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SSL_CTX_load_verify_locations, SSL_CTX_set_default_verify_pathsset default locations for trusted CA certificates

#include <openssl/ssl.h>

SSL_CTX_load_verify_locations(SSL_CTX *ctx, const char *CAfile, const char *CApath);

SSL_CTX_set_default_verify_paths(SSL_CTX *ctx);

() specifies the locations for ctx, at which CA certificates for verification purposes are located. The certificates available via CAfile and CApath are trusted.

() specifies that the default locations from which CA certificates are loaded should be used. There is one default directory and one default file. The default CA certificates directory is called certs in the default OpenSSL directory. The default CA certificates file is called cert.pem in the default OpenSSL directory.

If CAfile is not NULL, it points to a file of CA certificates in PEM format. The file can contain several CA certificates identified by sequences of:

 ... (CA certificate in base64 encoding) ...

Before, between, and after the certificates arbitrary text is allowed which can be used, e.g., for descriptions of the certificates.

The CAfile is processed on execution of the () function.

If CApath is not NULL, it points to a directory containing CA certificates in PEM format. The files each contain one CA certificate. The files are looked up by the CA subject name hash value, which must hence be available. If more than one CA certificate with the same name hash value exist, the extension must be different (e.g., 9d66eef0.0, 9d66eef0.1, etc.). The search is performed in the ordering of the extension number, regardless of other properties of the certificates.

The certificates in CApath are only looked up when required, e.g., when building the certificate chain or when actually performing the verification of a peer certificate.

When looking up CA certificates, the OpenSSL library will first search the certificates in CAfile, then those in CApath. Certificate matching is done based on the subject name, the key identifier (if present), and the serial number as taken from the certificate to be verified. If these data do not match, the next certificate will be tried. If a first certificate matching the parameters is found, the verification process will be performed; no other certificates for the same parameters will be searched in case of failure.

In server mode, when requesting a client certificate, the server must send the list of CAs of which it will accept client certificates. This list is not influenced by the contents of CAfile or CApath and must explicitly be set using the SSL_CTX_set_client_CA_list(3) family of functions.

When building its own certificate chain, an OpenSSL client/server will try to fill in missing certificates from CAfile/ CApath, if the certificate chain was not explicitly specified (see SSL_CTX_add_extra_chain_cert(3) and SSL_CTX_use_certificate(3)).

For SSL_CTX_load_verify_locations(), the following return values can occur:

The operation failed because CAfile and CApath are NULL or the processing at one of the locations specified failed. Check the error stack to find out the reason.
The operation succeeded.

SSL_CTX_set_default_verify_paths() returns 1 on success or 0 on failure. A missing default location is still treated as a success.

Generate a CA certificate file with descriptive text from the CA certificates ca1.pem ca2.pem ca3.pem:

rm CAfile.pem
for i in ca1.pem ca2.pem ca3.pem; do
	openssl x509 -in $i -text >> CAfile.pem

Prepare the directory /some/where/certs containing several CA certificates for use as CApath:

$ cd /some/where/certs
$ rm -f *.[0-9]* *.r[0-9]*
$ for c in *.pem; do
>    [ "$c" = "*.pem" ] && continue
>    hash=$(openssl x509 -noout -hash -in "$c")
>    if egrep -q -- '-BEGIN( X509 | TRUSTED | )CERTIFICATE-' "$c"; then
>      suf=0
>      while [ -e $hash.$suf ]; do suf=$(( $suf + 1 )); done
>      ln -s "$c" $hash.$suf
>    fi
>    if egrep -q -- '-BEGIN X509 CRL-' "$c"; then
>      suf=0
>      while [ -e $hash.r$suf ]; do suf=$(( $suf + 1 )); done
>      ln -s "$c" $hash.r$suf
>    fi
> done

ssl(3), SSL_CTX_add_extra_chain_cert(3), SSL_CTX_set_cert_store(3), SSL_CTX_set_client_CA_list(3), SSL_CTX_use_certificate(3), SSL_get_client_CA_list(3)

SSL_CTX_load_verify_locations() and SSL_CTX_set_default_verify_paths() first appeared in SSLeay 0.8.0 and have been available since OpenBSD 2.4.

If several CA certificates matching the name, key identifier, and serial number condition are available, only the first one will be examined. This may lead to unexpected results if the same CA certificate is available with different expiration dates. If a “certificate expired” verification error occurs, no other certificate will be searched. Make sure to not have expired certificates mixed with valid ones.

March 27, 2018 OpenBSD-7.3