Heuristics Inc. Cipher Challenge

[HeuristicsInc]

Some of you may have noticed the garble of letters in my sig. Some of you have gone so far as to solve the puzzles within. Just thought I'd mention it here so that others may try if they wish.
Basically there is a cipher, a message written with letter replacements. The early ones were simple cryptograms, and now they are becoming more challenging.

Here is one of the old ones:

art fexxcii rb fkc mwwicbf bwglnrpkfcx yxwhgo!

(this one is kind of silly)
-bill

[HeuristicsInc]

Here's a more challenging one:

ujlw ju b tkptqk qqocfrwpjlpfvq dksljx

-bill

[HeuristicsInc]

A couple of old ones that I just found:

azvv nctkco ckizjo ifni z jfncmoe pt uzm vzco?

and

nabmb zao hzvsewp zpj yzw hincatpw bhk!

-bill

[Reist]

Is this part of some sick april fools joke, or am I just bad at puzzles?

[HeuristicsInc]

Nope, not a joke. There are at least two others around here who have solved these (may be others, I don't recall).
-bill

[fluffy]

I have to admit that I generally solved them with the help of software.

[Märk]

Nope, not a joke. There are at least two others around here who have solved these (may be others, I don't recall).
-bill

Me being one. Your latest sig looks kind of intimidating, though.

[HeuristicsInc]

Fluffy: well, sure. This new one might be challenging for the software, though

Mark: Yeah? Did I know that? Sorry if I forgot. As far as the new one, I've been reading this book on codes and ciphers and it gives me all sort of ideas...
-bill

[fluffy]

Yeah, I'm kind of wondering what it could be, although my early ideas don't work out (since there are number pairs greater than 26).

[Spud]

Yeah, I'm kind of wondering what it could be, although my early ideas don't work out (since there are number pairs greater than 26).

although, there are none less than 12.

[jimtyrrell]

And no zeroes at all. Still working on this one.

[anti-m]

I had an idea for the current one... but it was not a good idea, evidently!

(I assume you've read the Stephenson book, yes?)

[HeuristicsInc]

Yes! Last year. Great book.
But actually I have also read a good bit of actual history about cryptography. I am currently reading The Codebreakers: The Comprehensive History of Secret Communication from Ancient Times to the Internet (by David Kahn) - a fantastic read but not for the faint of heart (1200 pages or so). Also his book about the Enigma was great and a lot shorter.
Also, I just joined this organization: The American Cryptogram Association which is a hobbyist club dedicated to this sort of puzzles. Looks like they get way harder
-bill

[jimtyrrell]

I haven't forgotten about this.

A few peculiarities about the number sequence:

1) There are no zeroes.
2) Every other number (1, 3, 5...) is a 1, a 2, or a 3.

So my idea is to set up a letter chart in three columns and nine rows, which places the letters in coordinates. Then the number sequence can be broken up and read like this:

15 26 12 14 16 17 12 33 26 21 13 16 12 14 16 17 23 29 29 21 19 16 23 16 33 18 29 38 24 12 35 14 16 13 21 17 15 23 32 25 29 21

It's a nice enough idea, but I haven't found a letter placement that makes any sense. Still, I feel like I'm on to something.

[HeuristicsInc]

Doing well! Keep it up
-bill

[jimtyrrell]

From this point, random letters could be assigned, and then it's basically a regular old cryptogram. Except for the fact that there's no word breaks. So there goes my shortcut.

Ooh, and some of the random assigned letters could actually be CORRECT, further muddying the soup. This puzzle is affecting my ability to construct decent metaphors.

[jimtyrrell]

Other notable things:

3) the sequence 12 14 16 17 occurs twice.

4) the only instance of a double letter* is 29 29.

*assuming the numeric value of a letter is constant.