Mainly for Dan...
Getting away from Jprogramming, but I'll leave it here for continuity.
Now I'm about to go away from my home router etc for a few days,
only Salisbury Wilts- no carnies,* though possibly some Magna Carta
celebrations - so am in any case unlikely to try to post at Rosetta for the
time being.
Meanwhile, fyi, I've copied the C code in making the states global
rather than local. This saves copying tranches of aa bb cc mm randrsl
from verb to verb, but is rather against the J grain. I usually
reserve =: assignments for debugging. I suppose the C code has
local scope within the main module. Perhaps an Isaac locale is called
for, but I haven't bothered.
I don't know how much one is allowed to transgress the C paradigm;
I've merged iRandA with iRandom, and iSeed with randinit. There
doesn't seem much point, in J, in defining MAXMSG.
Good luck,
Mike
* I didn't know what carnies were when reading Ray
Bradbury years ago. I don't think we have a word for
them in common parlance here. Just fairground people,
stallholders etc.
On 08/09/2015 16:58, Dan Bron wrote:
Hey everyone!
Sorry for starting a thread and then going silent. The long weekend got away
from me (did you know Staten Island has its own county fair, with carnies and
everything? Neither did I).
I’ll have to take some time today to catch up, but in re:
Not sure about posting it @ Rosetta, though.
Please do! If we need to make refinements later, we can; we can even do it
collaboratively. That’s the beauty of the Wiki process.
I think I’ll get this code running and then take a whack at making it as
functional/stateless as the algorithm will permit.
-Dan
On Sep 7, 2015, at 2:01 PM, Mike Day <[email protected]> wrote:
Caesar/MOD ok too, now.
ISAAC''
Message: a Top Secret secret
Key: this is my secret key
XOR encr:1c0636190b1260233b35125f1e1d0e2f4c5422
XOR decr:a Top Secret secret
MOD encr:734270227d36772a783b4f2a5f206266236978
MOD decr:a Top Secret secret
The Rosetta examples effectively do (32+ 95&|) twice for
Caesar (MOD), once in iRandA, whereas I'd only been
applying it once.
Not sure about posting it @ Rosetta, though.
Dan?
M
On 07/09/2015 11:15, Mike Day wrote:
OK - fwiw I'll reply to self...
Q0 - ok
Q1 - still not clear
Q2 - ascii encoding ok - eg 'a' => 97 etc
Q3 - yes - but upper 32 bits of words are wasted in my current version
Q4 - the vigenere (XOR) encryption is now correct. I'd overlooked the
aa^ ... part in isaac() - eg I'd coded
aa^= aa<<13; (C)
as
aa =. 13 shift4 aa
(where shift4 is obvious enough).
presumably my Caesar shift encryption isn't quite right, but I'm
greatly reassured by the XOR, so I'm on the home straight!
Mike
On 06/09/2015 20:20, Mike Day wrote:
Hello Dan and/or others...
Some questions and remarks below.
I spent (wasted?) a lot of time yesterday and again today, looking
at mix and the rest of the stuff about Isaac, both at Rosetta, and
at the author's, Rob Jenkins', site:
http://www.burtleburtle.net/bob/rand/isaacafa.html
The author's own listing of his 32-bit "readable C" code is similar to
the first part of the Rosetta C listing, although the Rosetta listing
has several extras, from iSeed() downwards, including a different
main().
The core of the whole thing is described as algorithm 1.1 in Amasson:
http://eprint.iacr.org/2006/438.pdf,
and is quite concisely coded (as isaac()) in both listings. Amasson doesn't
mention mix.
Jenkins' site also includes a presumably non-readable C listing, and
a 64-bit version.
Q0 What is the difference between 32 b. , 33 b. and 34 b. for left
shift, ie with positive x?
Q1 Is mix truly a part of the encoding or not?
Q2 Is it sufficient, in J, to start of with
256 {.a. i. <string message> ?
I think that means that each byte becomes a word with 4 (or 8) bytes,
although this encoding should leave the upper 3 (or 7) bytes at zero.
I decode the results with output { a. . I don't understand C (nor the
other languages) well enough to see how they're doing it.
Q3 My pc's are 64-bit. The implementation appears to work with
characters encoded into (computer) words. Correct?
Q4 I've achieved a working version in the sense that a verb
can encipher and decipher the message, but the ciphers are
apparently wrong. I'm just printing them as integers, but
they seem to have no relation to the samples:
isaacrosetta'' NB.my usual apologies re word-wrap, LF etc
Message: a Top Secret secret
Key: this is my secret key
XOR encr:3 66 54 13 18 66 49 7 1 16 7 22 66 17 7 1 16 7 22
XOR decr:a Top Secret secret
MOD encr:68 98 55 82 83 98 54 72 70 85 72 87 98 86 72 70 85 72 87
MOD decr:a Top Secret secret
The message has 19 characters, while the required encryptions each
have 38 hex-digits, ie 2 per byte. The hex sample for MOD is
734270227D36772A783B4F2A5F206266236978
My version of mix is ok, but not worth reproducing here and trying your
patience. It produces the same results on simple input as Raul's explicit
verb, so I'll assume it's not at fault.
I suspect the problem is associated with my Q2 above, but it might easily
be that I've got the core Isaac code wrong, or am doing the wrong number
of mixes, etc. It can't be all wrong though, as the plaintext is recovered
correctly, both for the example, and for much longer inputs.
I could provide the script, but it's pretty long, though not as long as
the C code.
Any ideas?
Mike
On 05/09/2015 03:55, Dan Bron wrote:
Periodically I review the list of open J tasks on RosettaCode [1]. Today I came
across an obscure but (if you believe the task description) meritorious cipher,
called ISAAC ("Indirection, Shift, Accumulate, Add, and Count”).
I understand the basic concepts of cryptography, but am generally unversed in
the practical details of implementation. In other words: at the moment, I’m
blindly transliterating the C implementation (marked as canonical) to J, hewing
as closely to the source material as possible, loops and all.
Which, of course, results in some damn ugly J. Take, for example, this C
preprocessor macro, which I’ve dutifully transliterated as in the post-script.
#define mix(a,b,c,d,e,f,g,h) \
{ \
a^=b<<11; d+=a; b+=c; \
b^=c>>2; e+=b; c+=d; \
c^=d<<8; f+=c; d+=e; \
d^=e>>16; g+=d; e+=f; \
e^=f<<10; h+=e; f+=g; \
f^=g>>4; a+=f; g+=h; \
g^=h<<8; b+=g; h+=a; \
h^=a>>9; c+=h; a+=b; \
}
Can you write this function in idiomatic, perhaps even elegant, J? Extra
brownie points for something along the lines of f/ a,b,c,d,e,f,g,h ,
If it gives you a jumpstart, here is the pattern of variable names, as well as
the bitshift direction and degree:
abdabc < 11
bcebcd > 2
cdfcde < 8
degdef > 16
efhefg < 10
fgafgh > 4
ghbgha < 8
hachab > 9
Expressed as left-hand arguments to |.!.0, the bitshifts are 11 _2 8 _16 10 _4
8 _9 .
And the variable name matrix, expressed as indices into ‘abcdefgh’ is:
0 1 3 0 1 2
1 2 4 1 2 3
2 3 5 2 3 4
3 4 6 3 4 5
4 5 7 4 5 6
5 6 0 5 6 7
6 7 1 6 7 0
7 0 2 7 0 1
Which pattern can be expressed as 0 1 3 0 1 2 (|."0 1) i.8 if you conceive
of it column-wise, or 0 1 3 0 1 2 (8 | +/~) i.8 if row-wise. Either way, the
salient structure appears to be 0 1 3 0 1 2 .
-Dan
[1] Tasks on RosettaCode with no J implementation:
http://rosettacode.org/wiki/Reports:Tasks_not_implemented_in_J
<http://rosettacode.org/wiki/Reports:Tasks_not_implemented_in_J>
[2] The “wash shuffle” (which Wikipedia calls the “Corgi shuffle”) is that
basic, no-frills move you see at the cheap tables in Atlantic City: the dealer
simply spreads all the cards face down on the table and slides them all around
and over each other. Not pretty, but effective, and less susceptible to
sleight-of-hand cheating.
https://en.wikipedia.org/wiki/Shuffling#Corgi_shuffle
<https://en.wikipedia.org/wiki/Shuffling#Corgi_shuffle>
PS: Here is a direct transliteration, but be WARNED: I haven’t gotten the
overall ISAAC cypher to produce the correct outputs yet, so this is untested
and may be incorrect.
NB. ISAAC operates on 32-bit ints, meaning b. will break it on 64-bit systems
bww =: (32#2)&#:
hlfUnd =: 2 : 'v^:_1@:(u v)’
bwXor =: ~:&.bww
bwShift =: |.!.0 hlfUnd bww
mix =: verb define
'a b c d e f g h'=.y
NB. a^=b<<11; d+=a; b+=c;
a =. a bwXor 11 bwShift b
d =. d + a
b =. b + c
NB. b^=c>>2; e+=b; c+=d;
b =. b bwXor _2 bwShift c
e =. e + b
c =. c + d
NB. c^=d<<8; f+=c; d+=e;
c =. c bwXor 8 bwShift d
f =. f + c
d =. d + e
NB. d^=e>>16; g+=d; e+=f;
d =. d bwXor _16 bwShift e
g =. g + d
e =. e + f
NB. e^=f<<10; h+=e; f+=g;
e =. e bwXor 10 bwShift f
h =. h + e
f =. f + g
NB. f^=g>>4; a+=f; g+=h;
f =. f bwXor _4 bwShift g
a =. a + f
g =. g + h
NB. g^=h<<8; b+=g; h+=a;
g =. g bwXor 8 bwShift h
b =. b + g
h =. h + a
NB. h^=a>>9; c+=h; a+=b;
h =. h bwXor _9 bwShift a
c =. c + h
a =. a + b
".&> ;: 'a b c d e f g h'
)
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