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Secure Socket Layer

Secure Socket Layer. Originally by Yu Yang and Lilly Wang Modified by T. A. Yang. Agenda. SSL Basics WTLS. SSL Facts. SSL was first developed by Netscape in 1994 and became an internet standard in 1996 ( RFC 2246 – TLS V1.0)

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Secure Socket Layer

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  1. Secure Socket Layer Originally by Yu Yang and Lilly Wang Modified by T. A. Yang

  2. Agenda SSL Basics WTLS

  3. SSL Facts SSL was first developed by Netscape in 1994 and became an internet standard in 1996 ( RFC 2246 – TLS V1.0) SSL is a cryptographic protocol to secure network across a connection-oriented layer Any program using TCP can be modified to use SSL connection

  4. SSL Facts SSL connection uses a dedicated TCP/IP socket (e.g. port 443 for https) SSL is flexible in choice of which symmetric encryption, message digest, and authentication can be used SSL provides built-in data compression

  5. SSL Usage Authenticate the server to the client Allow the client and the server to select cryptographic algorithms, or ciphers, that they both support Optionally authenticate the client to the server Use public key encryption techniques to generate a shared secret Establish an encrypted SSL connection

  6. HTTPS FTPS SMTPS Application layer Transport layer TCP/IP layer Secure Socket Layer SSL is a secure protocol which runs above TCP/IP and allows users to encrypt data and to securely authenticate a server’s (or a vendor’s) identity SECURE SOCKET LAYER

  7. SSL Stack

  8. SSL Record Protocol Operation

  9. SSL Record Format

  10. SSL Handshake SSL handshake verifies the server and allows the client and the server to agree on an encryption set before any data is sent out

  11. SSL Handshake

  12. Server Public key Private key Client request Client Public key SSL Handshake

  13. Server Pre-Master Pre-Master Public key Private key Client Session key SSL Session Key Session key Public key Pre-Master

  14. Server Session key Data Public key Private key Client Session key Session key Data Data Data Data Secure Data on Network

  15. Server Session key Session key Public key Public key Public key Public key Private key Pre-master Private key Public key Pre-master Hacker Pre-master Client Public key Pre-master Man-in-the-Middle Attack

  16. Server Public key Private key SSL version number supported by the client(v2, v3) Ciphers supported by the client (DES, RC2, RC4) Client Random Number SSL version number picked by the server (v2, v3) Ciphers picked by the server (DES, RC2, RC4) Server Random Number Certificate Client Public key Key exchange and certificate

  17. Server Public key Private key Client request Certificate Certificate Client Public key Verify Certificate Certificate is Good and Valid Server/vendor has been verified and authenticated Client has vendor’s public key and can now encrypt pre-master to send to server/vendor Valid Checking

  18. Not-recognizable Certificate

  19. The TLS Handshake Protocol involves the following steps: • Exchange hello messages to agree on algorithms, exchange random values, and check for session resumption. • Exchange the necessary cryptographic parameters to allow the client and server to agree on a premaster secret. • Exchange certificates and cryptographic information to allow the client and server to authenticate themselves. • Generate a master secret from the premaster secret and exchanged random values. • Provide security parameters to the record layer. • Allow the client and server to verify that their peer has calculated the same security parameters and that the handshake occurred without tampering by an attacker. SSL Handshake

  20. 1. Client hello SSL Handshake 2. Server hello Present Server Certificate *Request Client Certificate Server Key Exchange Server Client 3. Client Finish *Present Client Certificate Client Key Exchange *Certificate Verify Change Cipher Spec 4. Server Finish Change Cipher Spec Application Data

  21. Client Hello Sent by the client When first connecting to a server In response to a hello request or on its own Contains 32 bytes random number created by a secure random number generator Protocol version Session ID A list of supported ciphers A list of compression methods

  22. Server Hello Sent as response if client hello is accepted If not, a handshake failure alert is sent Contains 32 bytes random number created by a secure random number generator Protocol version Session ID Cipher suite chosen Compression method selected

  23. Server Certificates Immediately following the server hello, the server sends its certificate Generally an X.509.v3 certificate Server sends server hello done message, indicating that the hello-message phase of the handshake is complete

  24. Verify Server Certificate

  25. Client Certificate (optional) Client only sends a certificate upon the receipt of a certificate request Sends after receiving server hello done If the client does not have a suitable certificate, it sends a certificate message with no certificates. Server will respond with a fatal handshake failure if a client certificate is necessary

  26. Key Exchange Client sends 48-bytes pre-master, encrypted using server’s public key, to the server Both server and client use the pre-master to generate the master secret The same session key is generated on both client and server side using the master secret

  27. Final Steps Client sends change_cipher_spec Client sends finished message Server sends change_cipher_spec Server sends finished message

  28. SSL Architecture

  29. Record Layer Compression and decompression A MAC is applied to each record using the MAC algorithm defined in the current cipher spec Encryption occurs after compression May need fragmentation

  30. SSL Architecture

  31. Alert Layer Explain severity of the message and a description fatal Immediate termination Other connections in session may continue Session ID invalidated to prevent failed session to open new sessions Alerts are compressed same as other data

  32. SSL Architecture

  33. Change Cipher Spec Protocol Notify the other party to use the new cipher suite Before the Finished message

  34. Comparison of SSL V2.0 and V3.0 SSL 2.0 is vulnerable to “man-in-the-middle” attack.The hello messagecan be modified to use 40 bits encryption. SSL 3.0 defends against this attack by having the last handshake message include a hash of all the previous handshake message

  35. Comparison of SSL V2.0 and V3.0 SSL 2.0 uses a weak MAC construction In SSL 3.0, the Message Authentication Hash uses a full 128 bits of key material for Export cipher+, while SSL 2.0 uses only 40 bits + See http://en.wikipedia.org/wiki/Export_of_cryptography

  36. Comparison of SSL V2.0 and V3.0 SSL 2.0 only allows a handshake at the beginning of the connection. In 3.0, the client can initiate a handshake routine any time SSL 3.0 allows server and client to send chains of certificate SSL 3.0 has a generalized key exchange protocol. It allows Diffie-Hellman and Fortezza key exchange SSL 3.0 allows for record compression and decompression

  37. Problem Free? Side channel attack – any attack based on information gained from the physical implementation of a cryptosystem, rather than brute force or theoretical weaknesses in the algorithms (compare cryptanalysis). See http://en.wikipedia.org/wiki/Side_channel_attack for details. Information leak in encrypted connections. Vulnerable openssl versions do not perform a MAC computation if an incorrect block cipher padding is used. An active attacker who can insert data into an existing encrypted connection is then able to measure time differences between the error messages the server sends. This information can make it easier to launch cryptographic attacks that rely on distinguishing between padding and MAC verification errors, possibly leading to extraction of the original plaintext.

  38. Wireless Transport Layer Security Part of the WAP (wireless application protocol) standard

  39. WTLS Overview

  40. WTLS Facts Mainly used to secure data transport between wireless device and gateway Built on top of datagram (UDP) instead of TCP WTLS provides full, optimized and abbreviated handshake to reduce roundtrips in high-latency networks

  41. WTLS Facts WTLS uses different format of certificates, mainly WTLS certificate, X509v1 and 968. It also supports additional cipher suites, such as RC5, short hashes, ECC, etc; WTLS provides built-in key-refresh mechanism for renegotiation; WTLS can also set session resumable to continue on a previous session.

  42. Reference [1] http://www.faqs.org/faqs/computer-security/ssl-talk faq/ [2] http://www.pcwebopedia.com/TERM/S/SSL.htm [3]http://developer.netscape.com/docs/manuals/security/sslin/contents.htm [4] http://www.ece.wpi.edu/~sunar/ee578/SSL.ppt

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