10.7. Asymmetric signature

There are two pairs of single-part functions for asymmetric signature:

  • The signature and verification functions psa_sign_message() and psa_verify_message() take a message as one of their inputs and perform a hash-and-sign algorithm.

  • The functions psa_sign_hash() and psa_verify_hash() take a message hash as one of their inputs. This is useful for signing pre-computed hashes, or for implementing hash-and-sign using a multi-part hash operation before signing the resulting hash. To determine which hash algorithm to use, call the macro PSA_ALG_GET_HASH() on the corresponding signature algorithm.

    Some hash-and-sign algorithms add padding to the message hash before completing the signing operation. The format of the padding that is used depends on the algorithm used to construct the signature, see the description of the specific algorithm for details.

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) /* specification-defined value */

Parameters

hash_alg

A hash algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_HASH(hash_alg) is true. This includes PSA_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 RSASSA-PKCS1-v1_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 EMSA-PKCS1-V1_5-ENCODE() in [RFC8017] §9.2. H is the message digest, computed using the hash_alg hash algorithm.

Compatible key types

PSA_KEY_TYPE_RSA_KEY_PAIR
PSA_KEY_TYPE_RSA_PUBLIC_KEY (signature verification only)

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 RSASSA-PKCS1-v1_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 EMSA-PKCS1-V1_5-ENCODE() in [RFC8017] §9.2. T is normally the DER encoding of the DigestInfo structure produced by step 2 in the message encoding algorithm, but it can be any byte string within the available length.

The wildcard key policy PSA_ALG_RSA_PKCS1V15_SIGN(PSA_ALG_ANY_HASH) also permits a key to be used with the PSA_ALG_RSA_PKCS1V15_SIGN_RAW signature algorithm.

Compatible key types

PSA_KEY_TYPE_RSA_KEY_PAIR
PSA_KEY_TYPE_RSA_PUBLIC_KEY (signature verification only)

PSA_ALG_RSA_PSS (macro)

The RSA PSS message signature scheme, with hashing.

#define PSA_ALG_RSA_PSS(hash_alg) /* specification-defined value */

Parameters

hash_alg

A hash algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_HASH(hash_alg) is true. This includes PSA_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 RSASSA-PSS, with the following options:

  • The mask generation function is MGF1 defined by [RFC8017] Appendix B.

  • When creating a signature, the salt length is equal to the length of the hash, or the largest possible salt length for the algorithm and key size if that is smaller than the hash length.

  • When verifying a signature, the salt length must be equal to the length of the hash, or the largest possible salt length for the algorithm and key size if that is smaller than the hash length.

  • The specified hash algorithm, hash_alg, is used to hash the input message, to create the salted hash, and for the mask generation.

When used with psa_sign_hash() or psa_verify_hash(), the provided hash parameter is the message digest, computed using the hash_alg hash algorithm.

Note

The PSA_ALG_RSA_PSS_ANY_SALT() algorithm is equivalent to PSA_ALG_RSA_PSS() when creating a signature, but permits any salt length when verifying a signature.

Compatible key types

PSA_KEY_TYPE_RSA_KEY_PAIR
PSA_KEY_TYPE_RSA_PUBLIC_KEY (signature verification only)

PSA_ALG_RSA_PSS_ANY_SALT (macro)

The RSA PSS message signature scheme, with hashing. This variant permits any salt length for signature verification.

#define PSA_ALG_RSA_PSS_ANY_SALT(hash_alg) /* specification-defined value */

Parameters

hash_alg

A hash algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_HASH(hash_alg) is true. This includes PSA_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 RSASSA-PSS, with the following options:

  • The mask generation function is MGF1 defined by [RFC8017] Appendix B.

  • When creating a signature, the salt length is equal to the length of the hash, or the largest possible salt length for the algorithm and key size if that is smaller than the hash length.

  • When verifying a signature, any salt length permitted by the RSASSA-PSS signature algorithm is accepted.

  • The specified hash algorithm, hash_alg, is used to hash the input message, to create the salted hash, and for the mask generation.

When used with psa_sign_hash() or psa_verify_hash(), the provided hash parameter is the message digest, computed using the hash_alg hash algorithm.

Note

The PSA_ALG_RSA_PSS() algorithm is equivalent to PSA_ALG_RSA_PSS_ANY_SALT() when creating a signature, but is strict about the permitted salt length when verifying a signature.

Compatible key types

PSA_KEY_TYPE_RSA_KEY_PAIR
PSA_KEY_TYPE_RSA_PUBLIC_KEY (signature verification only)

PSA_ALG_ECDSA (macro)

The randomized ECDSA signature scheme, with hashing.

#define PSA_ALG_ECDSA(hash_alg) /* specification-defined value */

Parameters

hash_alg

A hash algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_HASH(hash_alg) is true. This includes PSA_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.

When used with psa_sign_hash() or psa_verify_hash(), the provided hash parameter is the message digest, computed using the hash_alg hash algorithm.

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) [X9-62], with a random per-message 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 N-octet string, where N is the length of the base point of the curve in octets. Each value is represented in big-endian order, with the most significant octet first.

Compatible key types

PSA_KEY_TYPE_ECC_KEY_PAIR(family)
PSA_KEY_TYPE_ECC_PUBLIC_KEY(family) (signature verification only)

where family is a Weierstrass Elliptic curve family. That is, one of the following values:

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 already-calculated hash. Note that the input is padded with zeros on the left or truncated on the right as required to fit the curve size.

This algorithm cannot be used with the wildcard key policy PSA_ALG_ECDSA(PSA_ALG_ANY_HASH). It is only permitted when PSA_ALG_ECDSA_ANY is the key’s permitted-algorithm policy.

Compatible key types

PSA_KEY_TYPE_ECC_KEY_PAIR(family)
PSA_KEY_TYPE_ECC_PUBLIC_KEY(family) (signature verification only)

where family is a Weierstrass Elliptic curve family. That is, one of the following values:

PSA_ALG_DETERMINISTIC_ECDSA (macro)

Deterministic ECDSA signature scheme, with hashing.

#define PSA_ALG_DETERMINISTIC_ECDSA(hash_alg) /* specification-defined value */

Parameters

hash_alg

A hash algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_HASH(hash_alg) is true. This includes PSA_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.

When used with psa_sign_hash() or psa_verify_hash(), the provided hash parameter is the message digest, computed using the hash_alg hash algorithm.

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().

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.

Compatible key types

PSA_KEY_TYPE_ECC_KEY_PAIR(family)
PSA_KEY_TYPE_ECC_PUBLIC_KEY(family) (signature verification only)

where family is a Weierstrass Elliptic curve family. That is, one of the following values:

PSA_ALG_PURE_EDDSA (macro)

Edwards-curve digital signature algorithm without prehashing (PureEdDSA), using standard parameters.

#define PSA_ALG_PURE_EDDSA ((psa_algorithm_t) 0x06000800)

This algorithm can be only used with the psa_sign_message() and psa_verify_message() functions.

This is the PureEdDSA digital signature algorithm defined by Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032], using standard parameters.

PureEdDSA requires an elliptic curve key on a twisted Edwards curve. The following curves are supported:

  • Edwards25519: the Ed25519 algorithm is computed. The output signature is a 64-byte string: the concatenation of R and S as defined by [RFC8032] §5.1.6.

  • Edwards448: the Ed448 algorithm is computed with an empty string as the context. The output signature is a 114-byte string: the concatenation of R and S as defined by [RFC8032] §5.2.6.

Note

Contexts are not supported in the current version of this specification because there is no suitable signature interface that can take the context as a parameter. A future version of this specification may add suitable functions and extend this algorithm to support contexts.

Note

To sign or verify the pre-computed hash of a message using EdDSA, the HashEdDSA algorithms (PSA_ALG_ED25519PH and PSA_ALG_ED448PH) can be used with psa_sign_hash() and psa_verify_hash().

The signature produced by HashEdDSA is distinct from that produced by PureEdDSA.

Compatible key types

PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_TWISTED_EDWARDS)
PSA_KEY_TYPE_ECC_PUBLIC_KEY(PSA_ECC_FAMILY_TWISTED_EDWARDS) (signature verification only)

PSA_ALG_ED25519PH (macro)

Edwards-curve digital signature algorithm with prehashing (HashEdDSA), using the Edwards25519 curve.

#define PSA_ALG_ED25519PH ((psa_algorithm_t) 0x0600090B)

This algorithm can be used with both the message and hash signature functions.

This computes the Ed25519ph algorithm as specified in Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032] §5.1, and requires an Edwards25519 curve key. An empty string is used as the context. The prehash function is SHA-512.

When used with psa_sign_hash() or psa_verify_hash(), the provided hash parameter is the SHA-512 message digest.

Implementation note

When used with psa_sign_hash() or psa_verify_hash(), the hash parameter to the call should be used as PH(M) in the algorithms defined in [RFC8032] §5.1.

Usage

This is a hash-and-sign algorithm. To calculate a signature, use one of the following approaches:

Verifying a signature is similar, using psa_verify_message() or psa_verify_hash() instead of the signature function.

Compatible key types

PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_TWISTED_EDWARDS)
PSA_KEY_TYPE_ECC_PUBLIC_KEY(PSA_ECC_FAMILY_TWISTED_EDWARDS) (signature verification only)

PSA_ALG_ED448PH (macro)

Edwards-curve digital signature algorithm with prehashing (HashEdDSA), using the Edwards448 curve.

#define PSA_ALG_ED448PH ((psa_algorithm_t) 0x06000915)

This algorithm can be used with both the message and hash signature functions.

This computes the Ed448ph algorithm as specified in Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032] §5.2, and requires an Edwards448 curve key. An empty string is used as the context. The prehash function is the first 64 bytes of the output from SHAKE256.

When used with psa_sign_hash() or psa_verify_hash(), the provided hash parameter is the truncated SHAKE256 message digest.

Implementation note

When used with psa_sign_hash() or psa_verify_hash(), the hash parameter to the call should be used as PH(M) in the algorithms defined in [RFC8032] §5.2.

Usage

This is a hash-and-sign algorithm. To calculate a signature, use one of the following approaches:

Verifying a signature is similar, using psa_verify_message() or psa_verify_hash() instead of the signature function.

Compatible key types

PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_TWISTED_EDWARDS)
PSA_KEY_TYPE_ECC_PUBLIC_KEY(PSA_ECC_FAMILY_TWISTED_EDWARDS) (signature verification only)

10.7.2. Asymmetric signature functions

psa_sign_message (function)

Sign a message with a private key. For hash-and-sign 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 permit the usage PSA_KEY_USAGE_SIGN_MESSAGE.

alg

An asymmetric signature algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_SIGN_MESSAGE(alg) is true.

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) where key_type and key_bits are the type and bit-size respectively of key.

  • 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

Success. The first (*signature_length) bytes of signature contain the signature value.

PSA_ERROR_BAD_STATE

The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_HANDLE

key is not a valid key identifier.

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() or PSA_SIGNATURE_MAX_SIZE can be used to determine a sufficient buffer size.

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • alg is not an asymmetric signature algorithm.

  • key is not an asymmetric key pair, that is compatible with alg.

  • input_length is too large for the algorithm and key type.

PSA_ERROR_NOT_SUPPORTED

The following conditions can result in this error:

  • alg is not supported or is not an asymmetric signature algorithm.

  • key is not supported for use with alg.

  • input_length is too large for the implementation.

PSA_ERROR_INSUFFICIENT_ENTROPY

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

Note

To perform a multi-part hash-and-sign signature algorithm, first use a multi-part 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. For hash-and-sign algorithms, this includes the hashing step.

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 permit the usage PSA_KEY_USAGE_VERIFY_MESSAGE.

alg

An asymmetric signature algorithm: a value of type psa_algorithm_t such that PSA_ALG_IS_SIGN_MESSAGE(alg) is true.

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

Success. The signature is valid.

PSA_ERROR_BAD_STATE

The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_HANDLE

key is not a valid key identifier.

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

signature is not the result of signing the input message with algorithm alg using the private key corresponding to key.

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • alg is not an asymmetric signature algorithm.

  • key is not a public key or an asymmetric key pair, that is compatible with alg.

  • input_length is too large for the algorithm and key type.

PSA_ERROR_NOT_SUPPORTED

The following conditions can result in this error:

  • alg is not supported or is not an asymmetric signature algorithm.

  • key is not supported for use with alg.

  • input_length is too large for the implementation.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

Note

To perform a multi-part hash-and-sign signature verification algorithm, first use a multi-part 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 already-calculated 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 permit the usage PSA_KEY_USAGE_SIGN_HASH.

alg

An asymmetric signature algorithm that separates the hash and sign operations: a value of type psa_algorithm_t such that PSA_ALG_IS_SIGN_HASH(alg) is true.

hash

The input to sign. This is usually the hash of a message.

See the description of this function, or the description of individual signature algorithms, for details of the 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) where key_type and key_bits are the type and bit-size respectively of key.

  • 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

Success. The first (*signature_length) bytes of signature contain the signature value.

PSA_ERROR_BAD_STATE

The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_HANDLE

key is not a valid key identifier.

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() or PSA_SIGNATURE_MAX_SIZE can be used to determine a sufficient buffer size.

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • alg is not an asymmetric signature algorithm.

  • key is not an asymmetric key pair, that is compatible with alg.

  • hash_length is not valid for the algorithm and key type.

  • hash is not a valid input value for the algorithm and key type.

PSA_ERROR_NOT_SUPPORTED

The following conditions can result in this error:

  • alg is not supported or is not an asymmetric signature algorithm.

  • key is not supported for use with alg.

PSA_ERROR_INSUFFICIENT_ENTROPY

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

With most signature algorithms that follow the hash-and-sign paradigm, the hash input to this function is the hash of the message to sign. The algorithm used to compute this hash is encoded in the signature algorithm. For such algorithms, hash_length must equal the length of the hash output, and the following condition is true:

hash_length == PSA_HASH_LENGTH(PSA_ALG_GET_HASH(alg))

The current version of this specification defines the following signature algorithms with this property: PSA_ALG_RSA_PKCS1V15_SIGN, PSA_ALG_RSA_PSS, PSA_ALG_ECDSA, PSA_ALG_DETERMINISTIC_ECDSA, PSA_ALG_ED25519PH, and PSA_ALG_ED448PH.

Some hash-and-sign 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 hash-and-sign signature algorithm, the hash must be calculated before passing it to this function. This can be done by calling psa_hash_compute() or with a multi-part hash operation. The correct hash algorithm to use can be determined using PSA_ALG_GET_HASH().

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 permit the usage PSA_KEY_USAGE_VERIFY_HASH.

alg

An asymmetric signature algorithm that separates the hash and sign operations: a value of type psa_algorithm_t such that PSA_ALG_IS_SIGN_HASH(alg) is true.

hash

The input whose signature is to be verified. This is usually the hash of a message.

See the description of this function, or the description of individual signature algorithms, for details of the 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

Success. The signature is valid.

PSA_ERROR_BAD_STATE

The library requires initializing by a call to psa_crypto_init().

PSA_ERROR_INVALID_HANDLE

key is not a valid key identifier.

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

signature is not the result of signing hash with algorithm alg using the private key corresponding to key.

PSA_ERROR_INVALID_ARGUMENT

The following conditions can result in this error:

  • alg is not an asymmetric signature algorithm.

  • key is not a public key or an asymmetric key pair, that is compatible with alg.

  • hash_length is not valid for the algorithm and key type.

  • hash is not a valid input value for the algorithm and key type.

PSA_ERROR_NOT_SUPPORTED

The following conditions can result in this error:

  • alg is not supported or is not an asymmetric signature algorithm.

  • key is not supported for use with alg.

PSA_ERROR_INSUFFICIENT_MEMORY

PSA_ERROR_COMMUNICATION_FAILURE

PSA_ERROR_CORRUPTION_DETECTED

PSA_ERROR_STORAGE_FAILURE

PSA_ERROR_DATA_CORRUPT

PSA_ERROR_DATA_INVALID

Description

With most signature algorithms that follow the hash-and-sign paradigm, the hash input to this function is the hash of the message to verify. The algorithm used to compute this hash is encoded in the signature algorithm. For such algorithms, hash_length must equal the length of the hash output, and the following condition is true:

hash_length == PSA_HASH_LENGTH(PSA_ALG_GET_HASH(alg))

The current version of this specification defines the following signature algorithms with this property: PSA_ALG_RSA_PKCS1V15_SIGN, PSA_ALG_RSA_PSS, PSA_ALG_ECDSA, PSA_ALG_DETERMINISTIC_ECDSA, PSA_ALG_ED25519PH, and PSA_ALG_ED448PH.

Some hash-and-sign 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 hash-and-sign 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 multi-part hash operation. The correct hash algorithm to use can be determined using PSA_ALG_GET_HASH().

Alternatively, to hash and verify a message 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) /* specification-defined value */

Parameters

alg

An algorithm identifier: a 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 already-calculated 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) /* specification-defined value */

Parameters

alg

An algorithm identifier: a 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.

Description

This includes all algorithms such that PSA_ALG_IS_HASH_AND_SIGN() is true, as well as signature algorithms for which the input to psa_sign_hash() or psa_verify_hash() is not directly a hash, such as PSA_ALG_IS_RSA_PKCS1V15_SIGN.

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) /* specification-defined value */

Parameters

alg

An algorithm identifier: a 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) /* specification-defined value */

Parameters

alg

An algorithm identifier: a 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.

Description

This macro returns 1 for algorithms constructed using either PSA_ALG_RSA_PSS() or PSA_ALG_RSA_PSS_ANY_SALT().

PSA_ALG_IS_RSA_PSS_ANY_SALT (macro)

Whether the specified algorithm is an RSA PSS signature algorithm that permits any salt length.

#define PSA_ALG_IS_RSA_PSS_ANY_SALT(alg) /* specification-defined value */

Parameters

alg

An algorithm identifier: a value of type psa_algorithm_t.

Returns

1 if alg is an RSA PSS signature algorithm that permits any salt length, 0 otherwise.

This macro can return either 0 or 1 if alg is not a supported algorithm identifier.

Description

An RSA PSS signature algorithm that permits any salt length is constructed using PSA_ALG_RSA_PSS_ANY_SALT().

See also PSA_ALG_IS_RSA_PSS() and PSA_ALG_IS_RSA_PSS_STANDARD_SALT().

PSA_ALG_IS_RSA_PSS_STANDARD_SALT (macro)

Whether the specified algorithm is an RSA PSS signature algorithm that requires the standard salt length.

#define PSA_ALG_IS_RSA_PSS_STANDARD_SALT(alg) /* specification-defined value */

Parameters

alg

An algorithm identifier: a value of type psa_algorithm_t.

Returns

1 if alg is an RSA PSS signature algorithm that requires the standard salt length, 0 otherwise.

This macro can return either 0 or 1 if alg is not a supported algorithm identifier.

Description

An RSA PSS signature algorithm that requires the standard salt length is constructed using PSA_ALG_RSA_PSS().

See also PSA_ALG_IS_RSA_PSS() and PSA_ALG_IS_RSA_PSS_ANY_SALT().

PSA_ALG_IS_ECDSA (macro)

Whether the specified algorithm is ECDSA.

#define PSA_ALG_IS_ECDSA(alg) /* specification-defined value */

Parameters

alg

An algorithm identifier: a 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) /* specification-defined value */

Parameters

alg

An algorithm identifier: a 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) /* specification-defined value */

Parameters

alg

An algorithm identifier: a 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_EDDSA (macro)

Whether the specified algorithm is HashEdDSA.

#define PSA_ALG_IS_HASH_EDDSA(alg) /* specification-defined value */

Parameters

alg

An algorithm identifier: a value of type psa_algorithm_t.

Returns

1 if alg is a HashEdDSA algorithm, 0 otherwise.

This macro can return either 0 or 1 if alg is not a supported algorithm identifier.

PSA_ALG_IS_HASH_AND_SIGN (macro)

Whether the specified algorithm is a hash-and-sign algorithm that signs exactly the hash value.

#define PSA_ALG_IS_HASH_AND_SIGN(alg) /* specification-defined value */

Parameters

alg

An algorithm identifier: a value of type psa_algorithm_t.

Returns

1 if alg is a hash-and-sign 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.

A wildcard signature algorithm policy, using PSA_ALG_ANY_HASH, returns the same value as the signature algorithm parameterised with a valid hash algorithm.

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. For example, if PSA_ALG_IS_HASH_AND_SIGN(alg) is true, the following call sequence is equivalent to psa_sign_message(key, alg, msg, msg_len, ...):

psa_hash_operation_t op = {0};
uint8_t hash[PSA_HASH_MAX_SIZE];
size_t hash_len;
psa_hash_setup(&op, PSA_ALG_GET_HASH(alg));
psa_hash_update(&op, msg, msg_len);
psa_hash_finish(&op, hash, sizeof(hash), &hash_len);
psa_sign_hash(key, alg, hash, hash_len, ...);

This excludes hash-and-sign algorithms that require a encoded or modified hash for the signature step in the algorithm, such as PSA_ALG_RSA_PKCS1V15_SIGN_RAW. For such algorithms, PSA_ALG_IS_SIGN_HASH() is true but PSA_ALG_IS_HASH_AND_SIGN() is false.

PSA_ALG_ANY_HASH (macro)

When setting a hash-and-sign 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 cannot be used to build an algorithm specification to perform an operation. If used in this way, the operation will fail with an error.

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:

  1. 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));

  2. Import or generate key material.

  3. Call psa_sign_message() or psa_verify_message(), passing an algorithm built from PSA_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) \
    /* implementation-defined 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

A sufficient signature buffer size for the specified asymmetric signature algorithm and key parameters. An implementation can return either 0 or a correct size for an asymmetric signature algorithm and key parameters that it recognizes, but does not support. If the parameters are not valid, the return value is unspecified.

Description

If the size of the signature buffer is at least this large, it is guaranteed that psa_sign_message() and psa_sign_hash() will not fail due to an insufficient buffer size. The actual size of the output might be smaller in any given call.

See also PSA_SIGNATURE_MAX_SIZE.

PSA_SIGNATURE_MAX_SIZE (macro)

A sufficient signature buffer size for psa_sign_message() and psa_sign_hash(), for any of the supported key types and asymmetric signature algorithms.

#define PSA_SIGNATURE_MAX_SIZE /* implementation-defined value */

If the size of the signature buffer is at least this large, it is guaranteed that psa_sign_message() and psa_sign_hash() will not fail due to an insufficient buffer size.

See also PSA_SIGN_OUTPUT_SIZE().