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pico-fido/src/fido/cbor_vendor.c
Pol Henarejos 2174b516c3 Using ecdh interface from mbedtls. 
Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>
2022-11-07 13:15:09 +01:00

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/*
* This file is part of the Pico FIDO distribution (https://github.com/polhenarejos/pico-fido).
* Copyright (c) 2022 Pol Henarejos.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 3.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "common.h"
#include "ctap2_cbor.h"
#include "fido.h"
#include "ctap.h"
#include "files.h"
#include "apdu.h"
#include "hsm.h"
#include "random.h"
#include "mbedtls/ecdh.h"
#include "mbedtls/chachapoly.h"
#include "mbedtls/hkdf.h"
extern uint8_t keydev_dec[32];
extern bool has_keydev_dec;
mse_t mse = {.init = false};
int mse_decrypt_ct(uint8_t *data, size_t len) {
mbedtls_chachapoly_context chatx;
mbedtls_chachapoly_init(&chatx);
mbedtls_chachapoly_setkey(&chatx, mse.key_enc + 12);
int ret = mbedtls_chachapoly_auth_decrypt(&chatx, len - 16, mse.key_enc, mse.Qpt, 65, data + len - 16, data, data);
mbedtls_chachapoly_free(&chatx);
return ret;
}
int cbor_vendor_generic(uint8_t cmd, const uint8_t *data, size_t len) {
CborParser parser;
CborValue map;
CborError error = CborNoError;
CborByteString pinUvAuthParam = {0}, vendorParam = {0}, kax = {0}, kay = {0};
size_t resp_size = 0;
uint64_t vendorCmd = 0, pinUvAuthProtocol = 0;
int64_t kty = 0, alg = 0, crv = 0;
CborEncoder encoder, mapEncoder, mapEncoder2;
CBOR_CHECK(cbor_parser_init(data, len, 0, &parser, &map));
uint64_t val_c = 1;
CBOR_PARSE_MAP_START(map, 1) {
uint64_t val_u = 0;
CBOR_FIELD_GET_UINT(val_u, 1);
if (val_c <= 1 && val_c != val_u)
CBOR_ERROR(CTAP2_ERR_MISSING_PARAMETER);
if (val_u < val_c)
CBOR_ERROR(CTAP2_ERR_INVALID_CBOR);
val_c = val_u + 1;
if (val_u == 0x01) {
CBOR_FIELD_GET_UINT(vendorCmd, 1);
}
else if (val_u == 0x02) {
uint64_t subpara = 0;
CBOR_PARSE_MAP_START(_f1, 2) {
CBOR_FIELD_GET_UINT(subpara, 2);
if (subpara == 0x01) {
CBOR_FIELD_GET_BYTES(vendorParam, 2);
}
else if (subpara == 0x02) {
int64_t key = 0;
CBOR_PARSE_MAP_START(_f2, 3) {
CBOR_FIELD_GET_INT(key, 3);
if (key == 1) {
CBOR_FIELD_GET_INT(kty, 3);
}
else if (key == 3) {
CBOR_FIELD_GET_INT(alg, 3);
}
else if (key == -1) {
CBOR_FIELD_GET_INT(crv, 3);
}
else if (key == -2) {
CBOR_FIELD_GET_BYTES(kax, 3);
}
else if (key == -3) {
CBOR_FIELD_GET_BYTES(kay, 3);
}
else
CBOR_ADVANCE(3);
}
CBOR_PARSE_MAP_END(_f2, 3);
}
else
CBOR_ADVANCE(2);
}
CBOR_PARSE_MAP_END(_f1, 2);
}
else if (val_u == 0x03) {
CBOR_FIELD_GET_UINT(pinUvAuthProtocol, 1);
}
else if (val_u == 0x04) {
CBOR_FIELD_GET_BYTES(pinUvAuthParam, 1);
}
}
CBOR_PARSE_MAP_END(map, 1);
cbor_encoder_init(&encoder, ctap_resp->init.data + 1, CTAP_MAX_PACKET_SIZE, 0);
if (cmd == CTAP_VENDOR_BACKUP) {
if (vendorCmd == 0x01) {
if (has_keydev_dec == false)
CBOR_ERROR(CTAP2_ERR_PIN_AUTH_INVALID);
CBOR_CHECK(cbor_encoder_create_map(&encoder, &mapEncoder, 1));
CBOR_CHECK(cbor_encode_uint(&mapEncoder, 0x01));
CBOR_CHECK(cbor_encode_byte_string(&mapEncoder, file_get_data(ef_keydev_enc), file_get_size(ef_keydev_enc)));
}
else if (vendorCmd == 0x02) {
if (vendorParam.present == false)
CBOR_ERROR(CTAP2_ERR_MISSING_PARAMETER);
uint8_t zeros[32];
memset(zeros, 0, sizeof(zeros));
flash_write_data_to_file(ef_keydev_enc, vendorParam.data, vendorParam.len);
flash_write_data_to_file(ef_keydev, zeros, file_get_size(ef_keydev)); // Overwrite ef with 0
flash_write_data_to_file(ef_keydev, NULL, 0); // Set ef to 0 bytes
low_flash_available();
goto err;
}
else {
CBOR_ERROR(CTAP2_ERR_INVALID_SUBCOMMAND);
}
}
else if (cmd == CTAP_VENDOR_MSE) {
if (vendorCmd == 0x01) { // KeyAgreement
if (kax.present == false || kay.present == false || alg == 0)
CBOR_ERROR(CTAP2_ERR_MISSING_PARAMETER);
mbedtls_ecdh_context hkey;
mbedtls_ecdh_init(&hkey);
mbedtls_ecdh_setup(&hkey, MBEDTLS_ECP_DP_SECP256R1);
int ret = mbedtls_ecdh_gen_public(&hkey.ctx.mbed_ecdh.grp, &hkey.ctx.mbed_ecdh.d, &hkey.ctx.mbed_ecdh.Q, random_gen, NULL);
mbedtls_mpi_lset(&hkey.ctx.mbed_ecdh.Qp.Z, 1);
if (ret != 0) {
CBOR_ERROR(CTAP1_ERR_INVALID_PARAMETER);
}
if (mbedtls_mpi_read_binary(&hkey.ctx.mbed_ecdh.Qp.X, kax.data, kax.len) != 0) {
mbedtls_ecdh_free(&hkey);
CBOR_ERROR(CTAP1_ERR_INVALID_PARAMETER);
}
if (mbedtls_mpi_read_binary(&hkey.ctx.mbed_ecdh.Qp.Y, kay.data, kay.len) != 0) {
mbedtls_ecdh_free(&hkey);
CBOR_ERROR(CTAP1_ERR_INVALID_PARAMETER);
}
uint8_t buf[MBEDTLS_ECP_MAX_BYTES];
size_t olen = 0;
ret = mbedtls_ecp_point_write_binary(&hkey.ctx.mbed_ecdh.grp, &hkey.ctx.mbed_ecdh.Qp, MBEDTLS_ECP_PF_UNCOMPRESSED, &olen, mse.Qpt, sizeof(mse.Qpt));
if (ret != 0) {
mbedtls_ecdh_free(&hkey);
CBOR_ERROR(CTAP1_ERR_INVALID_PARAMETER);
}
ret = mbedtls_ecdh_calc_secret(&hkey, &olen, buf, MBEDTLS_ECP_MAX_BYTES, random_gen, NULL);
if (ret != 0) {
mbedtls_ecdh_free(&hkey);
mbedtls_platform_zeroize(buf, sizeof(buf));
CBOR_ERROR(CTAP1_ERR_INVALID_PARAMETER);
}
ret = mbedtls_hkdf(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), NULL, 0, buf, olen, mse.Qpt, sizeof(mse.Qpt), mse.key_enc, sizeof(mse.key_enc));
mbedtls_platform_zeroize(buf, sizeof(buf));
if (ret != 0) {
mbedtls_ecdh_free(&hkey);
CBOR_ERROR(CTAP1_ERR_INVALID_PARAMETER);
}
mse.init = true;
CBOR_CHECK(cbor_encoder_create_map(&encoder, &mapEncoder, 1));
CBOR_CHECK(cbor_encode_uint(&mapEncoder, 0x01));
CBOR_CHECK(cbor_encoder_create_map(&mapEncoder, &mapEncoder2, 5));
CBOR_CHECK(cbor_encode_uint(&mapEncoder2, 1));
CBOR_CHECK(cbor_encode_uint(&mapEncoder2, 2));
CBOR_CHECK(cbor_encode_uint(&mapEncoder2, 3));
CBOR_CHECK(cbor_encode_negative_int(&mapEncoder2, -FIDO2_ALG_ECDH_ES_HKDF_256));
CBOR_CHECK(cbor_encode_negative_int(&mapEncoder2, 1));
CBOR_CHECK(cbor_encode_uint(&mapEncoder2, FIDO2_CURVE_P256));
CBOR_CHECK(cbor_encode_negative_int(&mapEncoder2, 2));
uint8_t pkey[32];
mbedtls_mpi_write_binary(&hkey.ctx.mbed_ecdh.Q.X, pkey, 32);
CBOR_CHECK(cbor_encode_byte_string(&mapEncoder2, pkey, 32));
CBOR_CHECK(cbor_encode_negative_int(&mapEncoder2, 3));
mbedtls_mpi_write_binary(&hkey.ctx.mbed_ecdh.Q.Y, pkey, 32);
CBOR_CHECK(cbor_encode_byte_string(&mapEncoder2, pkey, 32));
CBOR_CHECK(cbor_encoder_close_container(&mapEncoder, &mapEncoder2));
mbedtls_ecdh_free(&hkey);
}
}
else if (cmd == CTAP_VENDOR_UNLOCK) {
if (mse.init == false)
CBOR_ERROR(CTAP2_ERR_NOT_ALLOWED);
mbedtls_chachapoly_context chatx;
int ret = mse_decrypt_ct(vendorParam.data, vendorParam.len);
if (ret != 0) {
CBOR_ERROR(CTAP1_ERR_INVALID_PARAMETER);
}
if (!file_has_data(ef_keydev_enc))
CBOR_ERROR(CTAP2_ERR_INTEGRITY_FAILURE);
uint8_t *keyenc = file_get_data(ef_keydev_enc);
size_t keyenc_len = file_get_size(ef_keydev_enc);
mbedtls_chachapoly_init(&chatx);
mbedtls_chachapoly_setkey(&chatx, vendorParam.data);
ret = mbedtls_chachapoly_auth_decrypt(&chatx, sizeof(keydev_dec), keyenc, NULL, 0, keyenc + keyenc_len - 16, keyenc + 12, keydev_dec);
mbedtls_chachapoly_free(&chatx);
if (ret != 0){
CBOR_ERROR(CTAP1_ERR_INVALID_PARAMETER);
}
has_keydev_dec = true;
goto err;
}
else
CBOR_ERROR(CTAP2_ERR_UNSUPPORTED_OPTION);
CBOR_CHECK(cbor_encoder_close_container(&encoder, &mapEncoder));
resp_size = cbor_encoder_get_buffer_size(&encoder, ctap_resp->init.data + 1);
err:
CBOR_FREE_BYTE_STRING(pinUvAuthParam);
CBOR_FREE_BYTE_STRING(vendorParam);
if (error != CborNoError) {
if (error == CborErrorImproperValue)
return CTAP2_ERR_CBOR_UNEXPECTED_TYPE;
return error;
}
res_APDU_size = resp_size;
return 0;
}
int cbor_vendor(const uint8_t *data, size_t len) {
if (len == 0)
return CTAP1_ERR_INVALID_LEN;
if (data[0] >= CTAP_VENDOR_BACKUP)
return cbor_vendor_generic(data[0], data + 1, len - 1);
return CTAP2_ERR_INVALID_CBOR;
}
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