include/openssl/dh.h

/*
 * Copyright 1995-2016 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
 */

#ifndef OPENSSL_HEADER_DH_H
#define OPENSSL_HEADER_DH_H

#include <openssl/base.h>

#include <openssl/thread.h>

#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 10000

// DH_bits returns the size of |dh|'s group modulus, in bits.
OPENSSL_EXPORT unsigned DH_bits(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.
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.
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.
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.
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.
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.
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.

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

// DH_num_bits returns the minimum number of bits needed to represent the
// absolute value of the DH group's prime.
OPENSSL_EXPORT unsigned DH_num_bits(const DH *dh);

#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