复旦大学：《信息安全》教学课件_05 Message authentication and Hash function

nformation Security 05 Message authentication and hash function Chapter 1 1 復大软件学院

1 Information Security 05 Message authentication and Hash function Chapter 11

Review Symmetric Cryptography Asymmetric Cryptography 復大软件学院

2 Review • Symmetric Cryptography • Asymmetric Cryptography

wo Review: Symmetric Model Secret key shared by Secret key shared by sender and recipient sender and recipient Transmitted ciphertext Plaintext Plaintext Input Encryption algorithm Decryption algorithm output (e.g, DES) (reverse of encryption algorithm) Bob Alice 3 復大软件学院 LiT

LiJT 3 Review: Symmetric Model Bob Alice

Asymmetric Model Bobs public key rIng Oy STed Mike Alice Alice's public Alice 's private e ke Transmitted ciphertext Plaintext Plaintext Encryption algorithm Decryption algorithm (e. g, RSA) (reverse of encryption algorithm Bob Alice 復大软件学院 LiT

LiJT 4 Asymmetric Model Bob Alice

Review Confidentiality 復大软件学院

5 Review • Confidentiality

Review Confidentiality enough? 復大软件学院

6 Review • Confidentiality • enough？

ef Security Requirements disclosure traffic analysis masquerade content modification sequence modification timing modification source repudiation destination repudiation 復大软件学院

7 Security Requirements • disclosure • traffic analysis • masquerade • content modification • sequence modification • timing modification • source repudiation • destination repudiation

Message Authentication message authentication is concerned with protecting the integrity of a message validating identity of originator non-repudiation of origin(dispute resolution will consider the security requirements then three alternative functions used message encryption message authentication code( MAC) hash function 復大软件学院

8 Message Authentication • message authentication is concerned with: – protecting the integrity of a message – validating identity of originator – non-repudiation of origin (dispute resolution) • will consider the security requirements • then three alternative functions used: – message encryption – message authentication code (MAC) – hash function

Note !! Message vs. Plaintext We will not consider Confidentiality sometimes Authentication 復大软件学院

9 Note !! • Message vs. Plaintext • We will not consider Confidentiality sometimes. • Authentication ?

Message Encryption message encryption by itself also provides a measure of authentication if symmetric encryption is used then receiver know sender must have created it since only sender and receiver now key used know content cannot of been altered if message has suitable structure, redundancy or a checksum to detect any changes 復大软件学院

10 Message Encryption • message encryption by itself also provides a measure of authentication • if symmetric encryption is used then: – receiver know sender must have created it – since only sender and receiver now key used – know content cannot of been altered – if message has suitable structure, redundancy or a checksum to detect any changes