# Tag Info

4

In DSA (and ECDSA), it is possible and common to share the same domain parameters, across multiples users. AFAIK (and according to common wisdom, including FIPS recommendations) this introduce no known security weakness. The only common reasons to change domain parameters are to increase key size, or purposely introduce on interoperability barrier (e.g. to ...

4

You got three equations with two unknowns ($k$ and $x$). You only need two signatures to solve the private key $x$: $s_1k \equiv h_1 + xr_1 \pmod q$ $s_2k + s_2 \equiv h_2 + xr_2 \pmod q$ This might be solved using Gaussian elimination. Step 1: $s_1k/r_1 \equiv h_1/r_1 + x \pmod q$ - Divide 0.1 by $r_1$ $s_2k + s_2 - s_1kr_2/r_1 \equiv h_2 - ... 4 Computations on elliptic curves are more efficient. Roughly speaking, when the base field has size$n$(for DH/ElGamal/DSA, the size in bits of the modulus$p$; for elliptic curves, the size of the field for point coordinates) and a "security level"$t$(e.g.$t = 80$for "80-bit security" as can be expected when using a 160-bit subgroup and a 160-bit hash ... 4 One rationale for avoiding randomized schemes in general, and in MACs in particular, is that the random in such schemes tends to increases the size of cryptograms or reduce the size of the payload. An example is scheme 2 in ISO/IEC 9796-2 RSA signature with message recovery, where the size of the random/salt field is directly antagonist with the amount of ... 2 If the messages are unknown, there are no two messages$m_i, m_j$such that$m_i = m_j\$ and the messages have sufficiently high entropy (which might be shared across several messages, if the hash function is a CSOWF and the messages e.g. have low entropy unique sub strings or are made unique in some other way), and the underlying hash function is secure in a ...

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Elliptic Curve Cryptography (ECC) is not known to be specifically more resistant to side channel attacks (of course the next question is more resistant than what). This paper reviews power analysis side-channel attacks against ECC and countermeasures. Given that ECC uses multiplication and many common implementations of the MUL instruction run in time ...

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So I actually asked the theoretical version of this question a while ago: what happens if you choose multiple keys from the same group? The answer, as best as I determined, is its still secure. First, this practice is used both in the Internet Key Agreement Protocole (IKE) in IPSEC, and for SSH. Second, the best algorithms for breaking DSA effectively ...

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Selecting domain parameters for assymmetric schemes such as DSA or ECDSA is a tricky task ( involves good prime number number generation, point counting algorithm ect). That means that most people aren't able to choose their own. Knowing that fact most standards publish, for each security level, a small set of parameters that everybody can use. In general ...

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I'm considering switching to ECDSA, would this require less space with the same level of encryption? The answer to that question is yes, both ECDSA signatures and public keys are much smaller than RSA signatures and public keys of similar security levels. If you compare a 192-bit ECDSA curve compared to a 1k RSA key (which are roughly the same security ...

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Original Answer (StackOverflow) Haven't got enough time to look up the details, but I would guess that you're applying (or not applying) padding correctly. That would cause the right result to come up for some input lengths, but not for others. I guess I'll look into this more, but I wanted to get something in under the bounty wire :) Edit: Ok, ...

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