3.2 (MPI) doesn't specify what the unused bits should be set
  to. This may be deliberate but I think it should either say they MUST
  be zero (which I prefer) or that their content is unspecified.

4.2 refers to Content Tags, but 4.3 calls them Packet Tags.

5.5.2 doesn't mention V2 keys.

In section 9.1, Schneier is given as the reference for DSA - why not refer to FIPS 186-2, which is freely available? Or, indeed, HAC 11.5.1, available here: http://www.cacr.math.uwaterloo.ca/hac/about/chap11.pdf.

Similarly 9.2, TripleDES (which, presumably is EDE 3DES - it'd be good
to be specific) is on some FIPS document which I forget or in HAC
chapter 7 (7.32 in 7.2.3 and 7.4.2).

----

In 5.2.1:

"0x10: Generic certification of a User ID and Public Key packet."

Does this mean that the signature is over the User ID packet and the Public Key packet, concatenated, in that order? Or what?

Also, what on earth does:

       Note that all PGP "key signatures" are this type of
       certification.

mean?

In 5.2.2:

   "The data being signed is hashed, and then the signature type and
   creation time from the signature packet are hashed (5 additional
   octets)."

is unclear, suggest:

"The concatenation of the data to be signed, the signature type and
creation time from the signature packet (5 additional octets) is hashed."

In 5.9:

   " - File name as a string (one-octet length, followed by file name),
       if the encrypted data should be saved as a file."

but no mention of what if it shouldn't be saved as a file. 0 length,
perhaps?

Then:

   " - A four-octet number that indicates the modification date of the
       file, or the creation time of the packet, or a zero that
       indicates the present time."

I would _guess_ that it means modification date of the file if there's
a filename, the creation time if there isn't. I have no idea what zero
is supposed to mean. Nothing, would be the obvious interpretation -
"the present time" is nonsensical.

Once more, when I know what its supposed to mean, I'll suggest
wording.

------

5.2.3.5 Issuer

should be:

5.2.3.5 Issuer key ID

A tiny point, I know, but it made it hard to find.

Key algorithms ... these are used in various contexts, and there's a
list in 9.1 - some of these are clearly unsuitable in some contexts -
for example, one would not expect to see RSA Ecnrpyt-Only (3) in a
signature. But I can't find any language saying anything about
this. Are there any rules?