/*

 * Copyright 2022-2023 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

 * EC keys (i.e. P-256, P-384 and P-521)

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

 */

#include "internal/deprecated.h"

#include <openssl/crypto.h>

#include <openssl/evp.h>

#include <openssl/core_dispatch.h>

#include <openssl/core_names.h>

#include <openssl/ec.h>

#include <openssl/params.h>

#include <openssl/err.h>

#include <openssl/proverr.h>

#include <openssl/kdf.h>

#include <openssl/rand.h>

#include "prov/provider_ctx.h"

#include "prov/implementations.h"

#include "prov/securitycheck.h"

#include "prov/providercommon.h"

#include <openssl/hpke.h>

#include "internal/hpke_util.h"

#include "crypto/ec.h"

#include "prov/ecx.h"

#include "eckem.h"

typedef struct {

    EC_KEY *recipient_key;

    EC_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_EC_CTX;

static OSSL_FUNC_kem_newctx_fn eckem_newctx;

static OSSL_FUNC_kem_encapsulate_init_fn eckem_encapsulate_init;

static OSSL_FUNC_kem_auth_encapsulate_init_fn eckem_auth_encapsulate_init;

static OSSL_FUNC_kem_encapsulate_fn eckem_encapsulate;

static OSSL_FUNC_kem_decapsulate_init_fn eckem_decapsulate_init;

static OSSL_FUNC_kem_auth_decapsulate_init_fn eckem_auth_decapsulate_init;

static OSSL_FUNC_kem_decapsulate_fn eckem_decapsulate;

static OSSL_FUNC_kem_freectx_fn eckem_freectx;

static OSSL_FUNC_kem_set_ctx_params_fn eckem_set_ctx_params;

static OSSL_FUNC_kem_settable_ctx_params_fn eckem_settable_ctx_params;

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

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

static int eckey_check(const EC_KEY *ec, int requires_privatekey)

{

    int rv = 0;

    BN_CTX *bnctx = NULL;

    BIGNUM *rem = NULL;

    const BIGNUM *priv = EC_KEY_get0_private_key(ec);

    const EC_POINT *pub = EC_KEY_get0_public_key(ec);

    /* Keys always require a public component */

    if (pub == NULL) {

        ERR_raise(ERR_LIB_PROV, PROV_R_NOT_A_PUBLIC_KEY);

        return 0;

    }

    if (priv == NULL) {

        return (requires_privatekey == 0);

    } else {

        /* If there is a private key, check that is non zero (mod order) */

        const EC_GROUP *group = EC_KEY_get0_group(ec);

        const BIGNUM *order = EC_GROUP_get0_order(group);

        bnctx = BN_CTX_new_ex(ossl_ec_key_get_libctx(ec));

        rem = BN_new();

        if (order != NULL && rem != NULL && bnctx != NULL) {

             rv = BN_mod(rem, priv, order, bnctx)

                  && !BN_is_zero(rem);

        }

    }

    BN_free(rem);

    BN_CTX_free(bnctx);

    return rv;

}

/* Returns NULL if the curve is not supported */

static const char *ec_curvename_get0(const EC_KEY *ec)

{

    const EC_GROUP *group = EC_KEY_get0_group(ec);

    return EC_curve_nid2nist(EC_GROUP_get_curve_name(group));

}

/*

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

 * ec can be NULL.

 * The ec key may have only a private or public component

 * (but it must have a group).

 */

static int recipient_key_set(PROV_EC_CTX *ctx, EC_KEY *ec)

{

    EC_KEY_free(ctx->recipient_key);

    ctx->recipient_key = NULL;

    if (ec != NULL) {

        const char *curve = ec_curvename_get0(ec);

        if (curve == NULL)

            return -2;

        ctx->info = ossl_HPKE_KEM_INFO_find_curve(curve);

        if (ctx->info == NULL)

            return -2;

        if (!EC_KEY_up_ref(ec))

            return 0;

        ctx->recipient_key = ec;

        ctx->kdfname = "HKDF";

    }

    return 1;

}

/*

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

 * ec can be NULL.

 */

static int sender_authkey_set(PROV_EC_CTX *ctx, EC_KEY *ec)

{

    EC_KEY_free(ctx->sender_authkey);

    ctx->sender_authkey = NULL;

    if (ec != NULL) {

        if (!EC_KEY_up_ref(ec))

            return 0;

        ctx->sender_authkey = ec;

    }

    return 1;

}

/*

 * Serializes a encoded public key buffer into a EC public key.

 * Params:

 *     in Contains the group.

 *     pubbuf The encoded public key buffer

 * Returns: The created public EC key, or NULL if there is an error.

 */

static EC_KEY *eckey_frompub(EC_KEY *in,

                             const unsigned char *pubbuf, size_t pubbuflen)

{

    EC_KEY *key;

    key = EC_KEY_new_ex(ossl_ec_key_get_libctx(in), ossl_ec_key_get0_propq(in));

    if (key == NULL)

        goto err;

    if (!EC_KEY_set_group(key, EC_KEY_get0_group(in)))

        goto err;

    if (!EC_KEY_oct2key(key, pubbuf, pubbuflen, NULL))

        goto err;

    return key;

err:

    EC_KEY_free(key);

    return NULL;

}

/*

 * Deserialises a EC public key into a encoded byte array.

 * Returns: 1 if successful or 0 otherwise.

 */

static int ecpubkey_todata(const EC_KEY *ec, unsigned char *out, size_t *outlen,

                           size_t maxoutlen)

{

    const EC_POINT *pub;

    const EC_GROUP *group;

    group = EC_KEY_get0_group(ec);

    pub = EC_KEY_get0_public_key(ec);

    *outlen = EC_POINT_point2oct(group, pub, POINT_CONVERSION_UNCOMPRESSED,

                                 out, maxoutlen, NULL);

    return *outlen != 0;

}

static void *eckem_newctx(void *provctx)

{

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

    if (ctx == NULL)

        return NULL;

    ctx->libctx = PROV_LIBCTX_OF(provctx);

    return ctx;

}

static void eckem_freectx(void *vectx)

{

    PROV_EC_CTX *ctx = (PROV_EC_CTX *)vectx;

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

    recipient_key_set(ctx, NULL);

    sender_authkey_set(ctx, NULL);

    OPENSSL_free(ctx);

}

static int ossl_ec_match_params(const EC_KEY *key1, const EC_KEY *key2)

{

    int ret;

    BN_CTX *ctx = NULL;

    const EC_GROUP *group1 = EC_KEY_get0_group(key1);

    const EC_GROUP *group2 = EC_KEY_get0_group(key2);

    ctx = BN_CTX_new_ex(ossl_ec_key_get_libctx(key1));

    if (ctx == NULL)

        return 0;

    ret = group1 != NULL

          && group2 != NULL

          && EC_GROUP_cmp(group1, group2, ctx) == 0;

    if (!ret)

        ERR_raise(ERR_LIB_PROV, PROV_R_MISMATCHING_DOMAIN_PARAMETERS);

    BN_CTX_free(ctx);

    return ret;

}

static int eckem_init(void *vctx, int operation, void *vec, void *vauth,

                      const OSSL_PARAM params[])

{

    int rv;

    PROV_EC_CTX *ctx = (PROV_EC_CTX *)vctx;

    EC_KEY *ec = vec;

    EC_KEY *auth = vauth;

    if (!ossl_prov_is_running())

        return 0;

    if (!eckey_check(ec, operation == EVP_PKEY_OP_DECAPSULATE))

        return 0;

    rv = recipient_key_set(ctx, ec);

    if (rv <= 0)

        return rv;

    if (auth != NULL) {

        if (!ossl_ec_match_params(ec, auth)

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

            || !sender_authkey_set(ctx, auth))

        return 0;

    }

    ctx->op = operation;

    return eckem_set_ctx_params(vctx, params);

}

static int eckem_encapsulate_init(void *vctx, void *vec,

                                   const OSSL_PARAM params[])

{

    return eckem_init(vctx, EVP_PKEY_OP_ENCAPSULATE, vec, NULL, params);

}

static int eckem_decapsulate_init(void *vctx, void *vec,

                                   const OSSL_PARAM params[])

{

    return eckem_init(vctx, EVP_PKEY_OP_DECAPSULATE, vec, NULL, params);

}

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

                                       const OSSL_PARAM params[])

{

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

}

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

                                       const OSSL_PARAM params[])

{

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

}

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

{

    PROV_EC_CTX *ctx = (PROV_EC_CTX *)vctx;

    const OSSL_PARAM *p;

    int mode;

    if (params == NULL)

        return 1;

    p = OSSL_PARAM_locate_const(params, OSSL_KEM_PARAM_IKME);

    if (p != NULL) {

        void *tmp = NULL;

        size_t tmplen = 0;

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

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

                return 0;

        }

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

        /* Set the ephemeral seed */

        ctx->ikm = tmp;

        ctx->ikmlen = tmplen;

    }

    p = OSSL_PARAM_locate_const(params, OSSL_KEM_PARAM_OPERATION);

    if (p != NULL) {

        if (p->data_type != OSSL_PARAM_UTF8_STRING)

            return 0;

        mode = ossl_eckem_modename2id(p->data);

        if (mode == KEM_MODE_UNDEFINED)

            return 0;

        ctx->mode = mode;

    }

    return 1;

}

static const OSSL_PARAM known_settable_eckem_ctx_params[] = {

    OSSL_PARAM_utf8_string(OSSL_KEM_PARAM_OPERATION, NULL, 0),

    OSSL_PARAM_octet_string(OSSL_KEM_PARAM_IKME, NULL, 0),

    OSSL_PARAM_END

};

static const OSSL_PARAM *eckem_settable_ctx_params(ossl_unused void *vctx,

                                                   ossl_unused void *provctx)

{

    return known_settable_eckem_ctx_params;

}

/*

 * 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;

    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 ec keygen.

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

 *

 * Params:

 *     ec An initialized ec key.

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

 *          this is of length alg->encodedprivlen).

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

 *     ikmlen size of the ikm buffer in bytes

 * Returns:

 *     1 if successful or 0 otherwise.

 */

int ossl_ec_dhkem_derive_private(EC_KEY *ec, BIGNUM *priv,

                                 const unsigned char *ikm, size_t ikmlen)

{

    int ret = 0;

    EVP_KDF_CTX *kdfctx = NULL;

    uint8_t suiteid[2];

    unsigned char prk[OSSL_HPKE_MAX_SECRET];

    unsigned char privbuf[OSSL_HPKE_MAX_PRIVATE];

    const BIGNUM *order;

    unsigned char counter = 0;

    const char *curve = ec_curvename_get0(ec);

    const OSSL_HPKE_KEM_INFO *info;

    if (curve == NULL)

        return -2;

    info = ossl_HPKE_KEM_INFO_find_curve(curve);

    if (info == NULL)

        return -2;

    kdfctx = ossl_kdf_ctx_create("HKDF", info->mdname,

                                 ossl_ec_key_get_libctx(ec),

                                 ossl_ec_key_get0_propq(ec));

    if (kdfctx == NULL)

        return 0;

    /* 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;

    }

    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;

    order = EC_GROUP_get0_order(EC_KEY_get0_group(ec));

    do {

        if (!ossl_hpke_labeled_expand(kdfctx, privbuf, info->Nsk,

                                      prk, info->Nsecret,

                                      LABEL_KEM, suiteid, sizeof(suiteid),

                                      OSSL_DHKEM_LABEL_CANDIDATE,

                                      &counter, 1))

            goto err;

        privbuf[0] &= info->bitmask;

        if (BN_bin2bn(privbuf, info->Nsk, priv) == NULL)

            goto err;

        if (counter == 0xFF) {

            ERR_raise(ERR_LIB_PROV, PROV_R_FAILED_TO_GENERATE_KEY);

            goto err;

        }

        counter++;

    } while (BN_is_zero(priv) || BN_cmp(priv, order) >= 0);

    ret = 1;

err:

    OPENSSL_cleanse(prk, sizeof(prk));

    OPENSSL_cleanse(privbuf, sizeof(privbuf));

    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 EC key, or NULL on failure.

 */

static EC_KEY *derivekey(PROV_EC_CTX *ctx,

                         const unsigned char *ikm, size_t ikmlen)

{

    int ret = 0;

    EC_KEY *key;

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

    size_t seedlen = ikmlen;

    unsigned char tmpbuf[OSSL_HPKE_MAX_PRIVATE];

    key = EC_KEY_new_ex(ctx->libctx, ctx->propq);

    if (key == NULL)

        goto err;

    if (!EC_KEY_set_group(key, EC_KEY_get0_group(ctx->recipient_key)))

        goto err;

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

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

        seedlen = ctx->info->Nsk;

        if (seedlen > sizeof(tmpbuf))

            goto err;

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

            goto err;

        seed = tmpbuf;

    }

    ret = ossl_ec_generate_key_dhkem(key, seed, seedlen);

err:

    if (seed != ikm)

        OPENSSL_cleanse(seed, seedlen);

    if (ret <= 0) {

        EC_KEY_free(key);

        key = NULL;

    }

    return key;

}

/*

 * Before doing a key exchange the public key of the peer needs to be checked

 * Note that the group check is not done here as we have already checked

 * that it only uses one of the approved curve names when the key was set.

 *

 * Returns 1 if the public key is valid, or 0 if it fails.

 */

static int check_publickey(const EC_KEY *pub)

{

    int ret = 0;

    BN_CTX *bnctx = BN_CTX_new_ex(ossl_ec_key_get_libctx(pub));

    if (bnctx == NULL)

        return 0;

    ret = ossl_ec_key_public_check(pub, bnctx);

    BN_CTX_free(bnctx);

    return ret;

}

/*

 * Do an ecdh key exchange.

 * dhkm = DH(sender, peer)

 *

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

 *       to avoid messy conversions back to EVP_PKEY.

 *

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

 */

static int generate_ecdhkm(const EC_KEY *sender, const EC_KEY *peer,

                           unsigned char *out, size_t maxout,

                           unsigned int secretsz)

{

    const EC_GROUP *group = EC_KEY_get0_group(sender);

    size_t secretlen = (EC_GROUP_get_degree(group) + 7) / 8;

    if (secretlen != secretsz || secretlen > maxout) {

        ERR_raise_data(ERR_LIB_PROV,  PROV_R_BAD_LENGTH, "secretsz invalid");

        return 0;

    }

    if (!check_publickey(peer))

        return 0;

    return ECDH_compute_key(out, secretlen, EC_KEY_get0_public_key(peer),

                            sender, NULL) > 0;

}

/*

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

 *

 * dhkm = Concat(ecdh(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 ECDH key derivation.

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

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

 *              It can be NULL.

 *     peerkey2 A optional public key used for a second ECDH 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_EC_CTX *ctx, unsigned char *secret,

                         const EC_KEY *privkey1, const EC_KEY *peerkey1,

                         const EC_KEY *privkey2, const EC_KEY *peerkey2,

                         const unsigned char *sender_pub,

                         const unsigned char *recipient_pub)

{

    int ret = 0;

    EVP_KDF_CTX *kdfctx = NULL;

    unsigned char sender_authpub[OSSL_HPKE_MAX_PUBLIC];

    unsigned char dhkm[OSSL_HPKE_MAX_PRIVATE * 2];

    unsigned char kemctx[OSSL_HPKE_MAX_PUBLIC * 3];

    size_t sender_authpublen;

    size_t kemctxlen = 0, dhkmlen = 0;

    const OSSL_HPKE_KEM_INFO *info = ctx->info;

    size_t encodedpublen = info->Npk;

    size_t encodedprivlen = info->Nsk;

    int auth = ctx->sender_authkey != NULL;

    if (!generate_ecdhkm(privkey1, peerkey1, dhkm, sizeof(dhkm), encodedprivlen))

        goto err;

    dhkmlen = encodedprivlen;

    kemctxlen = 2 * encodedpublen;

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

    if (auth) {

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

        if (!ecpubkey_todata(ctx->sender_authkey, sender_authpub,

                             &sender_authpublen, sizeof(sender_authpub)))

            goto err;

        if (sender_authpublen != encodedpublen) {

            ERR_raise_data(ERR_LIB_PROV, PROV_R_INVALID_KEY,

                           "Invalid sender auth public key");

            goto err;

        }

        if (!generate_ecdhkm(privkey2, peerkey2,

                             dhkm + dhkmlen, sizeof(dhkm) - dhkmlen,

                             encodedprivlen))

            goto err;

        dhkmlen += encodedprivlen;

        kemctxlen += encodedpublen;

    }

    if (kemctxlen > sizeof(kemctx))

        goto err;

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

    memcpy(kemctx, sender_pub, info->Npk);

    memcpy(kemctx + info->Npk, recipient_pub, info->Npk);

    if (auth)

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

    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_EC_CTX *ctx,

                       unsigned char *enc, size_t *enclen,

                       unsigned char *secret, size_t *secretlen)

{

    int ret = 0;

    EC_KEY *sender_ephemkey = NULL;

    unsigned char sender_pub[OSSL_HPKE_MAX_PUBLIC];

    unsigned char recipient_pub[OSSL_HPKE_MAX_PUBLIC];

    size_t sender_publen, recipient_publen;

    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);

    if (sender_ephemkey == NULL)

        goto err;

    if (!ecpubkey_todata(sender_ephemkey, sender_pub, &sender_publen,

                         sizeof(sender_pub))

            || !ecpubkey_todata(ctx->recipient_key, recipient_pub,

                                &recipient_publen, sizeof(recipient_pub)))

        goto err;

    if (sender_publen != info->Npk

            || recipient_publen != sender_publen) {

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

        goto err;

    }

    if (!derive_secret(ctx, secret,

                       sender_ephemkey, ctx->recipient_key,

                       ctx->sender_authkey, ctx->recipient_key,

                       sender_pub, recipient_pub))

        goto err;

    /* Return the senders ephemeral public key in encoded form */

    memcpy(enc, sender_pub, sender_publen);

    *enclen = sender_publen;

    *secretlen = info->Nsecret;

    ret = 1;

err:

    EC_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_EC_CTX *ctx,

                       unsigned char *secret, size_t *secretlen,

                       const unsigned char *enc, size_t enclen)

{

    int ret = 0;

    EC_KEY *sender_ephempubkey = NULL;

    const OSSL_HPKE_KEM_INFO *info = ctx->info;

    unsigned char recipient_pub[OSSL_HPKE_MAX_PUBLIC];

    size_t recipient_publen;

    size_t encodedpublen = info->Npk;

    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 != encodedpublen) {

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

        return 0;

    }

    sender_ephempubkey = eckey_frompub(ctx->recipient_key, enc, enclen);

    if (sender_ephempubkey == NULL)

        goto err;

    if (!ecpubkey_todata(ctx->recipient_key, recipient_pub, &recipient_publen,

                         sizeof(recipient_pub)))

        goto err;

    if (recipient_publen != encodedpublen) {

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

        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:

    EC_KEY_free(sender_ephempubkey);

    return ret;

}

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

                             unsigned char *secret, size_t *secretlen)

{

    PROV_EC_CTX *ctx = (PROV_EC_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 eckem_decapsulate(void *vctx, unsigned char *out, size_t *outlen,

                             const unsigned char *in, size_t inlen)

{

    PROV_EC_CTX *ctx = (PROV_EC_CTX *)vctx;

    switch (ctx->mode) {

        case KEM_MODE_DHKEM:

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

        default:

            ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_MODE);

            return -2;

    }

}

const OSSL_DISPATCH ossl_ec_asym_kem_functions[] = {

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

    { OSSL_FUNC_KEM_ENCAPSULATE_INIT,

      (void (*)(void))eckem_encapsulate_init },

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

    { OSSL_FUNC_KEM_DECAPSULATE_INIT,

      (void (*)(void))eckem_decapsulate_init },

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

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

    { OSSL_FUNC_KEM_SET_CTX_PARAMS,

      (void (*)(void))eckem_set_ctx_params },

    { OSSL_FUNC_KEM_SETTABLE_CTX_PARAMS,

      (void (*)(void))eckem_settable_ctx_params },

    { OSSL_FUNC_KEM_AUTH_ENCAPSULATE_INIT,

      (void (*)(void))eckem_auth_encapsulate_init },

    { OSSL_FUNC_KEM_AUTH_DECAPSULATE_INIT,

      (void (*)(void))eckem_auth_decapsulate_init },

    OSSL_DISPATCH_END

};