libspdm Common API (DRAFT)

December 22, 2025 ยท View on GitHub

Introduction

This document details the public API available to Integrators when constructing an SPDM Requester or Responder using libspdm.

SPDM Context

libspdm's spdm_context stores information about an SPDM endpoint and its connection with another SPDM endpoint. An Integrator must first populate the spdm_context to specify and configure the endpoint's capabilities. This includes information such as

  • The endpoint's SPDM capabilities such PSK_CAP or KEY_EX_CAP.
  • The endpoint's cryptography algorithms such as RSASSA_2048 or ECC_NIST_P256.

libspdm_set_data

Description

Populates an element of the spdm_context with the specified value.

Parameters

spdm_context
The SPDM context.

data_type
An enumeration value that specifies what element of the spdm_context to modify.

parameter

data
A pointer to the data that is to be inserted into the spdm_context.

data_size
The size, in bytes, of the data that is to be inserted into the spdm_context.

Details

TBD

libspdm_get_data

Description

Retrieves an element from the spdm_context.

Parameters

spdm_context
The SPDM context.

data_type
An enumeration value that specifies what element of the spdm_context to retrieve.

parameter

data
A pointer to the data that is to be retrieved from the spdm_context.

data_size
On input, the size, in bytes, of the buffer to store the data. On output, the size, in bytes, of the data.

Details

TBD

libspdm_data_type_t

Description

Enumeration value used for the libspdm_set_data and/or libspdm_get_data functions.

Values that can be both get and set.

  • LIBSPDM_DATA_SPDM_VERSION
    • The SPDM (DSP0274) version(s) (1.0, 1.1, 1.2, or 1.3) of an endpoint. These are communicated through the GET_VERSION / VERSION messages.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The SPDM version of the peer endpoint.
      • Cannot contain multiple entries.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The SPDM version(s) of the local endpoint.
      • Can contain multiple entries.
  • LIBSPDM_DATA_CAPABILITY_FLAGS
    • The SPDM capabilities of an endpoint. These are communicated through the GET_CAPABILITIES / CAPABILITIES messages. This is a bitmask whose fields are defined through the SPDM_GET_CAPABILITIES_* macros.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The capabilities of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The capabilities of the local endpoint.
  • LIBSPDM_DATA_CAPABILITY_CT_EXPONENT
    • CTExponent is used to calculate the maximum amount of time (CT) an endpoint needs to provide a response to messages that require cryptographic processing, such as CHALLENGE / CHALLENGE_AUTH. The value of CT is calculated as 2^CTExponent and has units of microseconds. Though CTExponent can range from 0 to 255, libspdm imposes a maximum value of LIBSPDM_MAX_CT_EXPONENT.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The CTExponent value of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The CTExponent value of the local endpoint.
  • LIBSPDM_DATA_CAPABILITY_RTT_US
    • The SPDM specification defines this value (RTT) as "the worst-case round-trip transport timing." and is in units of microseconds. This value is only used by a Requester and is used in the following scenarios.
      • It is the value of the timeout argument in libspdm_device_send_message_func. When sending a message this is a worst-case value, and the implementer of the function is free to reduce the timeout value based on knowledge of the underlying transport.
      • It is added to the Responder's CT or ST1 value and passed via the timeout argument in libspdm_device_receive_message_func.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The RTT value as measured by the Requester endpoint.
  • LIBSPDM_DATA_MEASUREMENT_SPEC
    • This value specifies the measurement specification(s) supported by an endpoint. These are are communicated through the NEGOTIATE_ALGORITHMS / ALGORITHMS messages. However the SPDM specification defines only one value, DMTFmeasSpec. If a Requester is not going to retrieve measurements from a Responder this can be 0. This is a bitmask whose fields are defined through the SPDM_MEASUREMENT_SPECIFICATION_* macros.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The measurement specification of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The measurement specification of the local endpoint.
  • LIBSPDM_DATA_MEASUREMENT_HASH_ALGO
    • The algorithm used to hash a Responder's measurements. This is communicated through the ALGORITHMS message. This is a bitmask whose fields are defined through the SPDM_ALGORITHMS_MEASUREMENT_HASH_ALGO_* macros. A value of SPDM_ALGORITHMS_MEASUREMENT_HASH_ALGO_RAW_BIT_STREAM_ONLY indicates that the Responder cannot provide a hash for any measurement and provides the measurement directly.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The measurement hash algorithm of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The measurement hash algorithm of the local endpoint.
  • LIBSPDM_DATA_BASE_ASYM_ALGO
    • The asymmetric cryptography algorithm used by the Responder to sign messages. This is a bitmask whose fields are defined through the SPDM_ALGORITHMS_BASE_ASYM_ALGO_* macros.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The asymmetric cryptography algorithm of the peer endpoint. -
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The asymmetric cryptography algorithm(s) of the local endpoint.
  • LIBSPDM_DATA_BASE_HASH_ALGO
    • The hash algorithm used to hash transcripts. This is a bitmask whose fields are defined through the SPDM_ALGORITHMS_BASE_HASH_ALGO_TPM_ALG_* macros.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The hash algorithm of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The hash algorithm(s) of the local endpoint.
  • LIBSPDM_DATA_DHE_NAME_GROUP
    • The Diffie-Hellman scheme used for key exchange. This is a bitmask whose fields are defined through the SPDM_ALGORITHMS_DHE_NAMED_GROUP_* macros.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The Diffie-Hellman scheme of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The Diffie-Hellman scheme(s) of the local endpoint.
  • LIBSPDM_DATA_AEAD_CIPHER_SUITE
    • The "authenticated encryption with associated data" algorithm used for symmetric cryptography. This is a bitmask whose fields are defined through the SPDM_ALGORITHMS_AEAD_CIPHER_SUITE_* macros
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The AEAD algorithm of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The AEAD algorithms(s) of the local endpoint.
  • LIBSPDM_DATA_REQ_BASE_ASYM_ALG
    • The asymmetric algorithm used by the Requester to sign messages. This is a bitmask whose fields are defined through the SPDM_ALGORITHMS_BASE_ASYM_ALGO_* macros.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The asymmetric cryptography algorithm of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The asymmetric cryptography algorithm(s) of the local endpoint.
  • LIBSPDM_DATA_KEY_SCHEDULE
    • The key schedule used for both symmetric and asymmetric key exchange. This is communicated through the NEGOTIATE_ALGORITHMS / ALGORITHMS messages. This is a bitmask whose fields are defined through the SPDM_ALGORITHMS_KEY_SCHEDULE_* macros.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The key schedule of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The key schedule of the local endpoint.
  • LIBSPDM_DATA_OTHER_PARAMS_SUPPORT
    • This field is included in the NEGOTIATE_ALGORITHMS / ALGORITHMS messages to advertise miscellaneous capabilities. This is a bitmask whose fields are defined through the SPDM_ALGORITHMS_OPAQUE_DATA_FORMAT_* and SPDM_ALGORITHMS_MULTI_KEY_CONN macros.
      • SPDM_ALGORITHMS_OPAQUE_DATA_FORMAT_0
        • The format for all OpaqueData fields is defined by the device vendor or other standards body.
      • SPDM_ALGORITHMS_OPAQUE_DATA_FORMAT_1
        • The format for all OpaqueData fields is defined by the SPDM specification's general opaque data format. For libspdm this format is required during key exchange to negotiate the version of the secured message binding specification.
      • SPDM_ALGORITHMS_MULTI_KEY_CONN
        • Specifies whether the Integrator wants the peer endpoint to support multi-key or not. This only applies when the value of the peer endpoint's MULTI_KEY_CAP is SPDM_GET_CAPABILITIES_RESPONSE_FLAGS_MULTI_KEY_CAP_NEG. If the value of the peer endpoint's MULTI_KEY_CAP is not that then libspdm will set the appropriate value in NEGOTIATE_ALGORITHMS / ALGORITHMS based on the peer endpoint's capabilities. LIBSPDM_DATA_MULTI_KEY_CONN_REQ and LIBSPDM_DATA_MULTI_KEY_CONN_RSP can be queried after a successful NEGOTIATE_ALGORITHMS / ALGORITHMS to determine the connection's multi-key state.
    • LIBSPDM_DATA_LOCATION_CONNECTION
      • The OtherParams value of the peer endpoint.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The OtherParams value of the local endpoint.
  • LIBSPDM_DATA_CONNECTION_STATE
    • The connection state of the two endpoints. Since the two endpoints share the same connection state the LIBSPDM_DATA_LOCATION_* value is not checked. Its value is one of
      • LIBSPDM_CONNECTION_STATE_NOT_STARTED
        • The initial state after the SPDM context has been initialized or reset.
      • LIBSPDM_CONNECTION_STATE_AFTER_VERSION
        • The state immediately after a successful GET_VERSION request and VERSION response.
      • LIBSPDM_CONNECTION_STATE_AFTER_CAPABILITIES
        • The state immediately after a successful GET_CAPABILITIES request and CAPABILITIES response.
      • LIBSPDM_CONNECTION_STATE_NEGOTIATED
        • The state immediately after a successful NEGOTIATE_ALGORITHMS request and ALGORITHMS response.
      • LIBSPDM_CONNECTION_STATE_AFTER_DIGESTS
        • The state immediately after a successful GET_DIGESTS request and DIGESTS response.
      • LIBSPDM_CONNECTION_STATE_AFTER_CERTIFICATE
        • The state immediately after a successful GET_CERTIFICATE request and CERTIFICATE response.
      • LIBSPDM_CONNECTION_STATE_AUTHENTICATED
        • The state immediately after a successful CHALLENGE request and CHALLENGE_AUTH response.
  • LIBSPDM_DATA_PEER_PUBLIC_ROOT_CERT
    • Allows multiple pointers to root certificates to be stored in the spdm_context. These root certificates are then either compared against the root certificate returned by a peer endpoint, or appended to the partial (without root certificate) certificate chain returned by a peer endpoint. The root certificate(s) must be encoded as ASN.1 DER.
  • LIBSPDM_DATA_LOCAL_PUBLIC_CERT_CHAIN
    • Allows multiple pointers to SPDM certificate chains to be stored in slots through the additional_data field. An SPDM certificate chain can then be returned through a CERTIFICATE response message. The structure of the SPDM certificate chain is defined in the spdm_cert_chain_t struct in the spdm.h header.
  • LIBSPDM_DATA_PEER_USED_CERT_CHAIN_BUFFER
    • Allows multiple certificates, or values derived from the certificates, to be stored in the spdm_context. If LIBSPDM_RECORD_TRANSCRIPT_DATA_SUPPORT is 1 then the provided certificate chain is copied into the spdm_context. If LIBSPDM_RECORD_TRANSCRIPT_DATA_SUPPORT is 0 then the provided certificate chain is hashed and the public key of the leaf certificate is extracted.
  • LIBSPDM_DATA_PEER_PUBLIC_KEY
    • The raw public key of a peer endpoint. This is used when an endpoint does not support certificate chains and instead a public key is provisioned to its peer(s). While the SPDM specification does not mandate the format of the public key, libspdm implements the public key as described in RFC7250. It is ASN.1 DER-encoded.
  • LIBSPDM_DATA_LOCAL_PUBLIC_KEY
    • The raw public key of the local endpoint.
  • LIBSPDM_DATA_REQUEST_RETRY_TIMES
    • Specifies the number of times a Requester will retry a request message if the Responder returns a Busy error response.
  • LIBSPDM_DATA_REQUEST_RETRY_DELAY_TIME
    • Specifies the amount of time to wait before resending a request due to a Busy error response from the Responder.
  • LIBSPDM_DATA_MAX_DHE_SESSION_COUNT
    • Specifies the maximum number of secure sessions spawned through asymmetric key exchange.
  • LIBSPDM_DATA_MAX_PSK_SESSION_COUNT
    • Specifies the maximum number of secure sessions spawned through symmetric key exchange.
  • LIBSPDM_DATA_HANDLE_ERROR_RETURN_POLICY
    • Specifies how some errors are handled. It is a bitmask whose fields are defined by the LIBSPDM_DATA_HANDLE_ERROR_RETURN_POLICY_* macros.
    • LIBSPDM_DATA_HANDLE_ERROR_RETURN_POLICY_DROP_ON_DECRYPT_ERROR
      • If set then, if the Responder is unable to verify the MAC of an AEAD message, it will not provide an ERROR response to the Requester. If not set then the Responder will provide a DecryptError response to the Requester.
  • LIBSPDM_DATA_VCA_CACHE
    • A buffer that contains the appended VCA messages. It can be used to restore connections if the endpoints support CACHE_CAP.
  • LIBSPDM_DATA_IS_REQUESTER
    • Specifies if the local endpoint is a Requester (true) or Responder (false).
  • LIBSPDM_DATA_APP_CONTEXT_DATA
    • Is used to hold a pointer to Integrator-defined data that is tied to the spdm_context. Via this mechanism an Integrator can extend the spdm_context.
  • LIBSPDM_DATA_HEARTBEAT_PERIOD
    • Specifies the Responder's HeartbeatPeriod in units of seconds. This value is communicated to the Requester in the KEY_EXCHANGE_RSP and PSK_EXCHANGE_RSP messages. The actual timeout limit is twice the HeartbeatPeriod.
  • LIBSPDM_DATA_MUT_AUTH_REQUESTED
    • Specifies whether the Responder requires session-based mutual authentication with the Requester via asymmetric key exchange. Its value can be one of
      • SPDM_KEY_EXCHANGE_RESPONSE_MUT_AUTH_REQUESTED
        • Used when the Responder is in possession of the Requester's public key and does not want to issue encapsulated requests to get a certificate chain from the Requester.
      • SPDM_KEY_EXCHANGE_RESPONSE_MUT_AUTH_REQUESTED_WITH_ENCAP_REQUEST
        • Used when the Responder wants to issue GET_CERTIFICATE encapsulated requests to the Requester to retrieve certificate chains.
      • SPDM_KEY_EXCHANGE_RESPONSE_MUT_AUTH_REQUESTED_WITH_GET_DIGESTS
        • Similar to SPDM_KEY_EXCHANGE_RESPONSE_MUT_AUTH_REQUESTED_WITH_ENCAP_REQUEST except the Responder embeds a GET_DIGESTS request in its response to the Requester. This may improve performance.
  • LIBSPDM_DATA_MAX_SPDM_SESSION_SEQUENCE_NUMBER
    • Specifies the number of messages that can encrypted or decrypted before an error is returned to the Integrator. The sequence number used to track these messages is 64 bits and the default maximum value is 0xffffffffffffffff. If LIBSPDM_DATA_MAX_SPDM_SESSION_SEQUENCE_NUMBER is set to 0 then the default value is used.
  • LIBSPDM_DATA_SPDM_VERSION_10_11_VERIFY_SIGNATURE_ENDIAN
    • Specifies how verification of asymmetric signatures is handled when the negotiated SPDM version is 1.0 or 1.1. Its value is one of
      • LIBSPDM_SPDM_10_11_VERIFY_SIGNATURE_ENDIAN_BIG_ONLY
        • The endianness of the signature is only interpreted as big-endian. (default)
      • LIBSPDM_SPDM_10_11_VERIFY_SIGNATURE_ENDIAN_LITTLE_ONLY
        • The endianness of the signature is only interpreted as little-endian.
      • LIBSPDM_SPDM_10_11_VERIFY_SIGNATURE_ENDIAN_BIG_OR_LITTLE
        • The endianness of the signature is first interpreted as big-endian. If verification fails then little-endian is tried.
  • LIBSPDM_DATA_SEQUENCE_NUMBER_ENDIAN
    • Specifies the endianness of the AEAD sequence number used in secured message encryption and decryption when the negotiated secured SPDM version is 1.0 or 1.1. Its value is one of
      • LIBSPDM_DATA_SESSION_SEQ_NUM_ENC_LITTLE_DEC_LITTLE
        • Data is both encrypted and decrypted with a little-endian sequence number. (default)
      • LIBSPDM_DATA_SESSION_SEQ_NUM_ENC_LITTLE_DEC_BOTH
        • Data is encrypted with a little-endian sequence number and data is initially decrypted with a little-endian sequence number. If decryption fails then a big-endian sequence number is tried.
      • LIBSPDM_DATA_SESSION_SEQ_NUM_ENC_BIG_DEC_BIG
        • Data is both encrypted and decrypted with a big-endian sequence number.
      • LIBSPDM_DATA_SESSION_SEQ_NUM_ENC_BIG_DEC_BOTH
        • Data is encrypted with a big-endian sequence number and data is initially decrypted with a big-endian sequence number. If decryption fails then a little-endian sequence number is tried.
    • For practical purposes *_BOTH only applies to Responder endpoints. In the scenario where Requester and Responder exclusively support different endianness encodings, the Responder may return a DecryptError to the Requester or it may not return an error and terminate the session. In such a situation the Requester Integrator may change the sequence number endianness to the opposite value and try again with session establishment. Once a session has been successfully established, the correct endianness can be queried from LIBSPDM_DATA_SESSION_SEQUENCE_NUMBER_ENDIAN.
    • When the negotiated secured SPDM version is 1.2 or greater then libspdm unconditionally uses LIBSPDM_DATA_SESSION_SEQ_NUM_ENC_LITTLE_DEC_LITTLE.
  • LIBSPDM_DATA_MULTI_KEY_CONN_REQ
    • Specifies the Requester's multi-key state for the connection. This is set following NEGOTIATE_ALGORITHMS / ALGORITHMS.
      • If true then the Requester supports multi-key capabilities during the connection.
      • If false then Requester does not support multi-key capabilities and only supports a single asymmetric key during the connection.
    • Only LIBSPDM_DATA_LOCATION_CONNECTION is allowed.
  • LIBSPDM_DATA_MULTI_KEY_CONN_RSP
    • Specifies the Responder's multi-key state for the connection. This is set following NEGOTIATE_ALGORITHMS / ALGORITHMS.
      • If true then the Responder supports multi-key capabilities during the connection.
      • If false then Responder does not support multi-key capabilities and only supports a single asymmetric key during the connection.
    • Only LIBSPDM_DATA_LOCATION_CONNECTION is allowed.

Values that can only be get.

  • LIBSPDM_DATA_PEER_SLOT_MASK
    • The value of the peer's certificate chain slot mask that was returned in the most recent DIGESTS response. It is a bitmask that indicates if a certificate chain slot is populated, where the least significant bit corresponds to slot 0 and the most significant bit corresponds to slot 7.
  • LIBSPDM_DATA_SESSION_SECURED_MESSAGE_VERSION
    • For a given session ID, returns the negotiated secured message version.
  • LIBSPDM_DATA_SESSION_USE_PSK
    • For a given session ID, returns whether the session was established via symmetric key exchange (true) or asymmetric key exchange (false).
  • LIBSPDM_DATA_SESSION_MUT_AUTH_REQUESTED
    • For a given session ID, returns whether the Responder has requested mutual authentication with the Requester.
  • LIBSPDM_DATA_SESSION_END_SESSION_ATTRIBUTES
    • Can be get with either a session ID or without one. If a session ID is present then this returns the end session attributes for the session. If a session ID is not present then this returns the union of the end session attributes for all sessions, and is a sticky bit such that once set to 1 it cannot be set to 0 except by initializing the SPDM context. This value is only used by a Responder.
    • This is a bitmask whose fields are defined by the SPDM_END_SESSION_REQUEST_ATTRIBUTES_* macros.
    • SPDM_END_SESSION_REQUEST_ATTRIBUTES_PRESERVE_NEGOTIATED_STATE_CLEAR
      • If set then the Responder will clear its negotiated connection state derived from VCA. If not set then Responder will maintain its negotiated connection state.
      • Only valid if the Responder supports VCA caching (CACHE_CAP is set).
  • LIBSPDM_DATA_SESSION_SEQUENCE_NUMBER_REQ_DIR
    • For a given session ID, returns the number of application data messages that have been encrypted / decrypted in the request (Requester to Responder) direction.
    • This value is only applicable when the local endpoint is in the LIBSPDM_SESSION_STATE_ESTABLISHED state.
  • LIBSPDM_DATA_SESSION_SEQUENCE_NUMBER_RSP_DIR
    • For a given session ID, returns the number of application data messages that have been encrypted / decrypted in the response (Responder to Requester) direction.
    • This value is only applicable when the local endpoint is in the LIBSPDM_SESSION_STATE_ESTABLISHED state.
  • LIBSPDM_DATA_SESSION_SEQUENCE_NUMBER_ENDIAN
    • For a given session ID, returns the endianness of the AEAD sequence number when the negotiated secured SPDM version is 1.0 or 1.1. Its value is one of
      • LIBSPDM_DATA_SESSION_SEQ_NUM_ENC_LITTLE_DEC_LITTLE
        • The endianness of the sequence number is little-endian.
      • LIBSPDM_DATA_SESSION_SEQ_NUM_ENC_BIG_DEC_BIG
        • The endianness of the sequence number is big-endian.
  • LIBSPDM_DATA_REQUEST_AND_SIZE
    • Returns a pointer to the raw command buffer and the size of the command in bytes.
    • This pointer is valid after libspdm_set_scratch_buffer is called, but the command itself is not valid unless the size returned is greater than zero. The command and its size will persist until the next command is received or the libspdm context is reset.

Values that can only be set.

  • LIBSPDM_DATA_SECURED_MESSAGE_VERSION
    • The SPDM secured message (DSP0277) version(s) (1.0/1.1/1.2) of the local endpoint. These are communicated through the opaque data fields in KEY_EXCHANGE / KEY_EXCHANGE_RSP or PSK_EXCHANGE / PSK_EXCHANGE messages.
    • Once a secure session has been established then LIBSPDM_DATA_SESSION_SECURED_MESSAGE_VERSION can be used to retrieve the negotiated secured message version.
    • LIBSPDM_DATA_LOCATION_LOCAL
      • The SPDM secured message version(s) of the local endpoint.
      • Can contain multiple entries.