/*

 * Copyright 2022-2025 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the Apache License 2.0 (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

/*

 * The following implementation is part of RFC 9180 related to DHKEM using

 * ECX keys (i.e. X25519 and X448)

 * References to Sections in the comments below refer to RFC 9180.

 */

#include "internal/deprecated.h"

#include <string.h>

#include <openssl/crypto.h>

#include <openssl/evp.h>

#include <openssl/core_dispatch.h>

#include <openssl/core_names.h>

#include <openssl/params.h>

#include <openssl/kdf.h>

#include <openssl/err.h>

#include <openssl/sha.h>

#include <openssl/rand.h>

#include <openssl/proverr.h>

#include "internal/cryptlib.h"

#include "prov/provider_ctx.h"

#include "prov/implementations.h"

#include "prov/securitycheck.h"

#include "prov/providercommon.h"

#include "prov/ecx.h"

#include "crypto/ecx.h"

#include <openssl/hpke.h>

#include "internal/hpke_util.h"

#include "prov/eckem.h"

#define MAX_ECX_KEYLEN X448_KEYLEN

/* KEM identifiers from Section 7.1 "Table 2 KEM IDs" */

#define KEMID_X25519_HKDF_SHA256 0x20

#define KEMID_X448_HKDF_SHA512   0x21

/* ASCII: "KEM", in hex for EBCDIC compatibility */

static const char LABEL_KEM[] = "\x4b\x45\x4d";

typedef struct {

    ECX_KEY *recipient_key;

    ECX_KEY *sender_authkey;

    OSSL_LIB_CTX *libctx;

    char *propq;

    unsigned int mode;

    unsigned int op;

    unsigned char *ikm;

    size_t ikmlen;

    const char *kdfname;

    const OSSL_HPKE_KEM_INFO *info;

} PROV_ECX_CTX;

static OSSL_FUNC_kem_newctx_fn ecxkem_newctx;

static OSSL_FUNC_kem_encapsulate_init_fn ecxkem_encapsulate_init;

static OSSL_FUNC_kem_encapsulate_fn ecxkem_encapsulate;

static OSSL_FUNC_kem_decapsulate_init_fn ecxkem_decapsulate_init;

static OSSL_FUNC_kem_decapsulate_fn ecxkem_decapsulate;

static OSSL_FUNC_kem_freectx_fn ecxkem_freectx;

static OSSL_FUNC_kem_set_ctx_params_fn ecxkem_set_ctx_params;

static OSSL_FUNC_kem_auth_encapsulate_init_fn ecxkem_auth_encapsulate_init;

static OSSL_FUNC_kem_auth_decapsulate_init_fn ecxkem_auth_decapsulate_init;

/*

 * Set KEM values as specified in Section 7.1 "Table 2 KEM IDs"

 * There is only one set of values for X25519 and X448.

 * Additional values could be set via set_params if required.

 */

static const OSSL_HPKE_KEM_INFO *get_kem_info(ECX_KEY *ecx)

{

    const char *name = NULL;

    if (ecx->type == ECX_KEY_TYPE_X25519)

        name = SN_X25519;

    else

        name = SN_X448;

    return ossl_HPKE_KEM_INFO_find_curve(name);

}

/*

 * Set the recipient key, and free any existing key.

 * ecx can be NULL. The ecx key may have only a private or public component.

 */

static int recipient_key_set(PROV_ECX_CTX *ctx, ECX_KEY *ecx)

{

    ossl_ecx_key_free(ctx->recipient_key);

    ctx->recipient_key = NULL;

    if (ecx != NULL) {

        ctx->info = get_kem_info(ecx);

        if (ctx->info == NULL)

            return -2;

        ctx->kdfname = "HKDF";

        if (!ossl_ecx_key_up_ref(ecx))

            return 0;

        ctx->recipient_key = ecx;

    }

    return 1;

}

/*

 * Set the senders auth key, and free any existing auth key.

 * ecx can be NULL.

 */

static int sender_authkey_set(PROV_ECX_CTX *ctx, ECX_KEY *ecx)

{

    ossl_ecx_key_free(ctx->sender_authkey);

    ctx->sender_authkey = NULL;

    if (ecx != NULL) {

        if (!ossl_ecx_key_up_ref(ecx))

            return 0;

        ctx->sender_authkey = ecx;

    }

    return 1;

}

/*

 * Serialize a public key from byte array's for the encoded public keys.

 * ctx is used to access the key type.

 * Returns: The created ECX_KEY or NULL on error.

 */

static ECX_KEY *ecxkey_pubfromdata(PROV_ECX_CTX *ctx,

                                   const unsigned char *pubbuf, size_t pubbuflen)

{

    ECX_KEY *ecx = NULL;

    OSSL_PARAM pub;

    pub = OSSL_PARAM_construct_octet_string(OSSL_PKEY_PARAM_PUB_KEY,

                                            (char *)pubbuf, pubbuflen);

    ecx = ossl_ecx_key_new(ctx->libctx, ctx->recipient_key->type, 1, ctx->propq);

    if (ecx == NULL)

        return NULL;

    if (ossl_ecx_key_fromdata(ecx, &pub, NULL, 0) <= 0) {

        ossl_ecx_key_free(ecx);

        ecx = NULL;

    }

    return ecx;

}

static unsigned char *ecx_pubkey(ECX_KEY *ecx)

{

    if (ecx == NULL || !ecx->haspubkey) {

        ERR_raise(ERR_LIB_PROV, PROV_R_NOT_A_PUBLIC_KEY);

        return 0;

    }

    return ecx->pubkey;

}

static void *ecxkem_newctx(void *provctx)

{

    PROV_ECX_CTX *ctx =  OPENSSL_zalloc(sizeof(PROV_ECX_CTX));

    if (ctx == NULL)

        return NULL;

    ctx->libctx = PROV_LIBCTX_OF(provctx);

    ctx->mode = KEM_MODE_DHKEM;

    return ctx;

}

static void ecxkem_freectx(void *vectx)

{

    PROV_ECX_CTX *ctx = (PROV_ECX_CTX *)vectx;

    OPENSSL_clear_free(ctx->ikm, ctx->ikmlen);

    recipient_key_set(ctx, NULL);

    sender_authkey_set(ctx, NULL);

    OPENSSL_free(ctx);

}

static int ecx_match_params(const ECX_KEY *key1, const ECX_KEY *key2)

{

    return (key1->type == key2->type && key1->keylen == key2->keylen);

}

static int ecx_key_check(const ECX_KEY *ecx, int requires_privatekey)

{

    if (ecx->privkey == NULL)

        return (requires_privatekey == 0);

    return 1;

}

static int ecxkem_init(void *vecxctx, int operation, void *vecx, void *vauth,

                       ossl_unused const OSSL_PARAM params[])

{

    int rv;

    PROV_ECX_CTX *ctx = (PROV_ECX_CTX *)vecxctx;

    ECX_KEY *ecx = vecx;

    ECX_KEY *auth = vauth;

    if (!ossl_prov_is_running())

        return 0;

    if (!ecx_key_check(ecx, operation == EVP_PKEY_OP_DECAPSULATE))

        return 0;

    rv = recipient_key_set(ctx, ecx);

    if (rv <= 0)

        return rv;

    if (auth != NULL) {

        if (!ecx_match_params(auth, ctx->recipient_key)

                || !ecx_key_check(auth, operation == EVP_PKEY_OP_ENCAPSULATE)

                || !sender_authkey_set(ctx, auth))

            return 0;

    }

    ctx->op = operation;

    return ecxkem_set_ctx_params(vecxctx, params);

}

static int ecxkem_encapsulate_init(void *vecxctx, void *vecx,

                                   const OSSL_PARAM params[])

{

    return ecxkem_init(vecxctx, EVP_PKEY_OP_ENCAPSULATE, vecx, NULL, params);

}

static int ecxkem_decapsulate_init(void *vecxctx, void *vecx,

                                   const OSSL_PARAM params[])

{

    return ecxkem_init(vecxctx, EVP_PKEY_OP_DECAPSULATE, vecx, NULL, params);

}

static int ecxkem_auth_encapsulate_init(void *vctx, void *vecx, void *vauthpriv,

                                        const OSSL_PARAM params[])

{

    return ecxkem_init(vctx, EVP_PKEY_OP_ENCAPSULATE, vecx, vauthpriv, params);

}

static int ecxkem_auth_decapsulate_init(void *vctx, void *vecx, void *vauthpub,

                                        const OSSL_PARAM params[])

{

    return ecxkem_init(vctx, EVP_PKEY_OP_DECAPSULATE, vecx, vauthpub, params);

}

/* Machine generated by util/perl/OpenSSL/paramnames.pm */

#ifndef ecxkem_set_ctx_params_list

static const OSSL_PARAM ecxkem_set_ctx_params_list[] = {

    OSSL_PARAM_utf8_string(OSSL_KEM_PARAM_OPERATION, NULL, 0),

    OSSL_PARAM_octet_string(OSSL_KEM_PARAM_IKME, NULL, 0),

    OSSL_PARAM_END

};

#endif

#ifndef ecxkem_set_ctx_params_st

struct ecxkem_set_ctx_params_st {

    OSSL_PARAM *ikme;

    OSSL_PARAM *op;

};

#endif

#ifndef ecxkem_set_ctx_params_decoder

static int ecxkem_set_ctx_params_decoder

    (const OSSL_PARAM *p, struct ecxkem_set_ctx_params_st *r)

{

    const char *s;

    memset(r, 0, sizeof(*r));

    if (p != NULL)

        for (; (s = p->key) != NULL; p++)

            switch(s[0]) {

            default:

                break;

            case 'i':

                if (ossl_likely(strcmp("kme", s + 1) == 0)) {

                    /* KEM_PARAM_IKME */

                    if (ossl_unlikely(r->ikme != NULL)) {

                        ERR_raise_data(ERR_LIB_PROV, PROV_R_REPEATED_PARAMETER,

                                       "param %s is repeated", s);

                        return 0;

                    }

                    r->ikme = (OSSL_PARAM *)p;

                }

                break;

            case 'o':

                if (ossl_likely(strcmp("peration", s + 1) == 0)) {

                    /* KEM_PARAM_OPERATION */

                    if (ossl_unlikely(r->op != NULL)) {

                        ERR_raise_data(ERR_LIB_PROV, PROV_R_REPEATED_PARAMETER,

                                       "param %s is repeated", s);

                        return 0;

                    }

                    r->op = (OSSL_PARAM *)p;

                }

            }

    return 1;

}

#endif

/* End of machine generated */

static int ecxkem_set_ctx_params(void *vctx, const OSSL_PARAM params[])

{

    PROV_ECX_CTX *ctx = (PROV_ECX_CTX *)vctx;

    struct ecxkem_set_ctx_params_st p;

    int mode;

    if (ctx == NULL || !ecxkem_set_ctx_params_decoder(params, &p))

        return 0;

    if (p.ikme != NULL) {

        void *tmp = NULL;

        size_t tmplen = 0;

        if (p.ikme->data != NULL && p.ikme->data_size != 0) {

            if (!OSSL_PARAM_get_octet_string(p.ikme, &tmp, 0, &tmplen))

                return 0;

        }

        OPENSSL_clear_free(ctx->ikm, ctx->ikmlen);

        ctx->ikm = tmp;

        ctx->ikmlen = tmplen;

    }

    if (p.op != NULL) {

        if (p.op->data_type != OSSL_PARAM_UTF8_STRING)

            return 0;

        mode = ossl_eckem_modename2id(p.op->data);

        if (mode == KEM_MODE_UNDEFINED)

            return 0;

        ctx->mode = mode;

    }

    return 1;

}

static const OSSL_PARAM *ecxkem_settable_ctx_params(ossl_unused void *vctx,

                                                   ossl_unused void *provctx)

{

    return ecxkem_set_ctx_params_list;

}

/*

 * See Section 4.1 DH-Based KEM (DHKEM) ExtractAndExpand

 */

static int dhkem_extract_and_expand(EVP_KDF_CTX *kctx,

                                    unsigned char *okm, size_t okmlen,

                                    uint16_t kemid,

                                    const unsigned char *dhkm, size_t dhkmlen,

                                    const unsigned char *kemctx,

                                    size_t kemctxlen)

{

    uint8_t suiteid[2];

    uint8_t prk[EVP_MAX_MD_SIZE];

    size_t prklen = okmlen; /* Nh */

    int ret;

    if (prklen > sizeof(prk))

        return 0;

    suiteid[0] = (kemid >> 8) &0xff;

    suiteid[1] = kemid & 0xff;

    ret = ossl_hpke_labeled_extract(kctx, prk, prklen,

                                    NULL, 0, LABEL_KEM, suiteid, sizeof(suiteid),

                                    OSSL_DHKEM_LABEL_EAE_PRK, dhkm, dhkmlen)

          && ossl_hpke_labeled_expand(kctx, okm, okmlen, prk, prklen,

                                      LABEL_KEM, suiteid, sizeof(suiteid),

                                      OSSL_DHKEM_LABEL_SHARED_SECRET,

                                      kemctx, kemctxlen);

    OPENSSL_cleanse(prk, prklen);

    return ret;

}

/*

 * See Section 7.1.3 DeriveKeyPair.

 *

 * This function is used by ecx keygen.

 * (For this reason it does not use any of the state stored in PROV_ECX_CTX).

 *

 * Params:

 *     ecx An initialized ecx key.

 *     privout The buffer to store the generated private key into (it is assumed

 *             this is of length ecx->keylen).

 *     ikm buffer containing the input key material (seed). This must be non NULL.

 *     ikmlen size of the ikm buffer in bytes

 * Returns:

 *     1 if successful or 0 otherwise.

 */

int ossl_ecx_dhkem_derive_private(ECX_KEY *ecx, unsigned char *privout,

                                  const unsigned char *ikm, size_t ikmlen)

{

    int ret = 0;

    EVP_KDF_CTX *kdfctx = NULL;

    unsigned char prk[EVP_MAX_MD_SIZE];

    uint8_t suiteid[2];

    const OSSL_HPKE_KEM_INFO *info = get_kem_info(ecx);

    /* ikmlen should have a length of at least Nsk */

    if (ikmlen < info->Nsk) {

        ERR_raise_data(ERR_LIB_PROV, PROV_R_INVALID_INPUT_LENGTH,

                       "ikm length is :%zu, should be at least %zu",

                       ikmlen, info->Nsk);

        goto err;

    }

    kdfctx = ossl_kdf_ctx_create("HKDF", info->mdname, ecx->libctx, ecx->propq);

    if (kdfctx == NULL)

        return 0;

    suiteid[0] = info->kem_id / 256;

    suiteid[1] = info->kem_id % 256;

    if (!ossl_hpke_labeled_extract(kdfctx, prk, info->Nsecret,

                                   NULL, 0, LABEL_KEM, suiteid, sizeof(suiteid),

                                   OSSL_DHKEM_LABEL_DKP_PRK, ikm, ikmlen))

        goto err;

    if (!ossl_hpke_labeled_expand(kdfctx, privout, info->Nsk, prk, info->Nsecret,

                                  LABEL_KEM, suiteid, sizeof(suiteid),

                                  OSSL_DHKEM_LABEL_SK, NULL, 0))

        goto err;

    ret = 1;

err:

    OPENSSL_cleanse(prk, sizeof(prk));

    EVP_KDF_CTX_free(kdfctx);

    return ret;

}

/*

 * Do a keygen operation without having to use EVP_PKEY.

 * Params:

 *     ctx Context object

 *     ikm The seed material - if this is NULL, then a random seed is used.

 * Returns:

 *     The generated ECX key, or NULL on failure.

 */

static ECX_KEY *derivekey(PROV_ECX_CTX *ctx,

                          const unsigned char *ikm, size_t ikmlen)

{

    int ok = 0;

    ECX_KEY *key;

    unsigned char *privkey;

    unsigned char *seed = (unsigned char *)ikm;

    size_t seedlen = ikmlen;

    unsigned char tmpbuf[OSSL_HPKE_MAX_PRIVATE];

    const OSSL_HPKE_KEM_INFO *info = ctx->info;

    key = ossl_ecx_key_new(ctx->libctx, ctx->recipient_key->type, 0, ctx->propq);

    if (key == NULL)

        return NULL;

    privkey = ossl_ecx_key_allocate_privkey(key);

    if (privkey == NULL)

        goto err;

    /* Generate a random seed if there is no input ikm */

    if (seed == NULL || seedlen == 0) {

        if (info->Nsk > sizeof(tmpbuf))

            goto err;

        if (RAND_priv_bytes_ex(ctx->libctx, tmpbuf, info->Nsk, 0) <= 0)

            goto err;

        seed = tmpbuf;

        seedlen = info->Nsk;

    }

    if (!ossl_ecx_dhkem_derive_private(key, privkey, seed, seedlen))

        goto err;

    if (!ossl_ecx_public_from_private(key))

        goto err;

    key->haspubkey = 1;

    ok = 1;

err:

    if (!ok) {

        ossl_ecx_key_free(key);

        key = NULL;

    }

    if (seed != ikm)

        OPENSSL_cleanse(seed, seedlen);

    return key;

}

/*

 * Do an ecxdh key exchange.

 * dhkm = DH(sender, peer)

 *

 * NOTE: Instead of using EVP_PKEY_derive() API's, we use ECX_KEY operations

 *       to avoid messy conversions back to EVP_PKEY.

 *

 * Returns the size of the secret if successful, or 0 otherwise,

 */

static int generate_ecxdhkm(const ECX_KEY *sender, const ECX_KEY *peer,

                           unsigned char *out,  size_t maxout,

                           unsigned int secretsz)

{

    size_t len = 0;

    /* NOTE: ossl_ecx_compute_key checks for shared secret being all zeros */

    return ossl_ecx_compute_key((ECX_KEY *)peer, (ECX_KEY *)sender,

                                 sender->keylen, out, &len, maxout);

}

/*

 * Derive a secret using ECXDH (code is shared by the encap and decap)

 *

 * dhkm = Concat(ecxdh(privkey1, peerkey1), ecdh(privkey2, peerkey2)

 * kemctx = Concat(sender_pub, recipient_pub, ctx->sender_authkey)

 * secret = dhkem_extract_and_expand(kemid, dhkm, kemctx);

 *

 * Params:

 *     ctx Object that contains algorithm state and constants.

 *     secret The returned secret (with a length ctx->alg->secretlen bytes).

 *     privkey1 A private key used for ECXDH key derivation.

 *     peerkey1 A public key used for ECXDH key derivation with privkey1

 *     privkey2 A optional private key used for a second ECXDH key derivation.

 *              It can be NULL.

 *     peerkey2 A optional public key used for a second ECXDH key derivation

 *              with privkey2,. It can be NULL.

 *     sender_pub The senders public key in encoded form.

 *     recipient_pub The recipients public key in encoded form.

 * Notes:

 *     The second ecdh() is only used for the HPKE auth modes when both privkey2

 *     and peerkey2 are non NULL (i.e. ctx->sender_authkey is not NULL).

 */

static int derive_secret(PROV_ECX_CTX *ctx, unsigned char *secret,

                         const ECX_KEY *privkey1, const ECX_KEY *peerkey1,

                         const ECX_KEY *privkey2, const ECX_KEY *peerkey2,

                         const unsigned char *sender_pub,

                         const unsigned char *recipient_pub)

{

    int ret = 0;

    EVP_KDF_CTX *kdfctx = NULL;

    unsigned char *sender_authpub = NULL;

    unsigned char dhkm[MAX_ECX_KEYLEN * 2];

    unsigned char kemctx[MAX_ECX_KEYLEN * 3];

    size_t kemctxlen = 0, dhkmlen = 0;

    const OSSL_HPKE_KEM_INFO *info = ctx->info;

    int auth = ctx->sender_authkey != NULL;

    size_t encodedkeylen = info->Npk;

    if (!generate_ecxdhkm(privkey1, peerkey1, dhkm, sizeof(dhkm),

                          (unsigned int)encodedkeylen))

        goto err;

    dhkmlen = encodedkeylen;

    /* Concat the optional second ECXDH (used for Auth) */

    if (auth) {

        if (!generate_ecxdhkm(privkey2, peerkey2,

                              dhkm + dhkmlen, sizeof(dhkm) - dhkmlen,

                              (unsigned int)encodedkeylen))

            goto err;

        /* Get the public key of the auth sender in encoded form */

        sender_authpub = ecx_pubkey(ctx->sender_authkey);

        if (sender_authpub == NULL)

            goto err;

        dhkmlen += encodedkeylen;

    }

    kemctxlen = encodedkeylen + dhkmlen;

    if (kemctxlen > sizeof(kemctx))

        goto err;

    /* kemctx is the concat of both sides encoded public key */

    memcpy(kemctx, sender_pub, encodedkeylen);

    memcpy(kemctx + encodedkeylen, recipient_pub, encodedkeylen);

    if (auth)

        memcpy(kemctx + 2 * encodedkeylen, sender_authpub, encodedkeylen);

    kdfctx = ossl_kdf_ctx_create(ctx->kdfname, info->mdname,

                                 ctx->libctx, ctx->propq);

    if (kdfctx == NULL)

        goto err;

    if (!dhkem_extract_and_expand(kdfctx, secret, info->Nsecret,

                                  info->kem_id, dhkm, dhkmlen,

                                  kemctx, kemctxlen))

        goto err;

    ret = 1;

err:

    OPENSSL_cleanse(dhkm, dhkmlen);

    EVP_KDF_CTX_free(kdfctx);

    return ret;

}

/*

 * Do a DHKEM encapsulate operation.

 *

 * See Section 4.1 Encap() and AuthEncap()

 *

 * Params:

 *     ctx A context object holding the recipients public key and the

 *         optional senders auth private key.

 *     enc A buffer to return the senders ephemeral public key.

 *         Setting this to NULL allows the enclen and secretlen to return

 *         values, without calculating the secret.

 *     enclen Passes in the max size of the enc buffer and returns the

 *            encoded public key length.

 *     secret A buffer to return the calculated shared secret.

 *     secretlen Passes in the max size of the secret buffer and returns the

 *               secret length.

 * Returns: 1 on success or 0 otherwise.

 */

static int dhkem_encap(PROV_ECX_CTX *ctx,

                       unsigned char *enc, size_t *enclen,

                       unsigned char *secret, size_t *secretlen)

{

    int ret = 0;

    ECX_KEY *sender_ephemkey = NULL;

    unsigned char *sender_ephempub, *recipient_pub;

    const OSSL_HPKE_KEM_INFO *info = ctx->info;

    if (enc == NULL) {

        if (enclen == NULL && secretlen == NULL)

            return 0;

        if (enclen != NULL)

            *enclen = info->Nenc;

        if (secretlen != NULL)

            *secretlen = info->Nsecret;

       return 1;

    }

    if (*secretlen < info->Nsecret) {

        ERR_raise_data(ERR_LIB_PROV, PROV_R_BAD_LENGTH, "*secretlen too small");

        return 0;

    }

    if (*enclen < info->Nenc) {

        ERR_raise_data(ERR_LIB_PROV, PROV_R_BAD_LENGTH, "*enclen too small");

        return 0;

    }

    /* Create an ephemeral key */

    sender_ephemkey = derivekey(ctx, ctx->ikm, ctx->ikmlen);

    sender_ephempub = ecx_pubkey(sender_ephemkey);

    recipient_pub = ecx_pubkey(ctx->recipient_key);

    if (sender_ephempub == NULL || recipient_pub == NULL)

        goto err;

    if (!derive_secret(ctx, secret,

                       sender_ephemkey, ctx->recipient_key,

                       ctx->sender_authkey, ctx->recipient_key,

                       sender_ephempub, recipient_pub))

        goto err;

    /* Return the public part of the ephemeral key */

    memcpy(enc, sender_ephempub, info->Nenc);

    *enclen = info->Nenc;

    *secretlen = info->Nsecret;

    ret = 1;

err:

    ossl_ecx_key_free(sender_ephemkey);

    return ret;

}

/*

 * Do a DHKEM decapsulate operation.

 * See Section 4.1 Decap() and Auth Decap()

 *

 * Params:

 *     ctx A context object holding the recipients private key and the

 *         optional senders auth public key.

 *     secret A buffer to return the calculated shared secret. Setting this to

 *            NULL can be used to return the secretlen.

 *     secretlen Passes in the max size of the secret buffer and returns the

 *               secret length.

 *     enc A buffer containing the senders ephemeral public key that was returned

 *         from dhkem_encap().

 *     enclen The length in bytes of enc.

 * Returns: 1 If the shared secret is returned or 0 on error.

 */

static int dhkem_decap(PROV_ECX_CTX *ctx,

                       unsigned char *secret, size_t *secretlen,

                       const unsigned char *enc, size_t enclen)

{

    int ret = 0;

    ECX_KEY *recipient_privkey = ctx->recipient_key;

    ECX_KEY *sender_ephempubkey = NULL;

    const OSSL_HPKE_KEM_INFO *info = ctx->info;

    unsigned char *recipient_pub;

    if (secret == NULL) {

        *secretlen = info->Nsecret;

        return 1;

    }

    if (*secretlen < info->Nsecret) {

        ERR_raise_data(ERR_LIB_PROV, PROV_R_BAD_LENGTH, "*secretlen too small");

        return 0;

    }

    if (enclen != info->Nenc) {

        ERR_raise_data(ERR_LIB_PROV, PROV_R_INVALID_KEY, "Invalid enc public key");

        return 0;

    }

    /* Get the public part of the ephemeral key created by encap */

    sender_ephempubkey = ecxkey_pubfromdata(ctx, enc, enclen);

    if (sender_ephempubkey == NULL)

        goto err;

    recipient_pub = ecx_pubkey(recipient_privkey);

    if (recipient_pub == NULL)

        goto err;

    if (!derive_secret(ctx, secret,

                       ctx->recipient_key, sender_ephempubkey,

                       ctx->recipient_key, ctx->sender_authkey,

                       enc, recipient_pub))

        goto err;

    *secretlen = info->Nsecret;

    ret = 1;

err:

    ossl_ecx_key_free(sender_ephempubkey);

    return ret;

}

static int ecxkem_encapsulate(void *vctx, unsigned char *out, size_t *outlen,

                              unsigned char *secret, size_t *secretlen)

{

    PROV_ECX_CTX *ctx = (PROV_ECX_CTX *)vctx;

    switch (ctx->mode) {

        case KEM_MODE_DHKEM:

            return dhkem_encap(ctx, out, outlen, secret, secretlen);

        default:

            ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_MODE);

            return -2;

    }

}

static int ecxkem_decapsulate(void *vctx, unsigned char *out, size_t *outlen,

                              const unsigned char *in, size_t inlen)

{

    PROV_ECX_CTX *ctx = (PROV_ECX_CTX *)vctx;

    switch (ctx->mode) {

        case KEM_MODE_DHKEM:

            return dhkem_decap(vctx, out, outlen, in, inlen);

        default:

            ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_MODE);

            return -2;

    }

}

const OSSL_DISPATCH ossl_ecx_asym_kem_functions[] = {

    { OSSL_FUNC_KEM_NEWCTX, (void (*)(void))ecxkem_newctx },

    { OSSL_FUNC_KEM_ENCAPSULATE_INIT,

      (void (*)(void))ecxkem_encapsulate_init },

    { OSSL_FUNC_KEM_ENCAPSULATE, (void (*)(void))ecxkem_encapsulate },

    { OSSL_FUNC_KEM_DECAPSULATE_INIT,

      (void (*)(void))ecxkem_decapsulate_init },

    { OSSL_FUNC_KEM_DECAPSULATE, (void (*)(void))ecxkem_decapsulate },

    { OSSL_FUNC_KEM_FREECTX, (void (*)(void))ecxkem_freectx },

    { OSSL_FUNC_KEM_SET_CTX_PARAMS,

      (void (*)(void))ecxkem_set_ctx_params },

    { OSSL_FUNC_KEM_SETTABLE_CTX_PARAMS,

      (void (*)(void))ecxkem_settable_ctx_params },

    { OSSL_FUNC_KEM_AUTH_ENCAPSULATE_INIT,

      (void (*)(void))ecxkem_auth_encapsulate_init },

    { OSSL_FUNC_KEM_AUTH_DECAPSULATE_INIT,

      (void (*)(void))ecxkem_auth_decapsulate_init },

    OSSL_DISPATCH_END

};