IDS> Min_Cipher_Suite and Min_Cipher_Key_Length attributes

IDS> Min_Cipher_Suite and Min_Cipher_Key_Length attributes

IDS> Min_Cipher_Suite and Min_Cipher_Key_Length attributes

Randy Turner rturner at amalfisystems.com
Sun Feb 1 19:16:19 EST 2009


Scratch my comment about IKE (and IPSEC) below, as RFC 4308 seems to  
suggest that IKE(and V2) use a multi-valued negotiation type which  
indicates more than just encryption strength....

R.


On Feb 1, 2009, at 2:06 PM, Randy Turner wrote:

>
> The "model" that we've discussed in the past is having a "scale" of  
> cryptographic protection, from weak to strong.
> And based on the model, I think the idea of these attributes was to  
> be able to specify a "minimum" cryptographic
> requirement for the device.
>
> The "model" that was originally referenced was that using SSL/TLS,  
> and the corresponding TLS/SSL IANA enumerations.
>
> If we're going to stick to the SSL/TLS enumerations, then the  
> minimum key-size wouldn't be needed because they offer no
> benefit to implementers - TLS/SSL only negotiates based on the  
> enumerations and not a separate parameter called "key length". I  
> believe
> (don't quote me on this) that IKE does the same thing when  
> negotiating IPSEC security associations.
>
> If we're going to just have a "minimum" key length for encryption,  
> then you wouldn't need to reference the enumerations.
>
> I think there are 4 alternatives:
>
> 1.  Just use a minimum key length, and we don't worry about a  
> particular "model" for levels of encryption, such as SSL/TLS
>
> 2. Just use the enumerations from the TLS/SSL IANA registry, and  
> dump the minimum key length.
>
> 3. Dump both and move on
>
> 4. Come up with a new proposal based on another set of enumerations  
> describing cryptographic algorithms
>
> My preference would be 2 or 3, since the guidance and direction for  
> implementers is very straightforward and unambiguous (being an
> OpenSSL implementer myself)
>
> Randy
>
>
> On Feb 1, 2009, at 10:52 AM, Ira McDonald wrote:
>
>> Hi,
>>
>> Just my two cents, but, I'd urge that either:
>>
>> (1) Both attributes stay REQUIRED; or
>> (2) Both attributes are deleted entirely from IDS.
>>
>> Having said that, the FIRST principal of security
>> audits is that EVERY network protocol has to be
>> secured on a device and the weakest security
>> configured for any of those network protocols is
>> the security rating of the entire device.
>>
>> Secure devices do NOT send or receive unsecured
>> email over SMTP (for example).
>>
>> MFDs shouldn't claim to be secure if they aren't.
>>
>> Cheers,
>> - Ira
>>
>> Ira McDonald (Musician / Software Architect)
>> Chair - Linux Foundation Open Printing WG
>> Blue Roof Music/High North Inc
>> email: blueroofmusic at gmail.com
>> winter:
>> 579 Park Place  Saline, MI  48176
>> 734-944-0094
>> summer:
>> PO Box 221  Grand Marais, MI 49839
>> 906-494-2434
>>
>>
>>
>> On Sat, Jan 31, 2009 at 7:08 PM, Randy Turner <rturner at amalfisystems.com 
>> > wrote:
>>>
>>> I think so....when you actually code TLS connections using  
>>> OpenSSL, you can
>>> specify a minimum cipher suite to be negotiated...only the cipher  
>>> suite
>>> enumeration is specified, so I think it's ok to use just the  
>>> enumerations.
>>> R.
>>> On Jan 31, 2009, at 4:03 PM, Brian Smithson wrote:
>>>
>>> Thanks, Randy.
>>>
>>> So is our key length attribute redundant?
>>>
>>> --
>>> Regards,
>>> Brian Smithson
>>> PM, Security Research
>>> PMP, CISSP, CISA, ISO 27000 PA
>>> Advanced Imaging and Network Technologies
>>> Ricoh Americas Corporation
>>> (408)346-4435
>>>
>>> Randy Turner wrote:
>>>
>>> Hi Brian,
>>> I think the IANA registry actually has the key length specified as  
>>> part of
>>> the suite enumeration.
>>> Examples are:
>>> TLS_RSA_WITH_AES_128_CBC_SHA256
>>> TLS_RSA_WITH_AES_256_CBC_SHA256
>>> There are other suites that don't specify numeric key sizes, but  
>>> in these
>>> cases, the algorithm itself
>>> (3DES for example) work with a specific key size that doesn't vary.
>>> In this case, we may be able to just specify that we're talking  
>>> about a
>>> minimum suite, with a reference to RFC 5246 and
>>> the IANA registry itself.
>>> Randy
>>>
>>> On Jan 30, 2009, at 6:26 PM, Brian Smithson wrote:
>>>
>>> I am still wondering how these two attributes can be used in  
>>> practice. I
>>> know that we can uniquely identify cipher suites using the IANA
>>> registry, but is there an authoritative source to specify that one  
>>> suite
>>> is "more minimum" than another? And if you consider different key
>>> lengths that might be acceptable for a given suite, then can we  
>>> really
>>> say that suite X is more minimum than suite Y even if an HCD  
>>> supports a
>>> relatively long key length for X but only supports a relatively  
>>> short
>>> one for Y?
>>>
>>> --
>>> Regards,
>>> Brian Smithson
>>> PM, Security Research
>>> PMP, CISSP, CISA, ISO 27000 PA
>>> Advanced Imaging and Network Technologies
>>> Ricoh Americas Corporation
>>> (408)346-4435
>>>
>>>
>>>
>>>
>>>
>>
>




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