Password-authenticated key exchange (PAKE)#

psa_pake_role_t#

typedef uint8_t psa_pake_role_t

Encoding of the application role of PAKE.

Encodes the application's role in the algorithm is being executed. For more information see the documentation of individual PSA_PAKE_ROLE_XXX constants.

psa_pake_step_t#

typedef uint8_t psa_pake_step_t

Encoding of input and output indicators for PAKE.

Some PAKE algorithms need to exchange more data than just a single key share. This type is for encoding additional input and output data for such algorithms.

psa_pake_primitive_type_t#

typedef uint8_t psa_pake_primitive_type_t

Encoding of the type of the PAKE's primitive.

Values defined by this standard will never be in the range 0x80-0xff. Vendors who define additional types must use an encoding in this range.

For more information see the documentation of individual PSA_PAKE_PRIMITIVE_TYPE_XXX constants.

psa_pake_family_t#

typedef uint8_t psa_pake_family_t

Encoding of the family of the primitive associated with the PAKE.

For more information see the documentation of individual PSA_PAKE_PRIMITIVE_TYPE_XXX constants.

psa_pake_primitive_t#

typedef uint32_t psa_pake_primitive_t

Encoding of the primitive associated with the PAKE.

For more information see the documentation of the PSA_PAKE_PRIMITIVE macro.

psa_pake_cipher_suite_init#

static struct psa_pake_cipher_suite_s psa_pake_cipher_suite_init (void )

Return an initial value for a PAKE cipher suite object.

psa_pake_cs_get_algorithm#

static psa_algorithm_t psa_pake_cs_get_algorithm (const psa_pake_cipher_suite_t * cipher_suite)

Retrieve the PAKE algorithm from a PAKE cipher suite.

Returns

• The PAKE algorithm stored in the cipher suite structure.

psa_pake_cs_set_algorithm#

static void psa_pake_cs_set_algorithm (psa_pake_cipher_suite_t * cipher_suite, psa_algorithm_t algorithm)

Declare the PAKE algorithm for the cipher suite.

This function overwrites any PAKE algorithm previously set in cipher_suite.

psa_pake_cs_get_primitive#

static psa_pake_primitive_t psa_pake_cs_get_primitive (const psa_pake_cipher_suite_t * cipher_suite)

Retrieve the primitive from a PAKE cipher suite.

Returns

• The primitive stored in the cipher suite structure.

psa_pake_cs_set_primitive#

static void psa_pake_cs_set_primitive (psa_pake_cipher_suite_t * cipher_suite, psa_pake_primitive_t primitive)

Declare the primitive for a PAKE cipher suite.

This function overwrites any primitive previously set in cipher_suite.

psa_pake_cs_get_family#

static psa_pake_family_t psa_pake_cs_get_family (const psa_pake_cipher_suite_t * cipher_suite)

Retrieve the PAKE family from a PAKE cipher suite.

Returns

• The PAKE family stored in the cipher suite structure.

psa_pake_cs_get_bits#

static uint16_t psa_pake_cs_get_bits (const psa_pake_cipher_suite_t * cipher_suite)

Retrieve the PAKE primitive bit-size from a PAKE cipher suite.

Returns

• The PAKE primitive bit-size stored in the cipher suite structure.

psa_pake_cs_get_hash#

static psa_algorithm_t psa_pake_cs_get_hash (const psa_pake_cipher_suite_t * cipher_suite)

Retrieve the hash algorithm from a PAKE cipher suite.

Returns

• The hash algorithm stored in the cipher suite structure. The return value is 0 if the PAKE is not parametrised by a hash algorithm or if the hash algorithm is not set.

psa_pake_cs_set_hash#

static void psa_pake_cs_set_hash (psa_pake_cipher_suite_t * cipher_suite, psa_algorithm_t hash)

Declare the hash algorithm for a PAKE cipher suite.

This function overwrites any hash algorithm previously set in cipher_suite.

Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

psa_pake_operation_init#

static struct psa_pake_operation_s psa_pake_operation_init (void )

Return an initial value for an PAKE operation object.

psa_pake_setup#

psa_status_t psa_pake_setup (psa_pake_operation_t * operation, const psa_pake_cipher_suite_t * cipher_suite)

Set the session information for a password-authenticated key exchange.

The sequence of operations to set up a password-authenticated key exchange is as follows:

1. Allocate an operation object which will be passed to all the functions listed here.

2. Initialize the operation object with one of the methods described in the documentation for #psa_pake_operation_t, e.g. #PSA_PAKE_OPERATION_INIT.

3. Call psa_pake_setup() to specify the cipher suite.

4. Call psa_pake_set_xxx() functions on the operation to complete the setup. The exact sequence of psa_pake_set_xxx() functions that needs to be called depends on the algorithm in use.

Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

A typical sequence of calls to perform a password-authenticated key exchange:

1. Call psa_pake_output(operation, PSA_PAKE_STEP_KEY_SHARE, ...) to get the key share that needs to be sent to the peer.

2. Call psa_pake_input(operation, PSA_PAKE_STEP_KEY_SHARE, ...) to provide the key share that was received from the peer.

3. Depending on the algorithm additional calls to psa_pake_output() and psa_pake_input() might be necessary.

4. Call psa_pake_get_implicit_key() for accessing the shared secret.

Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

If an error occurs at any step after a call to psa_pake_setup(), the operation will need to be reset by a call to psa_pake_abort(). The application may call psa_pake_abort() at any time after the operation has been initialized.

After a successful call to psa_pake_setup(), the application must eventually terminate the operation. The following events terminate an operation:

• A call to psa_pake_abort().

• A successful call to psa_pake_get_implicit_key().

psa_pake_set_password_key#

psa_status_t psa_pake_set_password_key (psa_pake_operation_t * operation, mbedtls_svc_key_id_t password)

Set the password for a password-authenticated key exchange from key ID.

Call this function when the password, or a value derived from the password, is already present in the key store.

psa_pake_set_user#

psa_status_t psa_pake_set_user (psa_pake_operation_t * operation, const uint8_t * user_id, size_t user_id_len)

Set the user ID for a password-authenticated key exchange.

Call this function to set the user ID. For PAKE algorithms that associate a user identifier with each side of the session you need to call psa_pake_set_peer() as well. For PAKE algorithms that associate a single user identifier with the session, call psa_pake_set_user() only.

Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

psa_pake_set_peer#

psa_status_t psa_pake_set_peer (psa_pake_operation_t * operation, const uint8_t * peer_id, size_t peer_id_len)

Set the peer ID for a password-authenticated key exchange.

Call this function in addition to psa_pake_set_user() for PAKE algorithms that associate a user identifier with each side of the session. For PAKE algorithms that associate a single user identifier with the session, call psa_pake_set_user() only.

Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

psa_pake_set_role#

psa_status_t psa_pake_set_role (psa_pake_operation_t * operation, psa_pake_role_t role)

Set the application role for a password-authenticated key exchange.

Not all PAKE algorithms need to differentiate the communicating entities. It is optional to call this function for PAKEs that don't require a role to be specified. For such PAKEs the application role parameter is ignored, or PSA_PAKE_ROLE_NONE can be passed as role.

Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

psa_pake_output#

psa_status_t psa_pake_output (psa_pake_operation_t * operation, psa_pake_step_t step, uint8_t * output, size_t output_size, size_t * output_length)

Get output for a step of a password-authenticated key exchange.

Depending on the algorithm being executed, you might need to call this function several times or you might not need to call this at all.

The exact sequence of calls to perform a password-authenticated key exchange depends on the algorithm in use. Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

If this function returns an error status, the operation enters an error state and must be aborted by calling psa_pake_abort().

psa_pake_input#

psa_status_t psa_pake_input (psa_pake_operation_t * operation, psa_pake_step_t step, const uint8_t * input, size_t input_length)

Provide input for a step of a password-authenticated key exchange.

Depending on the algorithm being executed, you might need to call this function several times or you might not need to call this at all.

The exact sequence of calls to perform a password-authenticated key exchange depends on the algorithm in use. Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

If this function returns an error status, the operation enters an error state and must be aborted by calling psa_pake_abort().

psa_pake_get_implicit_key#

psa_status_t psa_pake_get_implicit_key (psa_pake_operation_t * operation, psa_key_derivation_operation_t * output)

Get implicitly confirmed shared secret from a PAKE.

At this point there is a cryptographic guarantee that only the authenticated party who used the same password is able to compute the key. But there is no guarantee that the peer is the party it claims to be and was able to do so.

That is, the authentication is only implicit. Since the peer is not authenticated yet, no action should be taken yet that assumes that the peer is who it claims to be. For example, do not access restricted files on the peer's behalf until an explicit authentication has succeeded.

This function can be called after the key exchange phase of the operation has completed. It imports the shared secret output of the PAKE into the provided derivation operation. The input step PSA_KEY_DERIVATION_INPUT_SECRET is used when placing the shared key material in the key derivation operation.

The exact sequence of calls to perform a password-authenticated key exchange depends on the algorithm in use. Refer to the documentation of individual PAKE algorithm types (PSA_ALG_XXX values of type psa_algorithm_t such that PSA_ALG_IS_PAKE(alg) is true) for more information.

When this function returns successfully, operation becomes inactive. If this function returns an error status, both operation and key_derivation operations enter an error state and must be aborted by calling psa_pake_abort() and psa_key_derivation_abort() respectively.

psa_pake_abort#

psa_status_t psa_pake_abort (psa_pake_operation_t * operation)

Abort a PAKE operation.

Aborting an operation frees all associated resources except for the operation structure itself. Once aborted, the operation object can be reused for another operation by calling psa_pake_setup() again.

This function may be called at any time after the operation object has been initialized as described in #psa_pake_operation_t.

In particular, calling psa_pake_abort() after the operation has been terminated by a call to psa_pake_abort() or psa_pake_get_implicit_key() is safe and has no effect.

PSA_PAKE_ROLE_NONE#

#define PSA_PAKE_ROLE_NONE

((psa_pake_role_t)0x00)

A value to indicate no role in a PAKE algorithm.

This value can be used in a call to psa_pake_set_role() for symmetric PAKE algorithms which do not assign roles.

PSA_PAKE_ROLE_FIRST#

#define PSA_PAKE_ROLE_FIRST

((psa_pake_role_t)0x01)

The first peer in a balanced PAKE.

Although balanced PAKE algorithms are symmetric, some of them needs an ordering of peers for the transcript calculations. If the algorithm does not need this, both PSA_PAKE_ROLE_FIRST and PSA_PAKE_ROLE_SECOND are accepted.

PSA_PAKE_ROLE_SECOND#

#define PSA_PAKE_ROLE_SECOND

((psa_pake_role_t)0x02)

The second peer in a balanced PAKE.

Although balanced PAKE algorithms are symmetric, some of them needs an ordering of peers for the transcript calculations. If the algorithm does not need this, either PSA_PAKE_ROLE_FIRST or PSA_PAKE_ROLE_SECOND are accepted.

PSA_PAKE_ROLE_CLIENT#

#define PSA_PAKE_ROLE_CLIENT

((psa_pake_role_t)0x11)

The client in an augmented PAKE.

Augmented PAKE algorithms need to differentiate between client and server.

PSA_PAKE_ROLE_SERVER#

#define PSA_PAKE_ROLE_SERVER

((psa_pake_role_t)0x12)

The server in an augmented PAKE.

Augmented PAKE algorithms need to differentiate between client and server.

PSA_PAKE_PRIMITIVE_TYPE_ECC#

#define PSA_PAKE_PRIMITIVE_TYPE_ECC

((psa_pake_primitive_type_t)0x01)

The PAKE primitive type indicating the use of elliptic curves.

The values of the family and bits fields of the cipher suite identify a specific elliptic curve, using the same mapping that is used for ECC (psa_ecc_family_t) keys.

(Here family means the value returned by psa_pake_cs_get_family() and bits means the value returned by psa_pake_cs_get_bits().)

Input and output during the operation can involve group elements and scalar values:

1. The format for group elements is the same as for public keys on the specific curve would be. For more information, consult the documentation of psa_export_public_key().

2. The format for scalars is the same as for private keys on the specific curve would be. For more information, consult the documentation of psa_export_key().

PSA_PAKE_PRIMITIVE_TYPE_DH#

#define PSA_PAKE_PRIMITIVE_TYPE_DH

((psa_pake_primitive_type_t)0x02)

The PAKE primitive type indicating the use of Diffie-Hellman groups.

The values of the family and bits fields of the cipher suite identify a specific Diffie-Hellman group, using the same mapping that is used for Diffie-Hellman (psa_dh_family_t) keys.

(Here family means the value returned by psa_pake_cs_get_family() and bits means the value returned by psa_pake_cs_get_bits().)

Input and output during the operation can involve group elements and scalar values:

1. The format for group elements is the same as for public keys on the specific group would be. For more information, consult the documentation of psa_export_public_key().

2. The format for scalars is the same as for private keys on the specific group would be. For more information, consult the documentation of psa_export_key().

PSA_PAKE_PRIMITIVE#

#define PSA_PAKE_PRIMITIVE

Construct a PAKE primitive from type, family and bit-size.

Returns

• The constructed primitive value of type psa_pake_primitive_t. Return 0 if the requested primitive can't be encoded as psa_pake_primitive_t.

PSA_PAKE_STEP_KEY_SHARE#

#define PSA_PAKE_STEP_KEY_SHARE

((psa_pake_step_t)0x01)

The key share being sent to or received from the peer.

The format for both input and output at this step is the same as for public keys on the group determined by the primitive (psa_pake_primitive_t) would be.

For more information on the format, consult the documentation of psa_export_public_key().

For information regarding how the group is determined, consult the documentation PSA_PAKE_PRIMITIVE.

PSA_PAKE_STEP_ZK_PUBLIC#

#define PSA_PAKE_STEP_ZK_PUBLIC

((psa_pake_step_t)0x02)

A Schnorr NIZKP public key.

This is the ephemeral public key in the Schnorr Non-Interactive Zero-Knowledge Proof (the value denoted by the letter 'V' in RFC 8235).

The format for both input and output at this step is the same as for public keys on the group determined by the primitive (psa_pake_primitive_t) would be.

For more information on the format, consult the documentation of psa_export_public_key().

For information regarding how the group is determined, consult the documentation PSA_PAKE_PRIMITIVE.

PSA_PAKE_STEP_ZK_PROOF#

#define PSA_PAKE_STEP_ZK_PROOF

((psa_pake_step_t)0x03)

A Schnorr NIZKP proof.

This is the proof in the Schnorr Non-Interactive Zero-Knowledge Proof (the value denoted by the letter 'r' in RFC 8235).

Both for input and output, the value at this step is an integer less than the order of the group selected in the cipher suite. The format depends on the group as well:

• For Montgomery curves, the encoding is little endian.

• For everything else the encoding is big endian (see Section 2.3.8 of SEC 1: Elliptic Curve Cryptography at https://www.secg.org/sec1-v2.pdf).

In both cases leading zeroes are allowed as long as the length in bytes does not exceed the byte length of the group order.

For information regarding how the group is determined, consult the documentation PSA_PAKE_PRIMITIVE.