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Date: Fri, 14 Aug 2015 22:12:06 +0800
From: Kai Zhao <>
Subject: Re: auditing our use of FMT_* flags

On Fri, Aug 14, 2015 at 9:01 PM, magnum <> wrote:
> On 2015-08-14 14:51, Solar Designer wrote:
>> On Fri, Aug 14, 2015 at 10:55:06AM +0800, Kai Zhao wrote:
>>> Before strncmp(), we also should check the length of string returned
>>> by get_key() should not smaller than plaintext_min_length.
>>> So the length should between plaintext_min_length and plaintext_length,
>>> including.
>> Oh, plaintext_min_length is a jumbo addition that I wasn't even aware
>> of.  I guess it was added for WPA PSK.
> That (and some SRP IIRC?) was what initiated it. I think we also have some
> format(s) that can't use length 0.
>> I think the check you suggest would be fine, but not of much use.  For
>> those formats, all test vectors are probably of at least the minimum
>> length, so a shorter get_key() string would be detected through it being
>> different from what was provided.  And if there's a shorter test vector,
>> violating plaintext_min_length, then your check would detect it as an
>> error... but do we want that?  magnum?
> I think we do. I'm pretty sure it wont trigger with current code anyway.

So I think I can check the plaintext_min_length and plaintext_length before
compare the plaintext and get_key().



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