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EEC 688/788 Secure and Dependable Computing

EEC 688/788 Secure and Dependable Computing. Lecture 8 Wenbing Zhao Department of Electrical and Computer Engineering Cleveland State University wenbing@ieee.org. Outline. Reminder: Lab 2 next Monday Secure Socket Layer Pretty Good Privacy. SSL: The Secure Sockets Layer.

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EEC 688/788 Secure and Dependable Computing

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  1. EEC 688/788Secure and Dependable Computing Lecture 8 Wenbing Zhao Department of Electrical and Computer Engineering Cleveland State University wenbing@ieee.org

  2. Outline Reminder: Lab 2 next Monday Secure Socket Layer Pretty Good Privacy EEC688/788: Secure & Dependable Computing

  3. SSL: The Secure Sockets Layer SSL (Secure Sockets Layer): a security package for secure communication over Internet Introduced in 1995, Netscape Communications Corp SSL builds a secure connection between two sockets, including Parameter negotiation between client and server Mutual authentication of client and server Secret communication Data integrity protection EEC688/788: Secure & Dependable Computing

  4. Secure Sockets Layer Documentation The SSL Protocol version 3.0 Internet Draft:http://home.netscape.com/eng/ssl3/ssl-toc.html The TLS Protocol version 1.0 Internet Draft: http://www.ietf.org/rfc/rfc2246.txt "HTTP Over TLS" Information RFC: http://www.ietf.org/rfc/rfc2818.txt SSL and TLS: Designing and Building Secure Systems by Eric Rescorla. Addison Wesley Professional, 2000 Analysis of the SSL 3.0 Protocol, by David Wagner and Bruce Schneier, http://www.schneier.com/paper-ssl-revised.pdf EEC688/788: Secure & Dependable Computing

  5. SSL: The Secure Sockets Layer HTTPS (Secure HTTP): HTTP over SSL Sometimes it is available at a new port (443) instead of the standard port (80) Layers (and protocols) for home user using HTTPS EEC688/788: Secure & Dependable Computing

  6. SSL: The Secure Sockets Layer SSL consists of two main subprotocols: handshake protocol record protocol SSL supports multiple cryptographic algorithms The strongest one uses triple DES with three separate keys for encryption and SHA-1 for message integrity For ordinary e-commerce applications, RC4 is used with a 128-bit key for encryption and MD5 is used for message authentication EEC688/788: Secure & Dependable Computing

  7. SSL: The Secure Sockets Layer Application software SSL Change Cipher Spec Protocol Application Data SSL Handshake Protocol SSL Alert Protocol SSL Record Layer Protocol TCP EEC688/788: Secure & Dependable Computing

  8. SSL HandshakeProtocol ClientKeyEx EEC688/788: Secure & Dependable Computing

  9. SSL HandshakeProtocol Message #1: Client hello SSL version; Random structure (timestamp and nonce); Session id; CipherSuites; Compression methods Message #2: Server hello SSL version*; Random structure (timestamp and nonce); Session id; CipherSuite*; Compression method* * selection based on client’s preference by the server EEC688/788: Secure & Dependable Computing

  10. SSL HandshakeProtocol Message #3: Server certificate (server key exchange message would be sent if there is no certificate) Message #4: Server hello done To indicate the end of the server hello and associated messages EEC688/788: Secure & Dependable Computing

  11. SSL HandshakeProtocol Message #5: ClientKeyExchange - RSA encrypted premaster secret message 48-byte long (version number and random bytes), encrypted using server’s public key EEC688/788: Secure & Dependable Computing

  12. SSL HandshakeProtocol Message #6&8: Change cipher spec Sent by both client and server to notify receiving party that subsequent records will be protected under the new CipherSpec and keys The client sends a change cipher spec message following handshake key exchange and certificate verifymessages (if any) The server sends one after successfully processing the key exchange message it received from the client EEC688/788: Secure & Dependable Computing

  13. SSL HandshakeProtocol The Change cipher spec message is an independent SSL Protocol content type, and is not actually an SSL handshake message This is designed as a performance improvement This message cannot be combined with the finished message (change cipher spec is unencrypted [or encrypted using the previous session key] and the finished message is encrypted using the new session key) EEC688/788: Secure & Dependable Computing

  14. SSL HandshakeProtocol Message #7&9: Finished Sent immediately after a change cipher specs msg The finished message is the first protected with the just-negotiated algorithms, keys, and secrets No acknowledgment of the finished message is required; parties may begin sending confidential data immediately after sending the finished message EEC688/788: Secure & Dependable Computing

  15. SSL HandshakeProtocol Output Server Random Pre-master Secret Client Random Master Secret Key Block Server Write Client Write Server IV Client MAC Server MAC Client IV EEC688/788: Secure & Dependable Computing

  16. SSL HandshakeProtocol Output Master secret: computed based on the premaster secret and the nonces proposed by the client and the servermaster_secret = MD5(pre_master_secret + SHA('A' + pre_master_secret + ClientHello.random + ServerHello.random)) + MD5(pre_master_secret + SHA('BB' + pre_master_secret + ClientHello.random + ServerHello.random)) + MD5(pre_master_secret + SHA('CCC' + pre_master_secret + ClientHello.random + ServerHello.random)); Session keys, MAC secrets, and IVs: the master secret is used as an entropy source, and the random values provide unencrypted salt material and IVs for exportable ciphers EEC688/788: Secure & Dependable Computing

  17. SSL HandshakeProtocol Output To generate the key material, computekey_block = MD5(master_secret + SHA('A' + master_secret + ServerHello.random + ClientHello.random)) + MD5(master_secret + SHA('BB' + master_secret + ServerHello.random + ClientHello.random)) + MD5(master_secret + SHA('CCC' + master_secret + ServerHello.random + ClientHello.random)) + [...];until enough output has been generated EEC688/788: Secure & Dependable Computing

  18. SSL HandshakeProtocol Output Then the key_block is partitioned as follows:client_write_MAC_secret[CipherSpec.hash_size] server_write_MAC_secret[CipherSpec.hash_size] client_write_key[CipherSpec.key_material] server_write_key[CipherSPec.key_material] client_write_IV[CipherSpec.IV_size] /* non-export ciphers */server_write_IV[CipherSpec.IV_size]/* non-export ciphers */ EEC688/788: Secure & Dependable Computing

  19. SSL Record Protocol MAC = hash(MAC_write_secret + pad_2 + hash(MAC_write_secret + pad_1 + seq_num + length + content)); <= 16 KB each Why? EEC688/788: Secure & Dependable Computing

  20. SSL and TLS In 1996, Netscape Communications Corp. turned SSL over to IETF for standardization. The result was TLS (Transport Layer Security) It is described in RFC 2246 The changes made to SSL were relatively small, but just enough that SSL version 3 and TLS cannot interoperate The TLS version is also known as SSL version 3.1 EEC688/788: Secure & Dependable Computing

  21. E-Mail Security PGP– Pretty Good Privacy PEM – Privacy Enhanced Mail S/MIME EEC688/788: Secure & Dependable Computing

  22. PGP – Pretty Good Privacy PGP (Pretty Good Privacy): e-mail security package that provides privacy, authentication, digital signatures, and compression, all in an easy-to-use form Created by Zimmermann, released in 1991 Zimmermann is a privacy advocate whose motto is: If privacy is outlawed, only outlaws will have privacy The complete package, including all the source code, is distributed free of charge via the Internet Due to its quality, price (zero), and easy availability on UNIX, Linux, Windows, and Mac OS platforms, it is widely used today EEC688/788: Secure & Dependable Computing

  23. PGP – Pretty Good Privacy PGP encrypts data by using a block cipher called IDEA (International Data Encryption Algorithm) It has been patented and OpenPGP has stopped using it Key management uses RSA Data integrity uses MD5 Compression uses the ZIP program, which uses the Ziv-Lempel algorithm (Ziv and Lempel, 1977) Compression saves bandwidth It also wipes out the frequency information contained in the plaintext. In effect, it converts the plaintext into junk EEC688/788: Secure & Dependable Computing

  24. PGP – Pretty Good Privacy PGP in operation for sending a message EEC688/788: Secure & Dependable Computing

  25. PGP – Pretty Good Privacy Alice sends an email P to Bob using PGP: Both Alice and Bob have private (DX) and public (EX) RSA keys. Assume that each one knows the other's public key PGP first hashes Alice’s message, P, using MD5, and then encrypts the resulting hash using her private RSA key, DA The encrypted hash and the original message are concatenated into a single message, P1, and compressed using the ZIP program, the output of this step is P1.Z EEC688/788: Secure & Dependable Computing

  26. PGP – Pretty Good Privacy Next, PGP prompts Alice for some random input. Both the content and the typing speed are used to generate a 128-bit IDEA message key, KM KMis now used to encrypt P1.Z with IDEA in cipher feedback mode In addition, KMis encrypted with Bob's public key, EB. These two components are then concatenated and converted to base64 EEC688/788: Secure & Dependable Computing

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