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Jul
9
comment RSA with $\lambda(n)$ or $\varphi(n)$
@all: I have the feeling the long discussion here was triggered by my comment not being precise enough. Sorry for the confusion. The attacks I was referring to were against a too short private exponent $d$ (Wiener and later). The check of the length of $d$ (derived using $\lambda$) is required at the end (2nd last sentence) of Appendix B.3.1 of NIST FIPS 186-4.
Jul
8
comment RSA with $\lambda(n)$ or $\varphi(n)$
@dannycrane The attacks work if the exponent you get with $\lambda$ is too small. If you calculate $d$ using $\varphi$, you generally get a bigger value. (In practice it's unlikely to be a problem, but for evaluations you might have to use $\lambda$.)
Jul
7
comment RSA with $\lambda(n)$ or $\varphi(n)$
... and as there are attacks against RSA with (too) small exponent, one couldn't detect that the exponent is too small if one just looks at the exponent one gets using $\varphi$ instead of $\lambda$.
Jun
23
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Jun
23
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May
22
comment Alternative to NSA encryption algorithm
If you are worried about NSA, look at crypto (also elliptic curves) done by Dan Bernstein. For post quantum cryptography look at pqcrypto.org (Dan is involved there too).
Apr
23
comment Is the reverse of the “discrete logarithm problem” equally dificult?
@fkraiem: With "when you know only n" in the sentence, I agree. It would be interesting to know a way to find the inverse mod $\phi$ without knowing the number $\phi$.
Apr
23
comment Is the reverse of the “discrete logarithm problem” equally dificult?
@fkraiem: It's never hard to invert modulo a number. It's just had to find that number ($\phi$) ;-).
Apr
23
comment Is the reverse of the “discrete logarithm problem” equally dificult?
@fkraiem: The question lacks the modulus one is working with, so I'm a bit confused which modulus you use. You can invert a number (your $k$) modulo another number (your $p-1$) without knowing the factorization of the latter by using the extended Euclidian algorithm. However, your statement that the question is (not just essentially, but exactly) the RSA problem is correct (for the modulus missing in the question).
Apr
13
comment Is there any opensource white-box implementation of AES or DES?
Not open source, but nice for learning to break a white-box aes implementation: kryptologik.com/demo/js/DemoKey_encrypt.js
Apr
8
comment Is the SEED blockcipher still secure?
If you are on an embedded device, you should consider using an implementation secured against side-channel attacks. When the AES was chosen, one criterion was how difficult it is to implement countermeasures against side-channel attacks. SEED is a bit more problematic (it needs switching from additive to boolean masks).
Feb
23
comment “Practical” operations supported by functional encryption?
One talk at Crypto 2012 was about the implementation of calculating an AES encryption via fully homomorphic encryption.
Dec
11
comment Are modified implementations of cryptographic algorithms a good idea?
@RichieFrame: Thanks a lot!
Dec
3
comment Are modified implementations of cryptographic algorithms a good idea?
@RichieFrame: Thanks, I didn't remember what it was exactly. Do you happen to have a link or reference?
Nov
25
comment Cracking RSA with Small exponent 5
You could take a look at these two questions about exponent 3 and RSA without padding and you should better stop your trial division project (waste of energy, sorry). Implement instead Pollard's rho or take a look here.
Nov
13
revised How does asymmetric encryption work?
added an important (missing) property of PKC pointed out by mikeazo
Nov
13
revised How does asymmetric encryption work?
removed edit by mikeazo that claimed exactly the common WRONG belief
Nov
12
comment Are modified implementations of cryptographic algorithms a good idea?
@CodesInChaos: Thanks, I adapted my answer accordingly. Unfortunately I misread the paragraph I intended to link to, and I cannot find currently the article about the modification of the DES.
Nov
12
revised Are modified implementations of cryptographic algorithms a good idea?
removed incorrect link; improved history of backdoor
Nov
11
comment How big an RSA key is considered secure today?
Do you consider Dan Bernstein's and Tanja Lange's article about Batch NSF worth including in your answer?