More changes after code review

- Added WORDS_BUFFER_SIZE constant for onboard_t
- Using sizeof() instead of SEEDSIZE constant for handling seed buffer

ledger/src/ui/src/onboard.c

@@ -73,16 +73,15 @@ unsigned int onboard_device(onboard_t *onboard_ctx, pin_t *pin_ctx) {
     // Generate 32 bytes of random with onboard rng
     cx_rng((unsigned char *)onboard_ctx->seed, sizeof(onboard_ctx->seed));
     // XOR with host-generated 32 bytes random
-    for (int i = 0; i < SEEDSIZE; i++) {
+    for (unsigned int i = 0; i < sizeof(onboard_ctx->seed); i++) {
         onboard_ctx->seed[i] ^= onboard_ctx->host_seed[i];
     }
     // The seed is now in onboard_ctx->seed, generate the mnemonic
     os_memset(onboard_ctx->words_buffer, 0, sizeof(onboard_ctx->words_buffer));
-    onboard_ctx->words_buffer_length =
-        bolos_ux_mnemonic_from_data((unsigned char *)onboard_ctx->seed,
-                                    SEEDSIZE,
-                                    (unsigned char *)onboard_ctx->words_buffer,
-                                    sizeof(onboard_ctx->words_buffer));
+    bolos_ux_mnemonic_from_data((unsigned char *)onboard_ctx->seed,
+                                sizeof(onboard_ctx->seed),
+                                (unsigned char *)onboard_ctx->words_buffer,
+                                sizeof(onboard_ctx->words_buffer));
     // Clear the seed
     explicit_bzero(onboard_ctx->seed, sizeof(onboard_ctx->seed));
 

ledger/src/ui/src/onboard.h

@@ -29,14 +29,15 @@
 #include "os_io_seproxyhal.h"
 #include "pin.h"
 
+// 128 of words (215 => hashed to 64, or 128) + HMAC_LENGTH*2 = 256
+#define WORDS_BUFFER_SIZE 257
 // Onboard context
 typedef struct {
     union {
-        unsigned char words_buffer[257];
+        unsigned char words_buffer[WORDS_BUFFER_SIZE];
         unsigned char host_seed[SEEDSIZE];
     };
     unsigned char seed[SEEDSIZE];
-    unsigned int words_buffer_length;
 } onboard_t;
 
 /*