# Tag Info

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These are standard terms in the cryptographic literature. Refer to Goldwasser's Lecture Notes on Cryptography, particularly section 10.3.1 where the definitions of forgery of digital signatures are introduced: Existential Forgery: The adversary succeeds in forging the signature of one message, not necessarily of his choice. Selective Forgery: The adversary ...

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Here's how the attack works: Select a random value $y$ Compute $a = y^2 \bmod n$ Ask for the signature of $a$, that is $x$ with $x^2 = a$ If $x \ne y$ and $x + y \ne n$, then $gcd(n, x+y)$ is a proper factor of $n$ The last step will succeed with probability $\approx 0.5$. You can make it probability 1 if you select a $y$ with Jacobi symbol -1.

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To forge a message using a hash collision, you need to generate a signature (using that hash function to sign a "good" message); then that signature is also a valid signature for the "bad" message. So, to prevent this from being a concern, you just never sign a message using MD5 as your hash function. Yes, the attacker can generate a "good" and a "bad" ...

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I think that I've found a good solution to this problem. In short terms it consists in generating an ECDSA signature using the point $R$ as generator, $s$ as private key and the result of $s*R$ as public key. So the $r$ part of the signature would be revealed but the $s$ part is still kept secret. The usual ECDSA signature generation consists in proving ...

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It is not safe at all since Factoring as a service project (https://github.com/eniac/faas) together with Amazon EC2 allows the factorization of a 512-bit key for less than $100 in only a few hours. 2 In short words: when you compute things modulo$n = pq$, you are really computing things simultaneously modulo$p$and modulo$q$. That's the gist of the Chinese Remainder Theorem. So to prove that$a = b \pmod n$, you just have to prove that$a = b \pmod p$and$a = b \pmod q$. Modulo$p$, for any$x$that is not a multiple of$p$,$x^{p-1} = 1 \pmod p\$ ...

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Is javascript RSA signing safe? …is safe or can people forge… In contrast to the accepted answer, I would not call it “safe” from a cryptographic point of view and I would definitely not say that “ if you take good care of securing your environment where you run the JS code you will be OK. ” because the sad fact is: that’s not enough to ensure ...

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The number of your ID card is not really a secret, and probably shouldn't even considered one. You could use it as a key for symmetric encryption (but for this purpose you'd have to share it with your communication partners, and everybody knowing the ID could read the communication), but not for public/private key cryptography. This is the reason why the ...

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