+#ifndef UTILS_H
+#define UTILS_H
+
+#define STREAM_BYTES 16
+#define MSG_BYTES 0
+
+enum GRAIN_ROUND {INIT, FP1, NORMAL};
+
+typedef struct {
+ uint8_t lfsr[128];
+ uint8_t nfsr[128];
+ uint8_t auth_acc[64];
+ uint8_t auth_sr[64];
+} grain_state;
+
+// TODO: add struct with output: keystream and optionally macstream and tag
+typedef struct {
+ uint8_t keystream[STREAM_BYTES];
+ uint8_t macstream[STREAM_BYTES];
+ uint8_t *message;
+} grain_data;
+
+void init_grain(grain_state *grain, uint8_t *key, uint8_t *iv);
+uint8_t next_lfsr_fb(grain_state *grain);
+uint8_t next_nfsr_fb(grain_state *grain);
+uint8_t next_h(grain_state *grain);
+uint8_t shift(uint8_t fsr[128], uint8_t fb);
+void auth_shift(uint8_t sr[32], uint8_t fb);
+uint8_t next_z(grain_state *grain, uint8_t);
+void generate_keystream(grain_state *grain, grain_data *data, uint8_t *);
+void print_state(grain_state *grain);
+
+#endif
