---
name: "libressl-SSL_CTX_use_certificate"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-SSL_CTX_use_certificate"
---

# libressl-SSL\_CTX\_use\_certificate(3)

load certificate and key data

## NAME

**SSL\_CTX\_use\_certificate**, **SSL\_CTX\_use\_certificate\_ASN1**, **SSL\_CTX\_use\_certificate\_file**, **SSL\_use\_certificate**, **SSL\_use\_certificate\_ASN1**, **SSL\_use\_certificate\_chain\_file**, **SSL\_use\_certificate\_file**, **SSL\_CTX\_use\_certificate\_chain\_file**, **SSL\_CTX\_use\_certificate\_chain\_mem**, **SSL\_CTX\_use\_PrivateKey**, **SSL\_CTX\_use\_PrivateKey\_ASN1**, **SSL\_CTX\_use\_PrivateKey\_file**, **SSL\_CTX\_use\_RSAPrivateKey**, **SSL\_CTX\_use\_RSAPrivateKey\_ASN1**, **SSL\_CTX\_use\_RSAPrivateKey\_file**, **SSL\_use\_PrivateKey\_file**, **SSL\_use\_PrivateKey\_ASN1**, **SSL\_use\_PrivateKey**, **SSL\_use\_RSAPrivateKey**, **SSL\_use\_RSAPrivateKey\_ASN1**, **SSL\_use\_RSAPrivateKey\_file**, **SSL\_CTX\_check\_private\_key**, **SSL\_check\_private\_key** – load certificate and key data

## SYNOPSIS

SSL Library (libssl, -lssl) libcrypto

**#include \<openssl/ssl.h\>**

*int*\

**SSL\_CTX\_use\_certificate**(*SSL\_CTX \*ctx*, *X509 \*x*);

*int*\

**SSL\_CTX\_use\_certificate\_ASN1**(*SSL\_CTX \*ctx*, *int len*, *unsigned char \*d*);

*int*\

**SSL\_CTX\_use\_certificate\_file**(*SSL\_CTX \*ctx*, *const char \*file*, *int type*);

*int*\

**SSL\_use\_certificate**(*SSL \*ssl*, *X509 \*x*);

*int*\

**SSL\_use\_certificate\_ASN1**(*SSL \*ssl*, *unsigned char \*d*, *int len*);

*int*\

**SSL\_use\_certificate\_chain\_file**(*SSL \*ssl*, *const char \*file*);

*int*\

**SSL\_use\_certificate\_file**(*SSL \*ssl*, *const char \*file*, *int type*);

*int*\

**SSL\_CTX\_use\_certificate\_chain\_file**(*SSL\_CTX \*ctx*, *const char \*file*);

*int*\

**SSL\_CTX\_use\_certificate\_chain\_mem**(*SSL\_CTX \*ctx*, *void \*buf*, *int len*);

*int*\

**SSL\_CTX\_use\_PrivateKey**(*SSL\_CTX \*ctx*, *EVP\_PKEY \*pkey*);

*int*\

**SSL\_CTX\_use\_PrivateKey\_ASN1**(*int pk*, *SSL\_CTX \*ctx*, *unsigned char \*d*, *long len*);

*int*\

**SSL\_CTX\_use\_PrivateKey\_file**(*SSL\_CTX \*ctx*, *const char \*file*, *int type*);

*int*\

**SSL\_CTX\_use\_RSAPrivateKey**(*SSL\_CTX \*ctx*, *RSA \*rsa*);

*int*\

**SSL\_CTX\_use\_RSAPrivateKey\_ASN1**(*SSL\_CTX \*ctx*, *unsigned char \*d*, *long len*);

*int*\

**SSL\_CTX\_use\_RSAPrivateKey\_file**(*SSL\_CTX \*ctx*, *const char \*file*, *int type*);

*int*\

**SSL\_use\_PrivateKey**(*SSL \*ssl*, *EVP\_PKEY \*pkey*);

*int*\

**SSL\_use\_PrivateKey\_ASN1**(*int pk*, *SSL \*ssl*, *unsigned char \*d*, *long len*);

*int*\

**SSL\_use\_PrivateKey\_file**(*SSL \*ssl*, *const char \*file*, *int type*);

*int*\

**SSL\_use\_RSAPrivateKey**(*SSL \*ssl*, *RSA \*rsa*);

*int*\

**SSL\_use\_RSAPrivateKey\_ASN1**(*SSL \*ssl*, *const unsigned char \*d*, *long len*);

*int*\

**SSL\_use\_RSAPrivateKey\_file**(*SSL \*ssl*, *const char \*file*, *int type*);

*int*\

**SSL\_CTX\_check\_private\_key**(*const SSL\_CTX \*ctx*);

*int*\

**SSL\_check\_private\_key**(*const SSL \*ssl*);

## DESCRIPTION

These functions load the certificates and private keys into the *SSL\_CTX* or *SSL* object, respectively.

The **SSL\_CTX\_\***() class of functions loads the certificates and keys into the *SSL\_CTX* object *ctx*. The information is passed to *SSL* objects *ssl* created from *ctx* with SSL\_new(3) by copying, so that changes applied to *ctx* do not propagate to already existing *SSL* objects.

The **SSL\_\***() class of functions only loads certificates and keys into a specific *SSL* object. The specific information is kept when SSL\_clear(3) is called for this *SSL* object.

**SSL\_CTX\_use\_certificate**() loads the certificate *x* into *ctx*; **SSL\_use\_certificate**() loads *x* into *ssl*. The rest of the certificates needed to form the complete certificate chain can be specified using the SSL\_CTX\_add\_extra\_chain\_cert(3) function.

**SSL\_CTX\_use\_certificate\_ASN1**() loads the ASN1 encoded certificate from the memory location *d* (with length *len*) into *ctx*; **SSL\_use\_certificate\_ASN1**() loads the ASN1 encoded certificate into *ssl*.

**SSL\_CTX\_use\_certificate\_file**() loads the first certificate stored in *file* into *ctx*. The formatting *type* of the certificate must be specified from the known types SSL\_FILETYPE\_PEM and SSL\_FILETYPE\_ASN1. **SSL\_use\_certificate\_file**() loads the certificate from *file* into *ssl*. See the NOTES section on why **SSL\_CTX\_use\_certificate\_chain\_file**() should be preferred.

The **SSL\_CTX\_use\_certificate\_chain\***() functions load a certificate chain into *ctx*. The certificates must be in PEM format and must be sorted starting with the subject's certificate (actual client or server certificate), followed by intermediate CA certificates if applicable, and ending at the highest level (root) CA. With the exception of **SSL\_use\_certificate\_chain\_file**(), there is no corresponding function working on a single *SSL* object.

**SSL\_CTX\_use\_PrivateKey**() adds *pkey* as private key to *ctx*. **SSL\_CTX\_use\_RSAPrivateKey**() adds the private key *rsa* of type RSA to *ctx*. **SSL\_use\_PrivateKey**() adds *pkey* as private key to *ssl*; **SSL\_use\_RSAPrivateKey**() adds *rsa* as private key of type RSA to *ssl*. If a certificate has already been set and the private does not belong to the certificate, an error is returned. To change a certificate private key pair, the new certificate needs to be set with **SSL\_use\_certificate**() or **SSL\_CTX\_use\_certificate**() before setting the private key with **SSL\_CTX\_use\_PrivateKey**() or **SSL\_use\_PrivateKey**().

**SSL\_CTX\_use\_PrivateKey\_ASN1**() adds the private key of type *pk* stored at memory location *d* (length *len*) to *ctx*. **SSL\_CTX\_use\_RSAPrivateKey\_ASN1**() adds the private key of type RSA stored at memory location *d* (length *len*) to *ctx*. **SSL\_use\_PrivateKey\_ASN1**() and **SSL\_use\_RSAPrivateKey\_ASN1**() add the private key to *ssl*.

**SSL\_CTX\_use\_PrivateKey\_file**() adds the first private key found in *file* to *ctx*. The formatting *type* of the private key must be specified from the known types SSL\_FILETYPE\_PEM and SSL\_FILETYPE\_ASN1. **SSL\_CTX\_use\_RSAPrivateKey\_file**() adds the first private RSA key found in *file* to *ctx*. **SSL\_use\_PrivateKey\_file**() adds the first private key found in *file* to *ssl*; **SSL\_use\_RSAPrivateKey\_file**() adds the first private RSA key found to *ssl*.

The **SSL\_CTX\_check\_private\_key**() function is seriously misnamed. It compares the *public* key components and parameters of an OpenSSL private key with the corresponding certificate loaded into *ctx*. If more than one key/certificate pair (RSA/ECDSA) is installed, the last item installed will be compared. If, e.g., the last item was an RSA certificate or key, the RSA key/certificate pair will be checked. **SSL\_check\_private\_key**() performs the same *public* key comparison for *ssl*. If no key/certificate was explicitly added for this *ssl*, the last item added into *ctx* will be checked.

Despite the name, neither **SSL\_CTX\_check\_private\_key**() nor **SSL\_check\_private\_key**() checks whether the private key component is indeed a private key, nor whether it matches the public key component. They merely compare the public materials (e.g. exponent and modulus of an RSA key) and/or key parameters (e.g. EC params of an EC key) of a key pair.

## NOTES

The internal certificate store of OpenSSL can hold several private key/certificate pairs at a time. The certificate used depends on the cipher selected. See also SSL\_CTX\_set\_cipher\_list(3).

When reading certificates and private keys from file, files of type SSL\_FILETYPE\_ASN1 (also known as *DER*, binary encoding) can only contain one certificate or private key; consequently, **SSL\_CTX\_use\_certificate\_chain\_file**() is only applicable to PEM formatting. Files of type SSL\_FILETYPE\_PEM can contain more than one item.

**SSL\_CTX\_use\_certificate\_chain\_file**() adds the first certificate found in the file to the certificate store. The other certificates are added to the store of chain certificates using SSL\_CTX\_add1\_chain\_cert(3). It is recommended to use the **SSL\_CTX\_use\_certificate\_chain\_file**() instead of the **SSL\_CTX\_use\_certificate\_file**() function in order to allow the use of complete certificate chains even when no trusted CA storage is used or when the CA issuing the certificate shall not be added to the trusted CA storage.

If additional certificates are needed to complete the chain during the TLS negotiation, CA certificates are additionally looked up in the locations of trusted CA certificates (see SSL\_CTX\_load\_verify\_locations(3)).

The private keys loaded from file can be encrypted. In order to successfully load encrypted keys, a function returning the passphrase must have been supplied (see SSL\_CTX\_set\_default\_passwd\_cb(3)). (Certificate files might be encrypted as well from the technical point of view, it however does not make sense as the data in the certificate is considered public anyway.)

## RETURN VALUES

On success, the functions return 1. Otherwise check out the error stack to find out the reason.

## SEE ALSO

[ssl(3)](/ssl/3.md), SSL\_clear(3), SSL\_CTX\_add1\_chain\_cert(3), SSL\_CTX\_add\_extra\_chain\_cert(3), SSL\_CTX\_load\_verify\_locations(3), SSL\_CTX\_set\_cipher\_list(3), SSL\_CTX\_set\_client\_CA\_list(3), SSL\_CTX\_set\_client\_cert\_cb(3), SSL\_CTX\_set\_default\_passwd\_cb(3), SSL\_new(3), X509\_check\_private\_key(3)

## HISTORY

**SSL\_use\_certificate**(), **SSL\_use\_certificate\_file**(), **SSL\_use\_RSAPrivateKey**(), and **SSL\_use\_RSAPrivateKey\_file**() appeared in SSLeay 0.4 or earlier. **SSL\_use\_certificate\_ASN1**() and **SSL\_use\_RSAPrivateKey\_ASN1**() first appeared in SSLeay 0.5.1. **SSL\_use\_PrivateKey\_file**(), **SSL\_use\_PrivateKey\_ASN1**(), and **SSL\_use\_PrivateKey**() first appeared in SSLeay 0.6.0. **SSL\_CTX\_use\_certificate**(), **SSL\_CTX\_use\_certificate\_ASN1**(), **SSL\_CTX\_use\_certificate\_file**(), **SSL\_CTX\_use\_PrivateKey**(), **SSL\_CTX\_use\_PrivateKey\_ASN1**(), **SSL\_CTX\_use\_PrivateKey\_file**(), **SSL\_CTX\_use\_RSAPrivateKey**(), **SSL\_CTX\_use\_RSAPrivateKey\_ASN1**(), and **SSL\_CTX\_use\_RSAPrivateKey\_file**() first appeared in SSLeay 0.6.1. **SSL\_CTX\_check\_private\_key**() and **SSL\_check\_private\_key**() first appeared in SSLeay 0.6.5. All these functions have been available since OpenBSD 2.4.

**SSL\_CTX\_use\_certificate\_chain\_file**() first appeared in OpenSSL 0.9.4 and has been available since OpenBSD 2.6.

**SSL\_use\_certificate\_chain\_file**() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 6.9.

Support for DER encoded private keys (SSL\_FILETYPE\_ASN1) in **SSL\_CTX\_use\_PrivateKey\_file**() and **SSL\_use\_PrivateKey\_file**() was added in 0.9.8.

**SSL\_CTX\_use\_certificate\_chain\_mem**() first appeared in OpenBSD 5.7.