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PSA_EXPORT_KEY_OUTPUT_SIZE macro
Sufficient output buffer size for psa_export_key() or psa_export_public_key(). This macro returns a compile-time constant if its arguments are compile-time constants. \warning This macro may evaluate its arguments multiple times or zero times, so you should not pass arguments that contain side effects. The following code illustrates how to allocate enough memory to export a key by querying the key type and size at runtime.
{c}
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
psa_status_t status;
status = psa_get_key_attributes(key, &attributes);
if (status != PSA_SUCCESS) handle_error(...);
psa_key_type_t key_type = psa_get_key_type(&attributes);
size_t key_bits = psa_get_key_bits(&attributes);
size_t buffer_size = PSA_EXPORT_KEY_OUTPUT_SIZE(key_type, key_bits);
psa_reset_key_attributes(&attributes);
uint8_t *buffer = malloc(buffer_size);
if (buffer == NULL) handle_error(...);
size_t buffer_length;
status = psa_export_key(key, buffer, buffer_size, &buffer_length);
if (status != PSA_SUCCESS) handle_error(...);
Syntax
#define PSA_EXPORT_KEY_OUTPUT_SIZE(key_type, key_bits) \
(PSA_KEY_TYPE_IS_UNSTRUCTURED(key_type) ? PSA_BITS_TO_BYTES(key_bits) : \
PSA_KEY_TYPE_IS_DH(key_type) ? PSA_BITS_TO_BYTES(key_bits) : \
(key_type) == PSA_KEY_TYPE_RSA_KEY_PAIR ? PSA_KEY_EXPORT_RSA_KEY_PAIR_MAX_SIZE(key_bits) : \
(key_type) == PSA_KEY_TYPE_RSA_PUBLIC_KEY ? PSA_KEY_EXPORT_RSA_PUBLIC_KEY_MAX_SIZE(key_bits) : \
(key_type) == PSA_KEY_TYPE_DSA_KEY_PAIR ? PSA_KEY_EXPORT_DSA_KEY_PAIR_MAX_SIZE(key_bits) : \
(key_type) == PSA_KEY_TYPE_DSA_PUBLIC_KEY ? PSA_KEY_EXPORT_DSA_PUBLIC_KEY_MAX_SIZE(key_bits) : \
PSA_KEY_TYPE_IS_ECC_KEY_PAIR(key_type) ? PSA_KEY_EXPORT_ECC_KEY_PAIR_MAX_SIZE(key_bits) : \
PSA_KEY_TYPE_IS_ECC_PUBLIC_KEY(key_type) ? PSA_KEY_EXPORT_ECC_PUBLIC_KEY_MAX_SIZE(key_bits) : \
0u)
Return value
If the parameters are valid and supported, return a buffer size in bytes that guarantees that psa_export_key() or psa_export_public_key() will not fail with #PSA_ERROR_BUFFER_TOO_SMALL. If the parameters are a valid combination that is not supported, return either a sensible size or 0. If the parameters are not valid, the return value is unspecified.
References
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