Doubt in MD5 hash algorithm

Hi guys,
A question regarding MD5 hash algorithm.

The MD5 algo accepts an input block of any arbitrary length and outputs an output of 128 bits.

Since the output is 128 bits, only 2^128 different outputs are possible using md5.

But the number of possible input sequences are far greater than 2^128.

So, md5 is definitely a many to one function.

If that's the case, why is it so difficult to find any two bit sequences whose hash values are the same?

Given the hash value, is it definitely not possible to find some sequence which will have the same hash value as is given?

Replies

  • dipen30
    dipen30
    in MD5 there are basically 5 steps to get message digest.

    1.padding.
    2.Append length.
    3.divide the input into 512-blocks.
    4.Initialize chaining variables.
    5.process block.

    we can get the same message digest upto step 4 but after step 5 we cannot get the two message digest same.
  • silverscorpion
    silverscorpion
    Why not?

    My basic question is, the total number of input strings possible is unlimited.
    But we only have 2^128 output strings.
    So, how is it a one way function?
  • silverscorpion
    silverscorpion
    Why not?

    My basic question is, the total number of input strings possible is unlimited.
    But we only have 2^128 output strings.
    So, how is it a one way function?
  • silverscorpion
    silverscorpion
    Why not?

    My basic question is, the total number of input strings possible is unlimited.
    But we only have 2^128 output strings.
    So, how is it a one way function?
  • silverscorpion
    silverscorpion
    oops!!!

    Dunno what happened!! It got posted 3 times! Sorry!!
  • dipen30
    dipen30
    I don't know this ans. if anyone know then please give the ans.

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