New algorithm category: key selection
A key selection algorithm is similar to a key derivation algorithm in
that it takes a secret input and produces a secret output stream.
However, unlike key derivation algorithms, there is no expectation
that the input cannot be reconstructed from the output. Key selection
algorithms are exclusively meant to be used on the output of a key
agreement algorithm to select chunks of the shared secret.
diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index 6efaa02..f344e14 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -603,6 +603,7 @@
#define PSA_ALG_CATEGORY_ASYMMETRIC_ENCRYPTION ((psa_algorithm_t)0x12000000)
#define PSA_ALG_CATEGORY_KEY_AGREEMENT ((psa_algorithm_t)0x22000000)
#define PSA_ALG_CATEGORY_KEY_DERIVATION ((psa_algorithm_t)0x30000000)
+#define PSA_ALG_CATEGORY_KEY_SELECTION ((psa_algorithm_t)0x31000000)
#define PSA_ALG_IS_VENDOR_DEFINED(alg) \
(((alg) & PSA_ALG_VENDOR_FLAG) != 0)
@@ -674,6 +675,7 @@
#define PSA_ALG_IS_ASYMMETRIC_ENCRYPTION(alg) \
(((alg) & PSA_ALG_CATEGORY_MASK) == PSA_ALG_CATEGORY_ASYMMETRIC_ENCRYPTION)
+#define PSA_ALG_KEY_SELECTION_FLAG ((psa_algorithm_t)0x01000000)
/** Whether the specified algorithm is a key agreement algorithm.
*
* \param alg An algorithm identifier (value of type #psa_algorithm_t).
@@ -683,7 +685,8 @@
* algorithm identifier.
*/
#define PSA_ALG_IS_KEY_AGREEMENT(alg) \
- (((alg) & PSA_ALG_CATEGORY_MASK) == PSA_ALG_CATEGORY_KEY_AGREEMENT)
+ (((alg) & PSA_ALG_CATEGORY_MASK & ~PSA_ALG_KEY_SELECTION_FLAG) == \
+ PSA_ALG_CATEGORY_KEY_AGREEMENT)
/** Whether the specified algorithm is a key derivation algorithm.
*
@@ -696,6 +699,17 @@
#define PSA_ALG_IS_KEY_DERIVATION(alg) \
(((alg) & PSA_ALG_CATEGORY_MASK) == PSA_ALG_CATEGORY_KEY_DERIVATION)
+/** Whether the specified algorithm is a key selection algorithm.
+ *
+ * \param alg An algorithm identifier (value of type #psa_algorithm_t).
+ *
+ * \return 1 if \p alg is a key selection algorithm, 0 otherwise.
+ * This macro may return either 0 or 1 if \p alg is not a supported
+ * algorithm identifier.
+ */
+#define PSA_ALG_IS_KEY_SELECTION(alg) \
+ (((alg) & PSA_ALG_CATEGORY_MASK) == PSA_ALG_CATEGORY_KEY_SELECTION)
+
#define PSA_ALG_HASH_MASK ((psa_algorithm_t)0x000000ff)
#define PSA_ALG_MD2 ((psa_algorithm_t)0x01000001)
#define PSA_ALG_MD4 ((psa_algorithm_t)0x01000002)
@@ -1185,6 +1199,25 @@
#define PSA_ALG_HKDF_GET_HASH(hkdf_alg) \
(PSA_ALG_CATEGORY_HASH | ((hkdf_alg) & PSA_ALG_HASH_MASK))
+#define PSA_ALG_KEY_DERIVATION_MASK ((psa_algorithm_t)0x010fffff)
+
+/** Use a shared secret as is.
+ *
+ * Specify this algorithm as the selection component of a key agreement
+ * to use the raw result of the key agreement as key material.
+ *
+ * \warning The raw result of a key agreement algorithm such as finite-field
+ * Diffie-Hellman or elliptic curve Diffie-Hellman has biases and should
+ * not be used directly as key material. It can however be used as the secret
+ * input in a key derivation algorithm.
+ */
+#define PSA_ALG_SELECT_RAW ((psa_algorithm_t)0x31000001)
+
+#define PSA_ALG_KEY_AGREEMENT_GET_KDF(alg) \
+ (((alg) & PSA_ALG_KEY_DERIVATION_MASK) | PSA_ALG_CATEGORY_KEY_DERIVATION)
+
+#define PSA_ALG_KEY_AGREEMENT_GET_BASE(alg) \
+ ((alg) & ~PSA_ALG_KEY_DERIVATION_MASK)
/**@}*/
/** \defgroup key_management Key management