text: /*
   * Copyright (C) 2013-2015 Marc Hoersken <info@marc-hoersken.de>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms,
   * with or without modification, are permitted provided
   * that the following conditions are met:
   *
   *   Redistributions of source code must retain the above
   *   copyright notice, this list of conditions and the
   *   following disclaimer.
   *
   *   Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials
   *   provided with the distribution.
   *
   *   Neither the name of the copyright holder nor the names
   *   of any other contributors may be used to endorse or
   *   promote products derived from this software without
   *   specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
   * USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
   * OF SUCH DAMAGE.
   */
  
  /* required for cross-compilation against the w64 mingw-runtime package */
  #if defined(_WIN32_WINNT) && (_WIN32_WINNT < 0x0600)
  #undef _WIN32_WINNT
  #endif
  #ifndef _WIN32_WINNT
  #define _WIN32_WINNT 0x0600
  #endif
  
  #include <windows.h>
  #include <bcrypt.h>
  
  
  #define LIBSSH2_MD5 1
  
  #define LIBSSH2_HMAC_RIPEMD 0
  #define LIBSSH2_HMAC_SHA256 1
  #define LIBSSH2_HMAC_SHA512 1
  
  #define LIBSSH2_AES 1
  #define LIBSSH2_AES_CTR 1
  #define LIBSSH2_BLOWFISH 0
  #define LIBSSH2_RC4 1
  #define LIBSSH2_CAST 0
  #define LIBSSH2_3DES 1
  
  #define LIBSSH2_RSA 1
  #define LIBSSH2_DSA 1
  #define LIBSSH2_ECDSA 0
  #define LIBSSH2_ED25519 0
  
  #define MD5_DIGEST_LENGTH 16
  #define SHA_DIGEST_LENGTH 20
  #define SHA256_DIGEST_LENGTH 32
  #define SHA512_DIGEST_LENGTH 64
  
  #define EC_MAX_POINT_LEN ((528 * 2 / 8) + 1)
  
  #if LIBSSH2_ECDSA
  #else
  #define _libssh2_ec_key void
  #endif
  
  /*******************************************************************/
  /*
   * Windows CNG backend: Global context handles
   */
  
  struct _libssh2_wincng_ctx {
      BCRYPT_ALG_HANDLE hAlgRNG;
      BCRYPT_ALG_HANDLE hAlgHashMD5;
      BCRYPT_ALG_HANDLE hAlgHashSHA1;
      BCRYPT_ALG_HANDLE hAlgHashSHA256;
      BCRYPT_ALG_HANDLE hAlgHashSHA512;
      BCRYPT_ALG_HANDLE hAlgHmacMD5;
      BCRYPT_ALG_HANDLE hAlgHmacSHA1;
      BCRYPT_ALG_HANDLE hAlgHmacSHA256;
      BCRYPT_ALG_HANDLE hAlgHmacSHA512;
      BCRYPT_ALG_HANDLE hAlgRSA;
      BCRYPT_ALG_HANDLE hAlgDSA;
      BCRYPT_ALG_HANDLE hAlgAES_CBC;
      BCRYPT_ALG_HANDLE hAlgAES_ECB;
      BCRYPT_ALG_HANDLE hAlgRC4_NA;
      BCRYPT_ALG_HANDLE hAlg3DES_CBC;
  };
  
  struct _libssh2_wincng_ctx _libssh2_wincng;
  
  
  /*******************************************************************/
  /*
   * Windows CNG backend: Generic functions
   */
  
  void _libssh2_wincng_init(void);
  void _libssh2_wincng_free(void);
  
  #define libssh2_crypto_init() \
    _libssh2_wincng_init()
  #define libssh2_crypto_exit() \
    _libssh2_wincng_free()
  
  #define _libssh2_random(buf, len) \
    _libssh2_wincng_random(buf, len)
  
  #define libssh2_prepare_iovec(vec, len)  /* Empty. */
  
  
  /*******************************************************************/
  /*
   * Windows CNG backend: Hash structure
   */
  
  typedef struct __libssh2_wincng_hash_ctx {
      BCRYPT_HASH_HANDLE hHash;
      unsigned char *pbHashObject;
      unsigned long dwHashObject;
      unsigned long cbHash;
  } _libssh2_wincng_hash_ctx;
  
  /*
   * Windows CNG backend: Hash functions
   */
  
  #define libssh2_sha1_ctx _libssh2_wincng_hash_ctx
  #define libssh2_sha1_init(ctx) \
    (_libssh2_wincng_hash_init(ctx, _libssh2_wincng.hAlgHashSHA1, \
                              SHA_DIGEST_LENGTH, NULL, 0) == 0)
  #define libssh2_sha1_update(ctx, data, datalen) \
    _libssh2_wincng_hash_update(&ctx, (unsigned char *) data, datalen)
  #define libssh2_sha1_final(ctx, hash) \
    _libssh2_wincng_hash_final(&ctx, hash)
  #define libssh2_sha1(data, datalen, hash) \
    _libssh2_wincng_hash(data, datalen, _libssh2_wincng.hAlgHashSHA1, \
                         hash, SHA_DIGEST_LENGTH)
  
  #define libssh2_sha256_ctx _libssh2_wincng_hash_ctx
  #define libssh2_sha256_init(ctx) \
    (_libssh2_wincng_hash_init(ctx, _libssh2_wincng.hAlgHashSHA256, \
                              SHA256_DIGEST_LENGTH, NULL, 0) == 0)
  #define libssh2_sha256_update(ctx, data, datalen) \
    _libssh2_wincng_hash_update(&ctx, (unsigned char *) data, datalen)
  #define libssh2_sha256_final(ctx, hash) \
    _libssh2_wincng_hash_final(&ctx, hash)
  #define libssh2_sha256(data, datalen, hash) \
    _libssh2_wincng_hash(data, datalen, _libssh2_wincng.hAlgHashSHA256, \
                         hash, SHA256_DIGEST_LENGTH)
  
  #define libssh2_sha512_ctx _libssh2_wincng_hash_ctx
  #define libssh2_sha512_init(ctx) \
    (_libssh2_wincng_hash_init(ctx, _libssh2_wincng.hAlgHashSHA512, \
                              SHA512_DIGEST_LENGTH, NULL, 0) == 0)
  #define libssh2_sha512_update(ctx, data, datalen) \
    _libssh2_wincng_hash_update(&ctx, (unsigned char *) data, datalen)
  #define libssh2_sha512_final(ctx, hash) \
    _libssh2_wincng_hash_final(&ctx, hash)
  #define libssh2_sha512(data, datalen, hash) \
    _libssh2_wincng_hash(data, datalen, _libssh2_wincng.hAlgHashSHA512, \
                         hash, SHA512_DIGEST_LENGTH)
  
  #define libssh2_md5_ctx _libssh2_wincng_hash_ctx
  #define libssh2_md5_init(ctx) \
    (_libssh2_wincng_hash_init(ctx, _libssh2_wincng.hAlgHashMD5, \
                              MD5_DIGEST_LENGTH, NULL, 0) == 0)
  #define libssh2_md5_update(ctx, data, datalen) \
    _libssh2_wincng_hash_update(&ctx, (unsigned char *) data, datalen)
  #define libssh2_md5_final(ctx, hash) \
    _libssh2_wincng_hash_final(&ctx, hash)
  #define libssh2_md5(data, datalen, hash) \
    _libssh2_wincng_hash(data, datalen, _libssh2_wincng.hAlgHashMD5, \
                         hash, MD5_DIGEST_LENGTH)
  
  /*
   * Windows CNG backend: HMAC functions
   */
  
  #define libssh2_hmac_ctx _libssh2_wincng_hash_ctx
  #define libssh2_hmac_ctx_init(ctx)
  #define libssh2_hmac_sha1_init(ctx, key, keylen) \
    _libssh2_wincng_hash_init(ctx, _libssh2_wincng.hAlgHmacSHA1, \
                              SHA_DIGEST_LENGTH, key, keylen)
  #define libssh2_hmac_md5_init(ctx, key, keylen) \
    _libssh2_wincng_hash_init(ctx, _libssh2_wincng.hAlgHmacMD5, \
                              MD5_DIGEST_LENGTH, key, keylen)
  #define libssh2_hmac_ripemd160_init(ctx, key, keylen)
    /* not implemented */
  #define libssh2_hmac_sha256_init(ctx, key, keylen) \
    _libssh2_wincng_hash_init(ctx, _libssh2_wincng.hAlgHmacSHA256, \
                              SHA256_DIGEST_LENGTH, key, keylen)
  #define libssh2_hmac_sha512_init(ctx, key, keylen) \
    _libssh2_wincng_hash_init(ctx, _libssh2_wincng.hAlgHmacSHA512, \
                              SHA512_DIGEST_LENGTH, key, keylen)
  #define libssh2_hmac_update(ctx, data, datalen) \
    _libssh2_wincng_hash_update(&ctx, (unsigned char *) data, datalen)
  #define libssh2_hmac_final(ctx, hash) \
    _libssh2_wincng_hmac_final(&ctx, hash)
  #define libssh2_hmac_cleanup(ctx) \
    _libssh2_wincng_hmac_cleanup(ctx)
  
  
  /*******************************************************************/
  /*
   * Windows CNG backend: Key Context structure
   */
  
  typedef struct __libssh2_wincng_key_ctx {
      BCRYPT_KEY_HANDLE hKey;
      unsigned char *pbKeyObject;
      unsigned long cbKeyObject;
  } _libssh2_wincng_key_ctx;
  
  
  /*
   * Windows CNG backend: RSA functions
   */
  
  #define libssh2_rsa_ctx _libssh2_wincng_key_ctx
  #define _libssh2_rsa_new(rsactx, e, e_len, n, n_len, \
                           d, d_len, p, p_len, q, q_len, \
                           e1, e1_len, e2, e2_len, c, c_len) \
    _libssh2_wincng_rsa_new(rsactx, e, e_len, n, n_len, \
                            d, d_len, p, p_len, q, q_len, \
                            e1, e1_len, e2, e2_len, c, c_len)
  #define _libssh2_rsa_new_private(rsactx, s, filename, passphrase) \
    _libssh2_wincng_rsa_new_private(rsactx, s, filename, passphrase)
  #define _libssh2_rsa_new_private_frommemory(rsactx, s, filedata, \
                                              filedata_len, passphrase) \
    _libssh2_wincng_rsa_new_private_frommemory(rsactx, s, filedata, \
                                               filedata_len, passphrase)
  #define _libssh2_rsa_sha1_sign(s, rsactx, hash, hash_len, sig, sig_len) \
    _libssh2_wincng_rsa_sha1_sign(s, rsactx, hash, hash_len, sig, sig_len)
  #define _libssh2_rsa_sha1_verify(rsactx, sig, sig_len, m, m_len) \
    _libssh2_wincng_rsa_sha1_verify(rsactx, sig, sig_len, m, m_len)
  #define _libssh2_rsa_free(rsactx) \
    _libssh2_wincng_rsa_free(rsactx)
  
  /*
   * Windows CNG backend: DSA functions
   */
  
  #define libssh2_dsa_ctx _libssh2_wincng_key_ctx
  #define _libssh2_dsa_new(dsactx, p, p_len, q, q_len, \
                           g, g_len, y, y_len, x, x_len) \
    _libssh2_wincng_dsa_new(dsactx, p, p_len, q, q_len, \
                            g, g_len, y, y_len, x, x_len)
  #define _libssh2_dsa_new_private(dsactx, s, filename, passphrase) \
    _libssh2_wincng_dsa_new_private(dsactx, s, filename, passphrase)
  #define _libssh2_dsa_new_private_frommemory(dsactx, s, filedata, \
                                              filedata_len, passphrase) \
    _libssh2_wincng_dsa_new_private_frommemory(dsactx, s, filedata, \
                                               filedata_len, passphrase)
  #define _libssh2_dsa_sha1_sign(dsactx, hash, hash_len, sig) \
    _libssh2_wincng_dsa_sha1_sign(dsactx, hash, hash_len, sig)
  #define _libssh2_dsa_sha1_verify(dsactx, sig, m, m_len) \
    _libssh2_wincng_dsa_sha1_verify(dsactx, sig, m, m_len)
  #define _libssh2_dsa_free(dsactx) \
    _libssh2_wincng_dsa_free(dsactx)
  
  /*
   * Windows CNG backend: Key functions
   */
  
  #define _libssh2_pub_priv_keyfile(s, m, m_len, p, p_len, pk, pw) \
    _libssh2_wincng_pub_priv_keyfile(s, m, m_len, p, p_len, pk, pw)
  #define _libssh2_pub_priv_keyfilememory(s, m, m_len, p, p_len, \
                                                       pk, pk_len, pw) \
    _libssh2_wincng_pub_priv_keyfilememory(s, m, m_len, p, p_len, \
                                                        pk, pk_len, pw)
  
  
  /*******************************************************************/
  /*
   * Windows CNG backend: Cipher Context structure
   */
  
  struct _libssh2_wincng_cipher_ctx {
      BCRYPT_KEY_HANDLE hKey;
      unsigned char *pbKeyObject;
      unsigned char *pbIV;
      unsigned char *pbCtr;
      unsigned long dwKeyObject;
      unsigned long dwIV;
      unsigned long dwBlockLength;
      unsigned long dwCtrLength;
  };
  
  #define _libssh2_cipher_ctx struct _libssh2_wincng_cipher_ctx
  
  /*
   * Windows CNG backend: Cipher Type structure
   */
  
  struct _libssh2_wincng_cipher_type {
      BCRYPT_ALG_HANDLE *phAlg;
      unsigned long dwKeyLength;
      int useIV;      /* TODO: Convert to bool when a C89 compatible bool type
                         is defined */
      int ctrMode;
  };
  
  #define _libssh2_cipher_type(type) struct _libssh2_wincng_cipher_type type
  
  #define _libssh2_cipher_aes256ctr { &_libssh2_wincng.hAlgAES_ECB, 32, 0, 1 }
  #define _libssh2_cipher_aes192ctr { &_libssh2_wincng.hAlgAES_ECB, 24, 0, 1 }
  #define _libssh2_cipher_aes128ctr { &_libssh2_wincng.hAlgAES_ECB, 16, 0, 1 }
  #define _libssh2_cipher_aes256 { &_libssh2_wincng.hAlgAES_CBC, 32, 1, 0 }
  #define _libssh2_cipher_aes192 { &_libssh2_wincng.hAlgAES_CBC, 24, 1, 0 }
  #define _libssh2_cipher_aes128 { &_libssh2_wincng.hAlgAES_CBC, 16, 1, 0 }
  #define _libssh2_cipher_arcfour { &_libssh2_wincng.hAlgRC4_NA, 16, 0, 0 }
  #define _libssh2_cipher_3des { &_libssh2_wincng.hAlg3DES_CBC, 24, 1, 0 }
  
  /*
   * Windows CNG backend: Cipher functions
   */
  
  #define _libssh2_cipher_init(ctx, type, iv, secret, encrypt) \
    _libssh2_wincng_cipher_init(ctx, type, iv, secret, encrypt)
  #define _libssh2_cipher_crypt(ctx, type, encrypt, block, blocklen) \
    _libssh2_wincng_cipher_crypt(ctx, type, encrypt, block, blocklen)
  #define _libssh2_cipher_dtor(ctx) \
    _libssh2_wincng_cipher_dtor(ctx)
  
  /*******************************************************************/
  /*
   * Windows CNG backend: BigNumber Context
   */
  
  #define _libssh2_bn_ctx int /* not used */
  #define _libssh2_bn_ctx_new() 0 /* not used */
  #define _libssh2_bn_ctx_free(bnctx) ((void)0) /* not used */
  
  
  /*******************************************************************/
  /*
   * Windows CNG backend: BigNumber structure
   */
  
  struct _libssh2_wincng_bignum {
      unsigned char *bignum;
      unsigned long length;
  };
  
  #define _libssh2_bn struct _libssh2_wincng_bignum
  
  /*
   * Windows CNG backend: BigNumber functions
   */
  
  _libssh2_bn *_libssh2_wincng_bignum_init(void);
  
  #define _libssh2_bn_init() \
    _libssh2_wincng_bignum_init()
  #define _libssh2_bn_init_from_bin() \
    _libssh2_bn_init()
  #define _libssh2_bn_set_word(bn, word) \
    _libssh2_wincng_bignum_set_word(bn, word)
  #define _libssh2_bn_from_bin(bn, len, bin) \
    _libssh2_wincng_bignum_from_bin(bn, len, bin)
  #define _libssh2_bn_to_bin(bn, bin) \
    _libssh2_wincng_bignum_to_bin(bn, bin)
  #define _libssh2_bn_bytes(bn) bn->length
  #define _libssh2_bn_bits(bn) \
    _libssh2_wincng_bignum_bits(bn)
  #define _libssh2_bn_free(bn) \
    _libssh2_wincng_bignum_free(bn)
  
  /*
   * Windows CNG backend: Diffie-Hellman support
   */
  
  #define _libssh2_dh_ctx struct _libssh2_wincng_bignum *
  #define libssh2_dh_init(dhctx) _libssh2_dh_init(dhctx)
  #define libssh2_dh_key_pair(dhctx, public, g, p, group_order, bnctx) \
          _libssh2_dh_key_pair(dhctx, public, g, p, group_order)
  #define libssh2_dh_secret(dhctx, secret, f, p, bnctx) \
          _libssh2_dh_secret(dhctx, secret, f, p)
  #define libssh2_dh_dtor(dhctx) _libssh2_dh_dtor(dhctx)
  
  /*******************************************************************/
  /*
   * Windows CNG backend: forward declarations
   */
  void _libssh2_wincng_init(void);
  void _libssh2_wincng_free(void);
  int _libssh2_wincng_random(void *buf, int len);
  
  int
  _libssh2_wincng_hash_init(_libssh2_wincng_hash_ctx *ctx,
                            BCRYPT_ALG_HANDLE hAlg, unsigned long hashlen,
                            unsigned char *key, unsigned long keylen);
  int
  _libssh2_wincng_hash_update(_libssh2_wincng_hash_ctx *ctx,
                              const unsigned char *data, unsigned long datalen);
  int
  _libssh2_wincng_hash_final(_libssh2_wincng_hash_ctx *ctx,
                             unsigned char *hash);
  int
  _libssh2_wincng_hash(unsigned char *data, unsigned long datalen,
                       BCRYPT_ALG_HANDLE hAlg,
                       unsigned char *hash, unsigned long hashlen);
  
  int
  _libssh2_wincng_hmac_final(_libssh2_wincng_hash_ctx *ctx,
                             unsigned char *hash);
  void
  _libssh2_wincng_hmac_cleanup(_libssh2_wincng_hash_ctx *ctx);
  
  int
  _libssh2_wincng_key_sha1_verify(_libssh2_wincng_key_ctx *ctx,
                                  const unsigned char *sig,
                                  unsigned long sig_len,
                                  const unsigned char *m,
                                  unsigned long m_len,
                                  unsigned long flags);
  
  int
  _libssh2_wincng_rsa_new(libssh2_rsa_ctx **rsa,
                          const unsigned char *edata,
                          unsigned long elen,
                          const unsigned char *ndata,
                          unsigned long nlen,
                          const unsigned char *ddata,
                          unsigned long dlen,
                          const unsigned char *pdata,
                          unsigned long plen,
                          const unsigned char *qdata,
                          unsigned long qlen,
                          const unsigned char *e1data,
                          unsigned long e1len,
                          const unsigned char *e2data,
                          unsigned long e2len,
                          const unsigned char *coeffdata,
                          unsigned long coefflen);
  int
  _libssh2_wincng_rsa_new_private(libssh2_rsa_ctx **rsa,
                                  LIBSSH2_SESSION *session,
                                  const char *filename,
                                  const unsigned char *passphrase);
  int
  _libssh2_wincng_rsa_new_private_frommemory(libssh2_rsa_ctx **rsa,
                                             LIBSSH2_SESSION *session,
                                             const char *filedata,
                                             size_t filedata_len,
                                             unsigned const char *passphrase);
  int
  _libssh2_wincng_rsa_sha1_verify(libssh2_rsa_ctx *rsa,
                                  const unsigned char *sig,
                                  unsigned long sig_len,
                                  const unsigned char *m,
                                  unsigned long m_len);
  int
  _libssh2_wincng_rsa_sha1_sign(LIBSSH2_SESSION *session,
                                libssh2_rsa_ctx *rsa,
                                const unsigned char *hash,
                                size_t hash_len,
                                unsigned char **signature,
                                size_t *signature_len);
  void
  _libssh2_wincng_rsa_free(libssh2_rsa_ctx *rsa);
  
  #if LIBSSH2_DSA
  int
  _libssh2_wincng_dsa_new(libssh2_dsa_ctx **dsa,
                          const unsigned char *pdata,
                          unsigned long plen,
                          const unsigned char *qdata,
                          unsigned long qlen,
                          const unsigned char *gdata,
                          unsigned long glen,
                          const unsigned char *ydata,
                          unsigned long ylen,
                          const unsigned char *xdata,
                          unsigned long xlen);
  int
  _libssh2_wincng_dsa_new_private(libssh2_dsa_ctx **dsa,
                                  LIBSSH2_SESSION *session,
                                  const char *filename,
                                  const unsigned char *passphrase);
  int
  _libssh2_wincng_dsa_new_private_frommemory(libssh2_dsa_ctx **dsa,
                                             LIBSSH2_SESSION *session,
                                             const char *filedata,
                                             size_t filedata_len,
                                             unsigned const char *passphrase);
  int
  _libssh2_wincng_dsa_sha1_verify(libssh2_dsa_ctx *dsa,
                                  const unsigned char *sig_fixed,
                                  const unsigned char *m,
                                  unsigned long m_len);
  int
  _libssh2_wincng_dsa_sha1_sign(libssh2_dsa_ctx *dsa,
                                const unsigned char *hash,
                                unsigned long hash_len,
                                unsigned char *sig_fixed);
  void
  _libssh2_wincng_dsa_free(libssh2_dsa_ctx *dsa);
  #endif
  
  int
  _libssh2_wincng_pub_priv_keyfile(LIBSSH2_SESSION *session,
                                   unsigned char **method,
                                   size_t *method_len,
                                   unsigned char **pubkeydata,
                                   size_t *pubkeydata_len,
                                   const char *privatekey,
                                   const char *passphrase);
  int
  _libssh2_wincng_pub_priv_keyfilememory(LIBSSH2_SESSION *session,
                                         unsigned char **method,
                                         size_t *method_len,
                                         unsigned char **pubkeydata,
                                         size_t *pubkeydata_len,
                                         const char *privatekeydata,
                                         size_t privatekeydata_len,
                                         const char *passphrase);
  
  int
  _libssh2_wincng_cipher_init(_libssh2_cipher_ctx *ctx,
                              _libssh2_cipher_type(type),
                              unsigned char *iv,
                              unsigned char *secret,
                              int encrypt);
  int
  _libssh2_wincng_cipher_crypt(_libssh2_cipher_ctx *ctx,
                               _libssh2_cipher_type(type),
                               int encrypt,
                               unsigned char *block,
                               size_t blocklen);
  void
  _libssh2_wincng_cipher_dtor(_libssh2_cipher_ctx *ctx);
  
  _libssh2_bn *
  _libssh2_wincng_bignum_init(void);
  int
  _libssh2_wincng_bignum_set_word(_libssh2_bn *bn, unsigned long word);
  unsigned long
  _libssh2_wincng_bignum_bits(const _libssh2_bn *bn);
  void
  _libssh2_wincng_bignum_from_bin(_libssh2_bn *bn, unsigned long len,
                                  const unsigned char *bin);
  void
  _libssh2_wincng_bignum_to_bin(const _libssh2_bn *bn, unsigned char *bin);
  void
  _libssh2_wincng_bignum_free(_libssh2_bn *bn);
  extern void
  _libssh2_dh_init(_libssh2_dh_ctx *dhctx);
  extern int
  _libssh2_dh_key_pair(_libssh2_dh_ctx *dhctx, _libssh2_bn *public,
                       _libssh2_bn *g, _libssh2_bn *p, int group_order);
  extern int
  _libssh2_dh_secret(_libssh2_dh_ctx *dhctx, _libssh2_bn *secret,
                     _libssh2_bn *f, _libssh2_bn *p);
  extern void
  _libssh2_dh_dtor(_libssh2_dh_ctx *dhctx);
  