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Code Issues Releases Wiki Activity

Removed more magic numbers.

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`KEY_PATH_LEN`: length of the derivation path in the key handle

`KEY_PATH_ENTRIES`: number of entries in derivation path including
initial BIP-43 selector.

`KEY_HANDLE_LEN`: length of key handle (derivation path + HMAC checksum)
This commit is contained in:
Jochen Hoenicke 2016-05-18 01:09:13 +02:00
parent 041eaa5e4b
commit a0571e02a7
2 changed files with 24 additions and 21 deletions
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42
firmware/u2f.c
View File

@ -56,7 +56,11 @@ static uint32_t u2f_out_end = 0;
static uint8_t u2f_out_packets[U2F_OUT_PKT_BUFFER_LEN][HID_RPT_SIZE];
#define U2F_PUBKEY_LEN 65
#define KEY_HANDLE_LEN 64
#define KEY_PATH_LEN 32
#define KEY_HANDLE_LEN (KEY_PATH_LEN + SHA256_DIGEST_LENGTH)
// Derivation path is m/U2F'/r'/r'/r'/r'/r'/r'/r'/r'
#define KEY_PATH_ENTRIES (1 + KEY_PATH_LEN / sizeof(uint32_t))
// Auth/Register request state machine
typedef enum {
@ -487,29 +491,28 @@ const HDNode *getDerivedNode(uint32_t *address_n, size_t address_n_count)
const HDNode *generateKeyHandle(const uint8_t app_id[], uint8_t key_handle[])
{
uint8_t keybase[64];
uint8_t keybase[U2F_APPID_SIZE + KEY_PATH_LEN];
// Derivation path is m/'U2F/'r/'r/'r/'r/'r/'r/'r/'r
uint32_t i, key_path[9];
// Derivation path is m/U2F'/r'/r'/r'/r'/r'/r'/r'/r'
uint32_t i, key_path[KEY_PATH_ENTRIES];
key_path[0] = U2F_KEY_PATH;
for (i = 1; i < 9; i++) {
for (i = 1; i < KEY_PATH_ENTRIES; i++) {
// high bit for hardened keys
key_path[i]= 0x80000000 | random32();
}
// First half of keyhandle is key_path
memcpy(key_handle, &key_path[1], 32);
memcpy(key_handle, &key_path[1], KEY_PATH_LEN);
// prepare keypair from /random data
const HDNode *node =
getDerivedNode(key_path, sizeof(key_path) / sizeof(uint32_t));
const HDNode *node = getDerivedNode(key_path, KEY_PATH_ENTRIES);
// For second half of keyhandle
// Signature of app_id and random data
memcpy(&keybase[0], app_id, 32);
memcpy(&keybase[32], key_handle, 32);
memcpy(&keybase[0], app_id, U2F_APPID_SIZE);
memcpy(&keybase[U2F_APPID_SIZE], key_handle, KEY_PATH_LEN);
hmac_sha256(node->private_key, sizeof(node->private_key),
keybase, sizeof(keybase), &key_handle[32]);
keybase, sizeof(keybase), &key_handle[KEY_PATH_LEN]);
// Done!
return node;
@ -518,23 +521,22 @@ const HDNode *generateKeyHandle(const uint8_t app_id[], uint8_t key_handle[])
const HDNode *validateKeyHandle(const uint8_t app_id[], const uint8_t key_handle[])
{
uint32_t key_path[9];
uint32_t key_path[KEY_PATH_ENTRIES];
key_path[0] = U2F_KEY_PATH;
memcpy(&key_path[1], key_handle, 32);
memcpy(&key_path[1], key_handle, KEY_PATH_LEN);
const HDNode *node =
getDerivedNode(key_path, sizeof(key_path) / sizeof(uint32_t));
const HDNode *node = getDerivedNode(key_path, KEY_PATH_ENTRIES);
uint8_t keybase[64];
memcpy(&keybase[0], app_id, 32);
memcpy(&keybase[32], key_handle, 32);
uint8_t keybase[U2F_APPID_SIZE + KEY_PATH_LEN];
memcpy(&keybase[0], app_id, U2F_APPID_SIZE);
memcpy(&keybase[U2F_APPID_SIZE], key_handle, KEY_PATH_LEN);
uint8_t hmac[32];
uint8_t hmac[SHA256_DIGEST_LENGTH];
hmac_sha256(node->private_key, sizeof(node->private_key),
keybase, sizeof(keybase), hmac);
if (memcmp(&key_handle[32], hmac, 32) != 0)
if (memcmp(&key_handle[KEY_PATH_LEN], hmac, SHA256_DIGEST_LENGTH) != 0)
return NULL;
// Done!

3
firmware/u2f_knownapps.h
View File

@ -21,9 +21,10 @@
#define __U2F_KNOWNAPPS_H_INCLUDED__
#include <stdint.h>
#include "u2f/u2f.h"
typedef struct {
uint8_t appid[32];
uint8_t appid[U2F_APPID_SIZE];
const char *appname;
} U2FWellKnown;