复旦大学：《密码学基础》课程教学资源（课件讲稿）05 Message authentication and Hash function

密码学基础(05) Message authentication and Hash function 復大辱软件学院

1 密码学基础（05） Message authentication and Hash function

Review Symmetric Cryptography Asymmetric Cryptography 復大辱软件学院

2 Review • Symmetric Cryptography • Asymmetric Cryptography

o 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 復大辱软件学院 LiST

LiJT 3 Review: Symmetric Model Bob Alice

Asymmetric Model B oDS S public key ring Ted Mike Alice Alice's public Alices private k key 圄「 Transmitted cipherte Plaintext Plaintext Input Encryption algorithm Decryption algorithm output (e. g, RSA) (reverse of encryption algorithm) Bob Alice 復大辱软件学院 LiJT

LiJT 4 Asymmetric Model Bob Alice

Review Confidentiality 復大辱软件学院

5 Review • Confidentiality

Review Confidentiality enough 復大辱软件学院

6 Review • Confidentiality • enough？

o Security Requirements disclosure traffic analysis masquerade content modification sequence modification timing modification source repudiation destination repudiation 復大辱软件学院

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

ef, 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 復大辱软件学院

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 復大辱软件学院

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

oe 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 復大辱软件学院

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