Case Study (Mid-term question)

Case Study (Mid-term question) • Bob sells BatLab • Software • License • Alice buys BatLab • Credit card information • Number of licenses Bob Alice

Security Requirements • Alice wants • Authentication of Bob • Confidentiality and integrity of the order information • Prevention of order replay • Bob wants • Non-repudiation of the order • Confidentiality and integrity of the licenses • Integrity of the software • Other Issues • DoS (message lost) • Attacks to the host Bob Alice

Security Mechanisms • What do we need/how we get them? • Authentication (of Bob)/Key distribution • Certificate  Public key • Public key  Secret session key • Confidentiality (order/license) • Symmetric cipher encryption based on secret key • E.g. AES • Message Integrity Protection (software) • Message authentication code based on secret key • E.g. HMAC-SHA1 • Non-repudiation (order) • Digital signature • Defense against replay attack • Usage of Timestamp

Questions • Where these security functions should be implemented? • Who should implement them? • Application developer? (BatLab.com) • Application service developer? (Apache/Mazilla) • System developer? (Microsoft) • Network service provider? (Sprint) • Etc.. • If it is not a single person’s job, what security protocols/services are available? How they are designed?

Network Design • Network Stack/Layer Internet Application (HTTP) Application (HTTP) Transport (TCP) Transport (TCP) End host Network (IP) Network (IP) Network (IP) Network (IP) network … Link Link Link Link

Placement of Security Function • What to encrypt/protect • Message format • Where the security function should be located? • Network stack • Link vs. End-to-end • Where each layer is located and how it may get attacked • Aspects to consider • Message security (which fields in the packet are protected) • Number of keys required • Number of encryption/decryptions • Transparency to users/end hosts

Link vs. End-to-End Encryption

Message format

Big Picture • Application-specific solutions • Web security • End-host-based solutions • Secure network-based applications • PGP, application layer solution • SSL, transportation layer solution • Network-based solutions • Secure network + support for application • IPsec • Internet Security • BGP security • Wireless Security • IEEE 802.11 security Application Web security PGP SSL Transport Connection-oriented vs. connectionless IPSec BGP Network WPA Link

Our Goal • Learn these important security protocols so that we can use them • Learn how they are designed and use similar design in our system • Many pitfalls exist in secure networking system design • Home-brew security solutions usually have many weaknesses • The correct usage of cryptography is crucial • Following conventions is very important

CS 285 Network SecurityPGP Fall 2011 Yuan Xue

Pretty Good Privacy • Overview • Phil Zimmermann in 1991 • Open PGP • Open Standard followed by PGP, GnuPG • PGP vs. GnuPG • PGP goes commercial in 1996 • GnuPG is a free replacement for PGP • Basics • Build a general-purpose security application that is independent of OS • Select the existing cryptographic algorithms as building blocks • Operations • Encryption • Signature • Key management More info: http://en.wikipedia.org/wiki/Pretty_Good_Privacy

Overview • Key Generation • public and privacy key pair/session keys • Key Storage • Key Distribution • Import/export • Fingerprint • Web of Trust • Security Operations • Encryption • Message Authentication • Signature and Verification Start with

Operation -- Authentication SHA-1 DSS/RSA ZIP

Operation -- Encryption ElGamal/RSA one-time session key CAST-128/IDEA/3DES in CFB mode

Operation – Put two together

Details • Compression • Signature before compression • Convenience of future verification • Flexibility in compression algorithm/implementation choice • Message encryption after compression • Less redundancy in plaintext strengthen cryptographic security • Email Capability • Usage of ASCII in Email • Converting 8-bit binary code to ASCII characters • Radix-64 conversion • 3 octets of binary code (3*8 = 24 bits)  4 ASCII characters (4*8 = 32 bits) why? • 33% expansion • compression offset

Keys • Types • Public and private key pair • One-time session symmetric key • Issues • Key generation • Key storage • Key management (distribution)

Key Identifier • A user may have multiple keys • Need an ID • Unique to user ID with very high probability • Key ID of KUa = KUa mod 264

Key Generation • Session Key Generation • Generating unpredictable session keys • E.g., 128-bit CAST key • Two 64-bit blocks encrypted by a 128-bit key in CFB mode  two 64-bit ciphertext as the 128-bit session key • Two 64-bit blocks from a 128-bit random stream based on keystroke input from the user • Previous session key and the random stream forms the 128-bit key input User input 64-bit block 64-bit block Previous Session key + Key input CAST-128 in CFB mode New session key

PGP Message Format • keys are needed for the recipient to identify the keys to • decrypt the key (KUb) • Verify the signature(KUa) Time the signature is made • Plaintext copy of the first two octets. • Enable the recipient to determine if the correct public key was used to decrypt the message digest • Error detection for the message Time the message is made

Key Storage • Pubic and Private Key Ring • Secure the private key with passphrase • Passphrase  hash code via SHA-1 • Encrypt the private key via CAST-128/IDEA/3DES with the hash code as the key • Store the encrypted private key

Put Things Together

Key management • Direct Verification • Physical delivery • Fingerprint • Trusted Third Party • Signed certificate of a key • Web of Trust • A self-organized trust management mechanism • Revoke Public Key • Key revocation certificate

Web of Trust • Directly signed by you • A,B,…,F (first tier) • By the ones you trust to sign (D, E, F, L) • L,M,N, O (2nd tier), P, Q (3rd tier) • By getting enough signatures from partially trusted parties (A,B) • H

Case Study (Mid-term question)