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Cryptography Primitives 1: Merkel - Damgard Construction

 This is basically a basic building block for constructing a hash function based on Ralph Merkel's PhD thesis which basically states that, 

if an appropriate padding scheme is used and the compression function is collision-resistant, then the hash function will also be collision-resistant


Block Diagram for Merkel Damgard Construction

Important things to consider,

  1. Padding
  2. IV



Padding is basically a long string of 1 followed by as many number of 0s as required and ends with a binary representation of the message length. So to pad a message,

1001101, we pad it with

1001101[100000...00111], where the part inside square brackets are the padded bits.


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