An attempt to implement SHA-256 from scratch using golang and reverse engineer.

Algorithm:

• Intialization of Hash Values(H0-H7) and the constants (K0-K63) - done

• Padding to ensure the message is near a 512 bits multiple. -- workflow of padding:

  1. add one "1" after converting the message to binary
  2. add "0"s till it satisfies 448(bits) mod 512(bits). In layman terms, there must be 64 bits space left after adding "0"s in the nearest 512 mulitple.
  3. In the end appending the 64-bit representation to the message we received.

• Parsing the message by sptlitting it into 512-bit blocks. W[0]-W[63]

• Scheduling the message: -- workflow of scheduling:

  1. W[0]-W[15] are extracted directly.
  2. Rest(W[16] - W[63]) are generated using this formula below:

• Compression Function -- workflow of compression:

  1. Intialize a,b...h as the first H0-H7 values respectively
  2. For each 64 rounds, following manipulations are done: where:

• Updating Hash after every 512-bit round:

  • H0 = H0 + a
  • H1 = H1 + b
  • H2 = H2 + c
  • H3 = H3 + d
  • H4 = H4 + e
  • H5 = H5 + f
  • H6 = H6 + g
  • H7 = H7 + h

• Finally, Cocatenate the hash values to get the final 256-bit hash.