Chapter 4 a - X.509 Authentication Network Security Spring 2017 http://www.faisalakhan.info/contentPage/Classes Dr. Faisal Khan faisal.khan@buitms.edu.pk Office: SS Block

X.509 Authentication Service • An International Telecommunications Union (ITU) recommendation (versus “standard”) for allowing computer host or users to securely identify themselves over a network. • An X.509 certificate purchased from a “Certificate Authority” (trusted third party) allows a merchant to give you his public key in a way that your Browser can generate a session key for a transaction, and securely send that to the merchant for use during the transaction (padlock icon on screen closes to indicate transmissions are encrypted). • Once a session key is established, no one can “high jack” the session (for example, after your enter your credit card information, an intruder can not change the order and delivery address). • User only needs a Browser that can encrypt/decrypt with the appropriate algorithm, and generate session keys from truly random numbers. • Merchant’s Certificate is available to the public, only the secret key must be protected. Certificates can be cancelled if secret key is compromised.

Raw “Certificate” has user name, public key, expiration date, ... CA’s Secure Area Generate hash code of Raw Certificate Raw Cert. MIC Hash Encrypt hash code with CA’s private key to form CA’s signature Signed Cert. Signed Certificate Recipient can verify signature using CA’s public key. Certificate Authority generates the “signature” that is added to raw “Certificate” 3

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Information Provided by Browser about a Certificate This Certificate belongs to: investing.schwab.com trading subnet a 1199 Charles Schwab & Co., Inc. Phoenix, Arizona, US This Certificate was issued by Secure Server Certification Authority RSA Data Security, Inc. US Serial Number: 6B:68:2F:3B:FD:8A:46:73:04:33:10:8A:32:1E:47:5B This Certificate is valid from Wed Nov 03, 1999 to Thu Nov 02, 2000 Certificate Fingerprint: 4B:80:C6:C5:2D:63:14:E7:6F:50:BD:16:39:3C:96:FD 5

Certificates Can Be Deleted (and Added) Are you sure that you want to delete this Site Certificate? This Certificate belongs to: endor.mcom.com Netscape Communications Corp. US This Certificate was issued by: rootca.netscape.com Information Systems Netscape Communications Corporation Serial Number: 01:77 This Certificate is valid from Thu May 15, 1997 to Tue Nov 11, 1997 Certificate Fingerprint: 06:BF:60:88:D9:E7:59:BF:3A:35:74:33:28:8E:26:F6 6

X.509 Chain of Authentication CA<<A>> = CA {A’s id and information} X<<A>> = certificate of A “signed” by X To authenticate X<<A>>, you must get the public key of X from a trusted source, such as Z - your own CA. ( Z<<X>>) Z in turn may have to get X’s certificate from a higher level CA. Ultimately there must be an “Authentication Tree” of CA’s so that a user can work up the tree (from Z) and back down to the issuer of the certificate in question, X. 7

Chain of Authentication In practice, there is no single top-level Certificate Authority (CA), only a group of CA’s that each Browser vendor deems fit to include in the installation program. X.509 Chain of Authentication 8

“Root” Certificate Authorities in Firefox (2010) 9 added by user

Safari Browser - Google Safe Browsing Service - 2011 Firefox Browser - OCSP - 2011 10