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Network Security Essentials Chapter 5 Fourth Edition by William Stallings Lecture slides by Lawrie Brown.

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Presentation on theme: "Network Security Essentials Chapter 5 Fourth Edition by William Stallings Lecture slides by Lawrie Brown."— Presentation transcript:

1 Network Security Essentials Chapter 5 Fourth Edition by William Stallings Lecture slides by Lawrie Brown

2 Chapter 5 – Transport-Level Security Use your mentality Wake up to reality —From the song, "I've Got You under My Skin“ by Cole Porter

3 Web Güvenliği   Web Artık yaygın iş, devlet, bireyler tarafından kullanılanılır  Fakat internet ve Web saldırılara açıktır  Değişik tehtitler mevcuttur integrity integrity confidentiality confidentiality denial of service denial of service authentication authentication  Güvenlik mekanizmaları eklenmesi gerekir

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5 Web Trafiği Güvenlik önerileri

6 SSL (Secure Socket Layer)  transport layer security hizmetleri  Netscape tarafından ilk olarak geliştirildi  V3 halka açık girişler kabul ediyor.  Sonradan TLS olarak internet standardı haline geldi (Transport Layer Security)  TCP yi uçtan uca güvenli servis verebilmek için kullanır  SSL in iki protokol katmanı vardır.

7 SSL Architecture

8  SSL Bağlantısı( connection) a transient, peer-to-peer, communications link a transient, peer-to-peer, communications link associated with 1 SSL session associated with 1 SSL session  SSL oturumu an association between client & server an association between client & server created by the Handshake Protocol created by the Handshake Protocol define a set of cryptographic parameters define a set of cryptographic parameters may be shared by multiple SSL connections may be shared by multiple SSL connections

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11 SSL Kayıt Protokolü ve servis  Gizlilik (confidentiality) using symmetric encryption with a shared secret key defined by Handshake Protocol using symmetric encryption with a shared secret key defined by Handshake Protocol AES, IDEA, RC2-40, DES-40, DES, 3DES, Fortezza, RC4-40, RC4-128 AES, IDEA, RC2-40, DES-40, DES, 3DES, Fortezza, RC4-40, RC4-128 message is compressed before encryption message is compressed before encryption  Mesaj Bütünlüğü using a MAC with shared secret key using a MAC with shared secret key similar to HMAC but with different padding similar to HMAC but with different padding

12 SSL Record Protocol Operation

13 MAC

14  The following encryption algorithms are permitted

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17 SSL Cipher özelliklerini değiştirme protokolü Change Chiper Spec Pro.  SSL Record protocol ı kullanan ve SSL has kullanılan 3 protokolden birisi  Tek bir mesaj içerir ( )  Bekleyen durumun aktif hale gelmesini sağlar.  Bu şekilde kullanılacak chiper listesini belirler

18 Chiper Spec Protocol (devam)  The sole purpose of this message is to cause the pending state to be copied into the current state,  which updates the cipher suite to be used on this connection

19 SSL Uyarı Protokolü Alert Protocol  SSL ile alakalı uyarıları karşıdaki eşe bildirir  Şiddeti, Önemi warning veya fatalwarning veya fatal  Bazı uyarılar fatal: unexpected message, bad record mac, decompression failure, handshake failure, illegal parameterfatal: unexpected message, bad record mac, decompression failure, handshake failure, illegal parameter warning: close notify, no certificate, bad certificate, unsupported certificate, certificate revoked, certificate expired, certificate unknownwarning: close notify, no certificate, bad certificate, unsupported certificate, certificate revoked, certificate expired, certificate unknown  Tüm SSL verileri gibi şıkıştırılıp&şifrelenir

20 Fatal Alerts

21 Diğer Alertler

22 SSL El sıkışma protokolü Handshake Protocol  İstemci ve sunucu arasında : Birbirlerini kimlik denetimi yapar Birbirlerini kimlik denetimi yapar to negotiate encryption & MAC algorithms to negotiate encryption & MAC algorithms to negotiate cryptographic keys to be used to negotiate cryptographic keys to be used  Fazlar halinde bir seri mesajlar içerir 1. Establish Security Capabilities 2. Server Authentication and Key Exchange 3. Client Authentication and Key Exchange 4. Finish

23 SSL Handshake Protocol

24 Phase 1 ESTABLISH SECURITY CAPABILITIES  is used to initiate a logical connection and to establish the security capabilities that will be associated with it

25 Server Key Exchange  RSA  Fixed Diffie Hellman  Ephemeral D-H  Ananoymous D-H  ForTezza

26 PHASE 2. SERVERAUTHENTICATION AND KEY EXCHANGE  The server begins this phase by sending its certificate if it needs to be authenticated; the message contains one or a chain of X.509 certificates  Next, a server_key_exchange message may be sent if it is required. It is not required in two instances: (1) The server has sent a certificate with fixed Diffie-Hellman parameters or (2) a RSA key exchange is to be used. The server_key_exchange message is needed for the following

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28 PHASE 3. CLIENT AUTHENTICATION AND KEY EXCHANGE  If the server has requested a certificate, the client begins this phase by sending a certificate message. If no suitable Certificate is available, the client sends a no_certificate alert instead.

29 SSL Handshake Protocol

30 Cryptographic Hesaplamalar  master secret creation Tek seferlik 48-byte value Tek seferlik 48-byte value generated using secure key exchange (RSA / Diffie-Hellman) and then hashing info generated using secure key exchange (RSA / Diffie-Hellman) and then hashing info  Kriptografik parametrelerin üretimi  client write MAC secret, a server write MAC secret, a client write key, a server write key, a client write IV, and a server write IV generated by hashing master secret generated by hashing master secret

31 TLS (Transport Layer Security)  IETF standardı, RFC 2246, SSLv3 e çok benzer  küçük farklar vardır in record format version number in record format version number uses HMAC for MAC uses HMAC for MAC a pseudo-random function expands secrets a pseudo-random function expands secrets based on HMAC using SHA-1 or MD5based on HMAC using SHA-1 or MD5 has additional alert codes has additional alert codes some changes in supported ciphers some changes in supported ciphers changes in certificate types & negotiations changes in certificate types & negotiations changes in crypto computations & padding changes in crypto computations & padding

32 HTTPS  HTTPS (HTTP over SSL) HTTP & SSL/TLS birlikte kullanılması bu şekilde browser & server arası güvenli iletişim HTTP & SSL/TLS birlikte kullanılması bu şekilde browser & server arası güvenli iletişim documented in RFC2818documented in RFC2818 no fundamental change using either SSL or TLSno fundamental change using either SSL or TLS  https:// URL rather than and port 443 rather than 80 and port 443 rather than 80  encrypts URL, document contents, form data, cookies, HTTP headers URL, document contents, form data, cookies, HTTP headers

33 Secure Shell (SSH)  Güvenli ağ iletişimi için bir protokol designed to be simple & inexpensive designed to be simple & inexpensive  İlk versiyon SSH1 güvenli ve uzaktan erişim içerir replace TELNET & other insecure schemes replace TELNET & other insecure schemes also has more general client/server capability also has more general client/server capability  SSH2 bir çok güvenlik açıklarını giderir  documented in RFCs 4250 through 4254  SSH clients & servers çok erişilebilir.  method of choice for remote login/ X tunnels

34 SSH Protocol Stack

35 SSH Transport Layer Protocol  server authentication occurs at transport layer, based on server/host key pair(s) server authentication requires clients to know host keys in advance server authentication requires clients to know host keys in advance  packet exchange establish TCP connection establish TCP connection can then exchange data can then exchange data 1.identification string exchange, 2.algorithm negotiation, 3. key exchange, 4.end of key exchange, 5. service request using specified packet format using specified packet format

36 SSH User Authentication Protocol  authenticates client to server  three message types: SSH_MSG_USERAUTH_REQUEST SSH_MSG_USERAUTH_REQUEST SSH_MSG_USERAUTH_FAILURE SSH_MSG_USERAUTH_FAILURE SSH_MSG_USERAUTH_SUCCESS SSH_MSG_USERAUTH_SUCCESS  authentication methods used public-key, password, host-based public-key, password, host-based

37 SSH Connection Protocol  runs on SSH Transport Layer Protocol  assumes secure authentication connection  used for multiple logical channels SSH communications use separate channels SSH communications use separate channels either side can open with unique id number either side can open with unique id number flow controlled flow controlled have three stages: have three stages: opening a channel, data transfer, closing a channelopening a channel, data transfer, closing a channel four types: four types: session, x11, forwarded-tcpip, direct-tcpip.session, x11, forwarded-tcpip, direct-tcpip.

38 SSH Connection Protocol Exchange

39 Port Forwarding  convert insecure TCP connection into a secure SSH connection SSH Transport Layer Protocol establishes a TCP connection between SSH client & server SSH Transport Layer Protocol establishes a TCP connection between SSH client & server client traffic redirected to local SSH, travels via tunnel, then remote SSH delivers to server client traffic redirected to local SSH, travels via tunnel, then remote SSH delivers to server  supports two types of port forwarding local forwarding – hijacks selected traffic local forwarding – hijacks selected traffic remote forwarding – client acts for server remote forwarding – client acts for server

40 Summary  have considered: need for web security need for web security SSL/TLS transport layer security protocols SSL/TLS transport layer security protocols HTTPS HTTPS secure shell (SSH) secure shell (SSH)


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