10.7. Asymmetric signature
10.7.1. Asymmetric signature algorithms
PSA_ALG_RSA_PKCS1V15_SIGN
(macro)
The RSA PKCS#1 v1.5 message signature scheme, with hashing.
#define PSA_ALG_RSA_PKCS1V15_SIGN(hash_alg) /* specificationdefined value */
Parameters

hash_alg
A hash algorithm (
PSA_ALG_XXX
value such thatPSA_ALG_IS_HASH
(
hash_alg
)
is true). This includesPSA_ALG_ANY_HASH
when specifying the algorithm in a key policy.
Returns
The corresponding RSA PKCS#1 v1.5 signature algorithm.
Unspecified if hash_alg
is not a supported hash algorithm.
Description
This algorithm can be used with both the message and hash signature functions.
This signature scheme is defined by PKCS #1: RSA Cryptography Specifications Version 2.2 [RFC8017] §8.2 under the name RSASSAPKCS1v1_5.
When used with psa_sign_hash()
or psa_verify_hash()
, the provided hash
parameter is used as H from step 2 onwards in the message encoding algorithm EMSAPKCS1V1_5ENCODE()
in [RFC8017] §9.2. H is usually the message digest, using the hash_alg
hash algorithm.
PSA_ALG_RSA_PKCS1V15_SIGN_RAW
(macro)
The raw RSA PKCS#1 v1.5 signature algorithm, without hashing.
#define PSA_ALG_RSA_PKCS1V15_SIGN_RAW ((psa_algorithm_t) 0x06000200)
This algorithm can be only used with the psa_sign_hash()
and psa_verify_hash()
functions.
This signature scheme is defined by PKCS #1: RSA Cryptography Specifications Version 2.2 [RFC8017] §8.2 under the name RSASSAPKCS1v1_5.
The hash
parameter to psa_sign_hash()
or psa_verify_hash()
is used as T from step 3 onwards in the message encoding algorithm EMSAPKCS1V1_5ENCODE()
in [RFC8017] §9.2. T is the DER encoding of the DigestInfo structure normally produced by step 2 in the message encoding algorithm.
PSA_ALG_RSA_PSS
(macro)
The RSA PSS message signature scheme, with hashing.
#define PSA_ALG_RSA_PSS(hash_alg) /* specificationdefined value */
Parameters

hash_alg
A hash algorithm (
PSA_ALG_XXX
value such thatPSA_ALG_IS_HASH
(
hash_alg
)
is true). This includesPSA_ALG_ANY_HASH
when specifying the algorithm in a key policy.
Returns
The corresponding RSA PSS signature algorithm.
Unspecified if hash_alg
is not a supported hash algorithm.
Description
This algorithm can be used with both the message and hash signature functions.
This algorithm is randomized: each invocation returns a different, equally valid signature.
This is the signature scheme defined by [RFC8017] §8.1 under the name RSASSAPSS, with the following options:
The mask generation function is MGF1 defined by [RFC8017] Appendix B.
The salt length is equal to the length of the hash.
The specified hash algorithm is used to hash the input message, to create the salted hash, and for the mask generation.
PSA_ALG_ECDSA
(macro)
The randomized ECDSA signature scheme, with hashing.
#define PSA_ALG_ECDSA(hash_alg) /* specificationdefined value */
Parameters

hash_alg
A hash algorithm (
PSA_ALG_XXX
value such thatPSA_ALG_IS_HASH
(
hash_alg
)
is true). This includesPSA_ALG_ANY_HASH
when specifying the algorithm in a key policy.
Returns
The corresponding randomized ECDSA signature algorithm.
Unspecified if hash_alg
is not a supported hash algorithm.
Description
This algorithm can be used with both the message and hash signature functions.
This algorithm is randomized: each invocation returns a different, equally valid signature.
Note
When based on the same hash algorithm, the verification operations for PSA_ALG_ECDSA
and PSA_ALG_DETERMINISTIC_ECDSA
are identical. A signature created using PSA_ALG_ECDSA
can be verified with the same key using either PSA_ALG_ECDSA
or PSA_ALG_DETERMINISTIC_ECDSA
. Similarly, a signature created using PSA_ALG_DETERMINISTIC_ECDSA
can be verified with the same key using either PSA_ALG_ECDSA
or PSA_ALG_DETERMINISTIC_ECDSA
.
In particular, it is impossible to determine whether a signature was produced with deterministic ECDSA or with randomized ECDSA: it is only possible to verify that a signature was made with ECDSA with the private key corresponding to the public key used for the verification.
This signature scheme is defined by SEC 1: Elliptic Curve Cryptography [SEC1], and also by Public Key Cryptography For The Financial Services Industry: The Elliptic Curve Digital Signature Algorithm (ECDSA) [X962], with a random permessage secret number k.
The representation of the signature as a byte string consists of the concatenation of the signature values r and s. Each of r and s is encoded as an Noctet string, where N is the length of the base point of the curve in octets. Each value is represented in bigendian order, with the most significant octet first.
PSA_ALG_ECDSA_ANY
(macro)
The randomized ECDSA signature scheme, without hashing.
#define PSA_ALG_ECDSA_ANY ((psa_algorithm_t) 0x06000600)
This algorithm can be only used with the psa_sign_hash()
and psa_verify_hash()
functions.
This algorithm is randomized: each invocation returns a different, equally valid signature.
This is the same signature scheme as PSA_ALG_ECDSA()
, but without specifying a hash algorithm, and skipping the message hashing operation.
This algorithm is only recommended to sign or verify a sequence of bytes that are an alreadycalculated hash. Note that the input is padded with zeros on the left or truncated on the right as required to fit the curve size.
PSA_ALG_DETERMINISTIC_ECDSA
(macro)
Deterministic ECDSA signature scheme, with hashing.
#define PSA_ALG_DETERMINISTIC_ECDSA(hash_alg) /* specificationdefined value */
Parameters

hash_alg
A hash algorithm (
PSA_ALG_XXX
value such thatPSA_ALG_IS_HASH
(
hash_alg
)
is true). This includesPSA_ALG_ANY_HASH
when specifying the algorithm in a key policy.
Returns
The corresponding deterministic ECDSA signature algorithm.
Unspecified if hash_alg
is not a supported hash algorithm.
Description
This algorithm can be used with both the message and hash signature functions.
Note
When based on the same hash algorithm, the verification operations for PSA_ALG_ECDSA
and PSA_ALG_DETERMINISTIC_ECDSA
are identical. A signature created using PSA_ALG_ECDSA
can be verified with the same key using either PSA_ALG_ECDSA
or PSA_ALG_DETERMINISTIC_ECDSA
. Similarly, a signature created using PSA_ALG_DETERMINISTIC_ECDSA
can be verified with the same key using either PSA_ALG_ECDSA
or PSA_ALG_DETERMINISTIC_ECDSA
.
In particular, it is impossible to determine whether a signature was produced with deterministic ECDSA or with randomized ECDSA: it is only possible to verify that a signature was made with ECDSA with the private key corresponding to the public key used for the verification.
This is the deterministic ECDSA signature scheme defined by Deterministic Usage of the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA) [RFC6979].
The representation of a signature is the same as with PSA_ALG_ECDSA()
.
10.7.2. Asymmetric signature functions
psa_sign_message
(function)
Sign a message with a private key. For hashandsign algorithms, this includes the hashing step.
psa_status_t psa_sign_message(psa_key_id_t key, psa_algorithm_t alg, const uint8_t * input, size_t input_length, uint8_t * signature, size_t signature_size, size_t * signature_length);
Parameters

key
Identifier of the key to use for the operation. It must be an asymmetric key pair. The key must allow the usage
PSA_KEY_USAGE_SIGN_MESSAGE
.
alg
An asymmetric signature algorithm (
PSA_ALG_XXX
value such thatPSA_ALG_IS_SIGN_MESSAGE
(
alg
)
is true), that is compatible with the type ofkey
.
input
The input message to sign.

input_length
Size of the
input
buffer in bytes.
signature
Buffer where the signature is to be written.

signature_size
Size of the
signature
buffer in bytes. This must be appropriate for the selected algorithm and key:The required signature size is
PSA_SIGN_OUTPUT_SIZE
(
key_type
,
key_bits
,
alg
)
wherekey_type
andkey_bits
are the type and bitsize respectively ofkey
.PSA_SIGNATURE_MAX_SIZE
evaluates to the maximum signature size of any supported signature algorithm.

signature_length
On success, the number of bytes that make up the returned signature value.
Returns: psa_status_t

PSA_SUCCESS

PSA_ERROR_INVALID_HANDLE

PSA_ERROR_NOT_PERMITTED
The key does not have the
PSA_KEY_USAGE_SIGN_MESSAGE
flag, or it does not permit the requested algorithm.
PSA_ERROR_BUFFER_TOO_SMALL
The size of the
signature
buffer is too small.PSA_SIGN_OUTPUT_SIZE()
orPSA_SIGNATURE_MAX_SIZE
can be used to determine the required buffer size.
PSA_ERROR_NOT_SUPPORTED

PSA_ERROR_INVALID_ARGUMENT

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_HARDWARE_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

PSA_ERROR_INSUFFICIENT_ENTROPY

PSA_ERROR_BAD_STATE
The library has not been previously initialized by
psa_crypto_init()
. It is implementationdependent whether a failure to initialize results in this error code.
Description
Note
To perform a multipart hashandsign signature algorithm, first use a multipart hash operation and then pass the resulting hash to psa_sign_hash()
. PSA_ALG_GET_HASH
(
alg
)
can be used to determine the hash algorithm to use.
psa_verify_message
(function)
Verify the signature of a message with a public key, using a hashandsign verification algorithm.
psa_status_t psa_verify_message(psa_key_id_t key, psa_algorithm_t alg, const uint8_t * input, size_t input_length, const uint8_t * signature, size_t signature_length);
Parameters

key
Identifier of the key to use for the operation. It must be a public key or an asymmetric key pair. The key must allow the usage
PSA_KEY_USAGE_VERIFY_MESSAGE
.
alg
An asymmetric signature algorithm (
PSA_ALG_XXX
value such thatPSA_ALG_IS_SIGN_MESSAGE
(
alg
)
is true), that is compatible with the type ofkey
.
input
The message whose signature is to be verified.

input_length
Size of the
input
buffer in bytes.
signature
Buffer containing the signature to verify.

signature_length
Size of the
signature
buffer in bytes.
Returns: psa_status_t

PSA_SUCCESS
The signature is valid.

PSA_ERROR_INVALID_HANDLE

PSA_ERROR_NOT_PERMITTED
The key does not have the
PSA_KEY_USAGE_VERIFY_MESSAGE
flag, or it does not permit the requested algorithm.
PSA_ERROR_INVALID_SIGNATURE
The calculation was performed successfully, but the passed signature is not a valid signature.

PSA_ERROR_NOT_SUPPORTED

PSA_ERROR_INVALID_ARGUMENT

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_HARDWARE_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

PSA_ERROR_BAD_STATE
The library has not been previously initialized by
psa_crypto_init()
. It is implementationdependent whether a failure to initialize results in this error code.
Description
Note
To perform a multipart hashandsign signature verification algorithm, first use a multipart hash operation to hash the message and then pass the resulting hash to psa_verify_hash()
. PSA_ALG_GET_HASH
(
alg
)
can be used to determine the hash algorithm to use.
psa_sign_hash
(function)
Sign an alreadycalculated hash with a private key.
psa_status_t psa_sign_hash(psa_key_id_t key, psa_algorithm_t alg, const uint8_t * hash, size_t hash_length, uint8_t * signature, size_t signature_size, size_t * signature_length);
Parameters

key
Identifier of the key to use for the operation. It must be an asymmetric key pair. The key must allow the usage
PSA_KEY_USAGE_SIGN_HASH
.
alg
An asymmetric signature algorithm that separates the hash and sign operations (
PSA_ALG_XXX
value such thatPSA_ALG_IS_SIGN_HASH
(
alg
)
is true), that is compatible with the type ofkey
.
hash
The input to sign. This is usually the hash of a message. See the detailed description of this function and the description of individual signature algorithms for a detailed description of acceptable inputs.

hash_length
Size of the
hash
buffer in bytes.
signature
Buffer where the signature is to be written.

signature_size
Size of the
signature
buffer in bytes. This must be appropriate for the selected algorithm and key:The required signature size is
PSA_SIGN_OUTPUT_SIZE
(
key_type
,
key_bits
,
alg
)
wherekey_type
andkey_bits
are the type and bitsize respectively ofkey
.PSA_SIGNATURE_MAX_SIZE
evaluates to the maximum signature size of any supported signature algorithm.

signature_length
On success, the number of bytes that make up the returned signature value.
Returns: psa_status_t

PSA_SUCCESS

PSA_ERROR_INVALID_HANDLE

PSA_ERROR_NOT_PERMITTED
The key does not have the
PSA_KEY_USAGE_SIGN_HASH
flag, or it does not permit the requested algorithm.
PSA_ERROR_BUFFER_TOO_SMALL
The size of the
signature
buffer is too small.PSA_SIGN_OUTPUT_SIZE()
orPSA_SIGNATURE_MAX_SIZE
can be used to determine the required buffer size.
PSA_ERROR_NOT_SUPPORTED

PSA_ERROR_INVALID_ARGUMENT

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_HARDWARE_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

PSA_ERROR_INSUFFICIENT_ENTROPY

PSA_ERROR_BAD_STATE
The library has not been previously initialized by
psa_crypto_init()
. It is implementationdependent whether a failure to initialize results in this error code.
Description
With most signature mechanisms that follow the hashandsign paradigm, the hash input to this function is the hash of the message to sign. The hash algorithm is encoded in the signature algorithm.
Some hashandsign mechanisms apply a padding or encoding to the hash. In such cases, the encoded hash must be passed to this function. The current version of this specification defines one such signature algorithm: PSA_ALG_RSA_PKCS1V15_SIGN_RAW
.
Note
To perform a hashandsign algorithm, the hash must be calculated before passing it to this function. This can be done by calling psa_hash_compute()
or with a multipart hash operation. Alternatively, to hash and sign a message in a single call, use psa_sign_message()
.
psa_verify_hash
(function)
Verify the signature of a hash or short message using a public key.
psa_status_t psa_verify_hash(psa_key_id_t key, psa_algorithm_t alg, const uint8_t * hash, size_t hash_length, const uint8_t * signature, size_t signature_length);
Parameters

key
Identifier of the key to use for the operation. It must be a public key or an asymmetric key pair. The key must allow the usage
PSA_KEY_USAGE_VERIFY_HASH
.
alg
An asymmetric signature algorithm that separates the hash and sign operations (
PSA_ALG_XXX
value such thatPSA_ALG_IS_SIGN_HASH
(
alg
)
is true), that is compatible with the type ofkey
.
hash
The input whose signature is to be verified. This is usually the hash of a message. See the detailed description of this function and the description of individual signature algorithms for a detailed description of acceptable inputs.

hash_length
Size of the
hash
buffer in bytes.
signature
Buffer containing the signature to verify.

signature_length
Size of the
signature
buffer in bytes.
Returns: psa_status_t

PSA_SUCCESS
The signature is valid.

PSA_ERROR_INVALID_HANDLE

PSA_ERROR_NOT_PERMITTED
The key does not have the
PSA_KEY_USAGE_VERIFY_HASH
flag, or it does not permit the requested algorithm.
PSA_ERROR_INVALID_SIGNATURE
The calculation was performed successfully, but the passed signature is not a valid signature.

PSA_ERROR_NOT_SUPPORTED

PSA_ERROR_INVALID_ARGUMENT

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_HARDWARE_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

PSA_ERROR_BAD_STATE
The library has not been previously initialized by
psa_crypto_init()
. It is implementationdependent whether a failure to initialize results in this error code.
Description
With most signature mechanisms that follow the hashandsign paradigm, the hash input to this function is the hash of the message to sign. The hash algorithm is encoded in the signature algorithm.
Some hashandsign mechanisms apply a padding or encoding to the hash. In such cases, the encoded hash must be passed to this function. The current version of this specification defines one such signature algorithm: PSA_ALG_RSA_PKCS1V15_SIGN_RAW
.
Note
To perform a hashandsign verification algorithm, the hash must be calculated before passing it to this function. This can be done by calling psa_hash_compute()
or with a multipart hash operation. Alternatively, to hash and verify a message signature in a single call, use psa_verify_message()
.
10.7.3. Support macros
PSA_ALG_IS_SIGN_MESSAGE
(macro)
Whether the specified algorithm is a signature algorithm that can be used with psa_sign_message()
and psa_verify_message()
.
#define PSA_ALG_IS_SIGN_MESSAGE(alg) /* specificationdefined value */
Parameters

alg
An algorithm identifier (value of type
psa_algorithm_t
).
Returns
1
if alg
is a signature algorithm that can be used to sign a message. 0
if alg
is a signature algorithm that can only be used to sign an alreadycalculated hash. 0
if alg
is not a signature algorithm. This macro can return either 0
or 1
if alg
is not a supported algorithm identifier.
PSA_ALG_IS_SIGN_HASH
(macro)
Whether the specified algorithm is a signature algorithm that can be used with psa_sign_hash()
and psa_verify_hash()
.
#define PSA_ALG_IS_SIGN_HASH(alg) /* specificationdefined value */
Parameters

alg
An algorithm identifier (value of type
psa_algorithm_t
).
Returns
1
if alg
is a signature algorithm that can be used to sign a hash. 0
if alg
is a signature algorithm that can only be used to sign a message. 0
if alg
is not a signature algorithm. This macro can return either 0
or 1
if alg
is not a supported algorithm identifier.
PSA_ALG_IS_RSA_PKCS1V15_SIGN
(macro)
Whether the specified algorithm is an RSA PKCS#1 v1.5 signature algorithm.
#define PSA_ALG_IS_RSA_PKCS1V15_SIGN(alg) /* specificationdefined value */
Parameters

alg
An algorithm identifier (value of type
psa_algorithm_t
).
Returns
1
if alg
is an RSA PKCS#1 v1.5 signature algorithm, 0
otherwise.
This macro can return either 0
or 1
if alg
is not a supported algorithm identifier.
PSA_ALG_IS_RSA_PSS
(macro)
Whether the specified algorithm is an RSA PSS signature algorithm.
#define PSA_ALG_IS_RSA_PSS(alg) /* specificationdefined value */
Parameters

alg
An algorithm identifier (value of type
psa_algorithm_t
).
Returns
1
if alg
is an RSA PSS signature algorithm, 0
otherwise.
This macro can return either 0
or 1
if alg
is not a supported algorithm identifier.
PSA_ALG_IS_ECDSA
(macro)
Whether the specified algorithm is ECDSA.
#define PSA_ALG_IS_ECDSA(alg) /* specificationdefined value */
Parameters

alg
An algorithm identifier (value of type
psa_algorithm_t
).
Returns
1
if alg
is an ECDSA algorithm, 0
otherwise.
This macro can return either 0
or 1
if alg
is not a supported algorithm identifier.
PSA_ALG_IS_DETERMINISTIC_ECDSA
(macro)
Whether the specified algorithm is deterministic ECDSA.
#define PSA_ALG_IS_DETERMINISTIC_ECDSA(alg) /* specificationdefined value */
Parameters

alg
An algorithm identifier (value of type
psa_algorithm_t
).
Returns
1
if alg
is a deterministic ECDSA algorithm, 0
otherwise.
This macro can return either 0
or 1
if alg
is not a supported algorithm identifier.
Description
See also PSA_ALG_IS_ECDSA()
and PSA_ALG_IS_RANDOMIZED_ECDSA()
.
PSA_ALG_IS_RANDOMIZED_ECDSA
(macro)
Whether the specified algorithm is randomized ECDSA.
#define PSA_ALG_IS_RANDOMIZED_ECDSA(alg) /* specificationdefined value */
Parameters

alg
An algorithm identifier (value of type
psa_algorithm_t
).
Returns
1
if alg
is a randomized ECDSA algorithm, 0
otherwise.
This macro can return either 0
or 1
if alg
is not a supported algorithm identifier.
Description
See also PSA_ALG_IS_ECDSA()
and PSA_ALG_IS_DETERMINISTIC_ECDSA()
.
PSA_ALG_IS_HASH_AND_SIGN
(macro)
Whether the specified algorithm is a hashandsign algorithm that signs exactly the hash value.
#define PSA_ALG_IS_HASH_AND_SIGN(alg) /* specificationdefined value */
Parameters

alg
An algorithm identifier (value of type
psa_algorithm_t
).
Returns
1
if alg
is a hashandsign algorithm that signs exactly the hash value, 0
otherwise. This macro can return either 0
or 1
if alg
is not a supported algorithm identifier.
Description
This macro identifies algorithms that can be used with psa_sign_hash()
that use the exact message hash value as an input the signature operation. This excludes hashandsign algorithms that require a encoded or modified hash for the signature step in the algorithm, such as PSA_ALG_RSA_PKCS1V15_SIGN_RAW
.
PSA_ALG_ANY_HASH
(macro)
When setting a hashandsign algorithm in a key policy, permit any hash algorithm.
#define PSA_ALG_ANY_HASH ((psa_algorithm_t)0x020000ff)
This value can be used to form the permitted algorithm attribute of a key policy for a signature algorithm that is parametrized by a hash. A key with this policy can then be used to perform operations using the same signature algorithm parametrized with any supported hash.
A signature algorithm created using this macro is a wildcard algorithm, and PSA_ALG_IS_WILDCARD()
will return true.
This value must not be used to build other algorithms that are parametrized over a hash. For any valid use of this macro to build an algorithm alg
, PSA_ALG_IS_HASH_AND_SIGN
(
alg
)
is true.
This value must not be used to build an algorithm specification to perform an operation. It is only valid for setting the permitted algorithm in a key policy.
Usage
For example, suppose that PSA_xxx_SIGNATURE
is one of the following macros:
The following sequence of operations shows how PSA_ALG_ANY_HASH
can be used in a key policy:
Set the key usage flags using
PSA_ALG_ANY_HASH
, for example:psa_set_key_usage_flags(&attributes, PSA_KEY_USAGE_SIGN_MESSAGE); // or VERIFY_MESSAGE psa_set_key_algorithm(&attributes, PSA_xxx_SIGNATURE(PSA_ALG_ANY_HASH));
Import or generate key material.
Call
psa_sign_message()
orpsa_verify_message()
, passing an algorithm built fromPSA_xxx_SIGNATURE
and a specific hash. Each call to sign or verify a message can use a different hash algorithm.psa_sign_message(key, PSA_xxx_SIGNATURE(PSA_ALG_SHA_256), ...); psa_sign_message(key, PSA_xxx_SIGNATURE(PSA_ALG_SHA_512), ...); psa_sign_message(key, PSA_xxx_SIGNATURE(PSA_ALG_SHA3_256), ...);
PSA_SIGN_OUTPUT_SIZE
(macro)
Sufficient signature buffer size for psa_sign_message()
and psa_sign_hash()
.
#define PSA_SIGN_OUTPUT_SIZE(key_type, key_bits, alg) \ /* implementationdefined value */
Parameters

key_type
An asymmetric key type. This can be a key pair type or a public key type.

key_bits
The size of the key in bits.

alg
The signature algorithm.
Returns
If the parameters are valid and supported, return a buffer size in bytes that guarantees that psa_sign_message()
and psa_sign_hash()
will not fail with PSA_ERROR_BUFFER_TOO_SMALL
. If the parameters are a valid combination that is not supported by the implementation, this macro must return either a sensible size or 0
. If the parameters are not valid, the return value is unspecified.
Description
This macro returns a sufficient buffer size for a signature using a key of the specified type and size, with the specified algorithm. Note that the actual size of the signature might be smaller, as some algorithms produce a variablesize signature.
Warning
This function might evaluate its arguments multiple times or zero times. Providing arguments that have side effects will result in implementationspecific behavior, and is nonportable.
See also PSA_SIGNATURE_MAX_SIZE
.
PSA_SIGNATURE_MAX_SIZE
(macro)
Maximum size of an asymmetric signature.
#define PSA_SIGNATURE_MAX_SIZE /* implementationdefined value */
This macro must expand to a compiletime constant integer. It is recommended that this value is the maximum size of an asymmetric signature supported by the implementation, in bytes. The value must not be smaller than this maximum.
See also PSA_SIGN_OUTPUT_SIZE()
.