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282765fdd4
RMA auth uses X25519 to generate a relatively small challenge and response. Currently, nothing calls the rma_auth code. We'll need console and TPM vendor commands to do so. BUG=b:37952913 BRANCH=none TEST=make buildall Change-Id: Iec7f2d0e3dc8243f79b009ead16bb3ba9f1bef9d Signed-off-by: Randall Spangler <rspangler@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/544184
124 lines
3.2 KiB
C
124 lines
3.2 KiB
C
/* Copyright 2017 The Chromium OS Authors. All rights reserved.
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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/* RMA authorization challenge-response */
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#include "common.h"
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#include "base32.h"
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#include "chip/g/board_id.h"
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#include "curve25519.h"
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#include "rma_auth.h"
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#include "sha256.h"
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#include "system.h"
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#include "timer.h"
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#include "util.h"
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/* Minimum time since system boot or last challenge before making a new one */
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#define CHALLENGE_INTERVAL (10 * SECOND)
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/* Number of tries to properly enter auth code */
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#define MAX_AUTHCODE_TRIES 3
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/* Server public key and key ID */
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static const uint8_t server_pub_key[32] = CONFIG_RMA_AUTH_SERVER_PUBLIC_KEY;
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static const uint8_t server_key_id = CONFIG_RMA_AUTH_SERVER_KEY_ID;
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static char challenge[RMA_CHALLENGE_BUF_SIZE];
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static char authcode[RMA_AUTHCODE_BUF_SIZE];
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static int tries_left;
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static uint64_t last_challenge_time;
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/**
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* Create a new RMA challenge/response
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*
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* @return EC_SUCCESS, EC_ERROR_TIMEOUT if too soon since the last challenge,
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* or other non-zero error code.
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*/
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int rma_create_challenge(void)
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{
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uint8_t temp[32]; /* Private key or HMAC */
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uint8_t secret[32];
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struct rma_challenge c;
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struct board_id bid;
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uint8_t *device_id;
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uint8_t *cptr = (uint8_t *)&c;
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uint64_t t;
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/* Clear the current challenge and authcode, if any */
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memset(challenge, 0, sizeof(challenge));
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memset(authcode, 0, sizeof(authcode));
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/* Rate limit challenges */
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t = get_time().val;
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if (t - last_challenge_time < CHALLENGE_INTERVAL)
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return EC_ERROR_TIMEOUT;
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last_challenge_time = t;
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memset(&c, 0, sizeof(c));
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c.version_key_id = RMA_CHALLENGE_VKID_BYTE(
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RMA_CHALLENGE_VERSION, server_key_id);
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if (read_board_id(&bid))
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return EC_ERROR_UNKNOWN;
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memcpy(c.board_id, &bid.type, sizeof(c.board_id));
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if (system_get_chip_unique_id(&device_id) != sizeof(c.device_id))
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return EC_ERROR_UNKNOWN;
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memcpy(c.device_id, device_id, sizeof(c.device_id));
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/* Calculate a new ephemeral key pair */
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X25519_keypair(c.device_pub_key, temp);
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/* Encode the challenge */
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if (base32_encode(challenge, sizeof(challenge), cptr, 8 * sizeof(c), 9))
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return EC_ERROR_UNKNOWN;
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/* Calculate the shared secret */
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X25519(secret, temp, server_pub_key);
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/*
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* Auth code is a truncated HMAC of the ephemeral public key, BoardID,
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* and DeviceID. Those are all in the right order in the challenge
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* struct, after the version/key id byte.
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*/
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hmac_SHA256(temp, secret, sizeof(secret), cptr + 1, sizeof(c) - 1);
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if (base32_encode(authcode, sizeof(authcode), temp,
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RMA_AUTHCODE_CHARS * 5, 0))
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return EC_ERROR_UNKNOWN;
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tries_left = MAX_AUTHCODE_TRIES;
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return EC_SUCCESS;
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}
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const char *rma_get_challenge(void)
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{
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return challenge;
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}
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int rma_try_authcode(const char *code)
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{
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int rv = EC_ERROR_INVAL;
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/* Fail if out of tries */
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if (!tries_left)
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return EC_ERROR_ACCESS_DENIED;
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if (safe_memcmp(authcode, code, RMA_AUTHCODE_CHARS)) {
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/* Mismatch */
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tries_left--;
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} else {
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rv = EC_SUCCESS;
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tries_left = 0;
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}
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/* Clear challenge and response if out of tries */
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if (!tries_left) {
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memset(challenge, 0, sizeof(challenge));
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memset(authcode, 0, sizeof(authcode));
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}
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return rv;
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}
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