Implement EVP_SKEY setting by EVP_KDF

crypto/evp/kdf_lib.c

@@ -144,6 +144,30 @@ int EVP_KDF_derive(EVP_KDF_CTX *ctx, unsigned char *key, size_t keylen,
     return ctx->meth->derive(ctx->algctx, key, keylen, params);
 }
 
+int EVP_KDF_derive_SKEY(EVP_KDF_CTX *ctx, EVP_SKEY *skey,
+                        const OSSL_PARAM params[])
+{
+    if (ctx == NULL || skey == NULL)
+        return 0;
+
+    if (ctx->meth->derive_opaque == NULL) {
+        ERR_raise(ERR_R_EVP_LIB, ERR_R_UNSUPPORTED);
+        return 0;
+    }
+
+    if (skey->keymgmt->prov != ctx->meth->prov) {
+        ERR_raise(ERR_R_EVP_LIB, ERR_R_UNSUPPORTED);
+        return 0;
+    }
+
+    if (skey->keydata != NULL) {
+        ERR_raise(ERR_R_EVP_LIB, ERR_R_UNSUPPORTED);
+        return 0;
+    }
+
+    return ctx->meth->derive_opaque(ctx->algctx, &(skey->keydata), params);
+}
+
 /*
  * The {get,set}_params functions return 1 if there is no corresponding
  * function in the implementation.  This is the same as if there was one,

crypto/evp/kdf_meth.c

@@ -137,9 +137,15 @@ static void *evp_kdf_from_algorithm(int name_id,
                 break;
             kdf->set_ctx_params = OSSL_FUNC_kdf_set_ctx_params(fns);
             break;
+        case OSSL_FUNC_KDF_DERIVE_OPAQUE:
+            if (kdf->derive_opaque != NULL)
+                break;
+            kdf->derive_opaque = OSSL_FUNC_kdf_derive_opaque(fns);
+            fnkdfcnt++;
+            break;
         }
     }
-    if (fnkdfcnt != 1 || fnctxcnt != 2) {
+    if (fnkdfcnt <= 1 || fnctxcnt != 2) {
         /*
          * In order to be a consistent set of functions we must have at least
          * a derive function, and a complete set of context management

doc/man3/EVP_KDF.pod

@@ -4,7 +4,7 @@
 
 EVP_KDF, EVP_KDF_fetch, EVP_KDF_free, EVP_KDF_up_ref,
 EVP_KDF_CTX, EVP_KDF_CTX_new, EVP_KDF_CTX_free, EVP_KDF_CTX_dup,
-EVP_KDF_CTX_reset, EVP_KDF_derive,
+EVP_KDF_CTX_reset, EVP_KDF_derive, EVP_KDF_derive_SKEY,
 EVP_KDF_CTX_get_kdf_size,
 EVP_KDF_get0_provider, EVP_KDF_CTX_kdf, EVP_KDF_is_a,
 EVP_KDF_get0_name, EVP_KDF_names_do_all, EVP_KDF_get0_description,
@@ -28,6 +28,8 @@ EVP_KDF_CTX_gettable_params, EVP_KDF_CTX_settable_params - EVP KDF routines
  size_t EVP_KDF_CTX_get_kdf_size(EVP_KDF_CTX *ctx);
  int EVP_KDF_derive(EVP_KDF_CTX *ctx, unsigned char *key, size_t keylen,
                     const OSSL_PARAM params[]);
+ int EVP_KDF_derive_SKEY(EVP_KDF_CTX *ctx, EVP_SKEY *skey,
+                         const OSSL_PARAM params[])
  int EVP_KDF_up_ref(EVP_KDF *kdf);
  void EVP_KDF_free(EVP_KDF *kdf);
  EVP_KDF *EVP_KDF_fetch(OSSL_LIB_CTX *libctx, const char *algorithm,
@@ -58,10 +60,10 @@ The EVP KDF routines are a high-level interface to Key Derivation Function
 algorithms and should be used instead of algorithm-specific functions.
 
 After creating a B<EVP_KDF_CTX> for the required algorithm using
-EVP_KDF_CTX_new(), inputs to the algorithm are supplied either by
-passing them as part of the EVP_KDF_derive() call or using calls
-to EVP_KDF_CTX_set_params() before calling EVP_KDF_derive() to derive
-the key.
+EVP_KDF_CTX_new(), inputs to the algorithm are supplied either by passing them
+as part of the EVP_KDF_derive() or EVP_KDF_derive_SKEY() call or using calls to
+EVP_KDF_CTX_set_params() before calling EVP_KDF_derive() or
+EVP_KDF_derive_SKEY() to derive the key.
 
 =head2 Types
 
@@ -108,6 +110,10 @@ If the algorithm produces a fixed amount of output then an error will
 occur unless the I<keylen> parameter is equal to that output size,
 as returned by EVP_KDF_CTX_get_kdf_size().
 
+EVP_KDF_derive_SKEY() behaves similar except it accepts an B<EVP_SKEY> object
+as an output argument. The B<EVP_SKEY> object must be the fresh one and have a
+keymgmt from the same provider as the ctx has.
+
 EVP_KDF_get_params() retrieves details about the implementation
 I<kdf>.
 The set of parameters given with I<params> determine exactly what
@@ -302,6 +308,8 @@ L<life_cycle-kdf(7)>.
 
 This functionality was added in OpenSSL 3.0.
 
+EVP_KDF_derive_SKEY() function was introduced in OpenSSL 3.5.
+
 =head1 COPYRIGHT
 
 Copyright 2019-2024 The OpenSSL Project Authors. All Rights Reserved.

include/crypto/evp.h

@@ -246,6 +246,7 @@ struct evp_kdf_st {
     OSSL_FUNC_kdf_get_params_fn *get_params;
     OSSL_FUNC_kdf_get_ctx_params_fn *get_ctx_params;
     OSSL_FUNC_kdf_set_ctx_params_fn *set_ctx_params;
+    OSSL_FUNC_kdf_derive_opaque_fn *derive_opaque;
 };
 
 #define EVP_ORIG_DYNAMIC    0

include/openssl/core_dispatch.h

@@ -452,6 +452,7 @@ OSSL_CORE_MAKE_FUNC(int, mac_set_ctx_params,
 # define OSSL_FUNC_KDF_GET_PARAMS                    9
 # define OSSL_FUNC_KDF_GET_CTX_PARAMS               10
 # define OSSL_FUNC_KDF_SET_CTX_PARAMS               11
+# define OSSL_FUNC_KDF_DERIVE_OPAQUE                12
 
 OSSL_CORE_MAKE_FUNC(void *, kdf_newctx, (void *provctx))
 OSSL_CORE_MAKE_FUNC(void *, kdf_dupctx, (void *src))
@@ -469,6 +470,8 @@ OSSL_CORE_MAKE_FUNC(int, kdf_get_ctx_params,
                     (void *kctx, OSSL_PARAM params[]))
 OSSL_CORE_MAKE_FUNC(int, kdf_set_ctx_params,
                     (void *kctx, const OSSL_PARAM params[]))
+OSSL_CORE_MAKE_FUNC(int, kdf_derive_opaque, (void *kctx, void *key,
+                                             const OSSL_PARAM params[]))
 
 /* RAND */
 

include/openssl/kdf.h

@@ -43,6 +43,8 @@ void EVP_KDF_CTX_reset(EVP_KDF_CTX *ctx);
 size_t EVP_KDF_CTX_get_kdf_size(EVP_KDF_CTX *ctx);
 int EVP_KDF_derive(EVP_KDF_CTX *ctx, unsigned char *key, size_t keylen,
                    const OSSL_PARAM params[]);
+int EVP_KDF_derive_SKEY(EVP_KDF_CTX *ctx, EVP_SKEY *skey,
+                        const OSSL_PARAM params[]);
 int EVP_KDF_get_params(EVP_KDF *kdf, OSSL_PARAM params[]);
 int EVP_KDF_CTX_get_params(EVP_KDF_CTX *ctx, OSSL_PARAM params[]);
 int EVP_KDF_CTX_set_params(EVP_KDF_CTX *ctx, const OSSL_PARAM params[]);

util/libcrypto.num

@@ -5757,3 +5757,4 @@ EVP_SKEY_export                         ?	3_5_0	EXIST::FUNCTION:
 EVP_SKEY_up_ref                         ?	3_5_0	EXIST::FUNCTION:
 EVP_SKEY_free                           ?	3_5_0	EXIST::FUNCTION:
 EVP_SKEY_dup                            ?	3_5_0	EXIST::FUNCTION:
+EVP_KDF_derive_SKEY                     ?	3_5_0	EXIST::FUNCTION: