to users account

Source: http://www.owasp.org/asac/auth-session/replay.shtml

CountermeasuresCountermeasures

Source: http://www.owasp.org/asac/auth-session/replay.shtml

““Generate hard to reverse-engineer Session Generate hard to reverse-engineer Session IDs for authenticated web users (i.e. IDs for authenticated web users (i.e. use strong crypto, MD5 use strong crypto, MD5 hashes, etc.)” hashes, etc.)”

““Build and require SSL (or other encryption) Build and require SSL (or other encryption) into the web application so that the into the web application so that the authentication token can not authentication token can not be easily sniffed in transit between be easily sniffed in transit between browser and server; Ensure that all cookies browser and server; Ensure that all cookies enable the "secure" field (see enable the "secure" field (see OWASP's explanation of cookies)”OWASP's explanation of cookies)”

CountermeasureCountermeasure

Source: http://www.owasp.org/asac/auth-session/replay.shtml

““Provide a logout function that expires all Provide a logout function that expires all cookies and other authentication cookies and other authentication tokens”tokens”

““Users can choose not to select the "Remember Users can choose not to select the "Remember Me" option on web application accounts so that Me" option on web application accounts so that authentication tokens are not persistent after authentication tokens are not persistent after logout”logout”

Another Problem: SpoofingAnother Problem: Spoofing

Web users rely on visual clues when deciding to Web users rely on visual clues when deciding to trust a sitetrust a site Location bar informationLocation bar information SSL iconsSSL icons SSL warningsSSL warnings Certificate informationCertificate information Response timeResponse time

These cues can be forgedThese cues can be forged

Source: http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/

SpoofingSpoofing

Source: http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/

SpoofingSpoofing

Source: http://www.cs.dartmouth.edu/~pkilab/demos/spoofing/

CountermeasuresCountermeasures

Mozilla with SRD Mozilla with SRD (synchronized random (synchronized random dynamic) Boundarydynamic) Boundary

Trusted Reference Trusted Reference Window in lower right Window in lower right cornercorner

Untrusted Outer Untrusted Outer WindowWindow

Colors chosen at Colors chosen at randomrandom

Source: http://www.cs.dartmouth.edu/~pkilab/demos/countermeasures/