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It's been a while since I know about cryptography, and always end up seing diagrams like this. ChaCha20 diagram

However I have never been able to understang their meaning. I hope someone can explain in detail. Thank you in advance

1 Answers1

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These are diagrams used to describe the round of symmetric ciphers. This one specifically I think is from Chacha20.

You can interpret your above example as follows :

  1. It is a function that takes 4 inputs of a specific size lets say 32 bits (total 128 bits) and has 4 outputs of again specific size (again 128 bits).
    • The circular operator is a bitwise XOR
    • The rectangular is addition without carry
    • The arrows operator is circular rotation by the specified amount of bits.
  2. The incoming edges to an operator are the inputs and the outcoming are the outputs.
  3. Now you can calculate every output wire by taking the reverse path from the end to the start of the circuit.

For example :

a += b
d = (a + d) <<< 16
c += d
b ^= (b + c) <<< 12

a += b d = (a + d) <<< 8 c += d b ^= (b + c) <<< 7

tur11ng
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