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• Computer Security0 1 0 COMP U TER 0 1 SECURITY 0 1 1 1BY 0 1 0 0NAUMAN 1 0 1 1 1SHAMIM

Authentication Requirments

• While communicating across a conversation can face the following types of

attacks

• Disclosure

 The information is disclosed to an unauthorized user, this happens when there is not enough security with network traffic such as FTP traffic

• Traffic Analysis

 The start end time and duration of conversation can reveal information that can beuse to launch further attacks

 Example: RSA Timing Attack

• Masquerade

 Insertion of message into network form unauthorized source, misleading the

recipient

 Example: Inserting desired packet in session of an authorized user to gain access to servers or critical information

Security Needs

• The need of security for the previous defined attacks can be categorized as  Confidentiality  The user have trust over the conversation, it is assured that the conversation will not be disclosed to unauthorized users  Message Authentication  If A and B are in communication, both of them can authenticate that the content of the message have not been modified  The message is sent by concerned parties  Digital Signature  An authentication technique

Authentication Function

• The over all process of providing authentication broadly consists of two parts

 Message Authenticator

 A value generated by some function, that is used for authentication

 Authentication Protocols

 The high level protocol that uses authentication functions at lower level to provide security

 Authentication Functions can be grouped as

 Message Encryption  Message Authentication Code  Hash Functions

Symmetric Encryption

• Scheme  A and B both maintains a secret key that is not known to any other party  If A needs to send something to B or vice versa, the selected encryption technique is used for encrypting message, the recipient decrypts the message by his copy of key
• Confidentiality  If the encryption schemes is strong the conversation is saved from disclosure problem  As information cannot be disclosed it cannot be altered

• Authentication  One A and B knows the secret key  If A receives a message and decrypts it is sure that the message is sent by B, same is the case with B
• Symmetric key encryption provides confidentiality and authentication?

• Solution 1  Add some structure with plain text such that  The structure should be a message dependent function  If the message is altered the value of structure should become invalid  Re-calculate the value of that structure at receiving end and compare
• FCS: Frame Check Sequence
• Internal Structures
• External Structures

Source A Destination B

Figure^ 11.2 Internal and External Error Control

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M | |

F (a) Internal error control

D M

K

F

F(M)M E F(M) Compare

M E | |

(b) External error control

D

K

F Compare

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F

EK[M]

F(EK[M])

EK[M]

EK[M || F(M)]

M

Source A Destination B M K

E (a) Symmetric encryption: confidentiality and authentication

D M K

Figure^ 11.1 Basic Uses of Message Encryption

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KUb

E (b) Public-key encryption: confidentialityEKUb(M)

EK(M)

EKRa(M)

EKRa(M)^ EKRa(M)

EKUb[EKRa(M)] EKUb[EKRa(M)]

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M (^) E D M

M (^) E D M

(c) Public-key encryption: authentication and signature

(d) Public-key encryption: confidentiality, authentication, and signature

E D

KRa KUa

KRb

KRa KRb KUa docsity.com

Public Key Cryptography

M Source A Destination B (a) Symmetric encryption: confidentiality and authenticationKE DK^ M

Figure 11.1 Basic Uses of Message Encryption

M KUb

KUb

E (b) Public-key encryption: confidentialityEKUb(M)

EK(M)

EKRa(M)

EKRa(M) EKRa(M)

EKUb[EKRa(M)] EKUb[EKRa(M)]

D M

M (^) E D M

M (^) E D M

(c) Public-key encryption: authentication and signature

(d) Public-key encryption: confidentiality, authentication, and signature

E D

KRa KUa

KRb

KRa KRb KUa