X509_cmp.3ssl - Man Page

compare X509 certificates and related values


 #include <openssl/x509.h>

 int X509_cmp(const X509 *a, const X509 *b);
 int X509_NAME_cmp(const X509_NAME *a, const X509_NAME *b);
 int X509_issuer_and_serial_cmp(const X509 *a, const X509 *b);
 int X509_issuer_name_cmp(const X509 *a, const X509 *b);
 int X509_subject_name_cmp(const X509 *a, const X509 *b);
 int X509_CRL_cmp(const X509_CRL *a, const X509_CRL *b);
 int X509_CRL_match(const X509_CRL *a, const X509_CRL *b);


This set of functions are used to compare X509 objects, including X509 certificates, X509 CRL objects and various values in an X509 certificate.

The X509_cmp() function compares two X509 objects indicated by parameters a and b. The comparison is based on the memcmp result of the hash values of two X509 objects and the canonical (DER) encoding values.

The X509_NAME_cmp() function compares two X509_NAME objects indicated by parameters a and b. The comparison is based on the memcmp result of the canonical (DER) encoding values of the two objects. i2d_X509_NAME(3) has a more detailed description of the DER encoding of the X509_NAME structure.

The X509_issuer_and_serial_cmp() function compares the serial number and issuer values in the given X509 objects a and b.

The X509_issuer_name_cmp(), X509_subject_name_cmp() and X509_CRL_cmp() functions are effectively wrappers of the X509_NAME_cmp() function. These functions compare issuer names and subject names of the  objects, or issuers of X509_CRL objects, respectively.

The X509_CRL_match() function compares two X509_CRL objects. Unlike the X509_CRL_cmp() function, this function compares the whole CRL content instead of just the issuer name.

Return Values

Like common memory comparison functions, the X509 comparison functions return an integer less than, equal to, or greater than zero if object a is found to be less than, to match, or be greater than object b, respectively.

X509_NAME_cmp(), X509_issuer_and_serial_cmp(), X509_issuer_name_cmp(), X509_subject_name_cmp() and X509_CRL_cmp() may return -2 to indicate an error.


These functions in fact utilize the underlying memcmp of the C library to do the comparison job. Data to be compared varies from DER encoding data, hash value or ASN1_STRING. The sign of the comparison can be used to order the objects but it does not have a special meaning in some cases.

X509_NAME_cmp() and wrappers utilize the value -2 to indicate errors in some circumstances, which could cause confusion for the applications.

See Also

i2d_X509_NAME(3), i2d_X509(3)

Referenced By

The man pages X509_CRL_cmp.3ssl(3), X509_CRL_match.3ssl(3), X509_issuer_and_serial_cmp.3ssl(3), X509_issuer_name_cmp.3ssl(3), X509_NAME_cmp.3ssl(3) and X509_subject_name_cmp.3ssl(3) are aliases of X509_cmp.3ssl(3).

2021-02-10 1.1.1i OpenSSL