OpenSSL

Cryptography and SSL/TLS Toolkit

X509_check_purpose

NAME

X509_check_purpose - Check the purpose of a certificate

SYNOPSIS

#include <openssl/x509v3.h>

int X509_check_purpose(X509 *x, int id, int ca);

DESCRIPTION

This function checks if certificate x was created with the purpose represented by id. If ca is nonzero, then certificate x is checked to determine if it's a possible CA with various levels of certainty possibly returned. The certificate x must be a complete certificate otherwise the function returns an error.

Below are the potential ID's that can be checked:

# define X509_PURPOSE_SSL_CLIENT        1
# define X509_PURPOSE_SSL_SERVER        2
# define X509_PURPOSE_NS_SSL_SERVER     3
# define X509_PURPOSE_SMIME_SIGN        4
# define X509_PURPOSE_SMIME_ENCRYPT     5
# define X509_PURPOSE_CRL_SIGN          6
# define X509_PURPOSE_ANY               7
# define X509_PURPOSE_OCSP_HELPER       8
# define X509_PURPOSE_TIMESTAMP_SIGN    9

The checks performed take into account the X.509 extensions keyUsage, extendedKeyUsage, and basicConstraints.

RETURN VALUES

For non-CA checks

-1 an error condition has occurred
1 if the certificate was created to perform the purpose represented by id
0 if the certificate was not created to perform the purpose represented by id

For CA checks the below integers could be returned with the following meanings:

-1 an error condition has occurred
0 not a CA or does not have the purpose represented by id
1 is a CA.
2 Only possible in old versions of openSSL when basicConstraints are absent. New versions will not return this value. May be a CA
3 basicConstraints absent but self signed V1.
4 basicConstraints absent but keyUsage present and keyCertSign asserted.
5 legacy Netscape specific CA Flags present

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