diff --git a/include/psa/crypto_extra.h b/include/psa/crypto_extra.h
index 99bb0635a..c5313d619 100644
--- a/include/psa/crypto_extra.h
+++ b/include/psa/crypto_extra.h
@@ -431,8 +431,9 @@ psa_status_t mbedtls_psa_inject_entropy(const uint8_t *seed,
  * #PSA_KEY_TYPE_DH_KEY_PAIR(#PSA_DH_GROUP_CUSTOM), the group data comes
  * from domain parameters set by psa_set_key_domain_parameters().
  */
-/* This value is reserved for private use in the TLS named group registry. */
-#define PSA_DH_GROUP_CUSTOM             ((psa_dh_group_t) 0x01fc)
+/* This value is a deprecated value meaning an explicit curve in the IANA
+ * registry. */
+#define PSA_DH_GROUP_CUSTOM             ((psa_dh_group_t) 0xff01)
 
 
 /**
diff --git a/include/psa/crypto_types.h b/include/psa/crypto_types.h
index b6b61984b..c4f9acd46 100644
--- a/include/psa/crypto_types.h
+++ b/include/psa/crypto_types.h
@@ -65,10 +65,82 @@ typedef int32_t psa_status_t;
  */
 typedef uint32_t psa_key_type_t;
 
-/** The type of PSA elliptic curve identifiers. */
+/** The type of PSA elliptic curve identifiers.
+ *
+ * The curve identifier is required to create an ECC key using the
+ * PSA_KEY_TYPE_ECC_KEY_PAIR() or PSA_KEY_TYPE_ECC_PUBLIC_KEY()
+ * macros.
+ *
+ * The encoding of curve identifiers is taken from the
+ * TLS Supported Groups Registry (formerly known as the
+ * TLS EC Named Curve Registry)
+ * https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-8
+ *
+ * This specification defines identifiers for some of the curves in the IANA
+ * registry. Implementations that support other curves that are in the IANA
+ * registry should use the IANA value and a implementation-specific identifier.
+ * Implemenations that support non-IANA curves should use one of the following
+ * approaches for allocating a key type:
+ *
+ * 1. Select a ::psa_ecc_curve_t value in the range #PSA_ECC_CURVE_VENDOR_MIN to
+ *    #PSA_ECC_CURVE_VENDOR_MAX, which is a subset of the IANA private use
+ *    range.
+ * 2. Use a ::psa_key_type_t value that is vendor-defined.
+ *
+ * The first option is recommended.
+ */
 typedef uint16_t psa_ecc_curve_t;
 
-/** The type of PSA Diffie-Hellman group identifiers. */
+/** The type of PSA Diffie-Hellman group identifiers.
+ *
+ * The group identifier is required to create an Diffie-Hellman key using the
+ * PSA_KEY_TYPE_DH_KEY_PAIR() or PSA_KEY_TYPE_DH_PUBLIC_KEY()
+ * macros.
+ *
+ * The encoding of group identifiers is taken from the
+ * TLS Supported Groups Registry (formerly known as the
+ * TLS EC Named Curve Registry)
+ * https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-8
+ *
+ * This specification defines identifiers for some of the groups in the IANA
+ * registry. Implementations that support other groups that are in the IANA
+ * registry should use the IANA value and a implementation-specific identifier.
+ * Implemenations that support non-IANA groups should use one of the following
+ * approaches for allocating a key type:
+ *
+ * 1. Select a ::psa_dh_group_t value in the range #PSA_DH_GROUP_VENDOR_MIN to
+ *    #PSA_DH_GROUP_VENDOR_MAX, which is a subset of the IANA private use
+ *    range.
+ * 2. Select a ::psa_dh_group_t value from the named groups allocated for
+ *    GREASE in the IETF draft specification. The GREASE specification and
+ *    values are listed below.
+ * 3. Use a ::psa_key_type_t value that is vendor-defined.
+ *
+ * Option 1 or 2 are recommended.
+ *
+ * The current draft of the GREASE specification is
+ * https://datatracker.ietf.org/doc/draft-ietf-tls-grease
+ *
+ * The following GREASE values are allocated for named groups:
+ * \code
+ * 0x0A0A
+ * 0x1A1A
+ * 0x2A2A
+ * 0x3A3A
+ * 0x4A4A
+ * 0x5A5A
+ * 0x6A6A
+ * 0x7A7A
+ * 0x8A8A
+ * 0x9A9A
+ * 0xAAAA
+ * 0xBABA
+ * 0xCACA
+ * 0xDADA
+ * 0xEAEA
+ * 0xFAFA
+ * \endcode
+ */
 typedef uint16_t psa_dh_group_t;
 
 /** \brief Encoding of a cryptographic algorithm.
diff --git a/include/psa/crypto_values.h b/include/psa/crypto_values.h
index 3a741b32e..1e0c2136a 100644
--- a/include/psa/crypto_values.h
+++ b/include/psa/crypto_values.h
@@ -424,10 +424,18 @@
 #define PSA_KEY_TYPE_ECC_PUBLIC_KEY_BASE        ((psa_key_type_t)0x60030000)
 #define PSA_KEY_TYPE_ECC_KEY_PAIR_BASE           ((psa_key_type_t)0x70030000)
 #define PSA_KEY_TYPE_ECC_CURVE_MASK             ((psa_key_type_t)0x0000ffff)
-/** Elliptic curve key pair. */
+/** Elliptic curve key pair.
+ *
+ * \param curve     A value of type ::psa_ecc_curve_t that identifies the
+ *                  ECC curve to be used.
+ */
 #define PSA_KEY_TYPE_ECC_KEY_PAIR(curve)         \
     (PSA_KEY_TYPE_ECC_KEY_PAIR_BASE | (curve))
-/** Elliptic curve public key. */
+/** Elliptic curve public key.
+ *
+ * \param curve     A value of type ::psa_ecc_curve_t that identifies the
+ *                  ECC curve to be used.
+ */
 #define PSA_KEY_TYPE_ECC_PUBLIC_KEY(curve)              \
     (PSA_KEY_TYPE_ECC_PUBLIC_KEY_BASE | (curve))
 
@@ -498,13 +506,34 @@
  */
 #define PSA_ECC_CURVE_CURVE448          ((psa_ecc_curve_t) 0x001e)
 
+/** Minimum value for a vendor-defined ECC curve identifier
+ *
+ * The range for vendor-defined curve identifiers is a subset of the IANA
+ * registry private use range, `0xfe00` - `0xfeff`.
+ */
+#define PSA_ECC_CURVE_VENDOR_MIN        ((psa_ecc_curve_t) 0xfe00)
+/** Maximum value for a vendor-defined ECC curve identifier
+ *
+ * The range for vendor-defined curve identifiers is a subset of the IANA
+ * registry private use range, `0xfe00` - `0xfeff`.
+ */
+#define PSA_ECC_CURVE_VENDOR_MAX        ((psa_ecc_curve_t) 0xfe7f)
+
 #define PSA_KEY_TYPE_DH_PUBLIC_KEY_BASE         ((psa_key_type_t)0x60040000)
 #define PSA_KEY_TYPE_DH_KEY_PAIR_BASE            ((psa_key_type_t)0x70040000)
 #define PSA_KEY_TYPE_DH_GROUP_MASK              ((psa_key_type_t)0x0000ffff)
-/** Diffie-Hellman key pair. */
+/** Diffie-Hellman key pair.
+ *
+ * \param group     A value of type ::psa_dh_group_t that identifies the
+ *                  Diffie-Hellman group to be used.
+ */
 #define PSA_KEY_TYPE_DH_KEY_PAIR(group)          \
     (PSA_KEY_TYPE_DH_KEY_PAIR_BASE | (group))
-/** Diffie-Hellman public key. */
+/** Diffie-Hellman public key.
+ *
+ * \param group     A value of type ::psa_dh_group_t that identifies the
+ *                  Diffie-Hellman group to be used.
+ */
 #define PSA_KEY_TYPE_DH_PUBLIC_KEY(group)               \
     (PSA_KEY_TYPE_DH_PUBLIC_KEY_BASE | (group))
 
@@ -538,6 +567,19 @@
 #define PSA_DH_GROUP_FFDHE6144          ((psa_dh_group_t) 0x0103)
 #define PSA_DH_GROUP_FFDHE8192          ((psa_dh_group_t) 0x0104)
 
+/** Minimum value for a vendor-defined Diffie Hellman group identifier
+ *
+ * The range for vendor-defined group identifiers is a subset of the IANA
+ * registry private use range, `0x01fc` - `0x01ff`.
+ */
+#define PSA_DH_GROUP_VENDOR_MIN         ((psa_dh_group_t) 0x01fc)
+/** Maximum value for a vendor-defined Diffie Hellman group identifier
+ *
+ * The range for vendor-defined group identifiers is a subset of the IANA
+ * registry private use range, `0x01fc` - `0x01ff`.
+ */
+#define PSA_DH_GROUP_VENDOR_MAX         ((psa_dh_group_t) 0x01fd)
+
 /** The block size of a block cipher.
  *
  * \param type  A cipher key type (value of type #psa_key_type_t).