List of SSL OP Flags
Option Flags[edit]
This page lists all the SSL_OP flags available in OpenSSL. These values are passed to the SSL_CTX_set_options(), SSL_CTX_clear_options() functions and returned by the SSL_CTX_get_options() function (and corresponding SSL-equivalents).
Options with a value of 0 have no effect.
OpenSSL 3.0 changed the type of the option value to be uint64_t, to support more than 32 options. In addition, the definitions were changed to use the SSL_OP_BIT() macro.
Table of Options[edit]
| Option Name | Description | 1.0.2 value | 1.1.0 value | 1.1.1 value | 3.0 value |
|---|---|---|---|---|---|
| SSL_OP_MICROSOFT_SESS_ID_BUG | No effect. | 0x00000001 | 0 | 0** | 0 |
| SSL_OP_NO_EXTENDED_MASTER_SECRET | Disables (RFC7627) Extended Master Secret support. | Not defined | Not defined | Not defined | SSL_OP_BIT(0) |
| SSL_OP_NETSCAPE_CHALLENGE_BUG | No effect. | 0x00000002 | 0 | 0** | 0 |
| SSL_OP_CLEANSE_PLAINTEXT | Cleanse plaintext copies of data delivered to the application. | Not defined | Not defined | Not defined | SSL_OP_BIT(1) |
| SSL_OP_LEGACY_SERVER_CONNECT | Allow legacy insecure renegotiation between OpenSSL and unpatched servers only. | 0x00000004 | 0x00000004 | 0x00000004U | SSL_OP_BIT(2) |
| SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG | No effect. | 0x00000008 | 0 | 0** | 0 |
| SSL_OP_ENABLE_KTLS | KTLS (Linux Kernel TLS) Support | Not defined | Not defined | Not defined | SSL_OP_BIT(3) |
| SSL_OP_TLSEXT_PADDING | Adds a padding extension to ensure the ClientHello size is never between 256 and 511 bytes in length. | 0x00000010 | 0x00000010 | 0x00000010U | SSL_OP_BIT(4) |
| SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER | Accept large records (18K+) from Microsoft servers/clients. | 0x00000020 | 0 | 0** | 0 |
| SSL_OP_SAFARI_ECDHE_ECDSA_BUG | Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari on OS X. OS X 10.8...10.8.3 has broken support for ECDHE-ECDSA ciphers. | 0x00000040 | 0x00000040 | 0x00000040U | SSL_OP_BIT(6) |
| SSL_OP_SSLEAY_080_CLIENT_DH_BUG | Allow invalid client DH parameters during client key exchange. | 0x00000080 | 0 | 0** | 0 |
| SSL_OP_IGNORE_UNEXPECTED_EOF | Ignore missing close-notify alerts. | Not defined | Not defined | Not defined | SSL_OP_BIT(7) |
| SSL_OP_TLS_D5_BUG | Allow invalid RSA encrypted length from client during client key exchange. | 0x00000100 | 0 | 0** | 0 |
| SSL_OP_ALLOW_CLIENT_RENEGOTIATION | Allow the use of client renegotiation. | Not defined | Not defined | Not defined | SSL_OP_BIT(8) |
| SSL_OP_TLS_BLOCK_PADDING_BUG | Compensate for incorrect padding. | 0x00000200 | 0 | 0** | 0 |
| SSL_OP_DISABLE_TLSEXT_CA_NAMES | Disable TLS extension CA names for Windows compatibility. | Not defined | Not defined | Not defined | SSL_OP_BIT(9) |
| SSL_OP_ALLOW_NO_DHE_KEX | In TLSv1.3 allow a non-(EC)DHE-based key exchange mode | Not defined | Not defined | 0x00000400U | SSL_OP_BIT(10) |
| SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS | Disables a counter-measure against a SSL 3.0/TLS 1.0 protocol vulnerability affecting CBC ciphers, which cannot be handled by some broken (Microsoft) SSL implementations. | 0x00000800 | 0x00000800 | 0x00000800U | SSL_OP_BIT(11) |
| SSL_OP_NO_QUERY_MTU | DTLS PMTU option. | 0x00001000 | 0x00001000 | 0x00001000U | SSL_OP_BIT(12) |
| SSL_OP_COOKIE_EXCHANGE | Turn on Cookie Exchange (on relevant for servers). | 0x00002000 | 0x00002000 | 0x00002000U | SSL_OP_BIT(13) |
| SSL_OP_NO_TICKET | Don't use RFC4507 ticket extension. | 0x00004000 | 0x00004000 | 0x00004000U | SSL_OP_BIT(14) |
| SSL_OP_CISCO_ANYCONNECT | Use Cisco's version identifier of DTLS_BAD_VER (only with deprecated DTLSv1_client_method()). | 0x00008000 | 0x00008000 | 0x00008000U | SSL_OP_BIT(15) |
| SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION | As server, disallow session resumption on renegotiation. | 0x00010000 | 0x00010000 | 0x00010000U | SSL_OP_BIT(16) |
| SSL_OP_NO_COMPRESSION | Don't use compression even if supported. This is on by default, but not in SSL_OP_ALL. | 0x00020000 | 0x00020000 | 0x00020000U | SSL_OP_BIT(17) |
| SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION | Permit unsafe legacy renegotiation. | 0x00040000 | 0x00040000 | 0x00040000U | SSL_OP_BIT(18) |
| SSL_OP_SINGLE_ECDH_USE | If set, always create a new key when using tmp_ecdh parameters. | 0x00080000 | 0 | 0 | 0 |
| SSL_OP_NO_ENCRYPT_THEN MAC | Disable encrypt-then-MAC | Not defined | Not defined | 0x00080000U | SSL_OP_BIT(19) |
| SSL_OP_SINGLE_DH_USE | If set, always create a new key when using tmp_dh parameters (In recent 1.0.2, does nothing: retained for compatibility). | 0x00100000 | 0 | 0 | 0 |
| SSL_OP_ENABLE_MIDDLEBOX_COMPAT | Enable TLSv1.3 Compatibility mode. This is on by default, but not in SSL_OP_ALL. | Not defined | Not defined | 0x00100000 | SSL_OP_BIT(20) |
| SSL_OP_PRIORITIZE_CHACHA | Prioritize ChaCha20Poly1305 on servers when client does. | Not defined | Not defined | 0x00200000U | SSL_OP_BIT(21) |
| SSL_OP_CIPHER_SERVER_PREFERENCE | Set on servers to choose the cipher according to the server's preferences | 0x00400000 | 0x00400000 | 0x00400000U | SSL_OP_BIT(22) |
| SSL_OP_TLS_ROLLBACK_BUG | Allow a client to specify SSLv3.0 in the pre-master secret even if TLSv1.0 was specified in the ClientHello. | 0x00800000 | 0x00800000 | 0x00800000U | SSL_OP_BIT(23) |
| SSL_OP_NO_SSLv2 | Disable SSLv2. | 0x01000000 | 0 | 0 | 0 |
| SSL_OP_NO_ANTI_REPLAY | Disable anti-replay support | Not defined | Not defined | 0x01000000U | SSL_OP_BIT(24) |
| SSL_OP_NO_SSLv3 | Disable SSLv3. | 0x02000000 | 0x02000000 | 0x02000000U | SSL_OP_BIT(25) |
| SSL_OP_NO_TLSv1/SSL_OP_NO_DTLSv1 | Disable TLSv1/DTLSv1. | 0x04000000 | 0x04000000 | 0x04000000U | SSL_OP_BIT(26) |
| SSL_OP_NO_TLSv1_2/SSL_OP_NO_DTLSv1_2 | Disable TLSv1.2/DTLSv1.2. | 0x08000000 | 0x08000000 | 0x08000000U | SSL_OP_BIT(27) |
| SSL_OP_NO_TLSv1_1 | Disable TLSv1.1. | 0x10000000 | 0x10000000 | 0x10000000U | SSL_OP_BIT(28) |
| SSL_OP_NETSCAPE_CA_DN_BUG | 0x20000000 | 0 | 0 | 0 | |
| SSL_OP_NO_TLSv1_3 | Diable TLSv1.3 | Not defined | Not defined | 0x20000000U | SSL_OP_BIT(29) |
| SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG | 0x40000000 | 0 | 0 | 0 | |
| SSL_OP_NO_RENEGOTIATION | Disallow all renegotiation | Not defined | Not defined | 0x40000000U | SSL_OP_BIT(30) |
| SSL_OP_CRYPTOPRO_TLSEXT_BUG | Adds a ServerHello TLSEXT when using a GOST cipher. | 0x80000000 | 0x80000000 | 0x80000000U | SSL_OP_BIT(31) |
| SSL_OP_PKCS1_CHECK_1 | No effect. | 0 | 0 | 0 | 0 |
| SSL_OP_PKCS1_CHECK_2 | No effect. | 0 | 0 | 0 | 0 |
| SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG | No effect. | 0 | 0 | 0 | 0 |
| SSL_OP_MSIE_SSLV2_RSA_PADDING | No effect. | 0 | 0 | 0 | 0 |
| SSL_OP_EPHEMERAL_RSA | No effect. | 0 | 0 | 0 | 0 |
| SSL_OP_NO_SSL_MASK | SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1 | SSL_OP_NO_TLSv1_1 | SSL_OP_NO_TLSv1_2 | SSL_OP_NO_TLSv1_3 | 0x1F000000 | 0x1E000000 | 0x3E000000U | (See description) |
| SSL_OP_NO_DTLS_MASK | SSL_OP_NO_DTLSv1 | SSL_OP_NO_DTLSv1_2 | Not defined | Not defined | 0x0C000000U | (See description) |
| SSL_OP_ALL | Default set of options. | 0x80000BFF | 0x80000BFF | 0x80000854U | (See below) |
Note: ** In this version, the original bit value (non-zero) is available for re-use in the next version.
SSL_OP_ALL[edit]
OpenSSL 3.0[edit]
In OpenSSL 3.0, the number of options contained within SSL_OP_ALL has been reduced:
- SSL_OP_CRYPTOPRO_TLSEXT_BUG
- SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
- SSL_OP_TLSEXT_PADDING
- SSL_OP_SAFARI_ECDHE_ECDSA_BUG
OpenSSL 1.1.1[edit]
In OpenSSL 1.1.1, the SSL_OP_ALL option changed value to include only those bits that have a defintion. This means that 1.1.0 and 1.1.1, although ABI compatible, have different values for default enabled options. The result of this is that several option bits marked by ** cannot be re-assigned until 3.0.0.
OpenSSL 1.1.0[edit]
As of 1.1.0, these options are enabled by default via SSL_OP_ALL:
- SSL_OP_CRYPTOPRO_TLSEXT_BUG
- SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
- SSL_OP_LEGACY_SERVER_CONNECT
- SSL_OP_TLSEXT_PADDING
- SSL_OP_SAFARI_ECDHE_ECDSA_BUG
Enabled by Default[edit]
The following options are enabled by default (1.1.1 and 3.0), but are not included in SSL_OP_ALL:
- SSL_OP_NO_COMPRESSION
- SSL_OP_ENABLE_MIDDLEBOX_COMPAT
They can be disabled via SSL_clear_options(). A future version of OpenSSL may not set these by default.
Protocol Version Options[edit]
The following options control the protocols enabled on an SSL or SSL_CTX:
- SSL_OP_NO_SSLv2
- SSL_OP_NO_SSLv3
- SSL_OP_NO_TLSv1
- SSL_OP_NO_TLSv1_1
- SSL_OP_NO_TLSv1_2
- SSL_OP_NO_TLSv1_3
- SSL_OP_NO_DTLSv1
- SSL_OP_NO_DTLSv1_2
These options are deprecated as of 1.1.0, use SSL_CTX_set_min_proto_version() and SSL_CTX_set_max_proto_version() instead.
Available Bits[edit]
The the change from unsigned long to uin64_t, many more options are now available.
As of this writing (just before 3.0 is released), the following bits are available (i.e. unused):
- SSL_OP_BIT(5)
- SSL_OP_BIT(32) through SSL_OP_BIT(63)
Bit values greater than 63 are not permitted and may cause undefined behavior.
Historical Options and Notes[edit]
SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG[edit]
This option does nothing, but was retained for compatibility. In 1.0.1 this option had a value of 0x00000010, but that was taken over by SSL_OP_TLS_PADDING in 1.0.2; this option's value was changed to 0 in 1.0.2. It was included in SSL_OP_ALL. The defintion was removed from 1.1.0.
SSL_OP_MSIE_SSLV2_RSA_PADDING[edit]
This option does nothing, but was retained for compatibility. In 1.0.1, this option had a value of 0x00000040; this option's value was changed to 0 in 1.0.2.
SSL_OP_SINGLE_DH_USE[edit]
If set, always create a new key when using tmp_dh parameters. As of 1.0.2f single-DH key use is always on, and this option does nothing, and is retained for compatibility.
SSL_OP_EPHEMERAL_RSA[edit]
This option does nothing, but was retained for compatibility. In 1.0.1, this option had a value of 0x00200000; this option's value was changed to 0 in 1.0.2. This option always used the tmp_rsa key when doing RSA operations, even when this violated protocol specs.
SSL_OP_PRIORITIZE_CHACHA[edit]
This option has no effect if SSL_OP_CIPHER_SERVER_PREFERENCE is not enabled.
SSL_OP_TLS_ROLLBACK_BUG[edit]
This option had a value of 0x00000400 in 0.9.6. If set, a server will allow a client to issue a SSLv3.0 version number as latest version supported in the premaster secret, even when TLSv1.0 (version 3.1) was announced in the client hello. Normally this is forbidden to prevent version rollback attacks.
Added in 0.9.6 and was automatically enabled via SSL_OP_ALL. In 0.9.7, it was removed from SSL_OP_ALL and must be explicitly set.
SSL_OP_PKCS1_CHECK_1[edit]
This option does nothing, but was retained for compatibility. Prior to 1.0.1, this option had a value of 0x08000000. The option would deliberately change the ciphertext, this is a check for the PKCS#1 attack.
SSL_OP_PKCS1_CHECK_2[edit]
This option does nothing, but was retained for compatibility. Prior to 1.0.1, this option had a value of 0x10000000. The option would deliberately change the ciphertext, this is a check for the PKCS#1 attack.
SSL_OP_CIPHER_SERVER_PREFERENCE[edit]
Added in 0.9.7.
SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION[edit]
Added in 0.9.7.
SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS[edit]
Added in 0.9.6e to disable the fragment insertion that was added in 0.9.6d (where it was always enabled). Versions up to 0.9.6c do not include the countermeasure.
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION[edit]
Added in 0.9.8m.
SSL_OP_LEGACY_SERVER_CONNECT[edit]
Added in 0.9.8m.
