tool - disable weak ciphers in SSL connection




tls version check (4)

What argument to pass to SSL_CTX_set_cipher_list to disable weak ciphers

It depends upon who's defintion of weak you are using. In 2015, you have to bump from effectively HIGH:!aNULL because modern browsers reject some of the ciphers included with HIGH. If you allow MD5 and/or RC4, then you get the obsolete cryptography warning.

HIGH:!aNULL:!MD5:!RC4

The call would look like so:

rc = SSL_CTX_set_cipher_list(ctx, "HIGH:!aNULL:!MD5:!RC4");
ASSERT(rc >= 1);

You should also disable SSLv2, SSLv3 and probably compression. You do it like so:

const long flags = SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3 | SSL_OP_NO_COMPRESSION;
SSL_CTX_set_options(ctx, flags);

SSL_CTX_set_options does not return a value, so there's nothing to test to ensure the call succeeds.

I am using the function SSL_CTX_set_cipher_list to set the ciphers supported for the SSL connection. What argument to pass to SSL_CTX_set_cipher_list to disable weak ciphers.

I tried passing ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH

but it doesn't seem to work.

My tool to detect weak cipher reports for the following as enabled still

** SSLv3:DES-CBC-SHA - ENABLED - WEAK 56 bits **

** TLSv1:DES-CBC-SHA - ENABLED - WEAK 56 bits **

** SSLv2:RC4-MD5 - ENABLED - WEAK 128 bits **
** SSLv2:RC2-CBC-MD5 - ENABLED - WEAK 128 bits **
** SSLv2:RC4-64-MD5 - ENABLED - WEAK 64 bits **
** SSLv2:DES-CBC-MD5 - ENABLED - WEAK 56 bits **
** SSLv2:EXP-RC4-MD5 - ENABLED - WEAK 40 bits **
** SSLv2:EXP-RC2-CBC-MD5 - ENABLED - WEAK 40 bits **
** SSLv2:DES-CBC3-MD5 - ENABLED - WEAK 168 bits **

What argument to pass to SSL_CTX_set_cipher_list to disable the above ciphers?


Your connection to website is encrypted with obsolete cryptography...
Any advice, please?

The SSLCipherSuite of HIGH:MEDIUM:!aNULL:!MD5 is not bad. You should change it to HIGH:!aNULL:!MD5:!RC4 because MEDIUM is weak and RC4 is weak/wounded.

The browsers are moving to flag/warn on RC4 use. See, for example, Connection information claims RC4 is "high grade"


If you want to only use ephemeral or temporary Diffie-Hellman keys (which you should), then you should remove RSA key transport, too:

SSLCipherSuite  HIGH:!aNULL:!kRSA:!MD5:!RC4

And as Anand pointed out, you should disable SSLv2 and SSLv3:

SSLProtocol all -SSLv2 -SSLv3

Related, you can get a list of the cipher suites enabled based on the string you are using with the openssl ciphers command. Because you are not using DSS, SRP or PSK, you can even include !DSS:!DSA:!SRP:!PSK in the string.

$ openssl ciphers -v 'HIGH:!aNULL:!kRSA:!MD5:!RC4:!DSS:!DSA:!SRP:!PSK'
ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AESGCM(256) Mac=AEAD
ECDHE-ECDSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=ECDSA Enc=AESGCM(256) Mac=AEAD
ECDHE-RSA-AES256-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AES(256)  Mac=SHA384
ECDHE-ECDSA-AES256-SHA384 TLSv1.2 Kx=ECDH     Au=ECDSA Enc=AES(256)  Mac=SHA384
ECDHE-RSA-AES256-SHA    SSLv3 Kx=ECDH     Au=RSA  Enc=AES(256)  Mac=SHA1
ECDHE-ECDSA-AES256-SHA  SSLv3 Kx=ECDH     Au=ECDSA Enc=AES(256)  Mac=SHA1
DHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(256) Mac=AEAD
DHE-RSA-AES256-SHA256   TLSv1.2 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA256
DHE-RSA-AES256-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(256)  Mac=SHA1
DHE-RSA-CAMELLIA256-SHA SSLv3 Kx=DH       Au=RSA  Enc=Camellia(256) Mac=SHA1
ECDH-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AESGCM(256) Mac=AEAD
ECDH-ECDSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(256) Mac=AEAD
ECDH-RSA-AES256-SHA384  TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AES(256)  Mac=SHA384
ECDH-ECDSA-AES256-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AES(256)  Mac=SHA384
ECDH-RSA-AES256-SHA     SSLv3 Kx=ECDH/RSA Au=ECDH Enc=AES(256)  Mac=SHA1
ECDH-ECDSA-AES256-SHA   SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=AES(256)  Mac=SHA1
ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AESGCM(128) Mac=AEAD
ECDHE-ECDSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=ECDSA Enc=AESGCM(128) Mac=AEAD
ECDHE-RSA-AES128-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AES(128)  Mac=SHA256
ECDHE-ECDSA-AES128-SHA256 TLSv1.2 Kx=ECDH     Au=ECDSA Enc=AES(128)  Mac=SHA256
ECDHE-RSA-AES128-SHA    SSLv3 Kx=ECDH     Au=RSA  Enc=AES(128)  Mac=SHA1
ECDHE-ECDSA-AES128-SHA  SSLv3 Kx=ECDH     Au=ECDSA Enc=AES(128)  Mac=SHA1
DHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(128) Mac=AEAD
DHE-RSA-AES128-SHA256   TLSv1.2 Kx=DH       Au=RSA  Enc=AES(128)  Mac=SHA256
DHE-RSA-AES128-SHA      SSLv3 Kx=DH       Au=RSA  Enc=AES(128)  Mac=SHA1
DHE-RSA-CAMELLIA128-SHA SSLv3 Kx=DH       Au=RSA  Enc=Camellia(128) Mac=SHA1
ECDH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AESGCM(128) Mac=AEAD
ECDH-ECDSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(128) Mac=AEAD
ECDH-RSA-AES128-SHA256  TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AES(128)  Mac=SHA256
ECDH-ECDSA-AES128-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AES(128)  Mac=SHA256
ECDH-RSA-AES128-SHA     SSLv3 Kx=ECDH/RSA Au=ECDH Enc=AES(128)  Mac=SHA1
ECDH-ECDSA-AES128-SHA   SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=AES(128)  Mac=SHA1
ECDHE-RSA-DES-CBC3-SHA  SSLv3 Kx=ECDH     Au=RSA  Enc=3DES(168) Mac=SHA1
ECDHE-ECDSA-DES-CBC3-SHA SSLv3 Kx=ECDH     Au=ECDSA Enc=3DES(168) Mac=SHA1
EDH-RSA-DES-CBC3-SHA    SSLv3 Kx=DH       Au=RSA  Enc=3DES(168) Mac=SHA1
ECDH-RSA-DES-CBC3-SHA   SSLv3 Kx=ECDH/RSA Au=ECDH Enc=3DES(168) Mac=SHA1
ECDH-ECDSA-DES-CBC3-SHA SSLv3 Kx=ECDH/ECDSA Au=ECDH Enc=3DES(168) Mac=SHA1

Visit http://ssllabs.com and verify your site as per the instructions. They will then tell you what is wrong and also how to fix it. Almost certainly you will have to remove the RC4 suites, but the site willl tell you, don't rely on me.


Obsolete cryptography warning from Browser

From https://www.chromium.org/Home/chromium-security/education/tls#TOC-Deprecation-of-TLS-Features-Algorithms-in-Chrome

Obsolete Cipher Suites

You may see:

“Your connection to example.com is encrypted with obsolete cryptography.”

This means that the connection to the current website is using an outdated cipher suite (which Chrome still allows if the server insists on it).

In order for the message to indicate “modern cryptography”, the connection should use forward secrecy and either AES-GCM or CHACHA20_POLY1305. Other cipher suites are known to have weaknesses. Most servers will wish to negotiate TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.

All this boils down to the following lines in your configuration, that determine which cipher suites are supported and prioritized for connections with clients.

SSLProtocol
SSLCipherSuite
SSLHonorCipherOrder

Per https://certsimple.com/blog/chrome-outdated-cryptography and https://mozilla.github.io/server-side-tls/ssl-config-generator/, you may want to give this a try:

SSLProtocol             all -SSLv2 -SSLv3
SSLCipherSuite          ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:ECDHE-RSA-DES-CBC3-SHA:ECDHE-ECDSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA
SSLHonorCipherOrder     on

See also:

[1] https://mozilla.github.io/server-side-tls/ssl-config-generator/ - Suggests security configurations

[2] https://www.ssllabs.com/ssltest/index.html -- Test your server's SSL configuration