2k views

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 ...
252 views

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))) ...
656 views

SHA1 collision event probability after n iterations

There are String1 and String2 - some variables-strings. The probability of collision for different ...
228 views

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 ...
116 views

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 ...
191 views

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“, ...
133 views

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 ...
143 views

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 ...
92 views

Hash ratchets with truncating hash function

I'm working on a forward secret messaging system that relies on hash ratchet. I'm using BLAKE2b as the one-way function, which by default produces 512-bit digests. These digests are truncated by my ...