[Dovecot] SIS Implementation

[Timo Sirainen]

On Aug 14, 2009, at 7:15 PM, WJCarpenter wrote:

>
>> Step 4) Figure out if base64-encoded attachments can be decoded in  
>> a way
>> that allows re-encoding them back to the exact original encoding.  
>> If so,
>> save the attachment decoded and add the necessary encoding info the  
>> dbox
>> metadata.
>>
>
> Although you might like to do that for some sort of tidiness or  
> whatever, I don't think there's an actual requirement to restore it  
> to base64 (or q-p or whatever).  Those are just transfer encodings,  
> and intermediate MTAs might in theory have transformed them (though  
> in practice that's doubtful).  The one use case for an exact  
> reconstruction might be some older digital signature schemes (which  
> were not so robust and probably lost if an intermediate MTA messed  
> with things).

I was thinking things like: upper vs. lowercase characters, different  
line wrapping lengths, possibly some other weird stuff.. I'd think  
that all digital signatures break if any of those change? Or do they  
really parse the headers and do calculate the signatures using the  
decoded base64?

Another issue is that the MIME structure (MIME part sizes, offsets)  
must match what got saved into dovecot's cache file, but that could be  
fixed with some extra code.