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X509_CHECK_PURPOSE(3ossl) OpenSSL X509_CHECK_PURPOSE(3ossl)

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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