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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: [OT] Problem: (GSKit) No compatible cipher suite available between SSL end points.
Date Wed, 04 Oct 2017 20:30:20 GMT
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James,

On 10/4/17 12:54 PM, James H. H. Lampert wrote:
> On the HTTPAPI/FTPAPI list, I was told that HTTPAPI uses the
> operating system's SSL support (which was how I thought it worked),
> and directed to look through the system values to see what it
> supports. What I found was:
> 
> QSSLPCL     *SEC     Secure sockets layer protocols
>> *OPSYS
> (which I'm pretty sure means that all OS-supported protocols are 
> available; they can also be individually specified as any or all
> of *TLSV1, *SSLV3, and *SSLV2)
> 
> QSSLCSL     *SEC     Secure sockets layer cipher specification
> list
>> *RSA_AES_128_CBC_SHA *RSA_RC4_128_SHA *RSA_RC4_128_MD5 
>> *RSA_AES_256_CBC_SHA *RSA_3DES_EDE_CBC_SHA *RSA_DES_CBC_SHA 
>> *RSA_EXPORT_RC4_40_MD5 *RSA_EXPORT_RC2_CBC_40_MD5 *RSA_NULL_SHA 
>> *RSA_NULL_MD5
> 
> and unfortunately, IBM doesn't backport new cipher suites to older
> OS releases.

Unfortunately, these ciphers suites should no longer be used for
several reasons:

>> *RSA_RC4_128_SHA *RSA_RC4_128_MD5

Use RC4 bulk cipher algorithm, which is known[1] to be weak.

>> *RSA_EXPORT_RC4_40_MD5 *RSA_EXPORT_RC2_CBC_40_MD5

Export-grade encryption. No better than rot13[2].

>> *RSA_NULL_SHA *RSA_NULL_MD5

rot26! Twice as good!

>> *RSA_DES_CBC_SHA

Hideously outdated. I'm sorry, I don't have a reference for this one,
but...

>> *RSA_3DES_EDE_CBC_SHA

3DES (triple DES... literally DES(DES(DES(message)))) is considered
weak[3], so... single-DES is weak(weak(weak(encryption))).

>> *RSA_AES_128_CBC_SHA *RSA_AES_256_CBC_SHA

Sadly, these remaining cipher suites use CBC mode which is also
weak[4] when used with TLSv1 and earlier. Using TLSv1.2 mitigates
these issues. Use of GCM would be better if you can use them. If this
is all the client supports, then that's what you'll have to live with.
But *definitely* disable all the other algorithms if you care even a
little bit about your traffic.

Are you able to use any other kind of client?

Hope that helps,
- -chris


[1]
https://blog.qualys.com/ssllabs/2013/03/19/rc4-in-tls-is-broken-now-what
[2]
https://nakedsecurity.sophos.com/2015/03/04/the-freak-bug-in-tlsssl-what
- -you-need-to-know/
[3]
https://community.qualys.com/thread/16555-triple-des-is-bad-now-sweet-32
- -cve-2016-2183-cve-2016-6329
[4] https://blog.qualys.com/ssllabs/2014/12/08/poodle-bites-tls (CBC=wea
k)
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