1 /*
2 * attest_symmetric_iat_decode.c
3 *
4 * Copyright (c) 2019, Laurence Lundblade.
5 * Copyright (c) 2020-2022, Arm Limited. All rights reserved.
6 *
7 * SPDX-License-Identifier: BSD-3-Clause
8 *
9 * See BSD-3-Clause license in README.md
10 */
11
12 #include "attest_token_decode.h"
13 #include "attest.h"
14 #include "psa/crypto.h"
15 #include "q_useful_buf.h"
16 #include "qcbor_util.h"
17 #include "t_cose_common.h"
18 #include "t_cose_mac0_verify.h"
19 #include "tfm_crypto_defs.h"
20
21 /* Only support HMAC as MAC algorithm in COSE_Mac0 so far */
22 #define SYMMETRIC_IAK_MAX_SIZE PSA_MAC_MAX_SIZE
23
24 #if DOMAIN_NS == 1U
25 /*
26 * Public function. See attest_token_decode.h
27 * It is not allowed to let NS side fetch the symmetric IAK and perform the MAC
28 * verification.
29 */
30 enum attest_token_err_t
attest_token_decode_validate_token(struct attest_token_decode_context * me,struct q_useful_buf_c token)31 attest_token_decode_validate_token(struct attest_token_decode_context *me,
32 struct q_useful_buf_c token)
33 {
34 enum t_cose_err_t t_cose_error;
35 enum attest_token_err_t return_value;
36 /* Decode only without signature verification */
37 int32_t t_cose_options = T_COSE_OPT_DECODE_ONLY;
38 struct t_cose_mac0_verify_ctx verify_ctx;
39 struct t_cose_key attest_key = T_COSE_NULL_KEY;
40
41 t_cose_mac0_verify_init(&verify_ctx, t_cose_options);
42
43 t_cose_mac0_set_verify_key(&verify_ctx, attest_key);
44
45 t_cose_error = t_cose_mac0_verify(&verify_ctx,
46 token, /* COSE to verify */
47 &me->payload, /* Payload from token */
48 NULL
49 );
50
51 return_value = map_t_cose_errors(t_cose_error);
52 me->last_error = return_value;
53
54 return return_value;
55 }
56
57 #else /* DOMAIN_NS == 1U */
58
59 /*
60 * Public function. See attest_token_decode.h
61 * Decode the received COSE_Mac0 structure and verify the tag. Authentication
62 * tag verification in tests is for debug purpose only. The symmetric Initial
63 * Attestation key (IAK) should not be able to be used by anything other than
64 * the Attestation partition in real products.
65 */
66 enum attest_token_err_t
attest_token_decode_validate_token(struct attest_token_decode_context * me,struct q_useful_buf_c token)67 attest_token_decode_validate_token(struct attest_token_decode_context *me,
68 struct q_useful_buf_c token)
69 {
70 enum t_cose_err_t t_cose_error;
71 enum attest_token_err_t return_value;
72 int32_t t_cose_options = 0;
73 struct t_cose_mac0_verify_ctx verify_ctx;
74 struct t_cose_key attest_key;
75 psa_key_handle_t key_handle = TFM_BUILTIN_KEY_ID_IAK;
76
77 if (me->options & TOKEN_OPT_SHORT_CIRCUIT_SIGN) {
78 t_cose_options |= T_COSE_OPT_ALLOW_SHORT_CIRCUIT;
79 }
80
81 t_cose_mac0_verify_init(&verify_ctx, t_cose_options);
82
83 attest_key.crypto_lib = T_COSE_CRYPTO_LIB_PSA;
84 attest_key.k.key_handle = (uint64_t)key_handle;
85 t_cose_mac0_set_verify_key(&verify_ctx, attest_key);
86
87 t_cose_error = t_cose_mac0_verify(&verify_ctx,
88 token, /* COSE to verify */
89 &me->payload, /* Payload from token */
90 NULL);
91
92 return_value = map_t_cose_errors(t_cose_error);
93 me->last_error = return_value;
94
95 return return_value;
96 }
97 #endif /* DOMAIN_NS == 1U */
98
