eadmund/ironclad — comment on commit 8555ac68f04c009b049faf7767343776c75c99b8
File: src/prng/generator.lisp line 7
By eadmund:

The advantage of the doubled-SHA construction is that it prevents extension attacks. Dunno if it's worth making visible to other folks or not.

The name is not mine--comes from Schneier, Ferguson & Kohno. They normally spell it as SHAd-256.