Several blockchains of various lengths are hidden in the grid. Blockchain blocks can connect orthogonally or diagonally.
Each of the letters in CRYPTO stands for a different digit from 1-6, indicating how many blockchain blocks touch that square. [Think of a blockchain block as a Minesweeper mine.]
No square containing a letter is part of a blockchain.
All squares that are not part of any blockchain form a single orthogonally-connected group. [Think of a blockchain block as a black square in Hitori, Statue Park, etc.]