Integrity and Authentication

Anmerkungen:

• The ability to guarantey that a given message has not been modified from its original content.

1. Manual

   Anmerkungen:

   • 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

   Anmerkungen:

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

   Anmerkungen:

   • Computed summaries are compared 
   1. Cryptographic Hash

      Anmerkungen:

      • Uses Hash Functions to provide: - performance - one-way (not invertible) - collision free -> impossible to achieve completely; alisiang probability is 1/(2^Nbit).
      1. MD2
      2. MD4
      3. MD5
      4. SHA-1
      5. SHA-2
      6. SHA-3
      7. RIPEMD
   2. Authentication
      1. Protected Digest
         1. MAC - Message Authentication Code

            Anmerkungen:

            • 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!
            1. is done by Cryptography

               Anlagen:

               • Cryptography
               1. based on Symmetric Cryptography

                  Anmerkungen:

                  • 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.
                  1. Authentication by means of symmetric encryption of the message
                  2. Authentication by means of symmetric encryption of the message digest
                  3. Authentication by keyed-digest
               2. based on Asymmetric Cryptography
                  1. Authentication by means of digital signature
            2. To provide both confidentiality and authentication (+ integrity) combine cryptography of data with symmetric alg and use MAC
               1. Different combinations of authentication and encryption exists
                  1. Authenticate-And-Encrypt
                  2. Authenticate-Then-Encrypt
                  3. Encrypt-Then-Authenticate
                  4. Authenticated Encryption
                     1. AEAD
                     2. IGE
         2. MIC - Message Integrity Code