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Re: <cert> versus <sequence>

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At 09:00 AM 8/28/97 GMT, William Allen Simpson wrote:
>( pgpki 6.0i
>  #12345678# |Z5pxCD64YwgS1IY4Rh61oA==|
>  ( assert
>    ( not-after 1970-01-02_03:04:05 )
>    ( user "test pgpki user <user@pgpki.test>" )
>    ( signature #87654321# verbal
>      (dsa-sha1 |Txoz1GxK/uBvJbx3prIhEw==|)
>    )
>  )
>  ( assert
>    ...
>  )
>)

I have a problem with signature on an object as the last element of the 
object.  I rated that as a bug in SDSI 1.0 and corrected in SPKI by 
separating signatures from the bodies they sign.

The problem here is that the object you're signing doesn't exist in this 
structure.

In the first one:

  ( assert
    ( not-after 1970-01-02_03:04:05 )
    ( user "test pgpki user <user@pgpki.test>" )
    ( signature #87654321# verbal
      (dsa-sha1 |Txoz1GxK/uBvJbx3prIhEw==|)
    )
  )

the signed object is

  ( assert
    ( not-after 1970-01-02_03:04:05 )
    ( user "test pgpki user <user@pgpki.test>" )
  )

which is an editing of the original object.  I've been burned too many times 
by having to do processing over the transmitted form in order to get the 
bytes which have to be hashed to form or verify a signature.  I wanted the 
hashed byte string to be transmitted and stored intact, with no editing 
necessary.

Granted, your editing is simple compared to the re-ordering and parsing and
packing involved in PEM's certificate verification, but from that one bad
example I learned that any editing is evil and should be avoided (and can 
be avoided easily since the signer had to put together the relevant byte string
and can just transmit it from then on).

 - Carl


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+------------------------------------------------------------------+
|Carl M. Ellison  cme@cybercash.com   http://www.clark.net/pub/cme |
|CyberCash, Inc.                      http://www.cybercash.com/    |
|207 Grindall Street   PGP 2.6.2: 61E2DE7FCB9D7984E9C8048BA63221A2 |
|Baltimore MD 21230-4103  T:(410) 727-4288  F:(410)727-4293        |
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