Message authentication - protect againts active attack
- verify receive message is authentic
- use conventional encryption / seperate authentication mechanism
Hash Function
- Hash value depends on algorithm
- algorithm (MD-5, SHA-1,SHA-256,384,512)
- produce fixed length output
- produce fixed length output
- easy to compute
- one way property - once u give a number, no more same number at another time
- weak & strong collision resistence.
MD5 (Message-Digest algorithm 5)
- different size of input, same size of output
- not recommend
SHA-1 (Secure Hash Algorithm)
- SHA-1 = MD-5 + DSS (Digital signature standard)
- handle by NIST & NSA
- produce 160 bit MAC
- message block has 512 bit represent 32 word
SHA-256
- use 6 function
- each function operates on 32 bit
- message block has 512 bit represent 32 word
- message block has 512 bit represent 32 word
Digital Signature
- algorithm = (RSA & El Gamal)
Certification authority (NA)
- body that responsible to ensure/ justify that the public key that u've got from your admin its really came from him.
Validation Authority (VA)
- end users ask the VA if a given certificate is still valid and receive a yes or no answer.
Method of attack againts encryption information:
- Ciphertext - only attack
- Known plaintext
- Choosen plaintext
- Choosen ciphertext
Method of attack againts encryption system:
- Brute-Force attack
- Replay attack
- Man-in-the-middle
- Fault in Cryptosystem