Openssl ciphers list sorting and removing

Question

I was playing with a ciphers app to create example list of suites.
Looking at the website (https://openssl.org/docs/manmaster/apps/ciphers.html) if I run one of the examples there:

openssl ciphers -v '3DES:+RSA'

I supposed to get a list of 3DES ciphers with any RSA ones at the end of the list (if I can read correctly). What I get instead is:

$ openssl ciphers -v '3DES:+RSA'
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
SRP-DSS-3DES-EDE-CBC-SHA SSLv3 Kx=SRP      Au=DSS  Enc=3DES(168) Mac=SHA1
SRP-RSA-3DES-EDE-CBC-SHA SSLv3 Kx=SRP      Au=RSA  Enc=3DES(168) Mac=SHA1
SRP-3DES-EDE-CBC-SHA    SSLv3 Kx=SRP      Au=SRP  Enc=3DES(168) Mac=SHA1
EDH-RSA-DES-CBC3-SHA    SSLv3 Kx=DH       Au=RSA  Enc=3DES(168) Mac=SHA1
EDH-DSS-DES-CBC3-SHA    SSLv3 Kx=DH       Au=DSS  Enc=3DES(168) Mac=SHA1
DH-RSA-DES-CBC3-SHA     SSLv3 Kx=DH/RSA   Au=DH   Enc=3DES(168) Mac=SHA1
DH-DSS-DES-CBC3-SHA     SSLv3 Kx=DH/DSS   Au=DH   Enc=3DES(168) Mac=SHA1
AECDH-DES-CBC3-SHA      SSLv3 Kx=ECDH     Au=None Enc=3DES(168) Mac=SHA1
ADH-DES-CBC3-SHA        SSLv3 Kx=DH       Au=None 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
PSK-3DES-EDE-CBC-SHA    SSLv3 Kx=PSK      Au=PSK  Enc=3DES(168) Mac=SHA1
DES-CBC3-SHA            SSLv3 Kx=RSA      Au=RSA  Enc=3DES(168) Mac=SHA1

Clearly, RSA ciphers are not at the end.
I have a similar situation with excluding ECDSA ciphers. Let's say I run the following:

$ openssl ciphers -v 'AESGCM'
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**
DH-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH/DSS   Au=DH   Enc=AESGCM(256) Mac=AEAD
DHE-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH       Au=DSS  Enc=AESGCM(256) Mac=AEAD
DH-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH/RSA   Au=DH   Enc=AESGCM(256) Mac=AEAD
DHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(256) Mac=AEAD
ADH-AES256-GCM-SHA384   TLSv1.2 Kx=DH       Au=None Enc=AESGCM(256) Mac=AEAD
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**
AES256-GCM-SHA384       TLSv1.2 Kx=RSA      Au=RSA  Enc=AESGCM(256) Mac=AEAD
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**
DH-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH/DSS   Au=DH   Enc=AESGCM(128) Mac=AEAD
DHE-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=DSS  Enc=AESGCM(128) Mac=AEAD
DH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH/RSA   Au=DH   Enc=AESGCM(128) Mac=AEAD
DHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(128) Mac=AEAD
ADH-AES128-GCM-SHA256   TLSv1.2 Kx=DH       Au=None Enc=AESGCM(128) Mac=AEAD
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**
AES128-GCM-SHA256       TLSv1.2 Kx=RSA      Au=RSA  Enc=AESGCM(128) Mac=AEAD

Now if I try to exclude all ECDSA ciphers:

$ openssl ciphers -v 'AESGCM:!ECDSA'
ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AESGCM(256) Mac=AEAD
DH-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH/DSS   Au=DH   Enc=AESGCM(256) Mac=AEAD
DHE-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH       Au=DSS  Enc=AESGCM(256) Mac=AEAD
DH-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH/RSA   Au=DH   Enc=AESGCM(256) Mac=AEAD
DHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(256) Mac=AEAD
ADH-AES256-GCM-SHA384   TLSv1.2 Kx=DH       Au=None Enc=AESGCM(256) Mac=AEAD
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**
AES256-GCM-SHA384       TLSv1.2 Kx=RSA      Au=RSA  Enc=AESGCM(256) Mac=AEAD
ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AESGCM(128) Mac=AEAD
DH-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH/DSS   Au=DH   Enc=AESGCM(128) Mac=AEAD
DHE-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=DSS  Enc=AESGCM(128) Mac=AEAD
DH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH/RSA   Au=DH   Enc=AESGCM(128) Mac=AEAD
DHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(128) Mac=AEAD
ADH-AES128-GCM-SHA256   TLSv1.2 Kx=DH       Au=None Enc=AESGCM(128) Mac=AEAD
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**
AES128-GCM-SHA256       TLSv1.2 Kx=RSA      Au=RSA  Enc=AESGCM(128) Mac=AEAD

I still get 2 ECDSA ciphers on the list (I marked them with **).

Is that a bug, or is it just my ignorance? I am working on openssl 1.0.2g. thanks.

Answer 1

Don't use aliases.

Short answer: Don't use aliases. List all cipher suites by full name and in the desired order.

Long answer: see below.

Re. RSA sorting

You tried:

openssl ciphers -v '3DES:+RSA'

And on my openssl that is the same as:

openssl ciphers -v '3DES:+kRSA'

But I think you wanted:

openssl ciphers -v '3DES:+aRSA'

• The "aRSA" alias means cipher suites using RSA authentication.
• The "kRSA" alias means cipher suites using RSA key exchange.
• And the "RSA" alias seems to mean the superset of both. But I don't know what tie breaker is used when you try to sort on that alias.

Re. ECDSA exclusion

You tried

$ openssl ciphers -v 'AESGCM:!ECDSA'

And on my openssl that is the same as:

$ openssl ciphers -v 'AESGCM:!aECDSA'

(I checked like this: The command diff <(openssl ciphers -v 'ECDSA') <(openssl ciphers -v 'aECDSA') returns nothing. The output is identical.)

I think you wanted:

$ openssl ciphers -v 'AESGCM:!aECDSA:!kECDHe'
ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AESGCM(256) Mac=AEAD
DH-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH/DSS   Au=DH   Enc=AESGCM(256) Mac=AEAD
DHE-DSS-AES256-GCM-SHA384 TLSv1.2 Kx=DH       Au=DSS  Enc=AESGCM(256) Mac=AEAD
DH-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH/RSA   Au=DH   Enc=AESGCM(256) Mac=AEAD
DHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(256) Mac=AEAD
ADH-AES256-GCM-SHA384   TLSv1.2 Kx=DH       Au=None Enc=AESGCM(256) Mac=AEAD
ECDH-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AESGCM(256) Mac=AEAD
AES256-GCM-SHA384       TLSv1.2 Kx=RSA      Au=RSA  Enc=AESGCM(256) Mac=AEAD
ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AESGCM(128) Mac=AEAD
DH-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH/DSS   Au=DH   Enc=AESGCM(128) Mac=AEAD
DHE-DSS-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=DSS  Enc=AESGCM(128) Mac=AEAD
DH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH/RSA   Au=DH   Enc=AESGCM(128) Mac=AEAD
DHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=DH       Au=RSA  Enc=AESGCM(128) Mac=AEAD
ADH-AES128-GCM-SHA256   TLSv1.2 Kx=DH       Au=None Enc=AESGCM(128) Mac=AEAD
ECDH-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH/RSA Au=ECDH Enc=AESGCM(128) Mac=AEAD
AES128-GCM-SHA256       TLSv1.2 Kx=RSA      Au=RSA  Enc=AESGCM(128) Mac=AEAD

Details

OpenSSL seems to use the cipher alias "ECDSA" to mean "grep for Au=ECDSA". In other words: "give me every cipher suite that uses an ECDSA certificate". (There is another, more explicit, alias for just that: aECDSA.)

And this is what you normally want.

So far so good. But what about the two cipher suites that you got?

$ openssl ciphers -V 'ECDH-ECDSA-AES256-GCM-SHA384'
          0xC0,0x2E - ECDH-ECDSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(256) Mac=AEAD

$ openssl ciphers -V 'ECDH-ECDSA-AES128-GCM-SHA256'
          0xC0,0x2D - ECDH-ECDSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH/ECDSA Au=ECDH Enc=AESGCM(128) Mac=AEAD

They both have Kx=ECDH/ECDSA Au=ECDH listed.

In other words: They are cipher suites that have an ECDH certificate and do key exchange with those ECDH parameters which are in turn signed by a CA that uses an ECDSA certificate. You are unlikely to ever come across such a thing in the wild.

Sources

• OpenSSL Man Page. Section "Cipher Strings" lists the aliases: https://wiki.openssl.org/index.php/Manual:Ciphers(1)
• Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS), https://www.rfc-editor.org/rfc/rfc4492#section-2.1
• How does non-ephemeral Diffie-Hellman key exchange become compromised in SSL when the RSA private key is leaked?

Further reading

For a very in depth discussion of cipher suite strings have a look at Ivan Ristic's OpenSSL cookbook. Namely the section called "Cipher suite selection".

But this is the key take away: Don't use aliases. They are too hard too understand at a glance. Quote:

In addition, I am going to change my approach from configuring suites using keywords to using suite names directly. I think that keywords, conceptually, are not a bad idea: you specify your security requirements and the library does the rest, without you having to know a lot about the suites that are going to be used. Unfortunately, this approach no longer works well in practice, as we’ve become quite picky about what suites we wish to have enabled and in what order.