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### The effect of truncated hash on entropy

Suppose I have a 128-bit random binary string (128 bits of entropy), then I hash it using SHA-256, then I take the first 128 bits of the output hash. Does the taken bit string still have (almost) 128 ...
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### Why not use ordinary hash functions for password hashing?

Assume we have a password and add a unique salt to prevent various precomputation attacks. Why don't we do this: SHA256(SHA256(SHA256 ...(Password || Salt))) ...
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### SHA1 collision event probability after n iterations

There are String1 and String2 - some variables-strings. The probability of collision for different ...
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### Can we estimate the loss of entropy when applying a N-bit hash function to and N-bit random input? [duplicate]

Someone pointed out recently to me that a cryptographic hash function " is not designed as a bijective mapping from N bit input to N bit output". So if I feed an N-bit cryptographic hash function ...
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### PBKDF security if all but one keys are exposed

I'm trying to understand the security of KDF but stuck with PBKDF case (case 3). Suppose, we have the following settings: $KDF(SK,salt_1) \rightarrow k_1$ $KDF(SK,salt_2) \rightarrow k_2$ The ...
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### Is there a practical upper limit for password rehashing?

When using PBKDF2, is there a practical upper limit to the iteration count above which we lose security? Note: If you answer “No”, that's fine. But if you answer: “There can't be an upper limit“, ...
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### Iterative hashing increases number of security bits?

Whatsapp uses 5200 iterations of SHA-512 over user's public key and identity according to WhatsApp Security Whitepaper. I wonder why? According to: Why iterate 5200 times when computing Safety ...
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### repeatedly hashing result and using reverse sequence as RNG secure?

I want to have a source of randomness for which: no one but me can predict the next number in the sequence. I know the entire sequence in advance, but I have no way of manipulating it once the first ...
121 views

### Losing entropy after re-hashing a hash

Suppose you have a string AAA that was hashed with SHA1 to produce 606ec6e9bd8a8ff2ad14e5fade3f264471e82251. If I rehash ...