Talk:Blowfish (cipher)

message: What does "symmetric, secret key, block cypher" mean? --LMS
: "symmetric, and secret key" means that it uses the same secret key for both encryption and decryption (compare public key cryptography), and "block cipher" means it encrypts data a block at a time (compare stream cipher).
What is the time complexity of the blowfish encryption/decryption algorithm? --DWB
:Quite obviously, O(1) for a single block, O(n) for n blocks since the number of rounds is constant regardless of key size. -- intgr 22:25, 27 September 2006 (UTC)
replies: text: Just like it says: if the key changes a lot, you'll spend all your time handling new keys.  There's no application it's insecure in, just some it's very slow in.  ciphergoth (talk) 09:25, 19 February 2009 (UTC)
thread_title: Question

message: On an email correspondense, I pointed out to Dieter Schmidt
that the conclusion of his cryptoanalysis paper is wrong, and
after this he retracted his article.  The problem is, that
while subkeys P3 and P4 do not depend on P1 and P2
(and this is a somewhat interesting observation),
this does not mean that P3 and P4 do not depend on 64 bits of
userkey.  This is because the userkey bits will be cycled
into the P-array, before any subkey encryptions take place.
So if, for example, the userkey is 448 bits long,
the first 64 bits will go to P1 and P2, and ALSO into P15 and P16.
Then, P15 and P16 (and thus the first 64 bits) WILL affect
the encryption iteration whose final value will be put into P3 and P4.
-- 84.251.21.229 13:04, 28 August 2006 (UTC)
replies: text: Thanks for letting us know. (The paper has been withdrawn from ePrint: ). — Matt Crypto 13:31, 28 August 2006 (UTC)
thread_title:  The removal of cryptoanalysis result by Schmidt 

message: Somewhere along the line a diagram went missing. The second paragraph refers to "the diagram on the right" that describes the F-function, but there is only one diagram. --Joe Sewell 20:58, 27 September 2006 (UTC)
replies: text: I can see two diagrams - one on the right in the infobox, and the other on the left under the "The algorithm" section. This particular paragraph refers to the image in the infobox. Now that I see it, I agree that it can be confusing. Unfortunately, moving infobox around is out of the question, and duplicating the image would be silly as well. Any ideas how to improve it? -- intgr 22:16, 27 September 2006 (UTC)
thread_title:  "Diagram on the right" isn't 

message: If I look at the image, I would think it's called 'blowfish' because it blows up the plaintext while encrypting (the S-boxes have an 8-bit input and a 32-bit output). If someone knows the official reason or explanation why this algorithm is called 'blowfish', please add it to the article. --Bernard François 15:37, 15 October 2006 (UTC)
replies: text: My memory is that the analogy was to the pufferfish which defends itself well by both armed and poisonous. A good cypher algorithm would do something similar, metaphorically. Having said that, however, I can't connect it to any particular source, and so I'm not sure it belongs in the article. ww 02:18, 16 October 2006 (UTC)
replies: text: Actually the pufferfish is also called blowfish. It blows itself up like a balloon to impress. The input of the S-boxes gets blown up in a similar way... --Bernard François 15:52, 5 January 2007 (UTC)
thread_title:  Why is this algorithm called 'blowfish'? 

message: Please pardon me if I am wrong, but it seems the use of P17 and 
P18 in the Blowfish article is misleading if not wrong. The
article states:
"Blowfish [...] can be inverted simply by XORing P17 and P18 to the ciphertext block, then using the P-entries in reverse order"
Though it seems reasonable at the first glance, I beleive 
that after application of XOR to P18 and Ln (the left part of
the of the ciphertext), you will NOT get the intput of the
last rounds F function, which is the case in the simpliest
Feistel network. Instead one gets the input scrabled 
by XOR with F17 (or F18, depending on how you
understand the fraze "using the P-entries in reverse order").
This means that there would be not guarantee in general that
the first decryption round F() xor Rn will give the correct
L[n-1].
If, instead, we just use P18 instead of P1, P17 instead of P2,
and so on, in a regular Blowfish net, we will get a
correct input for the last F() function in the first round
(namely, Ln xor P18). The F(Ln xor P18) xor Rn will give you
(L[n-1] xor P17), because xor is commutative and associative.
The result will be later XORed with P17 to yield the L[n-1] in the second round -- the correct input for the second
F(); by induction, one gets at the last round the correct
input for the last F(), which is L0 xor P1, and by using this
F() in (F() xor R1) we get (R0 xor P2) (since the xor with P2 
was not yet undeone). The final XOR operation will perform
(R0 xor P2) xor P2 = R0 (since we use P2 instead of P17)
and (L0 xor P1) xor P1 = L0, thus reconstituting the plaintext.
If the above is right, then the correct recomendation of
how to use Blowfish should read: "use P1, P2, ..., P18 entries
in reverse order to decrypt". The "XORing P17 and P18"
recommendation is wrong and should be omitted.
The similar wording to the one I suggest is used, by the
way, by Bruce Schneier himself in his blowfish paper:
http://www.schneier.com/paper-blowfish-fse.html
If my understanding is right I suggest that the article part
describing Blowfish decryption is corrected accordingly...
Sincerely,
Saulius Grazulis ((grazulis) commercial-at (akl) period (lt))
193.219.56.14
Saulius has a point. It is definitly wrong (and misleading)! Change it.  —Preceding unsigned comment added by 94.189.146.252 (talk) 22:36, 9 April 2009 (UTC)
thread_title:  Is the description of the Blowfish decryption right? 

message: While Twofish did get much more attention than Blowfish during the AES process, that no longer seems to be the case: Blowfish is still interesting because it's widely used in SSH implementations and so forth, but fewer applications use Twofish and it's no longer on a standards track.  If this seems incorrect, revert. 75.24.110.218 21:44, 22 July 2007 (UTC)
thread_title:  Changed lede not to say Twofish gets more attention than Blowfish 

message: The sign extension bug existed as early as 1994 (Dr. Dobb's Journal) and as late as 2004 (from the code available at Schneier.com) and was confirmed by Schneier and his employees.  The sign extension bug is quite serious for keys chosen at random. (No problem for ASCII keys, though, due to no sign extension of ASCII characters).  Ra2007 (talk) 20:54, 10 December 2007 (UTC)
replies: text: Just checked, although the sign extension bug has been confirmed at various places, the source code credited to Bruce Schneier at schneier.com still has the sign extension bug http://www.schneier.com/code/bfsh-sch.zip even today (12-10-2007).  The ohter links above should help confirm that this is a real bug and provide sources.  Ra2007 (talk) 21:00, 10 December 2007 (UTC)
thread_title:  sign extension bug 

message: "Bruce Schneier now advises against the use of Blowfish, and recommends using Twofish instead."
I think this sentence should be cleaned up - it doesn't appear to be accurately referencing its source.
Bruce Schneier does comment that he recommends Twofish instead. However he only indicates that he's "amazed" that Blowfish is still being used -- he doesn't explicitly state nor imply that Blowfish should not be used. Offering an up-to-date alternative is not an advisory against using the still-secure Blowfish algorithm.
This sentence should be cleaned up for clarity and for the sake of faithful referencing.  —Preceding unsigned comment added by 208.65.221.154 (talk) 00:02, 6 May 2008 (UTC)
replies: text: I edited the Twofish recommendation to read in a less "Blowfish negative" fashion; I hope it now reflects more closely what Schneier said in the referenced interview. -- Rydra Wong (talk) 05:00, 6 May 2008 (UTC)
thread_title:  Advising against Blowfish? 

message: Blowfish is specifically mentioned as being used by Agent Renee Walker to encrypt data in the "9:00 p.m.-10:00 p.m." episode in season 7 of 24. --Nlaverdure (talk) 00:41, 19 March 2009 (UTC)
replies: text: In my opinion they went WAY TO FAR. One thing is to "invent" in a TV-Show that you can break a "super-duper" cipher in a few seconds and without any software tool claiming your know "super hidden back doors". Another completely different thing is saying the cipher is called Blowfish and also have the character saying that he knows the inventor (this guy has a name and he's Bruce Schneier) and, last but not least claiming that Blowfish is riddled with backdoors and breakable in a few seconds! I can't even break a zip file in a "few seconds". If I was Schneier I would take serious offense to that. Up to date there is no proven attack that works with Blowfish, then Blowfish has a key size between 32bit and 448bit, so it seems to me pretty obvious that if you need to encrypt a secret you'd go for 448bit also due to the fact that for a modern CPU it makes not much difference in computational time and so why bother choosing a key of a middle size, in "24" however the FBI analyst says that it had been encrypted with a 148bit key which doesn't seem a possible number to me since it is not divisible per 8. Why do they love to screw up details so much? They could have invented a hypothetical new cipher, nobody would have argued then. Why hurting Bruce Schneier? --Legba (talk) 22:08, 24 March 2009 (UTC)
thread_title:  Pop culture reference 

message: Saulius has a point. It is definitely wrong (and misleading)! It's OK now. —Preceding unsigned comment added by 94.189.146.252 (talk) 22:42, 9 April 2009 (UTC)
thread_title:  Decryption description is wrong! 

message: Wrt this revert, why do you think this "bcrypt" encryption utility even warrants a mention on Wikipedia? Are there any reliable sources covering it? -- intgr [talk] 20:54, 31 August 2015 (UTC)
replies: text: Good question intgr. To now I was ensuring I moved someone else's content from the wrong article :bcrypt to the right article (here) and disambiguated it. If we delete it then the hatnote should go too. Neutral on the content itself....let's have a look...it arguably has at least one RS, so I'm happy to leave in. Widefox; talk 21:53, 31 August 2015 (UTC)
thread_title:  Inclusion of "Bcrypt" utility 

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thread_title:  External links modified 

message: Isn't the sentence "Blowfish provides a good encryption rate in software and no effective cryptanalysis of it has been found to date." in contradiction with the section "Weakness and successors"? Specifically, "the SWEET32 attack demonstrated how to leverage birthday attacks to perform plaintext recovery (i.e. decrypting ciphertext) against ciphers with a 64-bit block size such as Blowfish."?  — Preceding unsigned comment added by 2001:67C:1220:80C:C4E7:4F99:A58F:5989 (talk) 15:09, 9 October 2017 (UTC)
thread_title:  Weaknesses