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Theoretical pi-based stream cipher

Let's pretend that all digits of pi are known and arbitrarily long sequences of digits are trivial to get. Further, some mathematician proves that there are no patterns in pi. We could create a stream cipher by grabbing a piece of pi as long as our…
Joshua Galecki
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How to build a security model

What are the minimal components to build a security model proof for a protocol? This question might seem trivial, but having read many papers-- from the IEEE, ACM, etc., that talk about a KMP-- I still don't know where to start. For example, should…
CipherX
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Is there a length-preserving encryption scheme?

Is there a length-preserving encryption scheme, that preserves the lengths of input sizes such that the length of the input plain text is same as length of the output cipher text ?
Digerkam
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Initialize a PRNG with a password

Let's assume that we have a secure PRNG. Is it "safe" to initialize it with password, or seed based on a password like SHA256(password)? If yes, is it "safe" to generate an RSA or DSA key from it? The idea behind this is to initialize a PRNG with a…
esskar
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How to salt PBKDF2, when generating both an AES key and a HMAC key for Encrypt then MAC?

When using Encrypt-then-MAC with AES and HMAC by password, and given 128 bits of payload with the ciphertext to store a random salt, which would be more secure: Using PBKDF2 with then entire 128 bit random salt and generating 512 bits of derived…
jbtule
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How many trials does it take to break HMAC-MD5?

I know that you can find collision in MD5 with $2^{64}$ trials using Birthday paradox. Now everyone is saying that HMAC-MD5 is significantly more secure. How can I quantify this security? My question is how many trials does it take to find a…
ladybug
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Why xor the message into the state for sponge hashes?

Sponge hashes like Keccak(SHA-3) and CubeHash, xor a message block into part of the internal state. Why use a reversible operation like xor for that, instead of replacing that part of the state with the message block? It clearly has no effect on…
CodesInChaos
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Example Rainbow Table Generation

I have read up on rainbow tables and think I understand the idea behind them. However, I find that it would be better for me to actually attempt to implement a (very basic) rainbow table generator in order to get a proper feel to using rainbow…
calccrypto
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Should I salt an AES password at each encryption?

I saw a sample code where the same password is salted with a different value (using PBKDF2) for each encryption. That means that the salt must be stored for each encrypted message. I don't understand why they do that since AES is used here in CBC…
Benoit
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Can I find the encryption key if I know the plain text and the encrypted text (DES and AES)?

If I have the plain text and its output after encryption with a key K1, is it algorithmically feasible to find K1? I am specifically interested in the cases of DES and AES encryption algorithms.
Joezer
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Can AES-GCM be broken if initialisation vector is known?

We are using AES encryption in GCM block mode in order to encrypt a number of different kinds of data at rest on a mobile device - Android. The key used for encryption is stored in the protected key-store offered Android so I am assuming that it is…
Suhas
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How to evaluate chi squared result?

I've been recently working on a (supposedly) TRNG. I'm still at the beginning of the project, so it is certainly not cryptographically secure yet, for now I'm just playing around. In fact, I've already discussed the project and the chi square…
valerio_new
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What is RSA-PSS and how is it different from a hash?

I can't find any usable resources about it online (at least ones that make sense to me right now), so any links to articles or if you could explain it to me would be greatly appreciated. What I don't understand is what is PSS? I understand that RSA…
lougehrig10
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Can one have an authentic, but repudiable, message without a previously shared secret?

Bob wants to send a message to Alice, such that Alice can be sure that the message came from Bob, but can't prove it to anyone else. If I understand right, this means that the same message could have possibly also been constructed by Alice, but not…
Paŭlo Ebermann
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What is the signature scheme with the fastest batch verification protocol for multiple signers?

I'm looking for a scheme where signing may be costly (slow) but batch verification with different signers is the fastest possible. Modified ECDSA allows batch verification for different signers with a 4X speedup [1]. Is there any signature scheme…
SDL
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