Re: [manet] SAODV - signature

[Manel Guerrero <manel.guerrero@upf.edu>]

Hi Joao,

The size of the signature has variable length because different 
algorithms to generate signatures might generate signatures of different 
length. Anyway, when you generate an SAODV message you know which 
algorithm you are gonna use and, therefore, what is gonna be the length 
of the signature. Then, it is not a problem at all to calculate the 
length field before calculating the signature.

Hope this helps,

	Manel Guerrero


Joao Girao wrote:
> Hello,
>
> According to draft-guerrero-manet-saodv-00, in the signature for the
> extension, some fields of the extension itself are also signed. These
> normally include the Length of the extension.
>
> The Length of the extension is calculated as the size of the extension
> except the type and length fields. (according to the rfc)
>
> My question is simple: If the signature is variable in length and
> depends on the data, how can we sign over the length field of the
> extension which depends on the same signature we are producing?
> Depending on the algorithm being used, it can be impossible to predict a
> multiple of 4 bytes for the size of the signature.
>
> Should length be zeroed out for signature calculation?
>
> Thanks in advance,
>
> joao girao


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