Cryptography and Network Security UNIT IV — NETWORK

X. 509 Certificates Ø issued by a Certification Authority (CA), containing: l l l version 1, 2, or 3 serial number (unique within CA) identifying certificate signature algorithm identifier issuer X. 500 name (CA) period of validity (from - to dates) subject X. 500 name (name of owner) subject public-key info (algorithm, parameters, key) issuer unique identifier (v 2+) subject unique identifier (v 2+) extension fields (v 3) signature (of hash of all fields in certificate)

X. 509 Certificates

Obtaining a User Certificate Ø Certificate notation: CA{…} Ø Any user with CA’s public key can verify the user public key that was certified Ø No party other than the CA can modify the certificate without being detected Ø because cannot be forged, certificates can be placed in a public directory

CA Hierarchy if both users share a common CA then they are assumed to know its public key Ø otherwise CA's must form a hierarchy Ø use certificates linking members of hierarchy to validate other CA's l each CA has certificates for clients (forward) and parent (backward) Ø each client trusts parents certificates Ø enable verification of any certificate from one CA by users of all other CAs in hierarchy Ø

CA Hierarchy

Certificate Revocation Ø Ø certificates have a period of validity may need to revoke before expiry: 1. user's private key is compromised 2. user is no longer certified by this CA 3. CA's certificate is compromised CA’s maintain list of revoked certificates l the Certificate Revocation List (CRL) users should check certificates with CA’s CRL

Authentication Procedures Ø X. 509 includes three alternative authentication procedures: Ø One-Way Authentication Ø Two-Way Authentication Ø Three-Way Authentication Ø all use public-key signatures Ø See Figure 14. 6 for Authentication

One-Way Authentication Ø 1 message ( A->B) used to establish l the identity of A and that message is from A l message was intended for B l integrity & originality of message Ø message must include timestamp, nonce, B's identity and is signed by A Ø may include additional info for B l eg session key

Two-Way Authentication Ø 2 messages (A->B, B->A) which also establishes in addition: l the identity of B and that reply is from B l that reply is intended for A l integrity & originality of reply Ø reply includes original nonce from A, also timestamp and nonce from B Ø may include additional info for A

Three-Way Authentication Ø 3 messages (A->B, B->A, A->B) which enables above authentication without synchronized clocks Ø has reply from A back to B containing signed copy of nonce from B Ø means that timestamps need not be checked or relied upon

X. 509 Version 3 Ø has been recognised that additional information is needed in a certificate l email/URL, policy details, usage constraints Ø rather than explicitly naming new fields defined a general extension method Ø extensions consist of: l extension identifier l criticality indicator l extension value

Certificate Extensions Ø key and policy information l convey info about subject & issuer keys, plus indicators of certificate policy Ø certificate subject and issuer attributes l support alternative names, in alternative formats for certificate subject and/or issuer Ø certificate path constraints l allow constraints on use of certificates by other CA’s

Public Key Infrastructure

Chapter 15 – Electronic Mail Security Despite the refusal of VADM Poindexter and Lt. Col North to appear, the Board's access to other sources of information filled much of this gap. The FBI provided documents taken from the files of the National Security Advisor and relevant NSC staff members, including messages from the PROF system between VADM Poindexter and Lt. Col North. The PROF messages were conversations by computer, written at the time events occurred and presumed by the writers to be protected from disclosure. In this sense, they provide a first-hand, contemporaneous account of events. —The Tower Commission Report to President Reagan on the Iran-Contra Affair, 1987

Email Security Ø email is one of the most widely used and regarded network services Ø currently message contents are not secure l may be inspected either in transit l or by suitably privileged users on destination system

Email Security Enhancements Ø confidentiality l protection from disclosure Ø authentication l of sender of message Ø message integrity l protection from modification Ø non-repudiation of origin l protection from denial by sender

Pretty Good Privacy (PGP) Ø widely used de facto secure email Ø developed by Phil Zimmermann Ø selected best available crypto algs to use Ø integrated into a single program Ø on Unix, PC, Macintosh and other systems Ø originally free, now also have commercial versions available

PGP Operation – Authentication sender creates message use SHA-1 to generate 160 -bit hash of message 3. signed hash with RSA using sender's private key, and is attached to message 4. receiver uses RSA with sender's public key to decrypt and recover hash code 5. receiver verifies received message using hash of it and compares with decrypted hash code 1. 2.

PGP Operation – Confidentiality 1. 2. 3. 4. 5. sender generates message and 128 bit random number as session key for it encrypt message using CAST-128 / IDEA / 3 DES in CBC mode with session key encrypted using RSA with recipient's public key, & attached to msg receiver uses RSA with private key to decrypt and recover session key is used to decrypt message

PGP Operation – Confidentiality & Authentication Ø can use both services on same message l create signature & attach to message l encrypt both message & signature l attach RSA/El. Gamal encrypted session key

PGP Operation – Compression Ø by default PGP compresses message after signing but before encrypting l so can store uncompressed message & signature for later verification l & because compression is non deterministic Ø uses ZIP compression algorithm

PGP Operation – Email Compatibility when using PGP will have binary data to send (encrypted message etc) Ø however email was designed only for text Ø hence PGP must encode raw binary data into printable ASCII characters Ø uses radix-64 algorithm Ø maps 3 bytes to 4 printable chars l also appends a CRC l Ø PGP also segments messages if too big

PGP Operation – Summary

PGP Session Keys Ø need a session key for each message l of varying sizes: 56 -bit DES, 128 -bit CAST or IDEA, 168 -bit Triple-DES Ø generated using ANSI X 12. 17 mode Ø uses random inputs taken from previous uses and from keystroke timing of user

PGP Public & Private Keys Ø 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 l but this is inefficient l Ø rather use a key identifier based on key is least significant 64 -bits of the key l will very likely be unique l Ø also use key ID in signatures

PGP Message Format

PGP Key Rings Ø each PGP user has a pair of keyrings: l public-key ring contains all the public-keys of other PGP users known to this user, indexed by key ID l private-key ring contains the public/private key pair(s) for this user, indexed by key ID & encrypted keyed from a hashed passphrase Ø security of private keys thus depends on the pass-phrase security

PGP Message Generation

PGP Message Reception

PGP Key Management rather than relying on certificate authorities Ø in PGP every user is own CA Ø l Ø can sign keys for users they know directly forms a “web of trust” trust keys have signed l can trust keys others have signed if have a chain of signatures to them l key ring includes trust indicators Ø users can also revoke their keys Ø

S/MIME (Secure/Multipurpose Internet Mail Extensions) Ø security enhancement to MIME email l original Internet RFC 822 email was text only l MIME provided support for varying content types and multi-part messages l with encoding of binary data to textual form l S/MIME added security enhancements Ø have S/MIME support in many mail agents l eg MS Outlook, Mozilla, Mac Mail etc

S/MIME Functions Ø enveloped data l encrypted content and associated keys Ø signed data l encoded message + signed digest Ø clear-signed data l cleartext message + encoded signed digest Ø signed & enveloped data l nesting of signed & encrypted entities

S/MIME Cryptographic Algorithms Ø digital signatures: DSS & RSA Ø hash functions: SHA-1 & MD 5 Ø session key encryption: El. Gamal & RSA Ø message encryption: AES, Triple-DES, RC 2/40 and others Ø MAC: HMAC with SHA-1 Ø have process to decide which algs to use

S/MIME Messages Ø S/MIME secures a MIME entity with a signature, encryption, or both Ø forming a MIME wrapped PKCS object Ø have a range of content-types: l enveloped data l signed data l clear-signed data l registration request l certificate only message

S/MIME Certificate Processing Ø S/MIME uses X. 509 v 3 certificates Ø managed using a hybrid of a strict X. 509 CA hierarchy & PGP’s web of trust Ø each client has a list of trusted CA’s certs Ø and own public/private key pairs & certs Ø certificates must be signed by trusted CA’s

Certificate Authorities Ø have several well-known CA’s Ø Verisign one of most widely used Ø Verisign issues several types of Digital IDs Ø increasing levels of checks & hence trust Class 1 2 3 Identity Checks name/email check + enroll/addr check + ID documents Usage web browsing/email, subs, s/w validate e-banking/service access

Summary Ø have considered: l secure email l PGP l S/MIME

IP Security -

Outline Internetworking and Internet Protocols Ø IP Security Overview Ø IP Security Architecture Ø Authentication Header Ø Encapsulating Security Payload Ø Combinations of Security Associations Ø Key Management Ø

TCP/IP Example

IPv 4 Header

IPv 6 Header

IP Security Overview Ø Ø IPSec is not a single protocol. Instead, IPSec provides a set of security algorithms plus a general framework that allows a pair of communicating entities to use whichever algorithms to provide security appropriate for the communication. Ø Applications of IPSec Secure branch office connectivity over the Internet l Secure remote access over the Internet l Establsihing extranet and intranet connectivity with partners l Enhancing electronic commerce security l

IP Security Scenario

IP Security Overview Ø Benefits of IPSec Transparent to applications - below transport layer (TCP, UDP) l Provide security for individual users l Ø IPSec can assure that: A router or neighbor advertisement comes from an authorized router l A redirect message comes from the router to which the initial packet was sent l A routing update is not forged l

IP Security Architecture Ø IPSec documents: NEW updates in 2005! l RFC 2401: Security Architecture for the Internet Protocol. S. Kent, R. Atkinson. November 1998. (An overview of security architecture) RFC 4301 (12/2005) l RFC 2402: IP Authentication Header. S. Kent, R. Atkinson. November 1998. (Description of a packet encryption extension to IPv 4 and IPv 6) RFC 4302 (12/2005) l RFC 2406: IP Encapsulating Security Payload (ESP). S. Kent, R. Atkinson. November 1998. (Description of a packet emcryption extension to IPv 4 and IPv 6) RFC 4303 (12/2005) l RFC 2407 The Internet IP Security Domain of Interpretation for ISAKMP D. Piper. November 1998. PROPOSED STANDARD. (Obsoleted by RFC 4306) l RFC 2408: Internet Security Association and Key Management Protocol (ISAKMP). D. Maughan, M. Schertler, M. Schneider, J. Turner. November 1998. (Specification of key managament capabilities) (Obsoleted by RFC 4306) l RFC 2409 The Internet Key Exchange (IKE) D. Harkins, D. Carrel. November 1998. PROPOSED STANDARD. (Obsoleted by RFC 4306, Updated by RFC 4109)

IP Security Architecture Ø Internet Key Exchange (IKE) A method for establishing a security association (SA) that authenticates users, negotiates the encryption method and exchanges the secret key. IKE is used in the IPsec protocol. Derived from the ISAKMP framework for key exchange and the Oakley and SKEME key exchange techniques, IKE uses public key cryptography to provide the secure transmission of the secret key to the recipient so that the encrypted data may be decrypted at the other end. (http: //computing-dictionary. thefreedictionary. com/IKE) RFC 4306 Internet Key Exchange (IKEv 2) Protocol C. Kaufman, Ed. December 2005 (Obsoletes RFC 2407, RFC 2408, RFC 2409) PROPOSED STANDARD Ø RFC 4109 Algorithms for Internet Key Exchange version 1 (IKEv 1) P. Hoffman. May 2005 (Updates RFC 2409) PROPOSED STANDARD Ø

IPSec Document Overview

IPSec Services Ø Access Control Ø Connectionless integrity Ø Data origin authentication Ø Rejection of replayed packets Ø Confidentiality (encryption) Ø Limited traffic flow confidentiallity

Security Associations (SA) Ø A one way relationsship between a sender and a receiver. Ø Identified by three parameters: l Security Parameter Index (SPI) l IP Destination address l Security Protocol Identifier

Transport Mode SA Tunnel Mode SA AH Authenticates IP payload and Authenticates entire inner IP selected portions of IP header packet plus selected portions and IPv 6 extension headers of outer IP header ESP Encrypts IP payload any IPv 6 extesion header ESP with authentication Encrypts IP payload any Encrypts inner IP packet. IPv 6 extesion header. Authenticates inner IP Authenticates IP payload but packet. no IP header Encrypts inner IP packet

Before applying AH

Transport Mode (AH Authentication)

Tunnel Mode (AH Authentication)

Authentication Header Provides support for data integrity and authentication (MAC code) of IP packets. Ø Guards against replay attacks. Ø

End-to-end versus End-to. Intermediate Authentication

Encapsulating Security Payload Ø ESP provides confidentiality services

Encryption and Authentication Algorithms Ø Encryption: l l l Ø Three-key triple DES RC 5 IDEA Three-key triple IDEA CAST Blowfish Authentication: HMAC-MD 5 -96 l HMAC-SHA-1 -96 l

ESP Encryption and Authentication

ESP Encryption and Authentication

Combinations of Security Associations

Combinations of Security Associations

Combinations of Security Associations

Combinations of Security Associations

Key Management Ø Two types: l Manual l Automated Oakley Key Determination Protocol • Internet Security Association and Key Management Protocol (ISAKMP) •

Oakley Ø Three authentication methods: l Digital signatures l Public-key encryption l Symmetric-key encryption (aka. Preshare key)

ISAKMP

Cryptography and Network Security Third Edition by William Stallings Lecture slides by Lawrie Brown Edited by Dick Steflik

Web Security Ø Ø Web now widely used by business, government, individuals but Internet & Web are vulnerable have a variety of threats l integrity l confidentiality l denial of service l authentication need added security mechanisms

SSL (Secure Socket Layer) Ø transport layer security service Ø originally developed by Netscape Ø version 3 designed with public input Ø subsequently became Internet standard known as TLS (Transport Layer Security) Ø uses TCP to provide a reliable end-to-end service Ø SSL has two layers of protocols

Where SSL Fits HTTP SMTP POP 3 HTTPS SSMTP SPOP 3 80 443 25 110 465 995 Secure Sockets Layer Transport Network Link

Uses Public Key Scheme Ø Each client-server pair uses l 2 public keys • one for client (browser) l • created when browser is installed on client machine one for server (http server) l created when server is installed on server hardware l 2 private keys one for client browser • one for server (http server) •

SSL Architecture

SSL Architecture Ø SSL session l an association between client & server l created by the Handshake Protocol l define a set of cryptographic parameters l may be shared by multiple SSL connections Ø SSL connection l a transient, peer-to-peer, communications link l associated with 1 SSL session

SSL Record Protocol Ø confidentiality using symmetric encryption with a shared secret key defined by Handshake Protocol l IDEA, RC 2 -40, DES, 3 DES, Fortezza, RC 4 -40, RC 4 -128 l message is compressed before encryption l Ø message integrity l using a MAC (Message Authentication Code) created using a shared secret key and a short message

SSL Change Cipher Spec Protocol Ø one of 3 SSL specific protocols which use the SSL Record protocol Ø a single message Ø causes pending state to become current Ø hence updating the cipher suite in use

SSL Alert Protocol conveys SSL-related alerts to peer entity Ø severity Ø • Ø warning or fatal specific alert unexpected message, bad record mac, decompression failure, handshake failure, illegal parameter • close notify, no certificate, bad certificate, unsupported certificate, certificate revoked, certificate expired, certificate unknown • Ø compressed & encrypted like all SSL data

SSL Handshake Protocol Ø allows server & client to: authenticate each other l to negotiate encryption & MAC algorithms l to negotiate cryptographic keys to be used l Ø comprises a series of messages in phases Establish Security Capabilities l Server Authentication and Key Exchange l Client Authentication and Key Exchange l Finish l

SSL Handshake Protocol

TLS (Transport Layer Security) IETF standard RFC 2246 similar to SSLv 3 Ø with minor differences Ø in record format version number l uses HMAC for MAC l a pseudo-random function expands secrets l has additional alert codes l some changes in supported ciphers l changes in certificate negotiations l changes in use of padding l

Secure Electronic Transactions (SET) Ø open encryption & security specification Ø to protect Internet credit card transactions Ø developed in 1996 by Mastercard, Visa etc Ø not a payment system, rather a set of security protocols & formats l secure communications amongst parties l trust from use of X. 509 v 3 certificates l privacy by restricted info to those who need

SET Components

SET Transaction 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. customer opens account customer receives a certificate merchants have their own certificates customer places an order merchant is verified order and payment are sent merchant requests payment authorization merchant confirms order merchant provides goods or service merchant requests payment

Dual Signature Ø customer creates dual messages l order information (OI) for merchant l payment information (PI) for bank Ø neither party needs details of other Ø but must know they are linked Ø use a dual signature for this l signed concatenated hashes of OI & PI

Purchase Request – Customer

Purchase Request – Merchant

Purchase Request – Merchant 1. 2. 3. 4. verifies cardholder certificates using CA sigs 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 processes order and forwards the payment information to the payment gateway for authorization (described later) sends a purchase response to cardholder

Payment Gateway Authorization 1. 2. 3. 4. 5. 6. 7. 8. verifies all certificates decrypts digital envelope of authorization block to obtain symmetric key & then decrypts authorization block verifies merchant's signature on authorization block decrypts digital envelope of payment block to obtain symmetric key & then decrypts payment block verifies dual signature on payment block verifies that transaction ID received from merchant matches that in PI received (indirectly) from customer requests & receives an authorization from issuer sends authorization response back to merchant

Payment Capture Ø merchant sends payment gateway a payment capture request Ø gateway checks request Ø then causes funds to be transferred to merchants account Ø notifies merchant using capture response

Summary Ø have considered: l need for web security l SSL/TLS transport layer security protocols l SET secure credit card payment protocols