There seems to be a slight change in S-expressions (fortunately
backward compatible). There is also additional flag needed in rather
strange place (data section instead of key section), most probably a
bug in gcrypt.

Decrypting a 350MB file with gcrypt 1.5 takes around 4 seconds on Core
Quad Q9450 2.66GHz while with gcrypt 1.6 around 2.8s (the processor
does not support AES-NI).