these limits could definitely use review, but for now, i feel
consistency and erring on the side of preventing servers from getting
bogged down by excessively-slow user-provided settings (think
.htpasswd) are the best policy. blowfish should be updated to match.
#define SALT_MAX 16
#define ROUNDS_DEFAULT 5000
#define ROUNDS_MIN 1000
-#define ROUNDS_MAX 50000
+#define ROUNDS_MAX 20000
/* hash n bytes of the repeated md message digest */
static void hashmd(struct sha512 *s, unsigned int n, const void *md)