Security Basics. 2003-2004 - Information management 2 Groep T Leuven – Information department 2/31...

Security Basics

2003-2004 - Information management2Groep T Leuven – Information department2/31

Agenda• Properties of a secure communication • Symmetric encryption• Asymmetric encryption• Public key encryption• Digital Signatures• Encryption in the network• History


Properties of a secure communication

• Authentication (identity)–Who are you?

• Authorization–What can you do ?

• Accounting (active audit)–What did you do ?

• Confidentiality

–What can you see ?

• Integrity

–Nothing has been modified

• Non Repudiation

–The sender cannot deny he has sent it

• Anti Replay


Encryption: Basic Model

DecryptionEncryption

Cleartext

Decrypt KeyEncrypt Key

OriginalCleartextCiphertext

NetworkersNetworkers &^$!@#l:{Q&^$!@#l:{Q NetworkersNetworkers

• Encryption turns cleartext into ciphertext• Encryption key as parameter to algorithm• Decryption restores cleartext from ciphertext• Decryption key as parameter to algorithm


Symmetric Encryption

• Encryption and decryption use same mathematical function

• Encryption and decryption use same key• Example: Data Encryption Standard

DES, 3DES, RC2, RC4, AES

Key

NetworkersNetworkers &^$!@#l:{Q&^$!@#l:{Q NetworkersNetworkersDecryptionEncryption

Key


Challenges with Symmetric Encryption

• Keys must be changed frequentlyto avoid analysis, limit risks

• Shared keys must be generatedand distributed securely

• Multiple techniques to achieve this


• By exchanging numbers in the clear, two entities can determine a new uniquenumber known only to them

• Result is a shared key which can be usedas DES key—repeated as often as required

• Scalable and secure key generation

Diffie-Hellman Key Exchange

AliceXBXA

YA = (aXA) mod p YB= (aXB) mod p

a , p

Z = (YB ) XAmod p Z = (YA )XB mod p

Bob


Symmetric Encryption

• Provides confidentiality, data integrity• Relies on a shared secret (key)• Creates a flat community of trust• A relatively fast and efficient mechanism for

bulk data encryption


Asymmetric Encryption

• Encryptor and decryptor use pair of different keys

• Encryptor and decryptor use different functions

• Example: Public key algorithms (RSA, Diffie-Hellman)

Key

NetworkersNetworkers &^$!@#l:{Q&^$!@#l:{Q NetworkersNetworkersDecryptionEncryption

Key


Asymmetric Encryption

• Provides authentication, confidentiality, data integrity (basis for non-repudiation)

• Relies on individual key pairs• Allows for assurance among strangers• Relatively slow and cpu-intensive


Public Key Encryption

• Public/private keys• Digital signatures• Certificates• Certifying Authority (CA)


Authenticate Recipient

• Alice needs to send Bob an encrypted message– Alice picks up Bob’s public key– Alice encrypts the message with Bob’s public key– Alice sends the encrypted message

• Bob decrypts using his private key

Clear

BobAlice

ClearEncrypted

Bob’s Private KeyBob’s Public Key



• Bob needs to know that Alice sent a message– Alice picks up her own private key– Alice encrypts the message with her private key– Alice sends the encrypted message

• Bob decrypts using Alice’s public key

Authenticate Sender

Clear

BobAlice

ClearEncrypted

Alice’s Public KeyAlice’s Private Key



• A digital signature is a message thatis appended to a document

• It can be used to prove the identity of thesender and the integrity of the document

Digital Signature

Signature

InvoicePayment


Digital Signature

• How does Alice sign her message?

Encrypt Hash Using Alice’s Private Key

Hash of Message

Digital Signature = Encrypted Hash of Message

AliceAlice

Message

HashHashFunctionFunction


Digital Signature Verification

• How does Bob verify Alice’s signature ?

Message

If Hashes Are Equal, Signature Is Authentic.

HashHashFunctionFunction

SignatureSignature

Decrypt theReceived Signature

Decrypt Using Alice’s Public Key

Hash of Message

Re-Hash the Received Message

Hash of Message

Message withAppended Signature

SignatureSignature

Message

AliceAlice


• Two common public-key digitalsignature techniques:

• RSA (Rivest, Shamir, Adelman)• DSS (Digital Signature Standard)

• A sender uses his secret key to signsign a document• The receiver of the document uses the sender’s

public key to verifyverify the signature• If the verification is successful, we are

assured of two things:• The document has not been altered• The identity of the author

Digital Signature


Key Attack

Secure


• How can Bob be assured that Alice’s public key belongs to the real Alice?

Where Did the Public Key Come From?

“I’m Margaret Thatcher.” “I’m Mickey Mouse.”

Alice Bob


• A signed message that attests to the authenticity of the users public key

• A digital certificate contains:• Serial number of the certificate• Issuer algorithm information (digest/hash, PK

type, PK)• Valid to/from date• User public key information (PK type, PK)• Signature of issuing authority

Digital Certificate

00001230000123SHA,DH, 3837829....SHA,DH, 3837829....1/1/93 to 12/31/981/1/93 to 12/31/98Alice Smith, Acme CorporationAlice Smith, Acme CorporationDH, 3813710...DH, 3813710...Acme Corporation, Security Dept.Acme Corporation, Security Dept.SHA,DH, 2393702347 ...SHA,DH, 2393702347 ...


Certification AuthorityIssuing Certificates

Certification Authority

A’s Public A’s Public NumberNumber

CA’s CA’s SignatureSignature

Ca’s Ca’s Public NumberPublic Number

User A

Public Number

Certificate Certificate

Public Number

User B

B’s Public B’s Public NumberNumber

CA’s CA’s SignatureSignature

Ca’s Ca’s Public NumberPublic Number

Cisco Systems Confidential 96NWK_ekaufman.ppt 21Cisco Systems Confidential


Example of X.509 Hierarchical Authority Structure

CACA

CACA CACA

CC DDAA BB

Cert UK-IntCert UK-Int Cert UK-USCert UK-US Cert US-ICCert US-IC

Cert UK-BCert UK-B Cert US-CCert US-C Cert US-DCert US-DCert UK-ACert UK-A

UKUK

IntInt

USUS

Cert UK-Int Cert US-Int

Cert Int-USCert Int-USCert Int-UKCert Int-UK

Example: Certificates Used by A to Obtain Public Key of C:Example: Certificates Used by A to Obtain Public Key of C:


Policy Objectives

Access Security

Connectivity

Performance

Ease of use

Authenticity

Confidentiality

Integrity

Auditability


Encryption Alternatives

Network-Layer Encryption

Application-Layer Encryption

Link-LayerEncryption

Link-LayerEncryption

ApplicationLayers (5-7)

Transport/NetworkLayers (3-4)

Link/PhysicalLayers (1-2)


Application Encryption

• Encrypts traffic to/from interoperable applications• Specific to application, but network independent• Application dependent

– All users must have interoperable applications• Examples: S/MIME, https, ssh, ssl


• Encrypts traffic between specific networks, subnets,or address/port pairs

• Specific to protocol, but media/interface independent• Does not need to supported by intermediate network devices• Independent of intermediate topology

Network Encryption

HRServer

E-mailServer

A to HR Server—Encrypted

All Other Traffic—Clear

A

B

D


Link Encryption

• Encrypts all traffic on a link, including network-layer headers• Specific to media/interface type, but protocol independent• Topology dependent

– Traffic is encrypted/decrypted on link-by link basis– All alternative paths must be encrypted/decrypted


• 1976 Public key principles established by Diffie and Hellman

• 1978 Public key implementation defined by Rivest, Shamir, Aldeman for digital signatures

• 1985 First product incorporating public keyintroduced by Cylink

• 1985 El Gamal develops public key digital signatureand encryption scheme based on exponentiation

Evolution of Public Key Cryptography


Evolution of Public Key Cryptography (Cont.)

• 1987-89 Public key emerging as standard in Europe

• Endorsed by SWIFT, EFTPOS (1987)ISO/OSI standards in review phase (1988)

• 1987-95 Public key evolving as U.S. standard

• Used in STU-III Secure Telephone (1987)Adopted by Treasury and Justice (1988)Adopted by Internet (1989)NIST standards in review phase (1989)ANSI X9.17 proposal in review (1989)Digital signature standard (DSS) (1994)FIPS-186 DSS (1994)ANSI X0.42 (draft) for Diffie-Hellman (1995)


Public Key Standards

• OSI/IEC 9594-8 Recommendation X.509 (also ITU X.509):the Directory: Authentication Framework

• AS28095.5.3 (Australian Government)—Electronic DataTransfer-Requirements for Interfaces: Part 5.3 Data Encipherment Algorithms (RSA)

• ISO9796: Information Technology, Security Techniques: Digital Signature Scheme Giving Message Recovery

• ANSI X9.31 (Draft): Public Key Cryptography using Reversible Algorithms for the Financial Services Industry: Part 1: the RSA Signature Algorithm


• ANSI X9.30 (Draft): Public Key Cryptography forthe Financial Service Industry: Part 1: The DigitalSignature Algorithm

• X9.42 (Draft): Diffie-Hellman Public Key Exchange• Federal Information Processing Standard FIPS-186:

Digital Signature Standard• Federal Information Processing Standard FIPS-186:

Digital Signature Standard • Others:

– ETEBAC5, (France)ISO draft standard CD 11166IEEE draft 802.11 Secure Interoperability Standard for LANs

Public Key Standards (Cont.)

Security Basics. 2003-2004 - Information management 2 Groep T Leuven – Information department 2/31...

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