Add buffer size macro for psa_get_key_domain_parameters
diff --git a/include/psa/crypto_sizes.h b/include/psa/crypto_sizes.h
index 3c879e8..5f6282c 100644
--- a/include/psa/crypto_sizes.h
+++ b/include/psa/crypto_sizes.h
@@ -598,4 +598,36 @@
PSA_KEY_TYPE_IS_ECC_PUBLIC_KEY(key_type) ? PSA_KEY_EXPORT_ECC_PUBLIC_KEY_MAX_SIZE(key_bits) : \
0)
+/** Safe output buffer size for psa_get_key_domain_parameters().
+ *
+ * This macro returns a compile-time constant if its arguments are
+ * compile-time constants.
+ *
+ * \warning This function may call its arguments multiple times or
+ * zero times, so you should not pass arguments that contain
+ * side effects.
+ *
+ * \param key_type A supported key type.
+ * \param key_bits The size of the key in bits.
+ *
+ * \return If the parameters are valid and supported, return
+ * a buffer size in bytes that guarantees that
+ * psa_get_key_domain_parameters() 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 either shall return either a
+ * sensible size or 0.
+ * If the parameters are not valid, the
+ * return value is unspecified.
+ */
+#define PSA_KEY_DOMAIN_PARAMETERS_SIZE(key_type, key_bits) \
+ (PSA_KEY_TYPE_IS_RSA(key_type) ? sizeof(int) : \
+ PSA_KEY_TYPE_IS_DH(key_type) ? PSA_DH_KEY_DOMAIN_PARAMETERS_SIZE(key_bits) : \
+ PSA_KEY_TYPE_IS_DSA(key_type) ? PSA_DSA_KEY_DOMAIN_PARAMETERS_SIZE(key_bits) : \
+ 0)
+#define PSA_DH_KEY_DOMAIN_PARAMETERS_SIZE(key_bits) \
+ (4 + (PSA_BITS_TO_BYTES(key_bits) + 5) * 3 /*without optional parts*/)
+#define PSA_DSA_KEY_DOMAIN_PARAMETERS_SIZE(key_bits) \
+ (4 + (PSA_BITS_TO_BYTES(key_bits) + 5) * 2 /*p, g*/ + 34 /*q*/)
+
#endif /* PSA_CRYPTO_SIZES_H */