I have a table of values for which I need to compute a salted hash for each table-cell value. Furthermore, I need the salt for each table cell to be unique and unpredictable. (I can explain what motivates this need later, but for now I don't want to distract from the problem statement.)
Now I don't want to add an extra column per existing column in a table just to store this unique, per-cell salt. So a simple strategy I have in mind is to first generate a secret, secure random 32-byte sequence for the entire table, call it R_32, and then for any given cell compute its salt as the SHA-256 of R_32 concatenated with the cell's row/column coordinates. In pseudo code this look like
tableSalt(row, col) = SHA_256( R_32 + row + col )
+ here is taken to mean byte-string concatenation, not addition. (The row/column coordinates are represented as 8-byte values each.)
In my application it's critical that the secret seed hash R_32 above not be reverse-engineerable, no matter how many different cell-salts from the same table are known. Is the
tableSalt procedure above secure in this respect?