SSL_CTX_SET_SECURITY_LEVEL(3ossl) OpenSSL SSL_CTX_SET_SECURITY_LEVEL(3ossl)
NAME
SSL_CTX_set_security_level, SSL_set_security_level,
SSL_CTX_get_security_level, SSL_get_security_level,
SSL_CTX_set_security_callback, SSL_set_security_callback,
SSL_CTX_get_security_callback, SSL_get_security_callback,
SSL_CTX_set0_security_ex_data, SSL_set0_security_ex_data,
SSL_CTX_get0_security_ex_data, SSL_get0_security_ex_data - SSL/TLS
security framework
SYNOPSIS
#include <openssl/ssl.h>
void SSL_CTX_set_security_level(SSL_CTX *ctx, int level);
void SSL_set_security_level(SSL *s, int level);
int SSL_CTX_get_security_level(const SSL_CTX *ctx);
int SSL_get_security_level(const SSL *s);
void SSL_CTX_set_security_callback(SSL_CTX *ctx,
int (*cb)(const SSL *s, const SSL_CTX *ctx,
int op, int bits, int nid,
void *other, void *ex));
void SSL_set_security_callback(SSL *s,
int (*cb)(const SSL *s, const SSL_CTX *ctx,
int op, int bits, int nid,
void *other, void *ex));
int (*SSL_CTX_get_security_callback(const SSL_CTX *ctx))(const SSL *s,
const SSL_CTX *ctx,
int op, int bits,
int nid, void *other,
void *ex);
int (*SSL_get_security_callback(const SSL *s))(const SSL *s,
const SSL_CTX *ctx, int op,
int bits, int nid, void *other,
void *ex);
void SSL_CTX_set0_security_ex_data(SSL_CTX *ctx, void *ex);
void SSL_set0_security_ex_data(SSL *s, void *ex);
void *SSL_CTX_get0_security_ex_data(const SSL_CTX *ctx);
void *SSL_get0_security_ex_data(const SSL *s);
DESCRIPTION
The functions SSL_CTX_set_security_level(3) and SSL_set_security_level()
set the security level to level. If not set the library default security
level is used.
The functions SSL_CTX_get_security_level() and SSL_get_security_level()
retrieve the current security level.
SSL_CTX_set_security_callback(), SSL_set_security_callback(),
SSL_CTX_get_security_callback() and SSL_get_security_callback() get or
set the security callback associated with ctx or s. If not set a default
security callback is used. The meaning of the parameters and the
behaviour of the default callbacks is described below.
SSL_CTX_set0_security_ex_data(), SSL_set0_security_ex_data(),
SSL_CTX_get0_security_ex_data() and SSL_get0_security_ex_data() set the
extra data pointer passed to the ex parameter of the callback. This value
is passed to the callback verbatim and can be set to any convenient
application specific value.
DEFAULT CALLBACK BEHAVIOUR
If an application doesn't set its own security callback the default
callback is used. It is intended to provide sane defaults. The meaning of
each level is described below.
Level 0
Everything is permitted. This retains compatibility with previous
versions of OpenSSL.
Level 1
The security level corresponds to a minimum of 80 bits of security.
Any parameters offering below 80 bits of security are excluded. As a
result RSA, DSA and DH keys shorter than 1024 bits and ECC keys
shorter than 160 bits are prohibited. Any cipher suite using MD5 for
the MAC is also prohibited. Any cipher suites using CCM with a 64 bit
authentication tag are prohibited. Note that signatures using SHA1
and MD5 are also forbidden at this level as they have less than 80
security bits. Additionally, SSLv3, TLS 1.0, TLS 1.1 and DTLS 1.0 are
all disabled at this level.
Level 2
Security level set to 112 bits of security. As a result RSA, DSA and
DH keys shorter than 2048 bits and ECC keys shorter than 224 bits are
prohibited. In addition to the level 1 exclusions any cipher suite
using RC4 is also prohibited. Compression is disabled.
Level 3
Security level set to 128 bits of security. As a result RSA, DSA and
DH keys shorter than 3072 bits and ECC keys shorter than 256 bits are
prohibited. In addition to the level 2 exclusions cipher suites not
offering forward secrecy are prohibited. Session tickets are
disabled.
Level 4
Security level set to 192 bits of security. As a result RSA, DSA and
DH keys shorter than 7680 bits and ECC keys shorter than 384 bits are
prohibited. Cipher suites using SHA1 for the MAC are prohibited.
Level 5
Security level set to 256 bits of security. As a result RSA, DSA and
DH keys shorter than 15360 bits and ECC keys shorter than 512 bits
are prohibited.
APPLICATION DEFINED SECURITY CALLBACKS
An application defined security callback is installed with
SSL_CTX_set_security_callback() or SSL_set_security_callback() and
replaces the default callback. It is consulted whenever the library needs
to decide whether an algorithm, key, parameter or protocol version meets
the configured security level. It should return 1 to permit the operation
and 0 to reject it. A rejected parameter is not advertised or used, as
appropriate.
The callback arguments are:
s, ctx
The SSL or SSL_CTX the check applies to. One of the two is NULL:
checks originating from a connection pass s (with ctx NULL), and
checks originating from a context pass ctx (with s NULL).
op The operation being checked, one of the SSL_SECOP_* values below.
bits
The number of bits of security the parameter provides, or 0 when not
meaningful for op.
nid An identifier whose meaning depends on op, or NID_undef when not
applicable.
other
A pointer to the object being checked, whose type depends on op as
listed below. It is NULL when no object is associated with the
operation.
ex The extra data pointer previously set with
SSL_CTX_set0_security_ex_data() or SSL_set0_security_ex_data(), or
NULL.
Several operations have _SUPPORTED, _SHARED and _CHECK variants. The
supported variant checks a parameter before advertising support for it.
The shared variant checks a parameter when selecting from the options
offered by both peers. The check variant checks a parameter the peer has
selected before accepting it.
The defined operations, and the corresponding type of other, are:
SSL_SECOP_CIPHER_SUPPORTED, SSL_SECOP_CIPHER_SHARED,
SSL_SECOP_CIPHER_CHECK
Advertise/select/accept a TLS cipher suite. other is the SSL_CIPHER.
SSL_SECOP_CURVE_SUPPORTED, SSL_SECOP_CURVE_SHARED, SSL_SECOP_CURVE_CHECK
Advertise/select/accept a named group used for key exchange, either
an elliptic curve or a finite-field DH group. nid is the group and
other points to its two byte TLS codepoint.
SSL_SECOP_SIGALG_SUPPORTED, SSL_SECOP_SIGALG_SHARED,
SSL_SECOP_SIGALG_CHECK, SSL_SECOP_SIGALG_MASK
Advertise/select/accept a signature algorithm used in the handshake;
SSL_SECOP_SIGALG_MASK is used when building the mask of permitted
signature algorithms. nid is its hash and other points to its two
byte TLS codepoint.
SSL_SECOP_VERSION
Negotiate a protocol version. nid is the version, for example
TLS1_2_VERSION, and other is NULL.
SSL_SECOP_TMP_DH
Use an ephemeral DH key. other is the EVP_PKEY.
SSL_SECOP_EE_KEY, SSL_SECOP_CA_KEY
Accept an end entity or CA certificate public key. other is the X509
certificate.
SSL_SECOP_TICKET, SSL_SECOP_COMPRESSION
Issue or accept a session ticket, or enable record compression. other
is NULL.
NOTES
The default security level can be configured when OpenSSL is compiled by
setting -DOPENSSL_TLS_SECURITY_LEVEL=level. If not set then 2 is used.
The security framework disables or reject parameters inconsistent with
the set security level. In the past this was difficult as applications
had to set a number of distinct parameters (supported ciphers, supported
curves supported signature algorithms) to achieve this end and some cases
(DH parameter size for example) could not be checked at all.
By setting an appropriate security level much of this complexity can be
avoided.
The bits of security limits affect all relevant parameters including
cipher suite encryption algorithms, supported ECC curves, supported
signature algorithms, DH parameter sizes, certificate key sizes and
signature algorithms. This limit applies no matter what other custom
settings an application has set: so if the cipher suite is set to ALL
then only cipher suites consistent with the security level are
permissible.
See SP800-57 for how the security limits are related to individual
algorithms.
Some security levels require large key sizes for non-ECC public key
algorithms which can severely degrade performance. For example 256 bits
of security requires the use of RSA keys of at least 15360 bits in size.
Some restrictions can be gracefully handled: for example cipher suites
offering insufficient security are not sent by the client and will not be
selected by the server. Other restrictions such as the peer certificate
key size or the DH parameter size will abort the handshake with a fatal
alert.
Attempts to set certificates or parameters with insufficient security are
also blocked. For example trying to set a certificate using a 512 bit RSA
key or a certificate with a signature with SHA1 digest at level 1 using
SSL_CTX_use_certificate(). Applications which do not check the return
values for errors will misbehave: for example it might appear that a
certificate is not set at all because it had been rejected.
RETURN VALUES
SSL_CTX_set_security_level(3) and SSL_set_security_level() do not return
values.
SSL_CTX_get_security_level() and SSL_get_security_level() return a
integer that represents the security level with SSL_CTX or SSL,
respectively.
SSL_CTX_set_security_callback() and SSL_set_security_callback() do not
return values.
SSL_CTX_get_security_callback() and SSL_get_security_callback() return
the pointer to the security callback or NULL if the callback is not set.
SSL_CTX_get0_security_ex_data() and SSL_get0_security_ex_data() return
the extra data pointer or NULL if the ex data is not set.
SEE ALSO
ssl(7)
HISTORY
These functions were added in OpenSSL 1.1.0.
COPYRIGHT
Copyright 2014-2026 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>.
3.6.5 2026-09-29 SSL_CTX_SET_SECURITY_LEVEL(3ossl)
openssl 3.6.5 - Generated Sat Oct 3 08:34:16 CDT 2026