1. 09 Dec, 2022 13 commits
  2. 05 Dec, 2022 1 commit
  3. 02 Dec, 2022 25 commits
  4. 25 Nov, 2022 1 commit
    • Jason A. Donenfeld's avatar
      hwrng: u2fzero - account for high quality RNG · 83478938
      Jason A. Donenfeld authored
      The U2F zero apparently has a real TRNG in it with maximum quality, not
      one with quality of "1", which was likely a misinterpretation of the
      field as a boolean. So remove the assignment entirely, so that we get
      the default quality setting.
      
      In the u2f-zero firmware, the 0x21 RNG command used by this driver is
      handled as such [1]:
      
        case U2F_CUSTOM_GET_RNG:
          if (atecc_send_recv(ATECC_CMD_RNG,ATECC_RNG_P1,ATECC_RNG_P2,
            NULL, 0,
            appdata.tmp,
            sizeof(appdata.tmp), &res) == 0 )
          {
            memmove(msg->pkt.init.payload, res.buf, 32);
            U2FHID_SET_LEN(msg, 32);
            usb_write((uint8_t*)msg, 64);
          }
          else
          {
            U2FHID_SET_LEN(msg, 0);
            usb_write((uint8_t*)msg, 64);
          }
      
      This same call to `atecc_send_recv(ATECC_CMD_RNG,ATECC_RNG_P1,
      ATECC_RNG_P2,...)` is then also used in the token's cryptographically
      critical "u2f_new_keypair" function, as its rather straightforward
      source of random bytes [2]:
      
        int8_t u2f_new_keypair(uint8_t * handle, uint8_t * appid, uint8_t * pubkey)
        {
          struct atecc_response res;
          uint8_t private_key[36];
          int i;
      
          watchdog();
      
          if (atecc_send_recv(ATECC_CMD_RNG,ATECC_RNG_P1,ATECC_RNG_P2,
            NULL, 0,
            appdata.tmp,
            sizeof(appdata.tmp), &res) != 0 )
          {
            return -1;
          }
      
      So it seems rather plain that the ATECC RNG is considered to provide
      good random numbers.
      
      [1] https://github.com/conorpp/u2f-zero/blob/master/firmware/src/custom.c
      [2] https://github.com/conorpp/u2f-zero/blob/master/firmware/src/u2f_atecc.c
      
      Cc: Andrej Shadura <andrew.shadura@collabora.co.uk>
      Cc: Jiri Kosina <jkosina@suse.cz>
      Cc: Herbert Xu <herbert@gondor.apana.org.au>
      Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
      Acked-by: default avatarAndrej Shadura <andrew.shadura@collabora.co.uk>
      Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
      83478938