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why hash function is used in digital signature and why it is many - to - one??

please explain.
asked in Computer Networks by Active (2k points) | 409 views

2 Answers

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Hashing Functions

  • hashing functions are used to condense an arbitrary length message to a fixed size, usually for subsequent signature by a digital signature algorithm
  • good cryptographic hash function h should have the following properties:
    • h should destroy all homomorphic structures in the underlying public key cryptosystem (be unable to compute hash value of 2 messages combined given their individual hash values)
    • h should be computed on the entire message
    • h should be a one-way function so that messages are not disclosed by their signatures
    • it should be computationally infeasible given a message and its hash value to compute another message with the same hash value
    • should resist birthday attacks (finding any 2 messages with the same hash value, perhaps by iterating through minor permutations of 2 messages )
  • it is usually assumed that the hash function is public and not keyed
  • traditional CRCs do not satisfy the above requirements
  • length should be large enough to resist birthday attacks (64-bits is now regarded as too small, 128-512 proposed)

Refer the link mentioned below for more information 

answered by Boss (13.6k points)
Also refer the link below for detailed explanation.Although the above link is sufficient for your query.
0 votes
Suppose @indrajeet you have signup your password to GO, if any member of GO want to see your password this is becoz your password is store in GO database. for this purpose mainly hash is used. Your password will be combine with the function which will be in the hash form so that no anyone can decrypt it.

       Next time again when you try to logged in , by putting your own username and password again it will be combine with the same hash function which will be in the form of hash output.This hash will try to match with the hash which is previously stored in the GO server. If both hash output are matching then only you can log in.   and owner of GO who has the server he cant do anything with ur password. if they try to see your password they will get garbage value.
answered by (125 points)

see this Figure

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