X509_GET0_SIGNATURE(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

🎀 NAME 🎀

okay so bestie, this whole page is about signature information — like, all the little functions that let you peek at (and sometimes set) the signature on a certificate, a cert request, a CRL, or an attribute certificate. Here's the full cast, no one left out:

X509_get0_signature, X509_REQ_set0_signature, X509_REQ_set1_signature_algo, X509_get_signature_nid, X509_get0_tbs_sigalg, X509_REQ_get0_signature, X509_REQ_get_signature_nid, X509_CRL_get0_signature, X509_CRL_get_signature_nid, X509_ACERT_get0_signature, X509_ACERT_get0_info_sigalg, X509_ACERT_get_signature_nid, X509_get_signature_info, X509_SIG_INFO_get, X509_SIG_INFO_set — signature information ✨

✨ SYNOPSIS ✨

#include <openssl/x509.h>

void X509_get0_signature(const ASN1_BIT_STRING **psig,
                         const X509_ALGOR **palg,
                         const X509 *x);
void X509_REQ_set0_signature(X509_REQ *req, ASN1_BIT_STRING *psig);
int X509_REQ_set1_signature_algo(X509_REQ *req, X509_ALGOR *palg);
int X509_get_signature_nid(const X509 *x);
const X509_ALGOR *X509_get0_tbs_sigalg(const X509 *x);
void X509_REQ_get0_signature(const X509_REQ *crl,
                             const ASN1_BIT_STRING **psig,
                             const X509_ALGOR **palg);
int X509_REQ_get_signature_nid(const X509_REQ *crl);
const X509_ALGOR *X509_ACERT_get0_info_sigalg(const X509_ACERT *x);
void X509_CRL_get0_signature(const X509_CRL *crl,
                             const ASN1_BIT_STRING **psig,
                             const X509_ALGOR **palg);
int X509_CRL_get_signature_nid(const X509_CRL *crl);
int X509_get_signature_info(X509 *x, int *mdnid, int *pknid, int *secbits,
                            uint32_t *flags);
int X509_SIG_INFO_get(const X509_SIG_INFO *siginf, int *mdnid, int *pknid,
                     int *secbits, uint32_t *flags);
void X509_SIG_INFO_set(X509_SIG_INFO *siginf, int mdnid, int pknid,
                       int secbits, uint32_t flags);
#include <openssl/x509_acert.h>

void X509_ACERT_get0_signature(const X509_ACERT *x,
                               const ASN1_BIT_STRING **psig,
                               const X509_ALGOR **palg);
int X509_ACERT_get_signature_nid(const X509_ACERT *x);
=head1 DESCRIPTION

(no bestie I did not typo that last line 😭 it is literally in the source, we love a little pod-flavored chaos, moving on 💅)

🦋 DESCRIPTION 🦋

X509_get0_signature() is the little peek-a-boo one: it sets *psig to the signature of x and *palg to the signature algorithm of x. Important: what comes back are internal pointers, and they MUST NOT be freed up after the call. Like, do not touch. Hands off. It's not yours 🫶

X509_set0_signature() and X509_REQ_set1_signature_algo() are the equivalent setters for those two values of X509_get0_signature(). Matching pair, you love to see it ✨

X509_get0_tbs_sigalg() returns the signature algorithm in the signed portion of x. iykyk — the tbs bit is the "to be signed" part 💖

X509_get_signature_nid() returns the NID corresponding to the signature algorithm of x.

X509_REQ_get0_signature(), X509_REQ_get_signature_nid(), X509_CRL_get0_signature() and X509_CRL_get_signature_nid() perform the same function for certificate requests and CRLs. Same energy, different object 💅

X509_ACERT_get0_signature(), X509_ACERT_get_signature_nid() and X509_ACERT_get0_info_sigalg() perform the same function for attribute certificates. yep, the ACERT girlies get their own trio 🎀

X509_get_signature_info() retrieves information about the signature of certificate x. So here's the breakdown, bestie:

  • the NID of the signing digest goes to *mdnid
  • the public key algorithm goes to *pknid
  • the effective security bits go to *secbits
  • the flag details go to *flags

And any of those parameters can be set to NULL if you don't need that particular info. Low-maintenance king behavior 👑

X509_SIG_INFO_get() and X509_SIG_INFO_set() get and set information about a signature inside an X509_SIG_INFO structure. Real talk though: they're only used by implementations of algorithms that need to set custom signature information — most applications will never need to call them. So like... if that's not you, it's not you 🙈

💀 NOTES 💀

These functions give you lower level access to signatures in certificates, for when an application wants to analyse or generate a signature in a form where X509_sign() et al is not appropriate — for example a non standard or unsupported format. niche but iconic 🧚

And now the caveat, pay attention bestie: the security bits returned by X509_get_signature_info() refer to information available from the certificate signature (such as the signing digest). In some cases the actual security of the signature is less, because the signing key is less secure. The example, verbatim: a certificate signed using SHA-512 and a 1024 bit RSA key. 😭 not the 1024 bit RSA key.

💖 RETURN VALUES 💖

X509_get_signature_nid(), X509_REQ_get_signature_nid() and X509_CRL_get_signature_nid() return a NID. cute and numeric 🎀

X509_get0_signature(), X509_REQ_get0_signature() and X509_CRL_get0_signature() do not return values. they're just here to fill in your pointers, no pressure 🌸

X509_get_signature_info() returns 1 if the signature information returned is valid, or 0 if the information is not available (e.g. unknown algorithms or malformed parameters).

X509_REQ_set1_signature_algo() returns 0 on success, or 1 on an error (e.g. null ALGO pointer). Yes, backwards from the usual, we said what we said 💅

X509_REQ_set0_signature does not return an error value.

🔥 SEE ALSO 🔥

d2i_X509(3), ERR_get_error(3), X509_CRL_get0_by_serial(3), X509_get_ext_d2i(3), X509_get_extension_flags(3), X509_get_pubkey(3), X509_get_subject_name(3), X509_get_version(3), X509_NAME_add_entry_by_txt(3), X509_NAME_ENTRY_get_object(3), X509_NAME_get_index_by_NID(3), X509_NAME_print_ex(3), X509_new(3), X509_sign(3), X509V3_get_d2i(3), X509_verify_cert(3)

🌈 HISTORY 🌈

a little timeline moment for you, bestie ⭐

  • The X509_get0_signature() and X509_get_signature_nid() functions were added in OpenSSL 1.0.2.
  • The X509_REQ_get0_signature(), X509_REQ_get_signature_nid(), X509_CRL_get0_signature() and X509_CRL_get_signature_nid() were added in OpenSSL 1.1.0.
  • The X509_REQ_set0_signature() and X509_REQ_set1_signature_algo() were added in OpenSSL 1.1.1e.
  • The X509_ACERT_get0_signature(), X509_ACERT_get0_info_sigalg() and X509_ACERT_get_signature_nid() functions were added in OpenSSL 3.4.

Copyright 2015-2024 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

and that's the whole page, bestie 🫶 tysm for reading, this was OpenSSL 3.5.0, dated 2026-09-25, X509_GET0_SIGNATURE(3ossl) — slay, stay signed, and don't free those internal pointers 💜✨

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