X509_LOOKUP_HASH_DIR(3)

NAME
X509_LOOKUP_hash_dir, X509_LOOKUP_file, X509_load_cert_file, X509_load_crl_file, X509_load_cert_crl_file - default OpenSSL certificate lookup methods

SYNOPSIS
#include <openssl/x509_vfy.h>
X509_LOOKUP_METHOD *
X509_LOOKUP_hash_dir(void);
X509_LOOKUP_METHOD *
X509_LOOKUP_file(void);
int
X509_load_cert_file(X509_LOOKUP *ctx, const char *file, int type);
int
X509_load_crl_file(X509_LOOKUP *ctx, const char *file, int type);
int
X509_load_cert_crl_file(X509_LOOKUP *ctx, const char *file, int type);

DESCRIPTION
X509_LOOKUP_hash_dir() and X509_LOOKUP_file() are two certificate lookup methods to use with X509_STORE, provided by the OpenSSL library.

Users of the library typically do not need to create instances of these methods manually. They are created automatically by the X509_STORE_load_locations(3) or SSL_CTX_load_verify_locations(3) functions.

Internally, loading of certificates and CRLs is implemented via the functions X509_load_cert_crl_file(), X509_load_cert_file() and X509_load_crl_file(). These functions support a parameter type, which can be one of the constants FILETYPE_PEM, FILETYPE_ASN1, and FILETYPE_DEFAULT. They load certificates and/or CRLs from the specified file into a memory cache of X509_STORE objects which the given ctx parameter is associated with.

The functions X509_load_cert_file() and X509_load_crl_file() can load both PEM and DER formats depending on the type value. Because DER format cannot contain more than one certificate or CRL object (while PEM can contain several concatenated PEM objects), X509_load_cert_crl_file() with FILETYPE_ASN1 is equivalent to X509_load_cert_file().

The constant FILETYPE_DEFAULT with NULL filename causes these functions to load the default certificate store file (see X509_STORE_set_default_paths(3)).

These functions return the number of objects loaded from file or 0 in case of error.

Both methods support adding several certificate locations into one X509_STORE.

This page documents certificate store formats used by these methods and caching policy.

  File Method
The X509_LOOKUP_file() method loads all the certificates or CRLs present in a file into memory at the time the file is added as a lookup source.

The file format is ASCII text which contains concatenated PEM certificates and CRLs.

This method should be used by applications which work with a small set of CAs.

  Hashed Directory Method
X509_LOOKUP_hash_dir is a more advanced method which loads certificates and CRLs on demand, and caches them in memory once they are loaded. As of OpenSSL 1.0.0, it also checks for newer CRLs upon each lookup, so that newer CRLs are used as soon as they appear in the directory.

The directory should contain one certificate or CRL per file in PEM format, with a file name of the form hash.N for a certificate, or hash.rN for a CRL. The hash is the value returned by the X509_NAME_hash(3) function applied to the subject name for certificates or issuer name for CRLs. The hash can also be obtained via the -hash option of the openssl(1) x509 or crl commands.

The N suffix is a sequence number that starts at zero and is incremented consecutively for each certificate or CRL with the same hash value. Gaps in the sequence numbers are not supported. It is assumed that there are no more objects with the same hash beyond the first missing number in the sequence.

Sequence numbers make it possible for the directory to contain multiple certificates with the same subject name hash value. For example, it is possible to have in the store several certificates with the same subject or several CRLs with the same issuer (and, for example, a different validity period).

When checking for new CRLs, once one CRL for a given hash value is loaded, hash_dir lookup method checks only for certificates with sequence number greater than that of the already cached CRL.

Note that the hash algorithm used for subject name hashing changed in OpenSSL 1.0.0, and all certificate stores have to be rehashed when moving from OpenSSL 0.9.8 to 1.0.0.

SEE ALSO
d2i_X509_bio(3), PEM_read_PrivateKey(3), SSL_CTX_load_verify_locations(3), X509_STORE_load_locations(3)