curl / Docs / Protocols / Ciphers

SSL Ciphers

Ciphers

With curl's options CURLOPT_SSL_CIPHER_LIST and --ciphers users can control which ciphers to consider when negotiating TLS connections.

TLS 1.3 ciphers are supported since curl 7.61 for OpenSSL 1.1.1+, and since curl 7.85 for Schannel with options CURLOPT_TLS13_CIPHERS and --tls13-ciphers . If you are using a different SSL backend you can try setting TLS 1.3 cipher suites by using the respective regular cipher option.

The names of the known ciphers differ depending on which TLS backend that libcurl was built to use. This is an attempt to list known cipher names.

OpenSSL

(based on OpenSSL docs)

When specifying multiple cipher names, separate them with colon (:).

SSL3 cipher suites

NULL-MD5 NULL-SHA RC4-MD5 RC4-SHA IDEA-CBC-SHA DES-CBC3-SHA DH-DSS-DES-CBC3-SHA DH-RSA-DES-CBC3-SHA DHE-DSS-DES-CBC3-SHA DHE-RSA-DES-CBC3-SHA ADH-RC4-MD5 ADH-DES-CBC3-SHA

TLS v1.0 cipher suites

NULL-MD5 NULL-SHA RC4-MD5 RC4-SHA IDEA-CBC-SHA DES-CBC3-SHA DHE-DSS-DES-CBC3-SHA DHE-RSA-DES-CBC3-SHA ADH-RC4-MD5 ADH-DES-CBC3-SHA

AES cipher suites from RFC 3268, extending TLS v1.0

AES128-SHA AES256-SHA DH-DSS-AES128-SHA DH-DSS-AES256-SHA DH-RSA-AES128-SHA DH-RSA-AES256-SHA DHE-DSS-AES128-SHA DHE-DSS-AES256-SHA DHE-RSA-AES128-SHA DHE-RSA-AES256-SHA ADH-AES128-SHA ADH-AES256-SHA

SEED cipher suites from RFC 4162, extending TLS v1.0

SEED-SHA DH-DSS-SEED-SHA DH-RSA-SEED-SHA DHE-DSS-SEED-SHA DHE-RSA-SEED-SHA ADH-SEED-SHA

GOST cipher suites, extending TLS v1.0

GOST94-GOST89-GOST89 GOST2001-GOST89-GOST89 GOST94-NULL-GOST94 GOST2001-NULL-GOST94

Elliptic curve cipher suites

ECDHE-RSA-NULL-SHA ECDHE-RSA-RC4-SHA ECDHE-RSA-DES-CBC3-SHA ECDHE-RSA-AES128-SHA ECDHE-RSA-AES256-SHA ECDHE-ECDSA-NULL-SHA ECDHE-ECDSA-RC4-SHA ECDHE-ECDSA-DES-CBC3-SHA ECDHE-ECDSA-AES128-SHA ECDHE-ECDSA-AES256-SHA AECDH-NULL-SHA AECDH-RC4-SHA AECDH-DES-CBC3-SHA AECDH-AES128-SHA AECDH-AES256-SHA

TLS v1.2 cipher suites

NULL-SHA256 AES128-SHA256 AES256-SHA256 AES128-GCM-SHA256 AES256-GCM-SHA384 DH-RSA-AES128-SHA256 DH-RSA-AES256-SHA256 DH-RSA-AES128-GCM-SHA256 DH-RSA-AES256-GCM-SHA384 DH-DSS-AES128-SHA256 DH-DSS-AES256-SHA256 DH-DSS-AES128-GCM-SHA256 DH-DSS-AES256-GCM-SHA384 DHE-RSA-AES128-SHA256 DHE-RSA-AES256-SHA256 DHE-RSA-AES128-GCM-SHA256 DHE-RSA-AES256-GCM-SHA384 DHE-DSS-AES128-SHA256 DHE-DSS-AES256-SHA256 DHE-DSS-AES128-GCM-SHA256 DHE-DSS-AES256-GCM-SHA384 ECDHE-RSA-AES128-SHA256 ECDHE-RSA-AES256-SHA384 ECDHE-RSA-AES128-GCM-SHA256 ECDHE-RSA-AES256-GCM-SHA384 ECDHE-ECDSA-AES128-SHA256 ECDHE-ECDSA-AES256-SHA384 ECDHE-ECDSA-AES128-GCM-SHA256 ECDHE-ECDSA-AES256-GCM-SHA384 ADH-AES128-SHA256 ADH-AES256-SHA256 ADH-AES128-GCM-SHA256 ADH-AES256-GCM-SHA384 AES128-CCM AES256-CCM DHE-RSA-AES128-CCM DHE-RSA-AES256-CCM AES128-CCM8 AES256-CCM8 DHE-RSA-AES128-CCM8 DHE-RSA-AES256-CCM8 ECDHE-ECDSA-AES128-CCM ECDHE-ECDSA-AES256-CCM ECDHE-ECDSA-AES128-CCM8 ECDHE-ECDSA-AES256-CCM8

Camellia HMAC-Based cipher suites from RFC 6367, extending TLS v1.2

ECDHE-ECDSA-CAMELLIA128-SHA256 ECDHE-ECDSA-CAMELLIA256-SHA384 ECDHE-RSA-CAMELLIA128-SHA256 ECDHE-RSA-CAMELLIA256-SHA384

TLS 1.3 cipher suites

(Note these ciphers are set with CURLOPT_TLS13_CIPHERS and --tls13-ciphers)

TLS_AES_256_GCM_SHA384 TLS_CHACHA20_POLY1305_SHA256 TLS_AES_128_GCM_SHA256 TLS_AES_128_CCM_8_SHA256 TLS_AES_128_CCM_SHA256

WolfSSL

RC4-SHA, RC4-MD5, DES-CBC3-SHA, AES128-SHA, AES256-SHA, NULL-SHA, NULL-SHA256, DHE-RSA-AES128-SHA, DHE-RSA-AES256-SHA, DHE-PSK-AES256-GCM-SHA384, DHE-PSK-AES128-GCM-SHA256, PSK-AES256-GCM-SHA384, PSK-AES128-GCM-SHA256, DHE-PSK-AES256-CBC-SHA384, DHE-PSK-AES128-CBC-SHA256, PSK-AES256-CBC-SHA384, PSK-AES128-CBC-SHA256, PSK-AES128-CBC-SHA, PSK-AES256-CBC-SHA, DHE-PSK-AES128-CCM, DHE-PSK-AES256-CCM, PSK-AES128-CCM, PSK-AES256-CCM, PSK-AES128-CCM-8, PSK-AES256-CCM-8, DHE-PSK-NULL-SHA384, DHE-PSK-NULL-SHA256, PSK-NULL-SHA384, PSK-NULL-SHA256, PSK-NULL-SHA, HC128-MD5, HC128-SHA, HC128-B2B256, AES128-B2B256, AES256-B2B256, RABBIT-SHA, NTRU-RC4-SHA, NTRU-DES-CBC3-SHA, NTRU-AES128-SHA, NTRU-AES256-SHA, AES128-CCM-8, AES256-CCM-8, ECDHE-ECDSA-AES128-CCM, ECDHE-ECDSA-AES128-CCM-8, ECDHE-ECDSA-AES256-CCM-8, ECDHE-RSA-AES128-SHA, ECDHE-RSA-AES256-SHA, ECDHE-ECDSA-AES128-SHA, ECDHE-ECDSA-AES256-SHA, ECDHE-RSA-RC4-SHA, ECDHE-RSA-DES-CBC3-SHA, ECDHE-ECDSA-RC4-SHA, ECDHE-ECDSA-DES-CBC3-SHA, AES128-SHA256, AES256-SHA256, DHE-RSA-AES128-SHA256, DHE-RSA-AES256-SHA256, ECDH-RSA-AES128-SHA, ECDH-RSA-AES256-SHA, ECDH-ECDSA-AES128-SHA, ECDH-ECDSA-AES256-SHA, ECDH-RSA-RC4-SHA, ECDH-RSA-DES-CBC3-SHA, ECDH-ECDSA-RC4-SHA, ECDH-ECDSA-DES-CBC3-SHA, AES128-GCM-SHA256, AES256-GCM-SHA384, DHE-RSA-AES128-GCM-SHA256, DHE-RSA-AES256-GCM-SHA384, ECDHE-RSA-AES128-GCM-SHA256, ECDHE-RSA-AES256-GCM-SHA384, ECDHE-ECDSA-AES128-GCM-SHA256, ECDHE-ECDSA-AES256-GCM-SHA384, ECDH-RSA-AES128-GCM-SHA256, ECDH-RSA-AES256-GCM-SHA384, ECDH-ECDSA-AES128-GCM-SHA256, ECDH-ECDSA-AES256-GCM-SHA384, CAMELLIA128-SHA, DHE-RSA-CAMELLIA128-SHA, CAMELLIA256-SHA, DHE-RSA-CAMELLIA256-SHA, CAMELLIA128-SHA256, DHE-RSA-CAMELLIA128-SHA256, CAMELLIA256-SHA256, DHE-RSA-CAMELLIA256-SHA256, ECDHE-RSA-AES128-SHA256, ECDHE-ECDSA-AES128-SHA256, ECDH-RSA-AES128-SHA256, ECDH-ECDSA-AES128-SHA256, ECDHE-RSA-AES256-SHA384, ECDHE-ECDSA-AES256-SHA384, ECDH-RSA-AES256-SHA384, ECDH-ECDSA-AES256-SHA384, ECDHE-RSA-CHACHA20-POLY1305, ECDHE-ECDSA-CHACHA20-POLY1305, DHE-RSA-CHACHA20-POLY1305, ECDHE-RSA-CHACHA20-POLY1305-OLD, ECDHE-ECDSA-CHACHA20-POLY1305-OLD, DHE-RSA-CHACHA20-POLY1305-OLD, ADH-AES128-SHA, QSH, RENEGOTIATION-INFO, IDEA-CBC-SHA, ECDHE-ECDSA-NULL-SHA, ECDHE-PSK-NULL-SHA256, ECDHE-PSK-AES128-CBC-SHA256, PSK-CHACHA20-POLY1305, ECDHE-PSK-CHACHA20-POLY1305, DHE-PSK-CHACHA20-POLY1305, EDH-RSA-DES-CBC3-SHA,

Schannel

Schannel allows the enabling and disabling of encryption algorithms, but not specific cipher suites, prior to TLS 1.3. The algorithms are defined by Microsoft.

The algorithms below are for TLS 1.2 and earlier. TLS 1.3 is covered in the next section.

There is also the case that the selected algorithm is not supported by the protocol or does not match the ciphers offered by the server during the SSL negotiation. In this case curl will return error CURLE_SSL_CONNECT_ERROR (35) SEC_E_ALGORITHM_MISMATCH and the request will fail.

CALG_MD2, CALG_MD4, CALG_MD5, CALG_SHA, CALG_SHA1, CALG_MAC, CALG_RSA_SIGN, CALG_DSS_SIGN, CALG_NO_SIGN, CALG_RSA_KEYX, CALG_DES, CALG_3DES_112, CALG_3DES, CALG_DESX, CALG_RC2, CALG_RC4, CALG_SEAL, CALG_DH_SF, CALG_DH_EPHEM, CALG_AGREEDKEY_ANY, CALG_HUGHES_MD5, CALG_SKIPJACK, CALG_TEK, CALG_CYLINK_MEK, CALG_SSL3_SHAMD5, CALG_SSL3_MASTER, CALG_SCHANNEL_MASTER_HASH, CALG_SCHANNEL_MAC_KEY, CALG_SCHANNEL_ENC_KEY, CALG_PCT1_MASTER, CALG_SSL2_MASTER, CALG_TLS1_MASTER, CALG_RC5, CALG_HMAC, CALG_TLS1PRF, CALG_HASH_REPLACE_OWF, CALG_AES_128, CALG_AES_192, CALG_AES_256, CALG_AES, CALG_SHA_256, CALG_SHA_384, CALG_SHA_512, CALG_ECDH, CALG_ECMQV, CALG_ECDSA, CALG_ECDH_EPHEM,

As of curl 7.77.0, you can also pass SCH_USE_STRONG_CRYPTO as a cipher name to constrain the set of available ciphers as specified in the Schannel documentation. Note that the supported ciphers in this case follow the OS version, so if you are running an outdated OS you might still be supporting weak ciphers.

TLS 1.3 cipher suites

You can set TLS 1.3 ciphers for Schannel by using CURLOPT_TLS13_CIPHERS or --tls13-ciphers with the names below.

If TLS 1.3 cipher suites are set then libcurl will add or restrict Schannel TLS 1.3 algorithms automatically. Essentially, libcurl is emulating support for individual TLS 1.3 cipher suites since Schannel does not support it directly.

TLS_AES_256_GCM_SHA384 TLS_AES_128_GCM_SHA256 TLS_CHACHA20_POLY1305_SHA256 TLS_AES_128_CCM_8_SHA256 TLS_AES_128_CCM_SHA256

Note if you set TLS 1.3 ciphers without also setting the minimum TLS version to 1.3 then it is possible Schannel may negotiate an earlier TLS version and cipher suite if your libcurl and OS settings allow it. You can set the minimum TLS version by using CURLOPT_SSLVERSION or --tlsv1.3.

BearSSL

BearSSL ciphers can be specified by either the OpenSSL name (ECDHE-RSA-AES128-GCM-SHA256) or the IANA name (TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256).

Since BearSSL 0.1:

DES-CBC3-SHA AES128-SHA AES256-SHA AES128-SHA256 AES256-SHA256 AES128-GCM-SHA256 AES256-GCM-SHA384 ECDH-ECDSA-DES-CBC3-SHA ECDH-ECDSA-AES128-SHA ECDH-ECDSA-AES256-SHA ECDHE-ECDSA-DES-CBC3-SHA ECDHE-ECDSA-AES128-SHA ECDHE-ECDSA-AES256-SHA ECDH-RSA-DES-CBC3-SHA ECDH-RSA-AES128-SHA ECDH-RSA-AES256-SHA ECDHE-RSA-DES-CBC3-SHA ECDHE-RSA-AES128-SHA ECDHE-RSA-AES256-SHA ECDHE-ECDSA-AES128-SHA256 ECDHE-ECDSA-AES256-SHA384 ECDH-ECDSA-AES128-SHA256 ECDH-ECDSA-AES256-SHA384 ECDHE-RSA-AES128-SHA256 ECDHE-RSA-AES256-SHA384 ECDH-RSA-AES128-SHA256 ECDH-RSA-AES256-SHA384 ECDHE-ECDSA-AES128-GCM-SHA256 ECDHE-ECDSA-AES256-GCM-SHA384 ECDH-ECDSA-AES128-GCM-SHA256 ECDH-ECDSA-AES256-GCM-SHA384 ECDHE-RSA-AES128-GCM-SHA256 ECDHE-RSA-AES256-GCM-SHA384 ECDH-RSA-AES128-GCM-SHA256 ECDH-RSA-AES256-GCM-SHA384

Since BearSSL 0.2:

ECDHE-RSA-CHACHA20-POLY1305 ECDHE-ECDSA-CHACHA20-POLY1305

Since BearSSL 0.6:

AES128-CCM AES256-CCM AES128-CCM8 AES256-CCM8 ECDHE-ECDSA-AES128-CCM ECDHE-ECDSA-AES256-CCM ECDHE-ECDSA-AES128-CCM8 ECDHE-ECDSA-AES256-CCM8