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)

1 files changed, 64 insertions, 0 deletions

diff --git a/crypto/ec/ecx_key.c b/crypto/ec/ecx_key.c
index dcec26c2e9..8cf7f1708c 100644
--- a/crypto/ec/ecx_key.c
+++ b/crypto/ec/ecx_key.c
@@ -9,7 +9,13 @@
 
 #include <string.h>
 #include <openssl/err.h>
+#include <openssl/proverr.h>
 #include "crypto/ecx.h"
+#include "internal/common.h" /* for ossl_assert() */
+
+#ifdef S390X_EC_ASM
+# include "s390x_arch.h"
+#endif
 
 ECX_KEY *ossl_ecx_key_new(OSSL_LIB_CTX *libctx, ECX_KEY_TYPE type, int haspubkey,
                           const char *propq)
@@ -96,3 +102,61 @@ unsigned char *ossl_ecx_key_allocate_privkey(ECX_KEY *key)
 
     return key->privkey;
 }
+
+int ossl_ecx_compute_key(ECX_KEY *peer, ECX_KEY *priv, size_t keylen,
+                         unsigned char *secret, size_t *secretlen, size_t outlen)
+{
+    if (priv == NULL
+            || priv->privkey == NULL
+            || peer == NULL) {
+        ERR_raise(ERR_LIB_PROV, PROV_R_MISSING_KEY);
+        return 0;
+    }
+
+    if (!ossl_assert(keylen == X25519_KEYLEN
+            || keylen == X448_KEYLEN)) {
+        ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_KEY_LENGTH);
+        return 0;
+    }
+
+    if (secret == NULL) {
+        *secretlen = keylen;
+        return 1;
+    }
+    if (outlen < keylen) {
+        ERR_raise(ERR_LIB_PROV, PROV_R_OUTPUT_BUFFER_TOO_SMALL);
+        return 0;
+    }
+
+    if (keylen == X25519_KEYLEN) {
+#ifdef S390X_EC_ASM
+        if (OPENSSL_s390xcap_P.pcc[1]
+                & S390X_CAPBIT(S390X_SCALAR_MULTIPLY_X25519)) {
+            if (s390x_x25519_mul(secret, peer->pubkey, priv->privkey) == 0) {
+                ERR_raise(ERR_LIB_PROV, PROV_R_FAILED_DURING_DERIVATION);
+                return 0;
+            }
+        } else
+#endif
+        if (ossl_x25519(secret, priv->privkey, peer->pubkey) == 0) {
+            ERR_raise(ERR_LIB_PROV, PROV_R_FAILED_DURING_DERIVATION);
+            return 0;
+        }
+    } else {
+#ifdef S390X_EC_ASM
+        if (OPENSSL_s390xcap_P.pcc[1]
+                & S390X_CAPBIT(S390X_SCALAR_MULTIPLY_X448)) {
+            if (s390x_x448_mul(secret, peer->pubkey, priv->privkey) == 0) {
+                ERR_raise(ERR_LIB_PROV, PROV_R_FAILED_DURING_DERIVATION);
+                return 0;
+            }
+        } else
+#endif
+        if (ossl_x448(secret, priv->privkey, peer->pubkey) == 0) {
+            ERR_raise(ERR_LIB_PROV, PROV_R_FAILED_DURING_DERIVATION);
+            return 0;
+        }
+    }
+    *secretlen = keylen;
+    return 1;
+}