/*
 * Copyright 2006-2019 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (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
 */

#include <openssl/evp.h>

#include <assert.h>

#include <openssl/dh.h>
#include <openssl/err.h>
#include <openssl/mem.h>

#include "internal.h"


typedef struct dh_pkey_ctx_st {
  int pad;
} DH_PKEY_CTX;

static int pkey_dh_init(EVP_PKEY_CTX *ctx) {
  DH_PKEY_CTX *dctx = OPENSSL_zalloc(sizeof(DH_PKEY_CTX));
  if (dctx == NULL) {
    return 0;
  }

  ctx->data = dctx;
  return 1;
}

static int pkey_dh_copy(EVP_PKEY_CTX *dst, EVP_PKEY_CTX *src) {
  if (!pkey_dh_init(dst)) {
    return 0;
  }

  const DH_PKEY_CTX *sctx = src->data;
  DH_PKEY_CTX *dctx = dst->data;
  dctx->pad = sctx->pad;
  return 1;
}

static void pkey_dh_cleanup(EVP_PKEY_CTX *ctx) {
  OPENSSL_free(ctx->data);
  ctx->data = NULL;
}

static int pkey_dh_keygen(EVP_PKEY_CTX *ctx, EVP_PKEY *pkey) {
  DH *dh = DH_new();
  if (dh == NULL || !EVP_PKEY_assign_DH(pkey, dh)) {
    DH_free(dh);
    return 0;
  }

  if (ctx->pkey != NULL && !EVP_PKEY_copy_parameters(pkey, ctx->pkey)) {
    return 0;
  }

  return DH_generate_key(dh);
}

static int pkey_dh_derive(EVP_PKEY_CTX *ctx, uint8_t *out, size_t *out_len) {
  DH_PKEY_CTX *dctx = ctx->data;
  if (ctx->pkey == NULL || ctx->peerkey == NULL) {
    OPENSSL_PUT_ERROR(EVP, EVP_R_KEYS_NOT_SET);
    return 0;
  }

  DH *our_key = ctx->pkey->pkey;
  DH *peer_key = ctx->peerkey->pkey;
  if (our_key == NULL || peer_key == NULL) {
    OPENSSL_PUT_ERROR(EVP, EVP_R_KEYS_NOT_SET);
    return 0;
  }

  const BIGNUM *pub_key = DH_get0_pub_key(peer_key);
  if (pub_key == NULL) {
    OPENSSL_PUT_ERROR(EVP, EVP_R_KEYS_NOT_SET);
    return 0;
  }

  if (out == NULL) {
    *out_len = DH_size(our_key);
    return 1;
  }

  if (*out_len < (size_t)DH_size(our_key)) {
    OPENSSL_PUT_ERROR(EVP, EVP_R_BUFFER_TOO_SMALL);
    return 0;
  }

  int ret = dctx->pad ? DH_compute_key_padded(out, pub_key, our_key)
                      : DH_compute_key(out, pub_key, our_key);
  if (ret < 0) {
    return 0;
  }

  assert(ret <= DH_size(our_key));
  *out_len = (size_t)ret;
  return 1;
}

static int pkey_dh_ctrl(EVP_PKEY_CTX *ctx, int type, int p1, void *p2) {
  DH_PKEY_CTX *dctx = ctx->data;
  switch (type) {
    case EVP_PKEY_CTRL_PEER_KEY:
      // |EVP_PKEY_derive_set_peer| requires the key implement this command,
      // even if it is a no-op.
      return 1;

    case EVP_PKEY_CTRL_DH_PAD:
      dctx->pad = p1;
      return 1;

    default:
      OPENSSL_PUT_ERROR(EVP, EVP_R_COMMAND_NOT_SUPPORTED);
      return 0;
  }
}

const EVP_PKEY_METHOD dh_pkey_meth = {
    .pkey_id = EVP_PKEY_DH,
    .init = pkey_dh_init,
    .copy = pkey_dh_copy,
    .cleanup = pkey_dh_cleanup,
    .keygen = pkey_dh_keygen,
    .derive = pkey_dh_derive,
    .ctrl = pkey_dh_ctrl,
};

int EVP_PKEY_CTX_set_dh_pad(EVP_PKEY_CTX *ctx, int pad) {
  return EVP_PKEY_CTX_ctrl(ctx, EVP_PKEY_DH, EVP_PKEY_OP_DERIVE,
                           EVP_PKEY_CTRL_DH_PAD, pad, NULL);
}