DH_NEW(3) | Library Functions Manual | DH_NEW(3)

# NAME

`DH_new`, `DH_up_ref`, `DH_free` — allocate and free DH objects

# SYNOPSIS

library “libcrypto”
`#include <openssl/dh.h>`

DH*
`DH_new`(void);

int
`DH_up_ref`(DH *dh);

void
`DH_free`(DH *dh);

# DESCRIPTION

The DH functions implement the Diffie-Hellman key agreement protocol.

`DH_new`() allocates and initializes a DH structure, setting the reference count to 1. It is equivalent to DH_new_method(3) with a `NULL` argument.

`DH_up_ref`() increments the reference count by 1.

`DH_free`() decrements the reference count by 1. If it reaches 0, it frees the DH structure and its components. The values are erased before the memory is returned to the system. If dh is a `NULL` pointer, no action occurs.

# RETURN VALUES

If the allocation fails, `DH_new`() returns `NULL` and sets an error code that can be obtained by ERR_get_error(3). Otherwise it returns a pointer to the newly allocated structure.

`DH_up_ref`() returns 1 for success or 0 for failure.

# SEE ALSO

BN_new(3), crypto(3), d2i_DHparams(3), DH_generate_key(3), DH_generate_parameters(3), DH_get0_pqg(3), DH_get_ex_new_index(3), DH_security_bits(3), DH_set_method(3), DH_size(3), DHparams_print(3), DSA_dup_DH(3), EVP_PKEY_CTX_set_dh_paramgen_prime_len(3), EVP_PKEY_set1_DH(3)

# HISTORY

`DH_new`() and `DH_free`() first appeared in SSLeay 0.5.1 and have been available since OpenBSD 2.4.

`DH_up_ref`() first appeared in OpenSSL 0.9.7 and has been available since OpenBSD 3.2.

June 8, 2025 | Debian