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The Scrypt paper here defines memory-hard and sequential memory hard, and accordingly explains why one was used over the other. Definition 1. A memory-hard algorithm on a Random Access Machine is an algorithm which uses $S(n)$ space and $T(n)$ operations, where $S(n) \in \Omega (T(n)^{1-\epsilon})$ Definition 2. A sequential memory-hard function is a ...

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Generally we look at strength by looking at the order $O$ that it adds to the password search when an attacker is trying to guess passwords. That's just the same as the number of iterations basically, assuming a salt and correct password hash. Often it is simpler to just use bits, which is basically the $\log_2$ of the order. So if a password strength is an ...

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The question has opposite answers, depending on if we consider adversaries computationally bounded, or not. Actual adversaries are computationally bounded, that is have limited computational resources. Against these, any cipher that is secure against Chosen Plaintext Attack has the property that similarities between plaintexts are undetectable and ...

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Can you guarantee that the users are going to use high-strength passwords like dicewire? What if they are using simple passwords? Are they going to sue you when they are hacked and their data exposed? Lots of questions? Consider that all of your users are hacked due to a bug in your application, then the attackers can execute a batch attack, too. Using salts ...

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Generally it is possible and secure to hash other hash values. This includes password hashes or Password Based Key Derivation Schemes (which is what this looks like). Note that the security will obviously not be more than the smallest output size of any of the hashes - this is generally OK though since the output size is usually 256 bit or higher. However, ...

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Partially true. Kerckhoff's Principle states that we should always assume that the attacker always knows everything about the algorithm, and only the key or password is secret. Your scheme of key derivation, meets the three principles of key derivation, which are the following: Memory-hard: prevents usage of GPUs or asics Non-parallizeable: requires ...

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The combination of different schemes may be somewhat advantageous with regard to certain custom hardware (ASICs), but I think that the disadvantages outweigh them. I assume that there is some kind of fixed time that is acceptable to the user. Nobody will use a procedure where she or he has to wait several minutes. Modern password hashing schemes are ...

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