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35 votes

How to disable CBC-mode ciphers

You can use !SHA1:!SHA256:!SHA384 to disable all CBC mode ciphers. There are some non-CBC false positives that will also be disabled (RC4, NULL), but you probably also want to disable them anyway. ...
imgx64's user avatar
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18 votes
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How do I know which cipher suites can be disabled?

The required cipher suites depends entirely on the clients that are expected to use the service. As SSL Server Test from Qualys SSL Labs is designed for testing publicly accessible web servers, we can ...
Esa Jokinen's user avatar
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15 votes

How to disable CBC-mode ciphers

I've spent a fair amount of time over the last couple of days trying to get a perfect list for ssllabs. Thanks in part to this, here's what works: SSLCipherSuite ALL:!RSA:!CAMELLIA:!aNULL:!eNULL:!...
Bill Cheswick's user avatar
13 votes
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SSH Server Configuration Best Practices?

The defaults for a recent version of openssh are good. The server's asymmetric key type and client's asymmetric key type are specified in HostKeyAlgorithms and PubkeyAcceptedAlgorithms respectively. ...
Z.T.'s user avatar
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12 votes
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How to disable CBC-mode ciphers

According to the list of Cipher Strings given in the documentation (man ciphers) there is no string describing all CBC ciphers. This means there is no simple way to disable all of these (and only ...
Steffen Ullrich's user avatar
12 votes
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What are the 'P' values in some cipher string?

P521 is an elliptic curve “P521” is a dead giveaway for an elliptic curve which SECG and TLS formally call secp521r1 and which NIST FIPS 186-4 calls P-521. An elliptic curve is a mathematical domain ...
Gilles 'SO- stop being evil''s user avatar
10 votes
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Is the order of cipher suites related to the client's preferences ?

The order in the ClientHello shows what the client prefers, i.e. the preferred ciphers are on top. The server is still free to ignore this order and pick what it thinks is best. Often there is a ...
Steffen Ullrich's user avatar
8 votes

What are the 'P' values in some cipher string?

I would suggest that these mean the curve used within the ECDHE key exchange, i.e. NIST P-256, NIST P-384 and NIST P-521. These are not actually part of the cipher itself (i.e. the 16-bit cipher id ...
Steffen Ullrich's user avatar
7 votes
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Can web server have TLS version specific cipher suite configuration?

In theory it would be possible to set the available ciphers and cipher order depending on the TLS protocol version used by the client. In practice none of the common web servers supports this. Apart ...
Steffen Ullrich's user avatar
7 votes

TLS Version specific cipher suites

As an addon to Trey's answer: I use the string ALL:COMPLEMENTOFALL when want I every cipher suite. I use the -V (upper case V) option to make OpenSSL output the hex-IDs of the cipher suites. Note: ...
StackzOfZtuff's user avatar
6 votes
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TLS Version specific cipher suites

1.) See openssl output below and excellent Wikipedia page below 2.) No not all of them, see the tables at the URL below. 3.) No not all of them, see the tables at the URL below. https://en....
Trey Blalock's user avatar
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6 votes
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OpenSSH: Meaning of cipher with email address @openssh.com

Those are algorithms defined by vendors like openssh, not defined by the SSH standard (IETF RFCs). They are extensions to the protocol. Of course, you are not guaranteed that software other than ...
Z.T.'s user avatar
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5 votes
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Link between Cipher suites and certificate key

wikipedia.org has an EC 256 bits key and TLS_RSA_WITH_AES_128_CBC_SHA is an accepted cipher suite. According to this post SSL certificates and cipher suites correspondence (if I understand it ...
Steffen Ullrich's user avatar
5 votes

Guidelines for TLS cipher suites?

Mozilla: https://mozilla.github.io/server-side-tls/ssl-config-generator/ SSL Labs: https://github.com/ssllabs/research/wiki/SSL-and-TLS-Deployment-Best-Practices Cipherli.St: https://cipherli.st/ ...
StackzOfZtuff's user avatar
5 votes
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TLS Cipher Suites for MTA

Even with ciphers using 3DES or RC4 an attacker is not able to crack the cipher with moderate costs. And even secret services would probably rather do DNS MX spoofing or simply strip the STARTTLS from ...
Steffen Ullrich's user avatar
5 votes

Clarifications regarding ciphers and Nmap scan

You are asking multiple unrelated questions which is not the recommended way to ask and chances are that the question might be closed as too broad or as duplicate since some part was already answered ...
Steffen Ullrich's user avatar
5 votes

How does a client (like SSLLabs) know all the cipher suites a server supports if the server doesn’t send its list of supported cipher suites?

In TLS the client announces what kind of ciphers it supports inside the ClientHello and the server picks a cipher from these which is supported on the server too. While one cannot query the server ...
Steffen Ullrich's user avatar
5 votes

What are the 'P' values in some cipher string?

They are the naming for NIST ECC Curves. Also see at NIST.FIPS.186-4 NIST RFC 4492 P-256 secp256r1 P-384 secp384r1 P-521 secp521r1
kelalaka's user avatar
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5 votes

How do I verify the supported ciphersuites of a TLS server that only accepts POST requests?

It is totally irrelevant if GET or POST is used. The TLS handshake is done before any HTTP request is even send. So if the handshake fails it means that neither GET nor POST is possible. If the ...
Steffen Ullrich's user avatar
5 votes

If I control both sides of a connection, is there any reason to support alternate cipher suites?

If you control both ends of the tunnel, and there are no issues with intermediary server support, then it definitely makes sense to limit the ciphers. Additional ciphers just increases the attack ...
shellster's user avatar
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4 votes
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How to disable weak cipher suits in java application server for ssl

JAVA allows cipher suites to be removed/excluded from use in the security policy file called java.security that’s located in your JRE: $PATH/[JRE]/lib/security The jdk.tls.disabledAlgorithms property ...
munkeyoto's user avatar
  • 8,692
4 votes

OpenSSH default/preferred ciphers, hash, etc for SSH2

Answer valid in 2023: By default, OpenSSH uses the [email protected] cipher. Although, between machines with AES-NI support, you might want to force e.g. [email protected]. $ man ...
Smile.Hunter's user avatar
4 votes
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Do current eCommerce systems provide sufficient security?

Your question as originally posted is not very clear. If you require Public Key / Asymmetric Encryption algorithm, the safe/simple choice is to use RSA with a 2048 or better key size. If you require ...
700 Software's user avatar
4 votes
Accepted

Is there a tool to test whether a server supports any cipher suite?

Testssl.sh can detect bad ciphers and a lot of other things regarding SSL security. Edit: Even testssl.sh depends on OpenSSL for the ciphers it tests. It ships with its own OpenSSL libary that has ...
Sjoerd's user avatar
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4 votes

Difference between two TLS cipher suites

There is really no substitute for reading the TLS spec, but here's a quick explanation. There are essentially 4 different parts of a TLS 1.2 cipher suite: Authentication - what crypto is used to ...
bonsaiviking's user avatar
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4 votes

What is the difference between CBC and CBC3 cipher suites?

DES-CBC-SHA is DES encryption, SHA-1 as HMAC. DES-CBC3-SHA is 3DES encryption, SHA-1 as HMAC.
Steffen Ullrich's user avatar
4 votes

How to make TLS_RSA_WITH_3DES_EDE_CBC_SHA strong

If following that guide you used this line in your nginx configuration: ssl_ciphers 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-...
Z.T.'s user avatar
  • 8,524
4 votes

Why does tls_version "TLS 1.2" from howsmyssl rate "Probably Okay" in Chrome on Windows 10 but "Bad" in IE11 on Windows 7?

Well, from the error message you posted, your IE11 is willing to use some really out of date and broken crypto, but the Chrome does not. That tool even gives you a helpful description of why each one ...
Mike Ounsworth's user avatar
4 votes

What makes an SSL session pick one cipher over another?

In the first step the server aligns the ciphers offered by the client with the ciphers configured for the cipher to get a set of common ciphers. From this set the server then selects a single cipher. ...
Steffen Ullrich's user avatar
4 votes
Accepted

Understanding SSL Cipher suite in Apache

Yes, the order of Apache's SSLCipherSuite indicates the preferred order. To quote the link you've provided (emphasis mine), Now where this becomes interesting is that these can be put together ...
gowenfawr's user avatar
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