OPENSSL_SECURE_MALLOC(3SSL) OpenSSL OPENSSL_SECURE_MALLOC(3SSL)
NAME
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
- secure heap storage
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();
DESCRIPTION
In order to help protect applications (particularly long-running
servers) from pointer overruns or underruns that could return arbitrary
data from the program's dynamic memory area, where keys and other
sensitive information might be stored, OpenSSL supports the concept of a
"secure heap." The level and type of security guarantees depend on the
operating system. It is a good idea to review the code and see if it
addresses your threat model and concerns. It should be noted that the
secure heap uses a single read/write lock, and therefore any operations
that involve allocation or freeing of secure heap memory are serialised,
blocking 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. This protects long-term storage of private keys, but will not
necessarily put all intermediate values and computations there.
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.
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.
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 is a macro that expands to CRYPTO_secure_malloc()
and adds the "__FILE__" and "__LINE__" parameters.
OPENSSL_secure_zalloc() and CRYPTO_secure_zalloc() are like
OPENSSL_secure_malloc() and CRYPTO_secure_malloc(), respectively, except
that they call memset() to zero the memory before returning.
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.
OPENSSL_secure_clear_free() is 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.
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.
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.
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.
SEE ALSO
OPENSSL_malloc(3), BN_new(3)
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.
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>.
3.5.7 2026-06-09 OPENSSL_SECURE_MALLOC(3SSL)
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