SSL_CTX_SET_...ULT_PASSWD_CB(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💅 SSL_CTX_set_default_passwd_cb, SSL_CTX_set_default_passwd_cb_userdata, SSL_CTX_get_default_passwd_cb, SSL_CTX_get_default_passwd_cb_userdata, SSL_set_default_passwd_cb, SSL_set_default_passwd_cb_userdata, SSL_get_default_passwd_cb, SSL_get_default_passwd_cb_userdata — set or get passwd callback for encrypted PEM file handling

okay so this is the OpenSSL crew's page (3ossl, bestie, that's the manual section 🎀) and it's literally all about who holds the password when you're loading or storing an encrypted PEM file. Eight whole functions. Buckle up, it's not that deep but it is iconic ✨

🌸 SYNOPSIS 🌸

#include <openssl/ssl.h>

void SSL_CTX_set_default_passwd_cb(SSL_CTX *ctx, pem_password_cb *cb);
void SSL_CTX_set_default_passwd_cb_userdata(SSL_CTX *ctx, void *u);
pem_password_cb *SSL_CTX_get_default_passwd_cb(SSL_CTX *ctx);
void *SSL_CTX_get_default_passwd_cb_userdata(SSL_CTX *ctx);

void SSL_set_default_passwd_cb(SSL *s, pem_password_cb *cb);
void SSL_set_default_passwd_cb_userdata(SSL *s, void *u);
pem_password_cb *SSL_get_default_passwd_cb(SSL *s);
void *SSL_get_default_passwd_cb_userdata(SSL *s);

💖 DESCRIPTION 💖

so there's basically an SSL_CTX flavor and an SSL flavor, and they do the same little dance 🩰

The SSL_CTX squad:

  • SSL_CTX_set_default_passwd_cb() — sets the default password callback that gets called when you load/store a PEM certificate with encryption. that's her job 💅
  • SSL_CTX_set_default_passwd_cb_userdata() — sets a pointer to userdata, u, which gets handed to the password callback whenever it's invoked. think lil care package 🎁
  • SSL_CTX_get_default_passwd_cb() — returns a function pointer to the password callback currently set in ctx. and if nobody explicitly set one? you get the NULL pointer, sorry babe 😭
  • SSL_CTX_get_default_passwd_cb_userdata() — returns a pointer to the userdata currently set in ctx. again, no userdata explicitly set means NULL pointer. the vibes are empty 🫠

The SSL squad: SSL_set_default_passwd_cb(), SSL_set_default_passwd_cb_userdata(), SSL_get_default_passwd_cb() and SSL_get_default_passwd_cb_userdata() do literally the exact same function as their SSL_CTX counterparts, but on an SSL object instead. same energy, different struct 🦋

🧚 the callback itself (main character energy)

the password callback must be provided by the application — nobody's doing it for you, bestie. it hands back the password to be used during decryption. on invocation you get a pointer to userdata. the function must store the password into the provided buffer buf, which is of size size. the actual length of the password must be returned to the calling function. and rwflag tells you whether the callback is being used for reading/decryption (rwflag=0) or writing/encryption (rwflag=1). for more deets, go see pem_password_cb(3) 📖

🔥 NOTES 🔥

when loading or storing private keys, a password might be supplied to protect the private key. how you supply it is, like, very application-dependent:

  • if only one private key is handled, it can be practical to have the callback handle the password dialog interactively. cute, intimate, one-on-one 🫶
  • if several keys have to be handled, it can be practical to ask for the password once, then keep it in memory and use it several times. efficiency queen 👑 in that last case, the password could be stored into the userdata storage, and the callback just returns the password already stored.

when asking for the password interactively, the callback can use rwflag to check whether an item shall be encrypted (rwflag=1). in that case the password dialog may ask for the same password twice for comparison, to catch typos that would make decryption impossible. yes, it's the "confirm password" field and it's there for a reason 💀

other items in PEM formatting (certificates) can also be encrypted — it is however not usual, since certificate information is considered public. like, why hide it, it's giving nothing to hide 🙈

⭐ RETURN VALUES ⭐

these functions do not provide diagnostic information. that's it. that's the whole section. no notes 💅

🌈 EXAMPLES 🌈

this example returns the password provided as userdata to the calling function. the password is considered to be a '\0' terminated string. if the password does not fit into the buffer, the password is truncated (sorry, no overflow drama here 🍓):

int my_cb(char *buf, int size, int rwflag, void *u)
{
    strncpy(buf, (char *)u, size);
    buf[size - 1] = '\0';
    return strlen(buf);
}

🦋 SEE ALSO 🦋

👑 HISTORY 👑

SSL_CTX_get_default_passwd_cb(), SSL_CTX_get_default_passwd_cb_userdata(), SSL_set_default_passwd_cb() and SSL_set_default_passwd_cb_userdata() were added in OpenSSL 1.1.0. glow-up timing fr fr ✨

Copyright 2000-2019 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, go forth and encrypt responsibly

and that's a wrap bestie 🎀 this was OpenSSL 3.5.0, dated 2026-09-2, and it ate, no cap 💅✨

📦 where this page comes from