CS6004 CYBER FORENSICS
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This document provides an overview of email security, firewalls, and secure electronic transactions. It discusses Pretty Good Privacy (PGP) and S/MIME for securing emails, including their operations and key management. It also covers different types of firewalls like packet filters, application-level gateways, and circuit-level gateways. Finally, it summarizes the Secure Electronic Transaction (SET) protocol for protecting internet credit card transactions.
CS6004 CYBER FORENSICS
- 1. CS6004 CYBER FORENSICS UNIT – II Dr.A.Kathirvel, Professor, Dept of CSE M N M Jain Engineering College, Chennai
- 2. UNIT - II E-MAIL SECURITY & FIREWALLS PGP – S/MIME – Internet Firewalls for Trusted System: Roles of Firewalls – Firewall related terminology- Types of Firewalls – Firewall designs – SET for E-Commerce Transactions. 2
- 3. Pretty Good Privacy (PGP) • widely used de facto secure email • developed by Phil Zimmermann • selected best available crypto algs to use integrated into a single program • available on Unix, PC, Macintosh and Amiga systems • originally free, now have commercial versions available also 3
- 4. PGP Services 1 Authentication 2. Confidentiality 3. Compression 4.E-mail Compatibility 5.Segmentation & Reassembly 4
- 5. 5
- 6. PGP Operation – Authentication 1. sender creates a message 2. SHA-1 used to generate 160-bit hash code of message 3. hash code is encrypted with RSA using the sender's private key, and result is attached to message 4. receiver uses RSA or DSS with sender's public key to decrypt and recover hash code 5. receiver generates new hash code for message and compares with decrypted hash code, if match, message is accepted as authentic 6
- 7. PGP Operation – Confidentiality 1. sender generates message and random 128-bit number to be used as session key for this message only 2. message is encrypted, using CAST-128 / IDEA/3DES with session key 3. session key is encrypted using RSA with recipient's public key, then attached to message 4. receiver uses RSA with its private key to decrypt and recover session key 5. session key is used to decrypt message 7
- 8. PGP Operation – Confidentiality & Authentication • uses both services on same message –create signature & attach to message –encrypt both message & signature –attach RSA encrypted session key 8
- 9. PGP Operation – Compression • by default PGP compresses message after signing but before encrypting – One can store uncompressed message & signature for later verification – & because compression is non deterministic • uses ZIP compression algorithm 9
- 10. PGP Operation – Email Compatibility • when using PGP will have binary data to send (encrypted message etc) • however email was designed only for text • hence PGP must encode raw binary data into printable ASCII characters • uses radix-64 algorithm – maps 3 bytes to 4 printable chars(ASCII) – also appends a CRC • PGP also segments messages if too big 10
- 11. PGP Operation 11
- 12. Segmentation & Reassembly • PGP subdivides the original message(if length >50000 octects) which is too large to small enough to send via mail. • On the receiving end, PGP reassemble entire original block 12
- 13. PGP Session Keys • need a session key for each message –of varying sizes: 56-bit DES, 128-bit CAST or IDEA, 168-bit Triple-DES • generated using ANSI X12.17 mode • uses random inputs taken from previous uses and from keystroke timing of user 13
- 14. PGP Public & Private Keys • since many public/private keys may be in use, need to identify which is actually used to encrypt session key in a message –could send full public-key with every message –but this is inefficient • rather use a key identifier based on key –is least significant 64-bits of the key –will very likely be unique • also use key ID in signatures 14
- 15. PGP Key Rings • each PGP user has a pair of keyrings: – public-key ring contains all the public-keys of other PGP users known to this user, indexed by key ID – private-key ring contains the public/private key pair(s) for this user, indexed by key ID & encrypted keyed from a hashed passphrase 15
- 17. PGP Key Management • rather than relying on certificate authorities • in PGP every user is own CA – can sign keys for users they know directly • forms a “web of trust” – trust keys have signed – can trust keys others have signed if have a chain of signatures to them • key ring includes trust indicators • users can also revoke their keys 17
- 18. S/MIME (Secure/Multipurpose Internet Mail Extensions) • security enhancement to MIME email – original Internet RFC822 email was text only – MIME provided support for varying content types and multi-part messages – with encoding of binary data to textual form – S/MIME added security enhancements • have S/MIME support in various modern mail agents: MS Outlook, Netscape etc 18
- 19. S/MIME Functions • enveloped data –encrypted content and associated keys • signed data –encoded message + signed digest • clear-signed data –cleartext message + encoded signed digest • signed & enveloped data –nesting of signed & encrypted entities 19
- 20. S/MIME Cryptographic Algorithms • hash functions: SHA-1 & MD5 • digital signatures: DSS & RSA • session key encryption: ElGamal & RSA • message encryption: Triple-DES, RC2/40 and others • have a procedure to decide which algorithms to use 20
- 21. S/MIME Certificate Processing • S/MIME uses X.509 v3 certificates • managed using a hybrid of a strict X.509 CA hierarchy & PGP’s web of trust • each client has a list of trusted CA’s certs • and own public/private key pairs & certs • certificates must be signed by trusted CA’s 21
- 22. INTRODUCTION TO FIREWALL • now everyone want to be on the Internet and to interconnect networks • has persistent security concerns – can’t easily secure every system in org • typically use a Firewall • to provide perimeter defence • as part of comprehensive security strategy 22
- 23. What is a Firewall? • a choke point of control and monitoring • interconnects networks with differing trust • imposes restrictions on network services • auditing and controlling access • provide NAT & usage monitoring • implement VPNs using IPSec • must be immune to penetration • Effective means of protection a local system or network of systems from network-based security threats while affording access to the outside world via WAN`s or the Internet 23
- 24. Firewall Limitations • cannot protect from attacks bypassing it –eg sneaker net, utility modems, trusted organisations, trusted services (eg SSL/SSH) • cannot protect against internal threats –eg disgruntled or colluding employees • cannot protect against access via WLAN –if improperly secured against external use • cannot protect against malware imported via laptop, PDA, storage infected outside 24
- 25. 25 Firewall Design Principles • Information systems undergo a steady evolution (from small LAN`s to Internet connectivity) • Strong security features for all workstations and servers not established • The firewall is inserted between the premises network and the Internet • Aims: – Establish a controlled link – Protect the premises network from Internet-based attacks – Provide a single choke point 25
- 26. Firewall Characteristics • Design goals: –All traffic from inside to outside must pass through the firewall (physically blocking all access to the local network except via the firewall) –Only authorized traffic (defined by the local security police) will be allowed to pass –The firewall itself is immune to penetration (use of trusted system with a secure operating system) 26
- 27. Firewall Characteristics • Four general techniques: • Service control – Determines the types of Internet services that can be accessed, inbound or outbound • Direction control – Determines the direction in which particular service requests are allowed to flow • User control – Controls access to a service according to which user is attempting to access it • Behavior control – Controls how particular services are used (e.g. filter e- mail) 27
- 28. Types of Firewalls • Three common types of Firewalls: –Packet-filtering routers –Application-level gateways –Circuit-level gateways –(Bastion host) 28
- 29. Firewalls – Packet Filters • simplest, fastest firewall component • foundation of any firewall system • examine each IP packet (no context) and permit or deny according to rules 29
- 30. Firewalls – Packet Filters •hence restrict access to services (ports) •possible default policies •that not expressly permitted is prohibited •that not expressly prohibited is permitted 30
- 31. Firewalls – Packet Filters 31
- 32. Attacks on Packet Filters • IP address spoofing – fake source address to be trusted – add filters on router to block • source routing attacks – attacker sets a route other than default – block source routed packets • tiny fragment attacks – split header info over several tiny packets – either discard or reassemble before check 32
- 33. Firewalls – Stateful Packet Filters • traditional packet filters do not examine higher layer context – ie matching return packets with outgoing flow • stateful packet filters address this need • they examine each IP packet in context – keep track of client-server sessions – check each packet validly belongs to one • hence are better able to detect bogus packets out of context • may even inspect limited application data 33
- 34. Firewalls - Application Level Gateway (or Proxy) • have application specific gateway / proxy • has full access to protocol – user requests service from proxy – proxy validates request as legal – then actions request and returns result to user – can log / audit traffic at application level • need separate proxies for each service – some services naturally support proxying – others are more problematic 34
- 35. Firewalls - Application Level Gateway (or Proxy) 35
- 36. Firewalls - Circuit Level Gateway • relays two TCP connections • imposes security by limiting which such connections are allowed • once created usually relays traffic without examining contents 36 •typically used when trust internal users by allowing general outbound connections •SOCKS is commonly used
- 37. Bastion Host • highly secure host system • runs circuit / application level gateways • or provides externally accessible services • potentially exposed to "hostile" elements • hence is secured to withstand this – hardened O/S, essential services, extra auth – proxies small, secure, independent, non-privileged • may support 2 or more net connections • may be trusted to enforce policy of trusted separation between these net connections 37
- 38. Host-Based Firewalls • s/w module used to secure individual host – available in many operating systems – or can be provided as an add-on package • often used on servers • advantages: – can tailor filtering rules to host environment – protection is provided independent of topology – provides an additional layer of protection 38
- 39. Personal Firewalls • controls traffic between PC/workstation and Internet or enterprise network • a software module on personal computer • or in home/office DSL/cable/ISP router • typically much less complex than other firewall types • primary role to deny unauthorized remote access to the computer • and monitor outgoing activity for malware 39
- 42. Summary of Firewall Locations and Topologies • host-resident firewall • screening router • single bastion inline • single bastion T • double bastion inline • double bastion T • distributed firewall configuration 42
- 43. TRUSTED SYSTRM • Way to enhance the ability of a system to defend against intruders and malicious software. • Trusted system uses Data Access control Basic elements of access control system are Subject, Object & Access right. 43
- 44. Access Matrix • Sparse and implemented by decomposition in 2 ways. 1. Decomposition by columns called as Access Control lists. 2. Decomposition by rows yields capability tickets which specifies authorized objects and operation for a user. 44
- 45. Process Control List for Programs Process 1 (Read, Execute) ACL for Segment A: Process 1 ( Read, Write) ACL for Segment B: Process 2 (Read) Access Control List (ACL) Capability List (CL) Capability List for Process 1 Progress 1 (Read, Execute) Segment A (Read, Write) CL for Process 2: Segment B (Read) 45
- 46. Concept of trusted system This is commonly found in military, where information is categorized as • unclassified (U), • confidential (C), • secret (S), • top secret (TS), or • beyond. This concept is equally applicable in other areas, where information can be organized into categories 46
- 47. Multilevel security • When multiple categories or levels of data are defined, the requirement is referred to as multilevel security. • The general statement of the requirement for multilevel security is that a subject at a high level may not convey information to a subject at a lower or noncomparable level unless that flow accurately reflects the will of an authorized user • No read-up: A subject can only read an object of less or equal security level. This is referred to in the literature as the simple security property • No write-down: A subject can write into an object of greater or equal security level. This is referred to as the *-property (pronounced star property) 47
- 48. Reference Monitor Concept • These two rules( no read up and write down) , if properly enforced, provide multilevel security. For a data processing system, the approach that has been taken, and has been the object of much research and development, is based on the reference monitor concept. • The reference monitor is a controlling element in the hardware and operating system of a computer that regulates the access of subjects to objects on the basis of security parameters of the subject and object. • The reference monitor has access to a file, known as the security kernel database that lists the access privilege (security clearance) of each subject and the protection attributes (classification level) of each object. • The reference monitor enforces the security rules (no read-up, no write- down) and has the following properties: 1. Complete Meditation 2. Isolation 3.Verifiability 48
- 50. Trojan Horse defense • One way to secure against Trojan horse attacks is the use of a secure, trusted operating system • The Trojan horse attack begins when a hostile user, named Alice, gains legitimate access to the system and installs both a Trojan horse program and a private file to be used in the attack as a “back-pocket”. 5050
- 52. Trojan horse defense example • Alice gives read/write permission to herself and gives Bob write-only permission (Fig. a). • Alice now induces Bob to invoke the Trojan horse program, perhaps by advertising it as a useful utility. When the program detects that it is being executed by Bob, it reads the sensitive character string from Bob’s file and copies it into Alice’s back-pocket file (Fig.b). • Both the read and write operations satisfy the constraints imposed by access control lists. Alice then has only to access her file at a later time to learn the value of the string. • Now consider the use of a secure operating system in this scenario (Fig. 15.10c). Security levels are assigned to subjects at logon on the basis of criteria such as the terminal from which the computer is being accessed and the user involved, as identified by password/ID. • In this example, there are two security levels, sensitive (gray) and public (white), ordered so that sensitive is higher than public. Processes owned by Bob and Bob’s data file are assigned the security level sensitive. Alice’s files and processes are restricted to public. • If Bob invokes the Trojan horse program (Fig. 15.10d), that program acquires Bob’s level security. It is therefore able, under the simple security property, to observe the sensitive character string. • When the program attempts to store the string in a public file (the back pocket file), however, the *-property is violated and the attempt is disallowed by the reference monitor. • Thus, the attempt to write into the back-pocket file is denied even though the access control list permits it: The security policy takes precedence over the access control list mechanism. 52
- 53. Secure Electronic Transactions (SET) • Protocol- to protect Internet credit card transactions • developed in 1996 by Mastercard, Visa etc • not a payment system • rather a set of security protocols & formats – secure communications amongst parties – trust from use of X.509v3 certificates – privacy by restricted info to those who need it 53
- 55. SET Transaction 1. customer opens account 2. customer receives a certificate 3. merchants have their own certificates 4. customer places an order 5. merchant is verified 6. order and payment are sent 7. merchant requests payment authorization 8. merchant confirms order 9. merchant provides goods or service 10.merchant requests payment 55
- 56. Dual Signature • customer creates dual messages –order information (OI) for merchant –payment information (PI) for bank • neither party needs details of other • but must know they are linked • use a dual signature for this –Signed(by encryption) and concatenated hashes of OI & PI 56
- 57. Purchase Request – Customer 57
- 58. Purchase Request – Merchant 58
- 59. Purchase Request – Merchant 1. verifies cardholder certificates using CA signs 2. verifies dual signature using customer's public signature key to ensure order has not been tampered with in transit & that it was signed using cardholder's private signature key 3. processes order and forwards the payment information to the payment gateway for authorization (described later) 4. sends a purchase response to cardholder 59
- 60. Payment Gateway Authorization 1. verifies all certificates 2. decrypts digital envelope of authorization block to obtain symmetric key & then decrypts authorization block 3. verifies merchant's signature on authorization block 4. decrypts digital envelope of payment block to obtain symmetric key & then decrypts payment block 5. verifies dual signature on payment block 6. verifies that transaction ID received from merchant matches that in PI received (indirectly) from customer 7. requests & receives an authorization from issuer 8. sends authorization response back to merchant 60
- 61. Payment Capture • merchant sends payment gateway a payment capture request • gateway checks request • then causes funds to be transferred to merchants account • notifies merchant using capture response 61