RE: Generation of CHAP Secrets...

[Black_David@emc.com]

> Do the following statements mean that users should not be allowed to
> create their own secrets (passwords) to ensure the randomness of all
secrets?
>  
> When CHAP is performed over a non-encrypted channel, it is vulnerable
> to an off-line dictionary attack. Implementations MUST support
> use of up to 128 bits random CHAP secrets, including the means to
> generate such secrets and to accept them from an external generation
> source. Implementations MUST NOT provide secret generation (or expansion)
> means other than random generation.

Yes, that is correct.  iSCSI requires 96 or more bits of randomness in CHAP
secrets to thwart exhaustive search and dictionary attacks.  A typical user-
chosen password/secret has less than 20 bits of randomness.  If weaker
CHAP secrets are used, the iSCSI connection MUST be encrypted:

   An administrative entity of an environment in which CHAP is used with 
   a secret that has less than 96 random bits MUST enforce IPsec encryp-
   tion (according to the implementation requirements in Section 7.3.2 
   Confidentiality) to protect the connection.

Thanks,
--David
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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 249-6449            FAX: +1 (508) 497-8018
black_david@emc.com       Mobile: +1 (978) 394-7754
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