Integrity and Authentication

Integrity and Authentication

1. Manual

   • Choose randomly pieces of message and compare. There is no 100% assurance and comparing all pieces would take too long.

2. CRC - Cyclic Redundancy Check

   • not suitable for security: they expect that unpredictable events damage single equioprobable bits randomly.

3. Digest

   • Computed summaries are compared 
   • Cryptographic Hash
     • Uses Hash Functions to provide: - performance - one-way (not invertible) - collision free -> impossible to achieve completely; alisiang probability is 1/(2^Nbit).
     • MD2
     • MD4
     • MD5
     • SHA-1
     • SHA-2
     • SHA-3
     • RIPEMD
   • Authentication
     • Protected Digest
       • MAC - Message Authentication Code
         • it can support also a MID (Message IDentifier) to avoid replay attacks. Must always be associated to a MAC to avoid changes to data.  Consider that this has not the purpose of guaranteing confidentiality!
         • is done by Cryptography
           • Cryptography
           • based on Symmetric Cryptography
             • The authentication is based on the use of a symmetric key. Only who knows the key can modify the MAC. Being based on a shared key it is not possible to provide non-repudiation.
             • Authentication by means of symmetric encryption of the message
             • Authentication by means of symmetric encryption of the message digest
             • Authentication by keyed-digest
           • based on Asymmetric Cryptography
             • Authentication by means of digital signature
         • To provide both confidentiality and authentication (+ integrity) combine cryptography of data with symmetric alg and use MAC
           • Different combinations of authentication and encryption exists
             • Authenticate-And-Encrypt
             • Authenticate-Then-Encrypt
             • Encrypt-Then-Authenticate
             • Authenticated Encryption
               • AEAD
               • IGE
       • MIC - Message Integrity Code