OPENSSL_SECURE_MALLOC(3ossl)

💖 OPENSSL_SECURE_MALLOC 💖

okay so bestie, welcome to OPENSSL_SECURE_MALLOC(3ossl) — the page about secure heap storage and honestly? it's giving VIP lounge energy 🔐✨

the whole squad on this page is: CRYPTO_secure_malloc_init, CRYPTO_secure_malloc_initialized, CRYPTO_secure_malloc_done, OPENSSL_secure_malloc, CRYPTO_secure_malloc, OPENSSL_secure_zalloc, CRYPTO_secure_zalloc, OPENSSL_secure_free, CRYPTO_secure_free, OPENSSL_secure_clear_free, CRYPTO_secure_clear_free, OPENSSL_secure_actual_size, CRYPTO_secure_allocated, CRYPTO_secure_used. yeah that's a lot of besties, we'll get to all of them 💅

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🌸 SYNOPSIS 🌸

#include <openssl/crypto.h>

int CRYPTO_secure_malloc_init(size_t size, size_t minsize);

int CRYPTO_secure_malloc_initialized();

int CRYPTO_secure_malloc_done();

void *OPENSSL_secure_malloc(size_t num);
void *CRYPTO_secure_malloc(size_t num, const char *file, int line);

void *OPENSSL_secure_zalloc(size_t num);
void *CRYPTO_secure_zalloc(size_t num, const char *file, int line);

void OPENSSL_secure_free(void* ptr);
void CRYPTO_secure_free(void *ptr, const char *, int);

void OPENSSL_secure_clear_free(void* ptr, size_t num);
void CRYPTO_secure_clear_free(void *ptr, size_t num, const char *, int);

size_t OPENSSL_secure_actual_size(const void *ptr);

int CRYPTO_secure_allocated(const void *ptr);
size_t CRYPTO_secure_used();

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🦋 DESCRIPTION 🦋

so like, the whole point here? protecting applications (especially long-running servers, the ones that just never sleep 😭) from pointer overruns or underruns — you know, the kind of chaos that could hand back arbitrary data from the program's dynamic memory area, which is exactly where keys and other sensitive info might be chillin'. OpenSSL supports the concept of a "secure heap." 🎀

ngl though, the level and type of security guarantees depend on the operating system. so it's a genuinely good idea to review the code and see if it actually addresses your threat model and concerns. do your research bestie, no cap 🔍

also, real talk: the secure heap uses a single read/write lock, which means any operations that involve allocation or freeing of secure heap memory are serialised, and that blocks other threads. with that in mind, highly concurrent applications should enable the secure heap with caution and be aware of the performance implications for multi-threaded code. 💀

if a secure heap is used, then private key BIGNUM values are stored there. that protects long-term storage of private keys, but it will not necessarily put all intermediate values and computations there. important distinction, don't skip it 🫶

• CRYPTO_secure_malloc_init() — creates the secure heap, with the specified size in bytes. the minsize parameter is the minimum size to allocate from the heap, or zero to use a reasonable default value. both size and, if specified, minsize must be a power of two, and minsize should generally be small — for example 16 or 32. and minsize must be less than a quarter of size in any case. rules are rules 👑
• CRYPTO_secure_malloc_initialized() — indicates whether or not the secure heap has been initialized and is available. vibe check for the heap ✨
• CRYPTO_secure_malloc_done() — releases the heap and makes the memory unavailable to the process if all secure memory has been freed. heads up: it can take noticeably long to complete. like, go make a snack long 🍓
• OPENSSL_secure_malloc() — allocates num bytes from the heap. if CRYPTO_secure_malloc_init() is not called, this is equivalent to calling OPENSSL_malloc(). it's a macro that expands to CRYPTO_secure_malloc() and adds the __FILE__ and __LINE__ parameters. sneaky but iconic 💅
• OPENSSL_secure_zalloc() and CRYPTO_secure_zalloc() — like OPENSSL_secure_malloc() and CRYPTO_secure_malloc(), respectively, except that they call memset() to zero the memory before returning. clean slate behavior 🧚
• OPENSSL_secure_free() — releases the memory at ptr back to the heap. it must be called with a value previously obtained from OPENSSL_secure_malloc(). if CRYPTO_secure_malloc_init() is not called, this is equivalent to calling OPENSSL_free(). it exists for consistency with OPENSSL_secure_malloc(), and is a macro that expands to CRYPTO_secure_free() and adds the __FILE__ and __LINE__ parameters. if the argument to OPENSSL_secure_free() is NULL, nothing is done. no drama, no crash 🌈
• OPENSSL_secure_clear_free() — similar to OPENSSL_secure_free() except that it has an additional num parameter which is used to clear the memory if it was not allocated from the secure heap. if CRYPTO_secure_malloc_init() is not called, this is equivalent to calling OPENSSL_clear_free(). if the argument to OPENSSL_secure_clear_free() is NULL, nothing is done. bye bye data, securely 👋
• OPENSSL_secure_actual_size() — tells the actual size allocated to the pointer. implementations may allocate more space than initially requested, in order to "round up" and reduce secure heap fragmentation. it's not lying to you, it's just rounding up for the aesthetic 📐
• OPENSSL_secure_allocated() — tells if a pointer is allocated in the secure heap. yes/no, in or out 🎟️
• CRYPTO_secure_used() — returns the number of bytes allocated in the secure heap. the receipt 🧾

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✨ RETURN VALUES ✨

• CRYPTO_secure_malloc_init() returns 0 on failure, 1 if successful, and 2 if successful but the heap could not be protected by memory mapping. yeah, three possible outcomes, keep up 😌
• CRYPTO_secure_malloc_initialized() returns 1 if the secure heap is available (that is, if CRYPTO_secure_malloc_init() has been called, but CRYPTO_secure_malloc_done() has not been called or failed) or 0 if not.
• OPENSSL_secure_malloc() and OPENSSL_secure_zalloc() return a pointer into the secure heap of the requested size, or NULL if memory could not be allocated.
• CRYPTO_secure_allocated() returns 1 if the pointer is in the secure heap, or 0 if not.
• CRYPTO_secure_malloc_done() returns 1 if the secure memory area is released, or 0 if not.
• OPENSSL_secure_free() and OPENSSL_secure_clear_free() return no values. they just do the thing 💅

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👀 SEE ALSO 👀

• OPENSSL_malloc(3)
• BN_new(3)

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📜 HISTORY 📜

• The OPENSSL_secure_clear_free() function was added in OpenSSL 1.1.0g. throwback 🎀
• The second argument to CRYPTO_secure_malloc_init() was changed from an int to a size_t in OpenSSL 3.0. glow up ✨

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💜 COPYRIGHT 💜

Copyright 2015-2025 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>.

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and that's the whole page bestie, we ate and left no crumbs 🍽️💖 this was version 3.5.9, dated 2026-09-29 — go forth and secure-heap responsibly, mwah 💋