94 lines
3.7 KiB
C
94 lines
3.7 KiB
C
/*
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* This file is part of the Pico FIDO distribution (https://github.com/polhenarejos/pico-fido).
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* Copyright (c) 2022 Pol Henarejos.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 3.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "fido.h"
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#include "hsm.h"
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#include "apdu.h"
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#include "ctap.h"
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#include "mbedtls/ecdsa.h"
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#include "random.h"
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#include "files.h"
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int cmd_authenticate() {
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CTAP_AUTHENTICATE_REQ *req = (CTAP_AUTHENTICATE_REQ *)apdu.data;
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CTAP_AUTHENTICATE_RESP *resp = (CTAP_AUTHENTICATE_RESP *)res_APDU;
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if (scan_files() != CCID_OK)
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return SW_EXEC_ERROR();
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if (req->keyHandleLen != KEY_HANDLE_LEN)
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return SW_WRONG_DATA();
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if (P1(apdu) == CTAP_AUTH_ENFORCE && wait_button_pressed() == true)
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return SW_CONDITIONS_NOT_SATISFIED();
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mbedtls_ecdsa_context key;
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mbedtls_ecdsa_init(&key);
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int ret = derive_key(req->appId, false, req->keyHandle, MBEDTLS_ECP_DP_SECP256R1, &key);
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if (ret != CCID_OK) {
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mbedtls_ecdsa_free(&key);
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return SW_EXEC_ERROR();
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}
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if (P1(apdu) == CTAP_AUTH_CHECK_ONLY) {
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for (int i = 0; i < KEY_PATH_ENTRIES; i++) {
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uint32_t k = *(uint32_t *)&req->keyHandle[i*sizeof(uint32_t)];
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if (!(k & 0x80000000)) {
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mbedtls_ecdsa_free(&key);
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return SW_WRONG_DATA();
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}
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}
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uint8_t hmac[32], d[32];
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ret = mbedtls_ecp_write_key(&key, d, sizeof(d));
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mbedtls_ecdsa_free(&key);
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if (ret != 0)
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return SW_WRONG_DATA();
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uint8_t key_base[CTAP_APPID_SIZE + KEY_PATH_LEN];
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memcpy(key_base, req->appId, CTAP_APPID_SIZE);
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memcpy(key_base + CTAP_APPID_SIZE, req->keyHandle, KEY_PATH_LEN);
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ret = mbedtls_md_hmac(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), d, 32, key_base, sizeof(key_base), hmac);
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mbedtls_platform_zeroize(d, sizeof(d));
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if (memcmp(req->keyHandle + KEY_PATH_LEN, hmac, sizeof(hmac)) != 0)
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return SW_WRONG_DATA();
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return SW_CONDITIONS_NOT_SATISFIED();
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}
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resp->flags = 0;
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resp->flags |= P1(apdu) == CTAP_AUTH_ENFORCE ? CTAP_AUTH_FLAG_TUP : 0x0;
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uint32_t ctr = *(uint32_t *)file_get_data(ef_counter);
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resp->ctr[0] = ctr >> 24;
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resp->ctr[1] = ctr >> 16;
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resp->ctr[2] = ctr >> 8;
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resp->ctr[3] = ctr & 0xff;
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uint8_t hash[32], sig_base[CTAP_APPID_SIZE + 1 + 4 + CTAP_CHAL_SIZE];
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memcpy(sig_base, req->appId, CTAP_APPID_SIZE);
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memcpy(sig_base+CTAP_APPID_SIZE, &resp->flags, sizeof(uint8_t));
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memcpy(sig_base + CTAP_APPID_SIZE + 1, resp->ctr, 4);
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memcpy(sig_base + CTAP_APPID_SIZE + 1 + 4, req->chal, CTAP_CHAL_SIZE);
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ret = mbedtls_md(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), sig_base, sizeof(sig_base), hash);
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if (ret != 0) {
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mbedtls_ecdsa_free(&key);
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return SW_EXEC_ERROR();
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}
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size_t olen = 0;
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ret = mbedtls_ecdsa_write_signature(&key, MBEDTLS_MD_SHA256, hash, 32, (uint8_t *)resp->sig, CTAP_MAX_EC_SIG_SIZE, &olen, random_gen, NULL);
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mbedtls_ecdsa_free(&key);
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if (ret != 0)
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return SW_EXEC_ERROR();
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res_APDU_size = 1 + 4 + olen;
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ctr++;
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flash_write_data_to_file(ef_counter, (uint8_t *)&ctr, sizeof(ctr));
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low_flash_available();
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return SW_OK();
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}
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