Creating a Network of Trust Using X.509 Certifi cates - Implementing SSL/TLS Using Cryptography and PKI - page 266

Compare the x509_certificate structure in Listing 5-10 with the offi cial ITU
defi nition shown in Listing 5-1 and signed_x509_certificate with Listing 5-2.
The goal of the certifi cate parsing process is to take a “blob” of unstructured
bytes and turn it into a signed_x509_certificate instance. As you can see
above, there's quite a bit of unallocated memory in this structure defi nition,
so the fi rst thing you need is an initializer function, as shown in Listing 5-11.
Listing 5-11: “x509.c” init_x509_certifi cate
void init_x509_certificate( signed_x509_certificate *certificate )
{
set_huge( &certificate->tbsCertificate.serialNumber, 1 );
memset( &certificate->tbsCertificate.issuer, 0, sizeof( name ) );
memset( &certificate->tbsCertificate.subject, 0, sizeof( name ) );
certificate->tbsCertificate.subjectPublicKeyInfo.rsa_public_key.modulus =
malloc( sizeof( huge ) );
certificate->tbsCertificate.subjectPublicKeyInfo.rsa_public_key.exponent =
malloc( sizeof( huge ) );
set_huge(
certificate->tbsCertificate.subjectPublicKeyInfo.rsa_public_key.modulus,
0 );
set_huge(
certificate->tbsCertificate.subjectPublicKeyInfo.rsa_public_key.exponent,
0 );
set_huge( &certificate->signature_value, 0 );
certificate->tbsCertificate.certificate_authority = 0;
}
You also need, of course, a companion “free” function as shown in Listing 5-12.
Listing 5-12: “x509.c” free_x509_certifi cate
static void free_x500_name( name *x500_name )
{
if ( x500_name->idAtCountryName ) { free( x500_name->idAtCountryName ); }
if ( x500_name->idAtStateOrProvinceName ) { free( x500_name-
>idAtStateOrProvinceName ); }
if ( x500_name->idAtLocalityName ) { free( x500_name->idAtLocalityName ); }
if ( x500_name->idAtOrganizationName ) { free( x500_name->idAtOrganizationName
); }
if ( x500_name->idAtOrganizationalUnitName ) { free( x500_name-
>idAtOrganizationalUnitName ); }
if ( x500_name->idAtCommonName ) { free( x500_name->idAtCommonName ); }
}
void free_x509_certificate( signed_x509_certificate *certificate )
{
free_huge( &certificate->tbsCertificate.serialNumber );
free_x500_name( &certificate->tbsCertificate.issuer );