From 874a54a66540e10cc6a30f3295955228e7e32cb9 Mon Sep 17 00:00:00 2001
From: LoRd_MuldeR <mulder2@gmx.de>
Date: Sat, 3 Apr 2021 17:02:39 +0200
Subject: [PATCH] Slightly tweak stepping algorithm to include a counter.

---
 libslunkcrypt/src/slunkcrypt.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/libslunkcrypt/src/slunkcrypt.c b/libslunkcrypt/src/slunkcrypt.c
index 4cdc647..7378bab 100644
--- a/libslunkcrypt/src/slunkcrypt.c
+++ b/libslunkcrypt/src/slunkcrypt.c
@@ -57,6 +57,7 @@ typedef struct
 {
 	int reverse_mode;
 	uint8_t wheel[256U][256U];
+	uint32_t counter;
 	rand_state_t random;
 }
 crypt_state_t;
@@ -229,6 +230,10 @@ static int initialize_state(crypt_state_t *const state, const uint64_t nonce, co
 	slunkcrypt_bzero(state, sizeof(crypt_state_t));
 	state->reverse_mode = reverse;
 
+	/* initialize counter */
+	random_seed(&state->random, nonce, (uint16_t)(-1), passwd, passwd_len);
+	state->counter = random_next(&state->random);
+
 	/* set up the wheel permutations */
 	for (r = 0U; r < 256U; ++r)
 	{
@@ -266,7 +271,7 @@ static int initialize_state(crypt_state_t *const state, const uint64_t nonce, co
 	random_seed(&state->random, nonce, 256U, passwd, passwd_len);
 	return SLUNKCRYPT_SUCCESS;
 
-	/* user abort request */
+	/* aborted */
 aborted:
 	slunkcrypt_bzero(state, sizeof(crypt_state_t));
 	return SLUNKCRYPT_ABORTED;
@@ -276,28 +281,27 @@ aborted:
 // Encrypt / Decrypt
 // ==========================================================================
 
-static FORCE_INLINE void calculate_offsets(uint8_t *const offset, rand_state_t *const state, const int reverse)
+static FORCE_INLINE void update_offset(uint8_t *const offset, uint32_t seed, rand_state_t *const state, const int reverse)
 {
-	uint32_t temp = 0U;
 	size_t i;
-	for (i = 0U; i < 256U; ++i, temp >>= CHAR_BIT)
+	for (i = 0U; i < 256U; ++i, seed >>= CHAR_BIT)
 	{
-		if (!temp)
+		if (i && (!(i & 3U)))
 		{
-			temp = random_next(state);
+			seed = random_next(state);
 		}
-		offset[reverse ? (255U - i) : i] = (uint8_t)temp;
+		offset[reverse ? (255U - i) : i] = (uint8_t)seed;
 	}
 }
 
-static FORCE_INLINE uint8_t process_next_symbol(crypt_state_t *const crypt_state_t, uint8_t value)
+static FORCE_INLINE uint8_t process_next_symbol(crypt_state_t *const state, uint8_t value)
 {
 	uint8_t offset[256U];
 	size_t i;
-	calculate_offsets(offset, &crypt_state_t->random, crypt_state_t->reverse_mode);
+	update_offset(offset, state->counter++, &state->random, state->reverse_mode);
 	for (i = 0U; i < 256U; ++i)
 	{
-		value = (crypt_state_t->wheel[i][(value + offset[i]) & 0xFF] - offset[i]) & 0xFF;
+		value = (state->wheel[i][(value + offset[i]) & 0xFF] - offset[i]) & 0xFF;
 	}
 	return value;
 }