#include "includes.h"

#include "algo.h"

#include "buffer.h"

#include "session.h"

#include "bignum.h"

#include "dbrandom.h"

#include "crypto_desc.h"

#include "curve25519.h"

#include "kex.h"

/* PQ hybrids also use curve25519 internally */

#if DROPBEAR_CURVE25519_DEP

struct kex_curve25519_param *gen_kexcurve25519_param() {

    /* Per http://cr.yp.to/ecdh.html */

    struct kex_curve25519_param *param = m_malloc(sizeof(*param));

    const unsigned char basepoint[32] = {9};

    genrandom(param->priv, CURVE25519_LEN);

    dropbear_curve25519_scalarmult(param->pub, param->priv, basepoint);

    return param;

}

void free_kexcurve25519_param(struct kex_curve25519_param *param) {

    m_burn(param->priv, CURVE25519_LEN);

    m_free(param);

}

/* out must be CURVE25519_LEN */

void kexcurve25519_derive(const struct kex_curve25519_param *param, const buffer *buf_pub_them,

    unsigned char *out) {

    char zeroes[CURVE25519_LEN] = {0};

    if (buf_pub_them->len != CURVE25519_LEN)

    {

        dropbear_exit("Bad curve25519");

    }

    dropbear_curve25519_scalarmult(out, param->priv, buf_pub_them->data);

    if (constant_time_memcmp(zeroes, out, CURVE25519_LEN) == 0) {

        dropbear_exit("Bad curve25519");

    }

}

#endif /* DROPBEAR_CURVE25519_DEP */

#if DROPBEAR_CURVE25519

/* Only required for x25519 directly */

void kexcurve25519_comb_key(const struct kex_curve25519_param *param, const buffer *buf_pub_them,

    sign_key *hostkey) {

    unsigned char out[CURVE25519_LEN];

    const unsigned char* Q_C = NULL;

    const unsigned char* Q_S = NULL;

    kexcurve25519_derive(param, buf_pub_them, out);

    m_mp_alloc_init_multi(&ses.dh_K, NULL);

    bytes_to_mp(ses.dh_K, out, CURVE25519_LEN);

    m_burn(out, sizeof(out));

    /* Create the remainder of the hash buffer, to generate the exchange hash.

       See RFC5656 section 4 page 7 */

    if (IS_DROPBEAR_CLIENT) {

        Q_C = param->pub;

        Q_S = buf_pub_them->data;

    } else {

        Q_S = param->pub;

        Q_C = buf_pub_them->data;

    }

    /* K_S, the host key */

    buf_put_pub_key(ses.kexhashbuf, hostkey, ses.newkeys->algo_hostkey);

    /* Q_C, client's ephemeral public key octet string */

    buf_putstring(ses.kexhashbuf, (const char*)Q_C, CURVE25519_LEN);

    /* Q_S, server's ephemeral public key octet string */

    buf_putstring(ses.kexhashbuf, (const char*)Q_S, CURVE25519_LEN);

    /* K, the shared secret */

    buf_putmpint(ses.kexhashbuf, ses.dh_K);

    /* calculate the hash H to sign */

    finish_kexhashbuf();

}

#endif /* DROPBEAR_CURVE25519 */