diff --git a/Src/crypto/chacha20.c b/Src/crypto/chacha20.c
index 730f24a..5bfbfcb 100644
--- a/Src/crypto/chacha20.c
+++ b/Src/crypto/chacha20.c
@@ -76,7 +76,7 @@ quarterround(uint32_t* a, uint32_t* b, uint32_t* c, uint32_t* d) {
     *b = BitManipulation_rotl32(*b ^ *c, 7);
 }
 
-static void
+static bool
 chacha20_block(const byte_t key[CHACHA20_KEY_SIZE], const uint32_t counter, const byte_t nonce[CHACHA20_NONCE_SIZE],
                byte_t out[KEY_STREAM_SIZE]) {
 
@@ -153,9 +153,9 @@ chacha20(const byte_t* plaintext,
 
     uint32_t blocks = plaintext_len / BLOCK_SIZE;
     uint32_t remaining_bytes = plaintext_len % BLOCK_SIZE;
+    static byte_t key_stream[KEY_STREAM_SIZE] = ARRAY_64_ZERO_VALUES;
 
     for (uint32_t j = 0; j < blocks; ++j) {
-        byte_t key_stream[KEY_STREAM_SIZE] = ARRAY_64_ZERO_VALUES;
         chacha20_block(key, j + inc, nonce, key_stream);
 
         for (uint8_t i = 0; i < BLOCK_SIZE; ++i) {
@@ -164,7 +164,6 @@ chacha20(const byte_t* plaintext,
     }
 
     if (0U != remaining_bytes) {
-        byte_t key_stream[KEY_STREAM_SIZE] = ARRAY_64_ZERO_VALUES;
         chacha20_block(key, blocks + inc, nonce, key_stream);
 
         for (uint32_t i = 0; i < remaining_bytes; ++i) {