X509_NEW(3) | Library Functions Manual | X509_NEW(3)

# NAME

`X509_new`, `X509_dup`, `X509_REQ_to_X509`, `X509_free`, `X509_up_ref`, `X509_chain_up_ref` — X.509 certificate object

# SYNOPSIS

library “libcrypto”
`#include <openssl/x509.h>`

X509 *
`X509_new`(void);

X509 *
`X509_dup`(X509 *a);

X509 *
`X509_REQ_to_X509`(X509_REQ *req, int days, EVP_PKEY *pkey);

void
`X509_free`(X509 *a);

int
`X509_up_ref`(X509 *a);

STACK_OF(X509) *
`X509_chain_up_ref`(STACK_OF(X509) *chain);

# DESCRIPTION

`X509_new`() allocates and initializes an empty X509 object with reference count 1. It represents an ASN.1 Certificate structure defined in RFC 5280 section 4.1. It can hold a public key together with information about the person, organization, device, or function the associated private key belongs to.

`X509_dup`() creates a deep copy of a using ASN1_item_dup(3), setting the reference count of the copy to 1.

`X509_REQ_to_X509`() allocates a new certificate object, copies the public key from req into it, copies the subject name of req to both the subject and issuer names of the new certificate, sets the notBefore field to the current time and the notAfter field to the given number of days in the future, and signs the new certificate with X509_sign(3) using pkey and the MD5 algorithm. If req contains at least one attribute, the version of the new certificate is set to 2.

`X509_free`() decrements the reference count of the X509 structure a and frees it up if the reference count reaches 0. If a is a `NULL` pointer, no action occurs.

`X509_up_ref`() increments the reference count of a by 1. This function is useful if a certificate structure is being used by several different operations each of which will free it up after use: this avoids the need to duplicate the entire certificate structure.

`X509_chain_up_ref`() performs a shallow copy of the given chain using `sk_X509_dup`() and increments the reference count of each contained certificate by 1. Its purpose is similar to `X509_up_ref`(): The returned chain persists after the original is freed.

# RETURN VALUES

`X509_new`(), `X509_dup`(), and `X509_REQ_to_X509`() return a pointer to the newly allocated object or `NULL` if an error occurs; an error code can be obtained by ERR_get_error(3).

`X509_up_ref`() returns 1 for success or 0 for failure.

`X509_chain_up_ref`() returns the copy of the chain or `NULL` if an error occurs.

# SEE ALSO

ASIdentifiers_new(3), ASRange_new(3), AUTHORITY_KEYID_new(3), BASIC_CONSTRAINTS_new(3), crypto(3), d2i_X509(3), IPAddressRange_new(3), PKCS8_PRIV_KEY_INFO_new(3), X509_ALGOR_new(3), X509_ATTRIBUTE_new(3), X509_check_ca(3), X509_check_host(3), X509_check_issued(3), X509_check_private_key(3), X509_check_purpose(3), X509_CINF_new(3), X509_cmp(3), X509_CRL_new(3), X509_digest(3), X509_EXTENSION_new(3), X509_find_by_subject(3), X509_get0_notBefore(3), X509_get0_signature(3), X509_get1_email(3), X509_get_ex_new_index(3), X509_get_extension_flags(3), X509_get_pubkey(3), X509_get_pubkey_parameters(3), X509_get_serialNumber(3), X509_get_subject_name(3), X509_get_version(3), X509_INFO_new(3), X509_load_cert_file(3), X509_LOOKUP_hash_dir(3), X509_LOOKUP_new(3), X509_NAME_new(3), X509_OBJECT_new(3), X509_print_ex(3), X509_PUBKEY_new(3), X509_PURPOSE_set(3), X509_REQ_new(3), X509_SIG_new(3), X509_sign(3), X509_STORE_CTX_new(3), X509_STORE_get_by_subject(3), X509_STORE_new(3), X509v3_addr_add_inherit(3), X509v3_addr_get_range(3), X509v3_addr_inherits(3), X509v3_addr_subset(3), X509v3_addr_validate_path(3), X509v3_asid_add_id_or_range(3)

# STANDARDS

RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile

# HISTORY

`X509_new`() and `X509_free`() appeared in SSLeay 0.4 or earlier, `X509_dup`() in SSLeay 0.4.4, and `X509_REQ_to_X509`() in SSLeay 0.6.0 . These functions have been available since OpenBSD 2.4.

`X509_up_ref`() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 6.1.

`X509_chain_up_ref`() first appeared in OpenSSL 1.0.2 and has been available since OpenBSD 6.3.

# BUGS

The X.509 public key infrastructure and its data types contain too many design bugs to list them. For lots of examples, see the classic X.509 Style Guide that Peter Gutmann published in 2000.

July 16, 2025 | Debian