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refactor(core): move session keys to platform secure storage #67

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f33c75d
refactor(core): secure session keys using platform storage
Grolleau-Benjamin Feb 25, 2026
99f3889
feat(core): add secure session opening function with IDs
Grolleau-Benjamin Mar 3, 2026
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4 changes: 2 additions & 2 deletions core/stse_device.h
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Original file line number Diff line number Diff line change
Expand Up @@ -161,8 +161,8 @@ struct stse_session_t {
union {
struct {
stse_Handler_t *pSTSE;
PLAT_UI8 *pHost_MAC_key;
PLAT_UI8 *pHost_cypher_key;
PLAT_UI32 Host_MAC_key_idx;
PLAT_UI32 Host_cypher_key_idx;
stse_aes_key_type_t key_type;
PLAT_UI32 MAC_counter;
} host;
Expand Down
56 changes: 35 additions & 21 deletions core/stse_platform.h
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Original file line number Diff line number Diff line change
Expand Up @@ -209,15 +209,34 @@ stse_ReturnCode_t stse_platform_nist_kw_encrypt(PLAT_UI8 *pPayload, PLAT_UI32 pa

#if defined(STSE_CONF_USE_HOST_KEY_ESTABLISHMENT) || defined(STSE_CONF_USE_SYMMETRIC_KEY_ESTABLISHMENT) || defined(STSE_CONF_USE_HOST_SESSION)

/*!
* \brief Store session key in platform secure storage
* \param[in] pCypherKey Pointer to the cypher key
* \param[out] pCypherKeyIdx Pointer to receive the index of the stored cypher key
* \param[in] pMACKey Pointer to the MAC key
* \param[out] pMACKeyIdx Pointer to receive the index of the stored MAC key
* \param[in] key_length Length of the keys in bytes
* \return \ref STSE_OK on success; \ref stse_ReturnCode_t error code otherwise
*/
stse_ReturnCode_t stse_platform_store_session_key(PLAT_UI8 *pCypherKey, PLAT_UI32 *pCypherKeyIdx,
PLAT_UI8 *pMACKey, PLAT_UI32 *pMACKeyIdx,
PLAT_UI16 key_length);

/*!
* \brief Delete session key from platform secure storage
* \param[in] CypherKeyIdx Index of the cypher key to delete
* \param[in] MACKeyIdx Index of the MAC key to delete
* \return \ref STSE_OK on success; \ref stse_ReturnCode_t error code otherwise
*/
stse_ReturnCode_t stse_platform_delete_key(PLAT_UI32 CypherKeyIdx, PLAT_UI32 MACKeyIdx);

/*!
* \brief Initialize AES CMAC computation
* \param[in] pKey Pointer to the key
* \param[in] key_length Length of the key
* \param[in] key_idx Index of the key in secure storage
* \param[in] exp_tag_size Expected tag size
* \return \ref STSE_OK on success; \ref stse_ReturnCode_t error code otherwise
*/
stse_ReturnCode_t stse_platform_aes_cmac_init(const PLAT_UI8 *pKey,
PLAT_UI16 key_length,
stse_ReturnCode_t stse_platform_aes_cmac_init(const PLAT_UI32 key_idx,
PLAT_UI16 exp_tag_size);

/*!
Expand Down Expand Up @@ -247,76 +266,71 @@ stse_ReturnCode_t stse_platform_aes_cmac_verify_finish(PLAT_UI8 *pTag);
* \brief Perform an AES CMAC encryption
* \param[in] pPayload Pointer to Payload
* \param[in] payload_length Length of the payload in bytes
* \param[in] pKey Pointer to key
* \param[in] key_length Length of the key in bytes
* \param[in] key_idx Index of the key in secure storage
* \param[in] exp_tag_size Expected tag size in bytes
* \param[out] pTag Pointer to Tag
* \param[out] pTag_length Pointer to Tag length value output
* \return \ref STSE_OK on success; \ref stse_ReturnCode_t error code otherwise
*/
stse_ReturnCode_t stse_platform_aes_cmac_compute(const PLAT_UI8 *pPayload, PLAT_UI16 payload_length,
const PLAT_UI8 *pKey, PLAT_UI16 key_length,
const PLAT_UI32 key_idx,
PLAT_UI16 exp_tag_size,
PLAT_UI8 *pTag, PLAT_UI16 *pTag_length);

/*!
* \brief Perform an AES CMAC decryption
* \param[in] pPayload Pointer to Payload
* \param[in] payload_length Length of the payload in bytes
* \param[in] pKey Pointer to key
* \param[in] key_length Length of the key in bytes
* \param[in] key_idx Index of the key in secure storage
* \param[in] pTag Pointer to Tag
* \param[in] tag_length Pointer to Tag length value output
* \return \ref STSE_OK on success; \ref stse_ReturnCode_t error code otherwise
*/
stse_ReturnCode_t stse_platform_aes_cmac_verify(const PLAT_UI8 *pPayload, PLAT_UI16 payload_length,
const PLAT_UI8 *pKey, PLAT_UI16 key_length,
const PLAT_UI32 key_idx,
const PLAT_UI8 *pTag, PLAT_UI16 tag_length);

/*!
* \brief Perform an AES CBC encryption
* \param[in] pPlaintext Pointer to the plaintext data
* \param[in] plaintext_length Length of the plaintext data
* \param[in] pInitial_value Pointer to encryption IV
* \param[in] pKey Pointer to the key
* \param[in] key_length Length of the key
* \param[in] key_idx Index of the key in secure storage
* \param[out] pEncryptedtext Pointer to the encrypted payload
* \param[out] pEncryptedtext_length Length of encrypted payload
* \return \ref STSE_OK on success; \ref stse_ReturnCode_t error code otherwise
*/
stse_ReturnCode_t stse_platform_aes_cbc_enc(const PLAT_UI8 *pPlaintext, PLAT_UI16 plaintext_length,
PLAT_UI8 *pInitial_value, const PLAT_UI8 *pKey,
PLAT_UI16 key_length, PLAT_UI8 *pEncryptedtext,
PLAT_UI8 *pInitial_value, const PLAT_UI32 key_idx,
PLAT_UI8 *pEncryptedtext,
PLAT_UI16 *pEncryptedtext_length);

/*!
* \brief Perform an AES CBC decryption
* \param[in] pEncryptedtext Pointer to the encrypted payload
* \param[in] encryptedtext_length Length of encrypted payload
* \param[in] pInitial_value Pointer to decryption IV
* \param[in] pKey Pointer to the key
* \param[in] key_length Length of the key
* \param[in] key_idx Index of the key in secure storage
* \param[out] pPlaintext Pointer to PlainText payload
* \param[out] pPlaintext_length Length of the PlainText payload
* \return \ref STSE_OK on success; \ref stse_ReturnCode_t error code otherwise
*/
stse_ReturnCode_t stse_platform_aes_cbc_dec(const PLAT_UI8 *pEncryptedtext, PLAT_UI16 encryptedtext_length,
PLAT_UI8 *pInitial_value, const PLAT_UI8 *pKey,
PLAT_UI16 key_length, PLAT_UI8 *pPlaintext,
PLAT_UI8 *pInitial_value, const PLAT_UI32 key_idx,
PLAT_UI8 *pPlaintext,
PLAT_UI16 *pPlaintext_length);

/*!
* \brief Perform an AES ECB encryption
* \param[in] pPlaintext Pointer to the plaintext data
* \param[in] plaintext_length Length of the plaintext data
* \param[in] pKey Pointer to the key
* \param[in] key_length Length of the key
* \param[in] key_idx Index of the key in secure storage
* \param[out] pEncryptedtext Pointer to the encrypted payload
* \param[out] pEncryptedtext_length Length of encrypted payload
* \return \ref STSE_OK on success; \ref stse_ReturnCode_t error code otherwise
*/
stse_ReturnCode_t stse_platform_aes_ecb_enc(const PLAT_UI8 *pPlaintext, PLAT_UI16 plaintext_length,
const PLAT_UI8 *pKey, PLAT_UI16 key_length,
const PLAT_UI32 key_idx,
PLAT_UI8 *pEncryptedtext, PLAT_UI16 *pEncryptedtext_length);

#endif /* defined(STSE_CONF_USE_HOST_KEY_ESTABLISHMENT) || defined(STSE_CONF_USE_SYMMETRIC_KEY_ESTABLISHMENT) || defined(STSE_CONF_USE_HOST_SESSION) */
Expand Down
88 changes: 74 additions & 14 deletions services/stsafea/stsafea_sessions.c
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Original file line number Diff line number Diff line change
Expand Up @@ -75,9 +75,69 @@ stse_ReturnCode_t stsafea_open_host_session(stse_Handler_t *pSTSE, stse_session_
pSession->context.host.MAC_counter = ARRAY_3B_SWAP_TO_UI32(host_key_slot.cmac_sequence_counter);
}

PLAT_UI32 HostMacKeyIdx;
PLAT_UI32 HostCypherKeyIdx;
PLAT_UI16 key_length = (pSession->context.host.key_type == STSE_AES_128_KT) ? STSE_AES_128_KEY_SIZE : STSE_AES_256_KEY_SIZE;

ret = stse_platform_store_session_key(pHost_cypher_key, &HostCypherKeyIdx, pHost_MAC_key, &HostMacKeyIdx, key_length);
if (ret != STSE_OK) {
return ret;
}

memset(pHost_MAC_key, 0x00, key_length);
memset(pHost_cypher_key, 0x00, key_length);

pSession->type = STSE_HOST_SESSION;
pSession->context.host.pHost_MAC_key = pHost_MAC_key;
pSession->context.host.pHost_cypher_key = pHost_cypher_key;
pSession->context.host.Host_MAC_key_idx = HostMacKeyIdx;
pSession->context.host.Host_cypher_key_idx = HostCypherKeyIdx;
pSession->context.host.pSTSE = pSTSE;
pSTSE->pActive_host_session = pSession;

return (STSE_OK);
}

stse_ReturnCode_t stsafea_open_host_session_from_idx(stse_Handler_t *pSTSE, stse_session_t *pSession, PLAT_UI32 Host_MAC_key_idx, PLAT_UI32 Host_cypher_key_idx) {
stse_ReturnCode_t ret;

if (pSTSE == NULL) {
return STSE_CORE_HANDLER_NOT_INITIALISED;
}

if (pSession == NULL) {
return STSE_CORE_SESSION_ERROR;
}

if (pSTSE->device_type == STSAFE_A120) {
stsafea_host_key_slot_v2_t host_key_slot;

ret = stsafea_query_host_key_v2(pSTSE, &host_key_slot);
if (ret != STSE_OK) {
return ret;
}

if (host_key_slot.key_presence_flag == 0) {
return STSE_SERVICE_SESSION_ERROR;
}
pSession->context.host.key_type = (stse_aes_key_type_t)host_key_slot.key_type;
pSession->context.host.MAC_counter = ARRAY_4B_SWAP_TO_UI32(host_key_slot.cmac_sequence_counter);
} else {
stsafea_host_key_slot_t host_key_slot;

ret = stsafea_query_host_key(pSTSE, &host_key_slot);
if (ret != STSE_OK) {
return ret;
}

if (host_key_slot.key_presence_flag == 0) {
return STSE_SERVICE_SESSION_ERROR;
}
pSession->context.host.key_type = STSE_AES_128_KT;
pSession->context.host.MAC_counter = ARRAY_3B_SWAP_TO_UI32(host_key_slot.cmac_sequence_counter);
}

pSession->type = STSE_HOST_SESSION;
pSession->context.host.Host_MAC_key_idx = Host_MAC_key_idx;
pSession->context.host.Host_cypher_key_idx = Host_cypher_key_idx;
pSession->context.host.pSTSE = pSTSE;
pSTSE->pActive_host_session = pSession;

Expand Down Expand Up @@ -107,6 +167,12 @@ void stsafea_session_clear_context(stse_session_t *pSession) {
return;
}

if (pSession->context.host.Host_MAC_key_idx && pSession->context.host.Host_cypher_key_idx) {
stse_platform_delete_key(pSession->context.host.Host_cypher_key_idx, pSession->context.host.Host_MAC_key_idx);
pSession->context.host.Host_MAC_key_idx = 0x00;
pSession->context.host.Host_cypher_key_idx = 0x00;
}

/* - Clear session context */
memset(pSession, 0x00, sizeof(stse_session_t));
}
Expand Down Expand Up @@ -164,8 +230,7 @@ stse_ReturnCode_t stsafea_session_frame_encrypt(stse_session_t *pSession,
/* - Perform first AES ECB round on IV */
ret = stse_platform_aes_ecb_enc(initial_value,
STSAFEA_HOST_AES_BLOCK_SIZE,
pSession->context.host.pHost_cypher_key,
(pSession->context.host.key_type == STSE_AES_128_KT) ? STSE_AES_128_KEY_SIZE : STSE_AES_256_KEY_SIZE,
pSession->context.host.Host_cypher_key_idx,
initial_value,
&encrypted_iv_len);
if (ret != STSE_OK) {
Expand Down Expand Up @@ -196,8 +261,7 @@ stse_ReturnCode_t stsafea_session_frame_encrypt(stse_session_t *pSession,
pEnc_payload_element->pData,
pEnc_payload_element->length,
initial_value,
pSession->context.host.pHost_cypher_key,
(pSession->context.host.key_type == STSE_AES_128_KT) ? STSE_AES_128_KEY_SIZE : STSE_AES_256_KEY_SIZE,
pSession->context.host.Host_cypher_key_idx,
pEnc_payload_element->pData,
&encrypted_payload_len);
if (ret != 0) {
Expand Down Expand Up @@ -256,8 +320,7 @@ static stse_ReturnCode_t stsafea_session_frame_decrypt(stse_session_t *pSession,
/* - Transform IV using AES ECB */
ret = stse_platform_aes_ecb_enc(initial_value,
STSAFEA_HOST_AES_BLOCK_SIZE,
pSession->context.host.pHost_cypher_key,
(pSession->context.host.key_type == STSE_AES_128_KT) ? STSE_AES_128_KEY_SIZE : STSE_AES_256_KEY_SIZE,
pSession->context.host.Host_cypher_key_idx,
initial_value,
&out_len);

Expand All @@ -271,8 +334,7 @@ static stse_ReturnCode_t stsafea_session_frame_decrypt(stse_session_t *pSession,
ret = stse_platform_aes_cbc_dec(decrypt_buffer,
encrypted_payload_len,
initial_value,
pSession->context.host.pHost_cypher_key,
(pSession->context.host.key_type == STSE_AES_128_KT) ? STSE_AES_128_KEY_SIZE : STSE_AES_256_KEY_SIZE,
pSession->context.host.Host_cypher_key_idx,
decrypt_buffer,
&decrypted_payload_len);

Expand Down Expand Up @@ -328,8 +390,7 @@ static stse_ReturnCode_t stsafea_session_frame_c_mac_compute(stse_session_t *pSe

/*- Initialize AES C-MAC computation */

ret = stse_platform_aes_cmac_init(pSession->context.host.pHost_MAC_key,
(pSession->context.host.key_type == STSE_AES_128_KT) ? STSE_AES_128_KEY_SIZE : STSE_AES_256_KEY_SIZE,
ret = stse_platform_aes_cmac_init(pSession->context.host.Host_MAC_key_idx,
STSAFEA_MAC_SIZE);
if (ret != STSE_OK) {
return ret;
Expand Down Expand Up @@ -420,8 +481,7 @@ static stse_ReturnCode_t stsafea_session_frame_r_mac_verify(stse_session_t *pSes

/*- Initialize AES CMAC computation */
stse_platform_aes_cmac_init(
pSession->context.host.pHost_MAC_key,
(pSession->context.host.key_type == STSE_AES_128_KT) ? STSE_AES_128_KEY_SIZE : STSE_AES_256_KEY_SIZE,
pSession->context.host.Host_MAC_key_idx,
STSAFEA_MAC_SIZE);

/*- Perform First AES-CMAC round */
Expand Down
15 changes: 15 additions & 0 deletions services/stsafea/stsafea_sessions.h
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,21 @@ stse_ReturnCode_t stsafea_open_host_session(stse_Handler_t *pSTSE,
PLAT_UI8 *pHost_MAC_key,
PLAT_UI8 *pHost_cypher_key);

/*!
* \brief This Core function Create a session context and associate it to STSAFE handler based on provided key index
* \details In some configuration, the session keys are already stored in the platform secure storage. This function
* allows to open a session based on the key index in the platform secure storage without providing the key value in input.
* \param[in] *pSession \ref stse_session_t Pointer to session
* \param[in] Host_MAC_key_idx Index of the MAC key in the platform secure storage
* \param[in] Host_cypher_key_idx Index of the cypher key in the platform secure storage
* \return \ref STSE_OK on success ; \ref stse_ReturnCode_t error code otherwise
* \details \include{doc} stsafe_erase_context.dox
*/
stse_ReturnCode_t stsafea_open_host_session_from_idx(stse_Handler_t *pSTSE,
stse_session_t *pSession,
PLAT_UI32 Host_MAC_key_idx,
PLAT_UI32 Host_cypher_key_idx);

/*!
* \brief This Core function Close an existing host session context
* \param[in] *pSession \ref stse_session_t Pointer to session
Expand Down