C source file of program
#include <openssl/bio.h>
#include <openssl/err.h>
#include <openssl/pem.h>
#include <openssl/x509.h>
int X509_signature_dump(BIO *bp, const ASN1_STRING *sig, int indent);
int main() {
const char cert_filestr[] = "./cert-file.pem";
ASN1_STRING *asn1_sig = NULL;
X509_ALGOR *sig_type = NULL;
size_t sig_bytes = 0;
BIO *certbio = NULL;
BIO *outbio = NULL;
X509 *cert = NULL;
int ret;
OpenSSL_add_all_algorithms();
ERR_load_BIO_strings();
ERR_load_crypto_strings();
certbio = BIO_new(BIO_s_file());
outbio = BIO_new_fp(stdout, BIO_NOCLOSE);
ret = BIO_read_filename(certbio, cert_filestr);
if (! (cert = PEM_read_bio_X509(certbio, NULL, 0, NULL))) {
BIO_printf(outbio, "Error loading cert into memory\n");
exit(-1);
}
sig_type = cert->sig_alg;
asn1_sig = cert->signature;
sig_bytes = asn1_sig->length;
BIO_printf(outbio, "Signature Algorithm:\n");
if (i2a_ASN1_OBJECT(outbio, sig_type->algorithm) <= 0)
BIO_printf(outbio, "Error getting the signature algorithm.\n");
else BIO_puts(outbio, "\n\n");
BIO_printf(outbio, "Signature Length:\n%d Bytes\n\n", sig_bytes);
BIO_printf(outbio, "Signature Data:");
if (X509_signature_dump(outbio, asn1_sig, 0) != 1)
BIO_printf(outbio, "Error printing the signature data\n");
X509_free(cert);
BIO_free_all(certbio);
BIO_free_all(outbio);
exit(0);}
int X509_signature_dump(BIO *bp, const ASN1_STRING *sig, int indent) {
const unsigned char *s;
int i, n;
n=sig->length;
s=sig->data;
for (i=0; i<n; i++) {
if ((i%18) == 0) {
if (BIO_write(bp,"\n",1) <= 0) return 0;
if (BIO_indent(bp, indent, indent) <= 0) return 0;
}
if (BIO_printf(bp,"%02x%s",s[i],
((i+1) == n)?"":":") <= 0) return 0;
}
if (BIO_write(bp,"\n",1) != 1) return 0;
return 1;
}
Output :
