include/openssl/dh.h - boringssl - Git at Google

 // Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 #ifndef OPENSSL_HEADER_DH_H
 #define OPENSSL_HEADER_DH_H

 #include <openssl/base.h>   // IWYU pragma: export

 #if defined(__cplusplus)
 extern "C" {
 #endif


 // DH contains functions for performing Diffie-Hellman key agreement in
 // multiplicative groups.
 //
 // This module is deprecated and retained for legacy reasons only. It is not
 // considered a priority for performance or hardening work. Do not use it in
 // new code. Use X25519 or ECDH with P-256 instead.


 // Allocation and destruction.
 //
 // A `DH` object represents a Diffie-Hellman key or group parameters. A given
 // object may be used concurrently on multiple threads by non-mutating
 // functions, provided no other thread is concurrently calling a mutating
 // function. Unless otherwise documented, functions which take a `const` pointer
 // are non-mutating and functions which take a non-`const` pointer are mutating.

 // DH_new returns a new, empty DH object or NULL on error.
 OPENSSL_EXPORT DH *DH_new(void);

 // DH_free decrements the reference count of `dh` and frees it if the reference
 // count drops to zero.
 OPENSSL_EXPORT void DH_free(DH *dh);

 // DH_up_ref increments the reference count of `dh` and returns one. It does not
 // mutate `dh` for thread-safety purposes and may be used concurrently.
 OPENSSL_EXPORT int DH_up_ref(DH *dh);


 // Properties.

 // OPENSSL_DH_MAX_MODULUS_BITS is the maximum supported Diffie-Hellman group
 // modulus, in bits.
 #define OPENSSL_DH_MAX_MODULUS_BITS 8192

 // DH_bits returns the size of `dh`'s group modulus, in bits.
 OPENSSL_EXPORT unsigned DH_bits(const DH *dh);

 // DH_size returns the number of bytes in the DH group's prime.
 OPENSSL_EXPORT int DH_size(const DH *dh);

 // DH_get0_pub_key returns `dh`'s public key.
 OPENSSL_EXPORT const BIGNUM *DH_get0_pub_key(const DH *dh);

 // DH_get0_priv_key returns `dh`'s private key, or NULL if `dh` is a public key.
 OPENSSL_EXPORT const BIGNUM *DH_get0_priv_key(const DH *dh);

 // DH_get0_p returns `dh`'s group modulus.
 OPENSSL_EXPORT const BIGNUM *DH_get0_p(const DH *dh);

 // DH_get0_q returns the size of `dh`'s subgroup, or NULL if it is unset.
 OPENSSL_EXPORT const BIGNUM *DH_get0_q(const DH *dh);

 // DH_get0_g returns `dh`'s group generator.
 OPENSSL_EXPORT const BIGNUM *DH_get0_g(const DH *dh);

 // DH_get0_key sets `*out_pub_key` and `*out_priv_key`, if non-NULL, to `dh`'s
 // public and private key, respectively. If `dh` is a public key, the private
 // key will be set to NULL.
 OPENSSL_EXPORT void DH_get0_key(const DH *dh, const BIGNUM **out_pub_key,
                                 const BIGNUM **out_priv_key);

 // DH_set0_key sets `dh`'s public and private key to the specified values. If
 // NULL, the field is left unchanged. On success, it takes ownership of each
 // argument and returns one. Otherwise, it returns zero.
 OPENSSL_EXPORT int DH_set0_key(DH *dh, BIGNUM *pub_key, BIGNUM *priv_key);

 // DH_get0_pqg sets `*out_p`, `*out_q`, and `*out_g`, if non-NULL, to `dh`'s p,
 // q, and g parameters, respectively.
 OPENSSL_EXPORT void DH_get0_pqg(const DH *dh, const BIGNUM **out_p,
                                 const BIGNUM **out_q, const BIGNUM **out_g);

 // DH_set0_pqg sets `dh`'s p, q, and g parameters to the specified values.  If
 // NULL, the field is left unchanged. On success, it takes ownership of each
 // argument and returns one. Otherwise, it returns zero. `q` may be NULL, but
 // `p` and `g` must either be specified or already configured on `dh`.
 OPENSSL_EXPORT int DH_set0_pqg(DH *dh, BIGNUM *p, BIGNUM *q, BIGNUM *g);

 // DH_set_length sets the number of bits to use for the secret exponent when
 // calling `DH_generate_key` on `dh` and returns one. If unset,
 // `DH_generate_key` will use the bit length of p.
 OPENSSL_EXPORT int DH_set_length(DH *dh, unsigned priv_length);


 // Standard parameters.

 // DH_get_rfc7919_2048 returns the group `ffdhe2048` from
 // https://tools.ietf.org/html/rfc7919#appendix-A.1. It returns NULL if out
 // of memory.
 OPENSSL_EXPORT DH *DH_get_rfc7919_2048(void);

 // BN_get_rfc3526_prime_1536 sets `*ret` to the 1536-bit MODP group from RFC
 // 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
 // and returned. It returns NULL on allocation failure. The generator for this
 // group is 2.
 OPENSSL_EXPORT BIGNUM *BN_get_rfc3526_prime_1536(BIGNUM *ret);

 // BN_get_rfc3526_prime_2048 sets `*ret` to the 2048-bit MODP group from RFC
 // 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
 // and returned. It returns NULL on allocation failure. The generator for this
 // group is 2.
 OPENSSL_EXPORT BIGNUM *BN_get_rfc3526_prime_2048(BIGNUM *ret);

 // BN_get_rfc3526_prime_3072 sets `*ret` to the 3072-bit MODP group from RFC
 // 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
 // and returned. It returns NULL on allocation failure. The generator for this
 // group is 2.
 OPENSSL_EXPORT BIGNUM *BN_get_rfc3526_prime_3072(BIGNUM *ret);

 // BN_get_rfc3526_prime_4096 sets `*ret` to the 4096-bit MODP group from RFC
 // 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
 // and returned. It returns NULL on allocation failure. The generator for this
 // group is 2.
 OPENSSL_EXPORT BIGNUM *BN_get_rfc3526_prime_4096(BIGNUM *ret);

 // BN_get_rfc3526_prime_6144 sets `*ret` to the 6144-bit MODP group from RFC
 // 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
 // and returned. It returns NULL on allocation failure. The generator for this
 // group is 2.
 OPENSSL_EXPORT BIGNUM *BN_get_rfc3526_prime_6144(BIGNUM *ret);

 // BN_get_rfc3526_prime_8192 sets `*ret` to the 8192-bit MODP group from RFC
 // 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
 // and returned. It returns NULL on allocation failure. The generator for this
 // group is 2.
 OPENSSL_EXPORT BIGNUM *BN_get_rfc3526_prime_8192(BIGNUM *ret);


 // Parameter generation.

 #define DH_GENERATOR_2 2
 #define DH_GENERATOR_5 5

 // DH_generate_parameters_ex generates a suitable Diffie-Hellman group with a
 // prime that is `prime_bits` long and stores it in `dh`. The generator of the
 // group will be `generator`, which should be `DH_GENERATOR_2` unless there's a
 // good reason to use a different value. The `cb` argument contains a callback
 // function that will be called during the generation. See the documentation in
 // `bn.h` about this. In addition to the callback invocations from `BN`, `cb`
 // will also be called with `event` equal to three when the generation is
 // complete.
 OPENSSL_EXPORT int DH_generate_parameters_ex(DH *dh, int prime_bits,
                                              int generator, BN_GENCB *cb);


 // Diffie-Hellman operations.

 // DH_generate_key generates a new, random, private key and stores it in
 // `dh`, if `dh` does not already have a private key. Otherwise, it updates
 // `dh`'s public key to match the private key. It returns one on success and
 // zero on error.
 OPENSSL_EXPORT int DH_generate_key(DH *dh);

 // DH_compute_key_padded calculates the shared key between `dh` and `peers_key`
 // and writes it as a big-endian integer into `out`, padded up to `DH_size`
 // bytes. It returns the number of bytes written, which is always `DH_size`, or
 // a negative number on error. `out` must have `DH_size` bytes of space.
 //
 // WARNING: this differs from the usual BoringSSL return-value convention.
 //
 // Note this function differs from `DH_compute_key` in that it preserves leading
 // zeros in the secret. This function is the preferred variant. It matches PKCS
 // #3 and avoids some side channel attacks. However, the two functions are not
 // drop-in replacements for each other. Using a different variant than the
 // application expects will result in sporadic key mismatches.
 //
 // Callers that expect a fixed-width secret should use this function over
 // `DH_compute_key`. Callers that use either function should migrate to a modern
 // primitive such as X25519 or ECDH with P-256 instead.
 //
 // This function does not mutate `dh` for thread-safety purposes and may be used
 // concurrently.
 OPENSSL_EXPORT int DH_compute_key_padded(uint8_t *out, const BIGNUM *peers_key,
                                          DH *dh);

 // DH_compute_key_hashed calculates the shared key between `dh` and `peers_key`
 // and hashes it with the given `digest`. If the hash output is less than
 // `max_out_len` bytes then it writes the hash output to `out` and sets
 // `*out_len` to the number of bytes written. Otherwise it signals an error. It
 // returns one on success or zero on error.
 //
 // NOTE: this follows the usual BoringSSL return-value convention, but that's
 // different from `DH_compute_key` and `DH_compute_key_padded`.
 //
 // This function does not mutate `dh` for thread-safety purposes and may be used
 // concurrently.
 OPENSSL_EXPORT int DH_compute_key_hashed(DH *dh, uint8_t *out, size_t *out_len,
                                          size_t max_out_len,
                                          const BIGNUM *peers_key,
                                          const EVP_MD *digest);


 // Utility functions.

 #define DH_CHECK_P_NOT_PRIME 0x01
 #define DH_CHECK_P_NOT_SAFE_PRIME 0x02
 #define DH_CHECK_UNABLE_TO_CHECK_GENERATOR 0x04
 #define DH_CHECK_NOT_SUITABLE_GENERATOR 0x08
 #define DH_CHECK_Q_NOT_PRIME 0x10
 #define DH_CHECK_INVALID_Q_VALUE 0x20

 // These are compatibility defines.
 #define DH_NOT_SUITABLE_GENERATOR DH_CHECK_NOT_SUITABLE_GENERATOR
 #define DH_UNABLE_TO_CHECK_GENERATOR DH_CHECK_UNABLE_TO_CHECK_GENERATOR

 // DH_check checks the suitability of `dh` as a Diffie-Hellman group. and sets
 // `DH_CHECK_*` flags in `*out_flags` if it finds any errors. It returns one if
 // `*out_flags` was successfully set and zero on error.
 //
 // Note: these checks may be quite computationally expensive.
 OPENSSL_EXPORT int DH_check(const DH *dh, int *out_flags);

 #define DH_CHECK_PUBKEY_TOO_SMALL 0x1
 #define DH_CHECK_PUBKEY_TOO_LARGE 0x2
 #define DH_CHECK_PUBKEY_INVALID 0x4

 // DH_check_pub_key checks the suitability of `pub_key` as a public key for the
 // DH group in `dh` and sets `DH_CHECK_PUBKEY_*` flags in `*out_flags` if it
 // finds any errors. It returns one if `*out_flags` was successfully set and
 // zero on error.
 OPENSSL_EXPORT int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key,
                                     int *out_flags);

 // DHparams_dup allocates a fresh `DH` and copies the parameters from `dh` into
 // it. It returns the new `DH` or NULL on error.
 OPENSSL_EXPORT DH *DHparams_dup(const DH *dh);


 // ASN.1 functions.

 // DH_parse_parameters decodes a DER-encoded DHParameter structure (PKCS #3)
 // from `cbs` and advances `cbs`. It returns a newly-allocated `DH` or NULL on
 // error.
 OPENSSL_EXPORT DH *DH_parse_parameters(CBS *cbs);

 // DH_marshal_parameters marshals `dh` as a DER-encoded DHParameter structure
 // (PKCS #3) and appends the result to `cbb`. It returns one on success and zero
 // on error.
 OPENSSL_EXPORT int DH_marshal_parameters(CBB *cbb, const DH *dh);


 // Deprecated functions.

 // DH_generate_parameters behaves like `DH_generate_parameters_ex`, which is
 // what you should use instead. It returns NULL on error, or a newly-allocated
 // `DH` on success. This function is provided for compatibility only.
 OPENSSL_EXPORT DH *DH_generate_parameters(int prime_len, int generator,
                                           void (*callback)(int, int, void *),
                                           void *cb_arg);

 // d2i_DHparams parses a DER-encoded DHParameter structure (PKCS #3) from `len`
 // bytes at `*inp`, as in `d2i_SAMPLE`.
 //
 // Use `DH_parse_parameters` instead.
 OPENSSL_EXPORT DH *d2i_DHparams(DH **ret, const unsigned char **inp, long len);

 // i2d_DHparams marshals `in` to a DER-encoded DHParameter structure (PKCS #3),
 // as described in `i2d_SAMPLE`.
 //
 // Use `DH_marshal_parameters` instead.
 OPENSSL_EXPORT int i2d_DHparams(const DH *in, unsigned char **outp);

 // DH_compute_key behaves like `DH_compute_key_padded` but, contrary to PKCS #3,
 // returns a variable-length shared key with leading zeros. It returns the
 // number of bytes written, or a negative number on error. `out` must have
 // `DH_size` bytes of space.
 //
 // WARNING: this differs from the usual BoringSSL return-value convention.
 //
 // Note this function's running time and memory access pattern leaks information
 // about the shared secret. Particularly if `dh` is reused, this may result in
 // side channel attacks such as https://raccoon-attack.com/.
 //
 // `DH_compute_key_padded` is the preferred variant and avoids the above
 // attacks. However, the two functions are not drop-in replacements for each
 // other. Using a different variant than the application expects will result in
 // sporadic key mismatches.
 //
 // Callers that expect a fixed-width secret should use `DH_compute_key_padded`
 // instead. Callers that use either function should migrate to a modern
 // primitive such as X25519 or ECDH with P-256 instead.
 //
 // This function does not mutate `dh` for thread-safety purposes and may be used
 // concurrently.
 OPENSSL_EXPORT int DH_compute_key(uint8_t *out, const BIGNUM *peers_key,
                                   DH *dh);


 #if defined(__cplusplus)
 }  // extern C

 extern "C++" {

 BSSL_NAMESPACE_BEGIN

 BORINGSSL_MAKE_DELETER(DH, DH_free)
 BORINGSSL_MAKE_UP_REF(DH, DH_up_ref)

 BSSL_NAMESPACE_END

 }  // extern C++

 #endif

 #define DH_R_BAD_GENERATOR 100
 #define DH_R_INVALID_PUBKEY 101
 #define DH_R_MODULUS_TOO_LARGE 102
 #define DH_R_NO_PRIVATE_VALUE 103
 #define DH_R_DECODE_ERROR 104
 #define DH_R_ENCODE_ERROR 105
 #define DH_R_INVALID_PARAMETERS 106

 #endif  // OPENSSL_HEADER_DH_H
	// Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// https://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	#ifndef OPENSSL_HEADER_DH_H
	#define OPENSSL_HEADER_DH_H

	#include <openssl/base.h> // IWYU pragma: export

	#if defined(__cplusplus)
	extern "C" {
	#endif


	// DH contains functions for performing Diffie-Hellman key agreement in
	// multiplicative groups.
	//
	// This module is deprecated and retained for legacy reasons only. It is not
	// considered a priority for performance or hardening work. Do not use it in
	// new code. Use X25519 or ECDH with P-256 instead.


	// Allocation and destruction.
	//
	// A `DH` object represents a Diffie-Hellman key or group parameters. A given
	// object may be used concurrently on multiple threads by non-mutating
	// functions, provided no other thread is concurrently calling a mutating
	// function. Unless otherwise documented, functions which take a `const` pointer
	// are non-mutating and functions which take a non-`const` pointer are mutating.

	// DH_new returns a new, empty DH object or NULL on error.
	OPENSSL_EXPORT DH *DH_new(void);

	// DH_free decrements the reference count of `dh` and frees it if the reference
	// count drops to zero.
	OPENSSL_EXPORT void DH_free(DH *dh);

	// DH_up_ref increments the reference count of `dh` and returns one. It does not
	// mutate `dh` for thread-safety purposes and may be used concurrently.
	OPENSSL_EXPORT int DH_up_ref(DH *dh);


	// Properties.

	// OPENSSL_DH_MAX_MODULUS_BITS is the maximum supported Diffie-Hellman group
	// modulus, in bits.
	#define OPENSSL_DH_MAX_MODULUS_BITS 8192

	// DH_bits returns the size of `dh`'s group modulus, in bits.
	OPENSSL_EXPORT unsigned DH_bits(const DH *dh);

	// DH_size returns the number of bytes in the DH group's prime.
	OPENSSL_EXPORT int DH_size(const DH *dh);

	// DH_get0_pub_key returns `dh`'s public key.
	OPENSSL_EXPORT const BIGNUM DH_get0_pub_key(const DH dh);

	// DH_get0_priv_key returns `dh`'s private key, or NULL if `dh` is a public key.
	OPENSSL_EXPORT const BIGNUM DH_get0_priv_key(const DH dh);

	// DH_get0_p returns `dh`'s group modulus.
	OPENSSL_EXPORT const BIGNUM DH_get0_p(const DH dh);

	// DH_get0_q returns the size of `dh`'s subgroup, or NULL if it is unset.
	OPENSSL_EXPORT const BIGNUM DH_get0_q(const DH dh);

	// DH_get0_g returns `dh`'s group generator.
	OPENSSL_EXPORT const BIGNUM DH_get0_g(const DH dh);

	// DH_get0_key sets `out_pub_key` and `out_priv_key`, if non-NULL, to `dh`'s
	// public and private key, respectively. If `dh` is a public key, the private
	// key will be set to NULL.
	OPENSSL_EXPORT void DH_get0_key(const DH dh, const BIGNUM *out_pub_key,
	const BIGNUM **out_priv_key);

	// DH_set0_key sets `dh`'s public and private key to the specified values. If
	// NULL, the field is left unchanged. On success, it takes ownership of each
	// argument and returns one. Otherwise, it returns zero.
	OPENSSL_EXPORT int DH_set0_key(DH dh, BIGNUM pub_key, BIGNUM *priv_key);

	// DH_get0_pqg sets `out_p`, `out_q`, and `*out_g`, if non-NULL, to `dh`'s p,
	// q, and g parameters, respectively.
	OPENSSL_EXPORT void DH_get0_pqg(const DH dh, const BIGNUM *out_p,
	const BIGNUM out_q, const BIGNUM out_g);

	// DH_set0_pqg sets `dh`'s p, q, and g parameters to the specified values. If
	// NULL, the field is left unchanged. On success, it takes ownership of each
	// argument and returns one. Otherwise, it returns zero. `q` may be NULL, but
	// `p` and `g` must either be specified or already configured on `dh`.
	OPENSSL_EXPORT int DH_set0_pqg(DH dh, BIGNUM p, BIGNUM q, BIGNUM g);

	// DH_set_length sets the number of bits to use for the secret exponent when
	// calling `DH_generate_key` on `dh` and returns one. If unset,
	// `DH_generate_key` will use the bit length of p.
	OPENSSL_EXPORT int DH_set_length(DH *dh, unsigned priv_length);


	// Standard parameters.

	// DH_get_rfc7919_2048 returns the group `ffdhe2048` from
	// https://tools.ietf.org/html/rfc7919#appendix-A.1. It returns NULL if out
	// of memory.
	OPENSSL_EXPORT DH *DH_get_rfc7919_2048(void);

	// BN_get_rfc3526_prime_1536 sets `*ret` to the 1536-bit MODP group from RFC
	// 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
	// and returned. It returns NULL on allocation failure. The generator for this
	// group is 2.
	OPENSSL_EXPORT BIGNUM BN_get_rfc3526_prime_1536(BIGNUM ret);

	// BN_get_rfc3526_prime_2048 sets `*ret` to the 2048-bit MODP group from RFC
	// 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
	// and returned. It returns NULL on allocation failure. The generator for this
	// group is 2.
	OPENSSL_EXPORT BIGNUM BN_get_rfc3526_prime_2048(BIGNUM ret);

	// BN_get_rfc3526_prime_3072 sets `*ret` to the 3072-bit MODP group from RFC
	// 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
	// and returned. It returns NULL on allocation failure. The generator for this
	// group is 2.
	OPENSSL_EXPORT BIGNUM BN_get_rfc3526_prime_3072(BIGNUM ret);

	// BN_get_rfc3526_prime_4096 sets `*ret` to the 4096-bit MODP group from RFC
	// 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
	// and returned. It returns NULL on allocation failure. The generator for this
	// group is 2.
	OPENSSL_EXPORT BIGNUM BN_get_rfc3526_prime_4096(BIGNUM ret);

	// BN_get_rfc3526_prime_6144 sets `*ret` to the 6144-bit MODP group from RFC
	// 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
	// and returned. It returns NULL on allocation failure. The generator for this
	// group is 2.
	OPENSSL_EXPORT BIGNUM BN_get_rfc3526_prime_6144(BIGNUM ret);

	// BN_get_rfc3526_prime_8192 sets `*ret` to the 8192-bit MODP group from RFC
	// 3526 and returns `ret`. If `ret` is NULL then a fresh `BIGNUM` is allocated
	// and returned. It returns NULL on allocation failure. The generator for this
	// group is 2.
	OPENSSL_EXPORT BIGNUM BN_get_rfc3526_prime_8192(BIGNUM ret);


	// Parameter generation.

	#define DH_GENERATOR_2 2
	#define DH_GENERATOR_5 5

	// DH_generate_parameters_ex generates a suitable Diffie-Hellman group with a
	// prime that is `prime_bits` long and stores it in `dh`. The generator of the
	// group will be `generator`, which should be `DH_GENERATOR_2` unless there's a
	// good reason to use a different value. The `cb` argument contains a callback
	// function that will be called during the generation. See the documentation in
	// `bn.h` about this. In addition to the callback invocations from `BN`, `cb`
	// will also be called with `event` equal to three when the generation is
	// complete.
	OPENSSL_EXPORT int DH_generate_parameters_ex(DH *dh, int prime_bits,
	int generator, BN_GENCB *cb);


	// Diffie-Hellman operations.

	// DH_generate_key generates a new, random, private key and stores it in
	// `dh`, if `dh` does not already have a private key. Otherwise, it updates
	// `dh`'s public key to match the private key. It returns one on success and
	// zero on error.
	OPENSSL_EXPORT int DH_generate_key(DH *dh);

	// DH_compute_key_padded calculates the shared key between `dh` and `peers_key`
	// and writes it as a big-endian integer into `out`, padded up to `DH_size`
	// bytes. It returns the number of bytes written, which is always `DH_size`, or
	// a negative number on error. `out` must have `DH_size` bytes of space.
	//
	// WARNING: this differs from the usual BoringSSL return-value convention.
	//
	// Note this function differs from `DH_compute_key` in that it preserves leading
	// zeros in the secret. This function is the preferred variant. It matches PKCS
	// #3 and avoids some side channel attacks. However, the two functions are not
	// drop-in replacements for each other. Using a different variant than the
	// application expects will result in sporadic key mismatches.
	//
	// Callers that expect a fixed-width secret should use this function over
	// `DH_compute_key`. Callers that use either function should migrate to a modern
	// primitive such as X25519 or ECDH with P-256 instead.
	//
	// This function does not mutate `dh` for thread-safety purposes and may be used
	// concurrently.
	OPENSSL_EXPORT int DH_compute_key_padded(uint8_t out, const BIGNUM peers_key,
	DH *dh);

	// DH_compute_key_hashed calculates the shared key between `dh` and `peers_key`
	// and hashes it with the given `digest`. If the hash output is less than
	// `max_out_len` bytes then it writes the hash output to `out` and sets
	// `*out_len` to the number of bytes written. Otherwise it signals an error. It
	// returns one on success or zero on error.
	//
	// NOTE: this follows the usual BoringSSL return-value convention, but that's
	// different from `DH_compute_key` and `DH_compute_key_padded`.
	//
	// This function does not mutate `dh` for thread-safety purposes and may be used
	// concurrently.
	OPENSSL_EXPORT int DH_compute_key_hashed(DH dh, uint8_t out, size_t *out_len,
	size_t max_out_len,
	const BIGNUM *peers_key,
	const EVP_MD *digest);


	// Utility functions.

	#define DH_CHECK_P_NOT_PRIME 0x01
	#define DH_CHECK_P_NOT_SAFE_PRIME 0x02
	#define DH_CHECK_UNABLE_TO_CHECK_GENERATOR 0x04
	#define DH_CHECK_NOT_SUITABLE_GENERATOR 0x08
	#define DH_CHECK_Q_NOT_PRIME 0x10
	#define DH_CHECK_INVALID_Q_VALUE 0x20

	// These are compatibility defines.
	#define DH_NOT_SUITABLE_GENERATOR DH_CHECK_NOT_SUITABLE_GENERATOR
	#define DH_UNABLE_TO_CHECK_GENERATOR DH_CHECK_UNABLE_TO_CHECK_GENERATOR

	// DH_check checks the suitability of `dh` as a Diffie-Hellman group. and sets
	// `DH_CHECK_` flags in `out_flags` if it finds any errors. It returns one if
	// `*out_flags` was successfully set and zero on error.
	//
	// Note: these checks may be quite computationally expensive.
	OPENSSL_EXPORT int DH_check(const DH dh, int out_flags);

	#define DH_CHECK_PUBKEY_TOO_SMALL 0x1
	#define DH_CHECK_PUBKEY_TOO_LARGE 0x2
	#define DH_CHECK_PUBKEY_INVALID 0x4

	// DH_check_pub_key checks the suitability of `pub_key` as a public key for the
	// DH group in `dh` and sets `DH_CHECK_PUBKEY_` flags in `out_flags` if it
	// finds any errors. It returns one if `*out_flags` was successfully set and
	// zero on error.
	OPENSSL_EXPORT int DH_check_pub_key(const DH dh, const BIGNUM pub_key,
	int *out_flags);

	// DHparams_dup allocates a fresh `DH` and copies the parameters from `dh` into
	// it. It returns the new `DH` or NULL on error.
	OPENSSL_EXPORT DH DHparams_dup(const DH dh);


	// ASN.1 functions.

	// DH_parse_parameters decodes a DER-encoded DHParameter structure (PKCS #3)
	// from `cbs` and advances `cbs`. It returns a newly-allocated `DH` or NULL on
	// error.
	OPENSSL_EXPORT DH DH_parse_parameters(CBS cbs);

	// DH_marshal_parameters marshals `dh` as a DER-encoded DHParameter structure
	// (PKCS #3) and appends the result to `cbb`. It returns one on success and zero
	// on error.
	OPENSSL_EXPORT int DH_marshal_parameters(CBB cbb, const DH dh);


	// Deprecated functions.

	// DH_generate_parameters behaves like `DH_generate_parameters_ex`, which is
	// what you should use instead. It returns NULL on error, or a newly-allocated
	// `DH` on success. This function is provided for compatibility only.
	OPENSSL_EXPORT DH *DH_generate_parameters(int prime_len, int generator,
	void (callback)(int, int, void ),
	void *cb_arg);

	// d2i_DHparams parses a DER-encoded DHParameter structure (PKCS #3) from `len`
	// bytes at `*inp`, as in `d2i_SAMPLE`.
	//
	// Use `DH_parse_parameters` instead.
	OPENSSL_EXPORT DH d2i_DHparams(DH ret, const unsigned char *inp, long len);

	// i2d_DHparams marshals `in` to a DER-encoded DHParameter structure (PKCS #3),
	// as described in `i2d_SAMPLE`.
	//
	// Use `DH_marshal_parameters` instead.
	OPENSSL_EXPORT int i2d_DHparams(const DH in, unsigned char *outp);

	// DH_compute_key behaves like `DH_compute_key_padded` but, contrary to PKCS #3,
	// returns a variable-length shared key with leading zeros. It returns the
	// number of bytes written, or a negative number on error. `out` must have
	// `DH_size` bytes of space.
	//
	// WARNING: this differs from the usual BoringSSL return-value convention.
	//
	// Note this function's running time and memory access pattern leaks information
	// about the shared secret. Particularly if `dh` is reused, this may result in
	// side channel attacks such as https://raccoon-attack.com/.
	//
	// `DH_compute_key_padded` is the preferred variant and avoids the above
	// attacks. However, the two functions are not drop-in replacements for each
	// other. Using a different variant than the application expects will result in
	// sporadic key mismatches.
	//
	// Callers that expect a fixed-width secret should use `DH_compute_key_padded`
	// instead. Callers that use either function should migrate to a modern
	// primitive such as X25519 or ECDH with P-256 instead.
	//
	// This function does not mutate `dh` for thread-safety purposes and may be used
	// concurrently.
	OPENSSL_EXPORT int DH_compute_key(uint8_t out, const BIGNUM peers_key,
	DH *dh);


	#if defined(__cplusplus)
	} // extern C

	extern "C++" {

	BSSL_NAMESPACE_BEGIN

	BORINGSSL_MAKE_DELETER(DH, DH_free)
	BORINGSSL_MAKE_UP_REF(DH, DH_up_ref)

	BSSL_NAMESPACE_END

	} // extern C++

	#endif

	#define DH_R_BAD_GENERATOR 100
	#define DH_R_INVALID_PUBKEY 101
	#define DH_R_MODULUS_TOO_LARGE 102
	#define DH_R_NO_PRIVATE_VALUE 103
	#define DH_R_DECODE_ERROR 104
	#define DH_R_ENCODE_ERROR 105
	#define DH_R_INVALID_PARAMETERS 106

	#endif // OPENSSL_HEADER_DH_H