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Secure HTTP Herng-Yow Chen 1 Secure HTTP Herng-Yow Chen 1

Outline n n n When digest authentication is not strong enough? How a more Outline n n n When digest authentication is not strong enough? How a more complicated technology secures HTTP transactions from eavesdropping and tampering? Using digital cryptography. 2

HTTPS https scheme security icon 3 HTTPS https scheme security icon 3

HTTPS (cont. ) HTTP Application layer SSL or TLS Security layer TCP Transport layer HTTPS (cont. ) HTTP Application layer SSL or TLS Security layer TCP Transport layer IP Network layer Network interfaces Data link layer (a) HTTP (b) HTTPS 4

Digital cryptography n n n n Ciphers Keys Symmetric-key cryptosystems Asymmetric-key cryptosystems Public-key cryptography Digital cryptography n n n n Ciphers Keys Symmetric-key cryptosystems Asymmetric-key cryptosystems Public-key cryptography Digital signatures Digital certificates 5

Plaintext and Ciphertext Plaintext Ciphertext Meet me at the pier at midnight Phhw ph Plaintext and Ciphertext Plaintext Ciphertext Meet me at the pier at midnight Phhw ph dw wkh slhu dw plgqljkw Encoder Plaintext Meet me at the pier at midnight Decoder 6

Rotate-by-3 cipher example Cipher ABCDEFGHIJKLMNOPQRSTUVWXYZ ABCDEFGHI JKLMNOPQRSTUVWXYZABC Plaintext MEET ME AT THE AT PIRE Rotate-by-3 cipher example Cipher ABCDEFGHIJKLMNOPQRSTUVWXYZ ABCDEFGHI JKLMNOPQRSTUVWXYZABC Plaintext MEET ME AT THE AT PIRE AT MIDNIGHT Ciphertext PHHW PH DW WKH DW SLHU DW PLGQLJKW 7

Keyed Ciphers (rotate-by-n), using different keys (a) Plaintext Meet me at the pier at Keyed Ciphers (rotate-by-n), using different keys (a) Plaintext Meet me at the pier at midnight Ciphertext nffu nf bu uif qjfs bu njeojhiu Key=1 Rotate(n) encoder (b) Plaintext Meet me at the pier at midnight Ciphertext oggv og cv vjg rkgt cv okfpkijv Key=2 Rotate(n) encoder (c) Plaintext Meet me at the pier at midnight Ciphertext Key=3 Rotate(n) encoder phhw ph dw wkh slhu dw plgqlijkw 8

Digital Ciphers 9 Digital Ciphers 9

Plaintext is encoded with encoding key e C = E (P, e) Plaintext P Plaintext is encoded with encoding key e C = E (P, e) Plaintext P Key=e Ciphertext C Encoder E 10

Symmetric-Key Cryptography If d = e P = D (C, d) Ciphertext C Key=d Symmetric-Key Cryptography If d = e P = D (C, d) Ciphertext C Key=d Plaintext P Decoder D Popular symmetric-key cryptography algorithm are DES, Triple-DES, RC 2, and RC 4. 11

Key Length and Enumeration Attacks Attack cost 40 -bit key 56 -bit key 64 Key Length and Enumeration Attacks Attack cost 40 -bit key 56 -bit key 64 -bit key 80 -bit key 128 -bit key $100, 000 2 secs 35 hours 1 years 70, 000 years 1019 years $1, 000 200 msecs 3. 5 hours 37 days 7, 000 years 1018 years $10, 000 20 msecs 21 mins 4 days 700 years 1017 years $100, 000 2 msecs 2 mins 9 hours 70 years 1016 years 13 secs 1 hours 7 years 1015 years $1, 000, 000 200 usecs 12

Public-Key Cryptography Using different keys for encoding and decoding client Plaintext Public key=es Encrypted Public-Key Cryptography Using different keys for encoding and decoding client Plaintext Public key=es Encrypted ciphertext Private key=ds Internet Plaintext server 13

Public-Key cryptography assigns a single, public encoding key to each host A A k. Public-Key cryptography assigns a single, public encoding key to each host A A k. AX B k. BX ex k. DX D B ex k. CX C (a) Symmetric-key cryptography ex D ex C (b) Public-key cryptography 14

Signatures Are Cryptographic Checksums Plaintext message A Message digest D Private key=d. A Signature Signatures Are Cryptographic Checksums Plaintext message A Message digest D Private key=d. A Signature Message digest E B Same? Message digest Public key=e. A 15

The Guts of a Certificate 16 The Guts of a Certificate 16

X. 509 v 3 Certificates 17 X. 509 v 3 Certificates 17

Verifying that a signature is real B E Signing authority’s public key Message digest Verifying that a signature is real B E Signing authority’s public key Message digest Same? 18

HTTPS Overview HTTP Application layer SSL or TLS Security layer TCP Transport layer IP HTTPS Overview HTTP Application layer SSL or TLS Security layer TCP Transport layer IP Network layer Network interfaces Data link layer (a) HTTP (b) HTTPS 19

HTTPS Schemes (a) HTTP request 80 HTTP Server client (b) HTTPS request 443 HTTPS HTTPS Schemes (a) HTTP request 80 HTTP Server client (b) HTTPS request 443 HTTPS Secure Server client (C) HTTPS over HTTP tunnel 443 808 0 HTTPS client HTTP tunnel Proxy Secure Server 20

Secure Transport Setup 21 Secure Transport Setup 21

Secure Transport Setup (cont. ) (a) Unencrypted HTTP transaction (b) Enencrypted HTTPS transaction 22 Secure Transport Setup (cont. ) (a) Unencrypted HTTP transaction (b) Enencrypted HTTPS transaction 22

SSL Handshake (simplified) 23 SSL Handshake (simplified) 23

Server Certificates HTTPS certificates are X. 509 certificates with site information Internet client Server Server Certificates HTTPS certificates are X. 509 certificates with site information Internet client Server Certificate serial number 35: DE: F 4: CF Certificate expiration date Wed, Sep 17, 2003 Site’s organization name Joe’s Hardware Online Site’s DNS hostname www. joes-hardware. com Site’s public key Certificate issuer name RSA Data Security Certificate issuer signature Jone doe 24

Virtual Hosting and Certificates Certificate name mismatches bring up certificate error dialog boxes 25 Virtual Hosting and Certificates Certificate name mismatches bring up certificate error dialog boxes 25

Virtual Hosting and Certificates (cont. ) 26 Virtual Hosting and Certificates (cont. ) 26

Tunneling Secure Traffic Through Proxies Corporate firewall proxy Public Internet client Firewall proxy Security Tunneling Secure Traffic Through Proxies Corporate firewall proxy Public Internet client Firewall proxy Security perimeter 27

Tunneling Secure Traffic Through Proxies (cont. ) Proxy cannot proxy an encrypted request proxy. Tunneling Secure Traffic Through Proxies (cont. ) Proxy cannot proxy an encrypted request proxy. ncnu. edu. tw client. ncnu. edu. tw www. cajun-gifts. com bdfwr 73 ytr 6 ouydoiw 687 eqidfjwvd 76 weti 76 fig 287 hdi 9 8 r 82 yr 87 pfdy 72 y 87193836 PDUyqe 719 eyty 3 gee 98 y 8787 28

Reference n HTTP Security n Web Security, Privacy & Commerce Simson Garfinkel, O’reilly & Reference n HTTP Security n Web Security, Privacy & Commerce Simson Garfinkel, O’reilly & Associates, Inc. This is one of the best, most readable introductions to web security and the use of SSL/TLS and digital certificates. n http: //www. ietf. org/rfc 2818. txt RFC 2818, “HTTP Over TLS, ” specifies how to implement secure HTTP over Transport Layer Security (TLS), the modern successor to SSL. n http: //www. ietf. org/rfc 2246. txt RFC 2817, “Upgrading to TLS Within HTTP/1. 1, ” explains hoe to use the Upgrade mechanism in HTTP/1. 1 to initiate TLS over an existing TCP connection. This allows unsecured and secured HTTP traffic to share the same well-known port (in this case, http: at 80 rather than https: at 443). It also enables virtual hosting, so a single HTTP+TLS server can disambiguate traffic intended for several hostnames at a single IP address. 29

Reference (cont. ) n SSL and TLS n http: //ww. ietf. org/rfc 2246. txt Reference (cont. ) n SSL and TLS n http: //ww. ietf. org/rfc 2246. txt RFC 2246, “The TLS Protocol Version 1. 0, ” specifies Version 1. 0 of the TLS protocol (the successor to SSL). TLS provides communications privacy over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, and message forgery. n http: //developer. netscape. com/docs/manuals/security /sslin/contents. htm “Introduction to SSL” introduces the Secure Sockets Layer (SSL) protocol. Originally developed by Netscape, SSL has been universally accepted on the World Wide Web for authenticated and encrypted communication between clients and servers. n http: //www. netscape. com/eng/ssl 3/draft 302. txt “The SSL Protocol Version 3. 0” is Netscape’s 1996 specification for SSL. 30

Reference (cont. ) n n http: //developer. netscape. com/tech/security/s sl/howitworks. html “How SSL Works” Reference (cont. ) n n http: //developer. netscape. com/tech/security/s sl/howitworks. html “How SSL Works” is Netscape’s introduction to key cryptography. http: //www. openssl. org The Open. SSL Project is a collaborative effort to develop a robust, commercial-grade, full-featured, and open source toolkit implementing the Secure Sockets Layer (SSL v 2/v 3) and Transport Layer Security (TLS v 1) protocols, as well as a full-strength, general-purpose cryptography library. 31