X509_SIGN(3SSL)

📦
version 4.0.3 · 6 versions
, in ubuntu stonking

💖 X509_SIGN(3SSL) 💖

okay so bestie, welcome to X509_SIGN(3SSL) — the OpenSSL page about signing stuff. Not like signing a birthday card, we're talking certificates, certificate requests and CRLs. It's giving crypto glow-up, it's giving trust chain, it's giving "I put my name on this and I mean it." ✨

🌸 NAME 🌸

X509_sign, X509_sign_ctx, X509_REQ_sign, X509_REQ_sign_ctx, X509_ACERT_sign, X509_ACERT_sign_ctx, X509_CRL_sign, X509_CRL_sign_ctx — sign certificate, certificate request, or CRL signature. that's the whole job babe, that's the assignment 👑

✨ SYNOPSIS ✨

#include <openssl/x509.h>

int X509_sign(X509 *x, EVP_PKEY *pkey, const EVP_MD *md);
int X509_sign_ctx(X509 *x, EVP_MD_CTX *ctx);

int X509_REQ_sign(X509_REQ *x, EVP_PKEY *pkey, const EVP_MD *md);
int X509_REQ_sign_ctx(X509_REQ *x, EVP_MD_CTX *ctx);

int X509_CRL_sign(X509_CRL *x, EVP_PKEY *pkey, const EVP_MD *md);
int X509_CRL_sign_ctx(X509_CRL *x, EVP_MD_CTX *ctx);

#include <openssl/x509_acert.h>

int X509_ACERT_sign(X509_ACERT *x, EVP_PKEY *pkey, const EVP_MD *md);
int X509_ACERT_sign_ctx(X509_ACERT *x, EVP_MD_CTX *ctx);

two headers, eight functions, zero notes 🎀

🦋 DESCRIPTION 🦋

X509_sign() signs certificate x using private key pkey and message digest md, and sets the signature in x. yes bestie, it literally writes the signature back into the object. X509_sign_ctx() also signs certificate x, but instead of taking a key + digest pair it uses the parameters contained in digest context ctx. very "I brought my own setup" of it.

and here's the iconic part 💅: if the certificate information includes X.509 extensions, those two functions make sure the certificate bears X.509 version 3. slay.

X509_REQ_sign(), X509_REQ_sign_ctx(), X509_ACERT_sign(), X509_ACERT_sign_ctx(), X509_CRL_sign(), and X509_CRL_sign_ctx() sign certificate requests and CRLs, respectively. same energy, different little guy. 🫶

💀 NOTES 💀

X509_sign_ctx() is the one you reach for when the default parameters for the corresponding public key and digest are not suitable. it can be used to sign keys using RSA-PSS, for example. custom queen behaviour. 👑

okay now the real tea 🍓 — for efficiency reasons, and to work around ASN.1 encoding issues, the encoding of the signed portion of a certificate, certificate request and CRL is cached internally. and if the signed portion of the structure gets modified, the encoding is not always updated, meaning a stale version is sometimes used. 😭

is that scary? lowkey no, and here's why: this is not normally a problem, because modifying the signed portion will invalidate the signature anyway, and signing will always update the encoding. so it fixes itself fr fr.

⚠️ one more thing bestie, and it's a hard fail, not a soft fail: when signing X509 certificates and certificate requests, any empty subjectKeyIdentifier (empty string) or empty authorityKeyIdentifier (empty sequence) extensions are flagged as an error and the signature operation fails. so don't ship empty IDs and expect the vibe check to pass. 🚫

🌈 RETURN VALUES 🌈

all functions return the size of the signature in bytes for success, and zero for failure. that's it. no in-between, no "kinda worked", just bytes or nothing. 💜

👑 SEE ALSO 👑

the whole friend group, honestly 🫶

🧚 HISTORY 🧚

X509_sign(), X509_REQ_sign() and X509_CRL_sign() are available in all versions of OpenSSL. day-one legends, no cap. ⭐

X509_sign_ctx(), X509_REQ_sign_ctx() and X509_CRL_sign_ctx() were added in OpenSSL 1.0.1. ✨

X509_ACERT_sign() and X509_ACERT_sign_ctx() were added in OpenSSL 3.4. the new girls on the block 💅

Copyright 2015-2026 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>.

okay that's the whole page bestie, you're officially caught up 🦋 this was X509_SIGN(3SSL) from OpenSSL 4.0.3 — 2026-09-29. go sign something iconic and stay hydrated, mwah 💖🌸💅

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