+int journal_file_fsprg_seek(JournalFile *f, uint64_t goal) {
+ void *msk;
+ uint64_t epoch;
+
+ assert(f);
+
+ if (!f->seal)
+ return 0;
+
+ assert(f->fsprg_seed);
+
+ if (f->fsprg_state) {
+ /* Cheaper... */
+
+ epoch = FSPRG_GetEpoch(f->fsprg_state);
+ if (goal == epoch)
+ return 0;
+
+ if (goal == epoch+1) {
+ FSPRG_Evolve(f->fsprg_state);
+ return 0;
+ }
+ } else {
+ f->fsprg_state_size = FSPRG_stateinbytes(FSPRG_RECOMMENDED_SECPAR);
+ f->fsprg_state = malloc(f->fsprg_state_size);
+
+ if (!f->fsprg_state)
+ return -ENOMEM;
+ }
+
+ log_debug("Seeking FSPRG key to %llu.", (unsigned long long) goal);
+
+ msk = alloca(FSPRG_mskinbytes(FSPRG_RECOMMENDED_SECPAR));
+ FSPRG_GenMK(msk, NULL, f->fsprg_seed, f->fsprg_seed_size, FSPRG_RECOMMENDED_SECPAR);
+ FSPRG_Seek(f->fsprg_state, goal, msk, f->fsprg_seed, f->fsprg_seed_size);
+ return 0;
+}
+