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

2 Agenda SSL Basics SSL Basics WTLS 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 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 layerSSL is a cryptographic protocol to secure network across a connection-oriented layer Any program using TCP can be modified to use SSL connectionAny 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 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 usedSSL is flexible in choice of which symmetric encryption, message digest, and authentication can be used SSL provides built-in data compressionSSL provides built-in data compression

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

6 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 Application layer Transport layer TCP/IP layer SMTPSFTPSHTTPS 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 SSL Handshake Server Client Public key Private key Client request Public key

13 SSL Session Key Server Client Public key Private key Public keyPre-Master Session key

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

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

16 Key exchange and certificate 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 Server Client Public key Private key Public key Certificate

17 Verify Certificate Checking Server Client Public key Private key Client request Certificate Valid Public key 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

18 Not-recognizable Certificate

19 SSL Handshake The TLS Handshake Protocol involves the following steps: 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.

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

21 Client Hello Sent by the client Sent by the client –When first connecting to a server –In response to a hello request or on its own Contains 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 Sent as response if client hello is accepted –If not, a handshake failure alert is sent Contains 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 serverClient 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 secretBoth 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 secretThe 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 change_cipher_spec Client sends finished message Client sends finished message Server sends change_cipher_spec Server sends change_cipher_spec Server sends finished message Server sends finished message

28 SSL Architecture

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

30 SSL Architecture

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

32 SSL Architecture

33 Change Cipher Spec Protocol Notify the other party to use the new cipher suiteNotify the other party to use the new cipher suite Before the Finished messageBefore 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 message can be modified to use 40 bits encryption.SSL 2.0 is vulnerable to “man-in-the- middle” attack. The hello message can 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 messageSSL 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 constructionSSL 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 bitsIn 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

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 timeSSL 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 certificateSSL 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 exchangeSSL 3.0 has a generalized key exchange protocol. It allows Diffie-Hellman and Fortezza key exchange SSL 3.0 allows for record compression and decompressionSSL 3.0 allows for record compression and decompression

37 Problem Free? Side channel attack – discovered by Swiss Federal Institute of Technology in LausanneSide channel attack – discovered by Swiss Federal Institute of Technology in Lausannehttp:// 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.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

39 WTLS Overview

40 WTLS Facts Mainly used to secure data transport between wireless device and gatewayMainly used to secure data transport between wireless device and gateway Built on top of datagram (UDP) instead of TCPBuilt on top of datagram (UDP) instead of TCP WTLS provides full, optimized and abbreviated handshake to reduce roundtrips in high-latency networksWTLS 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 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 provides built-in key-refresh mechanism for renegotiation; WTLS can also set session resumable to continue on a previous session.WTLS can also set session resumable to continue on a previous session.

42 Web Service Security

43 Reference [1 [1] talk faq/ [2] [3] rity/sslin/contents.htm [4]