OPENSSL_SECURE_MALLOC(3SSL)

📦
version 4.0.3 · 3 versions
, in ubuntu stonking

💖 OPENSSL_SECURE_MALLOC 💖

okay bestie, welcome to OPENSSL_SECURE_MALLOC(3SSL), the page that's all about the secure heap — aka where the good stuff (private keys, obviously) goes to live its protected little life. 🌸✨

✨ NAME ✨

secure heap storage, brought to you by this whole girl gang right here:

  • 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_malloc_array
  • CRYPTO_secure_malloc_array
  • OPENSSL_secure_calloc
  • CRYPTO_secure_calloc
  • OPENSSL_secure_free
  • CRYPTO_secure_free
  • OPENSSL_secure_clear_free
  • CRYPTO_secure_clear_free
  • OPENSSL_secure_actual_size
  • CRYPTO_secure_actual_size
  • CRYPTO_secure_allocated
  • CRYPTO_secure_used

🎀 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_malloc_array(size_t num, size_t size);
void *CRYPTO_secure_malloc_array(size_t num, size_t size,
                                 const char *file, int line);

void *OPENSSL_secure_calloc(size_t num, size_t size);
void *CRYPTO_secure_calloc(size_t num, size_t size,
                           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);
size_t CRYPTO_secure_actual_size(const void *ptr);

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

🌈 DESCRIPTION 🌈

so like. pointer overruns and underruns? the little gremlins that could hand out arbitrary data from your program's dynamic memory area — where keys and other sensitive info might be chilling? yeah, no. 🙅‍♀️

to help protect applications (especially long-running servers) from exactly that mess, OpenSSL supports the concept of a "secure heap." the level and type of security guarantees you get depend on the operating system, so fr fr, it's a good idea to review the code and see if it addresses your threat model and concerns. 👀

heads up bestie: the secure heap uses a single read/write lock, so any operations that involve allocation or freeing of secure heap memory are serialised, and they block other threads. keep 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. lowkey important distinction!! 🌟

  • 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. minsize must be less than a quarter of size in any case.
  • CRYPTO_secure_malloc_initialized() — indicates whether or not the secure heap as been initialized and is available. (yes, "as been". iconic typo, we stan. 💅)
  • CRYPTO_secure_malloc_done() — releases the heap and makes the memory unavailable to the process if all secure memory has been freed. it can take noticeably long to complete, so don't be alarmed if it's giving slow. 🐌
  • 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! 🕵️‍♀️
  • 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 girl aesthetic. ✨
  • OPENSSL_secure_malloc_array(), CRYPTO_secure_malloc_array(), OPENSSL_secure_calloc(), and CRYPTO_secure_calloc() — variants of OPENSSL_secure_malloc(), CRYPTO_secure_malloc(), OPENSSL_secure_zalloc(), and CRYPTO_secure_zalloc(), respectively, that accept an additional parameter, size, which enables memory allocation operations for an array of num members size bytes each. these functions return an error if multiplication of num and size leads to an integer overflow, thus preventing allocations of an incorrect size. ty for protecting us from ourselves fr. 🫶
  • 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.. (two periods, we love a bonus dot 💀) if the argument to OPENSSL_secure_free() is NULL, nothing is done.
  • 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. wiping the receipts, as she should. 🧼
  • 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 giving generous✨
  • CRYPTO_secure_actual_size() — an alias to OPENSSL_secure_actual_size(), identical in arguments, return value, and behaviour. twin behaviour, no cap. 👯‍♀️
  • OPENSSL_secure_allocated() — tells if a pointer is allocated in the secure heap.
  • CRYPTO_secure_used() — returns the number of bytes allocated in the secure heap.

⭐ 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. (so like, success but make it ✨unprotected✨)
  • 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(), CRYPTO_secure_malloc(), OPENSSL_secure_zalloc(), CRYPTO_secure_zalloc(), OPENSSL_secure_malloc_array(), CRYPTO_secure_malloc_array(), OPENSSL_secure_calloc(), and CRYPTO_secure_calloc() return a pointer into the secure heap of the requested size, if it is initialised, a pointer returned by the underlying OPENSSL_malloc() call, if it is not, or NULL on error.
  • OPENSSL_secure_actual_size() and CRYPTO_secure_actual_size() return positive size in bytes on success or 0 on error.
  • 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 simply do not participate in the return-value economy. 🚫

🦋 SEE ALSO 🦋

👑 HISTORY 👑

  • the OPENSSL_secure_clear_free() function was added in OpenSSL 1.1.0g.
  • the second argument to CRYPTO_secure_malloc_init() was changed from an int to a size_t in OpenSSL 3.0. glow-up era. 💅
  • the OPENSSL_secure_malloc_array(), CRYPTO_secure_malloc_array(), OPENSSL_secure_calloc(), and CRYPTO_secure_calloc() functions were added in OpenSSL 3.6.

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>.

aaaand that's the whole page bestie, you ate it up. 🎀 this was version 4.0.3, dated 2026-09-29, from the OPENSSL_SECURE_MALLOC(3SSL) manual. go secure your heap, main character. 💜🦋✨

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