SHA-256 Cryptographic Hash Algorithm

• SHA-256 is a very important part of Bitcoin network and it ensures both mining process and security of the network.
• Producing the information about the previous block requires its header to pass through the SHA-256 algorithm two times, which is called double-SHA-256. This is how the formula looks like

  Previous Block Hash = SHA-256(SHA-256(Block Header))

• A cryptographic hash (digest) is a kind of signature for a text or a data file.
• A hash is not encryption because it cannot be decrypted back to the original text
• A one-way cryptographic function
• A fixed size for any size of source text
• Used to compared hashed versions of texts
  • hash tables
  • integrity verification
  • challenge handshake authentication: avoids transmissing passwords in clear
  • digital signatures

SHA-256 generates an almost-unique 256-bit(32-byte) signature for a text.

sha256(
  "abc"
) = "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad";