Add HPKE DHKEM provider support for EC, X25519 and X448.

The code is derived from @sftcd's work in PR #17172.
This PR puts the DHKEM algorithms into the provider layer as
KEM algorithms for EC and ECX.

This PR only implements the DHKEM component of HPKE as specified in
RFC 9180.

crypto/hpke/hpke_util.c has been added for fuctions that will
be shared between DHKEM and HPKE.

API's for EVP_PKEY_auth_encapsulate_init() and EVP_PKEY_auth_decapsulate_init()
have been added to support authenticated encapsulation. auth_init() functions
were chosen rather that a EVP_PKEY_KEM_set_auth() interface to support
future algorithms that could possibly need different init functions.

Internal code has been refactored, so that it can be shared between the DHKEM
and other systems. Since DHKEM operates on low level keys it needs to be
able to do low level ECDH and ECXDH calls without converting the keys
back into EVP_PKEY/EVP_PKEY_CTX form. See ossl_ecx_compute_key(),
ossl_ec_public_from_private()

DHKEM requires API's to derive a key using a seed (IKM). This did not sit
well inside the DHKEM itself as dispatch functions. This functionality
fits better inside the EC and ECX keymanagers keygen, since
they are just variations of keygen where the private key is generated
in a different manner. This should mainly be used for testing purposes.
See ossl_ec_generate_key_dhkem().
It supports this by allowing a settable param to be passed to keygen
(See OSSL_PKEY_PARAM_DHKEM_IKM).
The keygen calls code within ec and ecx dhkem implementation to handle this.
See ossl_ecx_dhkem_derive_private() and ossl_ec_dhkem_derive_private().
These 2 functions are also used by the EC/ECX DHKEM implementations to generate
the sender ephemeral keys.

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19068)

2 files changed, 73 insertions, 20 deletions

diff --git a/crypto/evp/evp_local.h b/crypto/evp/evp_local.h
index a853174452..8c26e8fd6d 100644
--- a/crypto/evp/evp_local.h
+++ b/crypto/evp/evp_local.h
@@ -228,6 +228,8 @@ struct evp_kem_st {
     OSSL_FUNC_kem_gettable_ctx_params_fn *gettable_ctx_params;
     OSSL_FUNC_kem_set_ctx_params_fn *set_ctx_params;
     OSSL_FUNC_kem_settable_ctx_params_fn *settable_ctx_params;
+    OSSL_FUNC_kem_auth_encapsulate_init_fn *auth_encapsulate_init;
+    OSSL_FUNC_kem_auth_decapsulate_init_fn *auth_decapsulate_init;
 } /* EVP_KEM */;
 
 int PKCS5_v2_PBKDF2_keyivgen(EVP_CIPHER_CTX *ctx, const char *pass,
diff --git a/crypto/evp/kem.c b/crypto/evp/kem.c
index bd28ede7ae..8c0c35b54b 100644
--- a/crypto/evp/kem.c
+++ b/crypto/evp/kem.c
@@ -18,13 +18,13 @@
 #include "evp_local.h"
 
 static int evp_kem_init(EVP_PKEY_CTX *ctx, int operation,
-                        const OSSL_PARAM params[])
+                        const OSSL_PARAM params[], EVP_PKEY *authkey)
 {
     int ret = 0;
     EVP_KEM *kem = NULL;
     EVP_KEYMGMT *tmp_keymgmt = NULL;
     const OSSL_PROVIDER *tmp_prov = NULL;
-    void *provkey = NULL;
+    void *provkey = NULL, *provauthkey = NULL;
     const char *supported_kem = NULL;
     int iter;
 
@@ -40,7 +40,10 @@ static int evp_kem_init(EVP_PKEY_CTX *ctx, int operation,
         ERR_raise(ERR_LIB_EVP, EVP_R_NO_KEY_SET);
         goto err;
     }
-
+    if (authkey != NULL && authkey->type != ctx->pkey->type) {
+        ERR_raise(ERR_LIB_EVP, EVP_R_DIFFERENT_KEY_TYPES);
+        return 0;
+    }
     /*
      * Try to derive the supported kem from |ctx->keymgmt|.
      */
@@ -114,16 +117,26 @@ static int evp_kem_init(EVP_PKEY_CTX *ctx, int operation,
          * same property query as when fetching the kem method.
          * With the keymgmt we found (if we did), we try to export |ctx->pkey|
          * to it (evp_pkey_export_to_provider() is smart enough to only actually
-
          * export it if |tmp_keymgmt| is different from |ctx->pkey|'s keymgmt)
          */
         tmp_keymgmt_tofree = tmp_keymgmt =
             evp_keymgmt_fetch_from_prov((OSSL_PROVIDER *)tmp_prov,
                                         EVP_KEYMGMT_get0_name(ctx->keymgmt),
                                         ctx->propquery);
-        if (tmp_keymgmt != NULL)
+        if (tmp_keymgmt != NULL) {
             provkey = evp_pkey_export_to_provider(ctx->pkey, ctx->libctx,
                                                   &tmp_keymgmt, ctx->propquery);
+            if (provkey != NULL && authkey != NULL) {
+                provauthkey = evp_pkey_export_to_provider(authkey, ctx->libctx,
+                                                          &tmp_keymgmt,
+                                                          ctx->propquery);
+                if (provauthkey == NULL) {
+                    EVP_KEM_free(kem);
+                    ERR_raise(ERR_LIB_EVP, EVP_R_INITIALIZATION_ERROR);
+                    goto err;
+                }
+            }
+        }
         if (tmp_keymgmt == NULL)
             EVP_KEYMGMT_free(tmp_keymgmt_tofree);
     }
@@ -144,20 +157,28 @@ static int evp_kem_init(EVP_PKEY_CTX *ctx, int operation,
 
     switch (operation) {
     case EVP_PKEY_OP_ENCAPSULATE:
-        if (kem->encapsulate_init == NULL) {
+        if (provauthkey != NULL && kem->auth_encapsulate_init != NULL) {
+            ret = kem->auth_encapsulate_init(ctx->op.encap.algctx, provkey,
+                                             provauthkey, params);
+        } else if (provauthkey == NULL && kem->encapsulate_init != NULL) {
+            ret = kem->encapsulate_init(ctx->op.encap.algctx, provkey, params);
+        } else {
             ERR_raise(ERR_LIB_EVP, EVP_R_OPERATION_NOT_SUPPORTED_FOR_THIS_KEYTYPE);
             ret = -2;
             goto err;
         }
-        ret = kem->encapsulate_init(ctx->op.encap.algctx, provkey, params);
         break;
     case EVP_PKEY_OP_DECAPSULATE:
-        if (kem->decapsulate_init == NULL) {
+        if (provauthkey != NULL && kem->auth_decapsulate_init != NULL) {
+            ret = kem->auth_decapsulate_init(ctx->op.encap.algctx, provkey,
+                                             provauthkey, params);
+        } else if (provauthkey == NULL && kem->encapsulate_init != NULL) {
+            ret = kem->decapsulate_init(ctx->op.encap.algctx, provkey, params);
+        } else {
             ERR_raise(ERR_LIB_EVP, EVP_R_OPERATION_NOT_SUPPORTED_FOR_THIS_KEYTYPE);
             ret = -2;
             goto err;
         }
-        ret = kem->decapsulate_init(ctx->op.encap.algctx, provkey, params);
         break;
     default:
         ERR_raise(ERR_LIB_EVP, EVP_R_INITIALIZATION_ERROR);
@@ -178,9 +199,17 @@ static int evp_kem_init(EVP_PKEY_CTX *ctx, int operation,
     return ret;
 }
 
+int EVP_PKEY_auth_encapsulate_init(EVP_PKEY_CTX *ctx, EVP_PKEY *authpriv,
+                                   const OSSL_PARAM params[])
+{
+    if (authpriv == NULL)
+        return 0;
+    return evp_kem_init(ctx, EVP_PKEY_OP_ENCAPSULATE, params, authpriv);
+}
+
 int EVP_PKEY_encapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[])
 {
-    return evp_kem_init(ctx, EVP_PKEY_OP_ENCAPSULATE, params);
+    return evp_kem_init(ctx, EVP_PKEY_OP_ENCAPSULATE, params, NULL);
 }
 
 int EVP_PKEY_encapsulate(EVP_PKEY_CTX *ctx,
@@ -209,7 +238,15 @@ int EVP_PKEY_encapsulate(EVP_PKEY_CTX *ctx,
 
 int EVP_PKEY_decapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[])
 {
-    return evp_kem_init(ctx, EVP_PKEY_OP_DECAPSULATE, params);
+    return evp_kem_init(ctx, EVP_PKEY_OP_DECAPSULATE, params, NULL);
+}
+
+int EVP_PKEY_auth_decapsulate_init(EVP_PKEY_CTX *ctx, EVP_PKEY *authpub,
+                                   const OSSL_PARAM params[])
+{
+    if (authpub == NULL)
+        return 0;
+    return evp_kem_init(ctx, EVP_PKEY_OP_DECAPSULATE, params, authpub);
 }
 
 int EVP_PKEY_decapsulate(EVP_PKEY_CTX *ctx,
@@ -288,6 +325,12 @@ static void *evp_kem_from_algorithm(int name_id, const OSSL_ALGORITHM *algodef,
             kem->encapsulate_init = OSSL_FUNC_kem_encapsulate_init(fns);
             encfncnt++;
             break;
+        case OSSL_FUNC_KEM_AUTH_ENCAPSULATE_INIT:
+            if (kem->auth_encapsulate_init != NULL)
+                break;
+            kem->auth_encapsulate_init = OSSL_FUNC_kem_auth_encapsulate_init(fns);
+            encfncnt++;
+            break;
         case OSSL_FUNC_KEM_ENCAPSULATE:
             if (kem->encapsulate != NULL)
                 break;
@@ -300,6 +343,12 @@ static void *evp_kem_from_algorithm(int name_id, const OSSL_ALGORITHM *algodef,
             kem->decapsulate_init = OSSL_FUNC_kem_decapsulate_init(fns);
             decfncnt++;
             break;
+        case OSSL_FUNC_KEM_AUTH_DECAPSULATE_INIT:
+            if (kem->auth_decapsulate_init != NULL)
+                break;
+            kem->auth_decapsulate_init = OSSL_FUNC_kem_auth_decapsulate_init(fns);
+            decfncnt++;
+            break;
         case OSSL_FUNC_KEM_DECAPSULATE:
             if (kem->decapsulate != NULL)
                 break;
@@ -348,19 +397,21 @@ static void *evp_kem_from_algorithm(int name_id, const OSSL_ALGORITHM *algodef,
         }
     }
     if (ctxfncnt != 2
-        || (encfncnt != 0 && encfncnt != 2)
-        || (decfncnt != 0 && decfncnt != 2)
-        || (encfncnt != 2 && decfncnt != 2)
+        || (encfncnt != 0 && encfncnt != 2 && encfncnt != 3)
+        || (decfncnt != 0 && decfncnt != 2 && decfncnt != 3)
+        || (encfncnt != decfncnt)
         || (gparamfncnt != 0 && gparamfncnt != 2)
         || (sparamfncnt != 0 && sparamfncnt != 2)) {
         /*
          * In order to be a consistent set of functions we must have at least
-         * a set of context functions (newctx and freectx) as well as a pair of
-         * "kem" functions: (encapsulate_init, encapsulate) or
-         * (decapsulate_init, decapsulate). set_ctx_params and settable_ctx_params are
-         * optional, but if one of them is present then the other one must also
-         * be present. The same applies to get_ctx_params and
-         * gettable_ctx_params. The dupctx function is optional.
+         * a set of context functions (newctx and freectx) as well as a pair
+         * (or triplet) of "kem" functions:
+         * (encapsulate_init, (and/or auth_encapsulate_init), encapsulate) or
+         * (decapsulate_init, (and/or auth_decapsulate_init), decapsulate).
+         * set_ctx_params and settable_ctx_params are optional, but if one of
+         * them is present then the other one must also be present. The same
+         * applies to get_ctx_params and gettable_ctx_params.
+         * The dupctx function is optional.
          */
         ERR_raise(ERR_LIB_EVP, EVP_R_INVALID_PROVIDER_FUNCTIONS);
         goto err;