- /*
- * 3. For each block of the derived key apply the function F defined
- * below to the password P, the salt S, the iteration count c, and
- * the block index to compute the block:
- *
- * T_1 = F (P, S, c, 1) ,
- * T_2 = F (P, S, c, 2) ,
- * ...
- * T_l = F (P, S, c, l) ,
- *
- * where the function F is defined as the exclusive-or sum of the
- * first c iterates of the underlying pseudorandom function PRF
- * applied to the password P and the concatenation of the salt S
- * and the block index i:
- *
- * F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
- *
- * where
- *
- * U_1 = PRF (P, S || INT (i)) ,
- * U_2 = PRF (P, U_1) ,
- * ...
- * U_c = PRF (P, U_{c-1}) .
- *
- * Here, INT (i) is a four-octet encoding of the integer i, most
- * significant octet first.
- *
- * 4. Concatenate the blocks and extract the first dkLen octets to
- * produce a derived key DK:
- *
- * DK = T_1 || T_2 || ... || T_l<0..r-1>
- *
- * 5. Output the derived key DK.
- *
- * Note. The construction of the function F follows a "belt-and-
- * suspenders" approach. The iterates U_i are computed recursively to
- * remove a degree of parallelism from an opponent; they are exclusive-
- * ored together to reduce concerns about the recursion degenerating
- * into a small set of values.
- *
- */