Tagged Questions

In cryptography, a key derivation function (or KDF) derives one or more secret keys from a secret value such as a master key or other known information such as a password or passphrase using a pseudo-random function. Keyed cryptographic hash functions are popular examples of pseudo-random functions ...

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Memory hard key derivation (password hash) using AES encryption

I am restricted on a certain environment involving PHP and am currently unable to implement new memory hard hashes such as scrypt (and I am not trying to compete with the likes of scrypt). My ...
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Key derivation function in theory & practice

I am implementing a cryptographic protocol and I'd like to generate a set of seeds using a seed for a pseudo-random function. The reason is that I can pass on only one seed and it can be used to ...
67 views

How is a group element converted into a key?

I've only just started research on cryptography so I apologize if this is a basic question or I'm getting terms confused. I'm researching braid group cryptography and currently looking at the Anshel-...
155 views

Is it true that 7zip doesn't use any salt with its KDF?

This issue claims that 7zip does not use any salt with its key derivation function: https://github.com/magnumripper/JohnTheRipper/issues/1679 If that's true, wouldn't that mean you can crack multiple ...
142 views

Private and Public Keys

I have a very basic understanding of encryption and the encapsulation process, but for the life of me I can't grasp how public keys and private keys work, how they're made, and how they're exchanged. ...
44 views

ECDH security when no KDF is used

Let's suppose our device performs ECDH with a fixed, unknown, private key $prv$. It accepts as input any point $Q$ lying in the proper subgroup of the proper ellipict curve, then computes: $P = prv*Q$...
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Which method to generate one time password?

I'm looking for a concrete algorithm to generate one time passwords. The situation is as follows: Alice and Bob exchanged a passphrase over a secure channel in the beginning. They want to ...
293 views

Public Key Encryption using ECDHE and AES-GCM

Using a text book example, Alice and Bob want to communicate securely using encrypted messages over an insecure channel (the Internet). Alice and Bob have decided to use ECDH (using ephemeral keys ...
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AES-256 mode with per-block-key being a SHA-256 of SHA-256 of secret key, random public salt and block number. What's amiss?

Please criticize the (homebrew?) mode described below; to point out a single major defect/uncertainty or the link to (the analysis of) an equivalent construction is quite enough. Assume the ...
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Hash functions vs. keyed hash functions in the context of private key generation

I'm designing a key distribution mechanism and have thought of using a securely generated/acquired private key as a seed for a sequence of private keys to be distributed to a number of users using a ...
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How to derive a key from an existing AES key?

Currently, the code I am staring at uses the CKM_EXTRACT_KEY_FROM_KEY mechanism. That has been disabled in our hardware module, so I need a different mechanism to ...
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How to generate backup key for PBKD functions?

I would like to encrypt some files using AES, Ill derive key from password using some standard PBKD function and use that as AES encryption key. My question is, if user forgets the main password, ...
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Is this scheme to derive multiple keys secure?

I need a cryptographic scheme to generate a deterministic chain of private keys that look random to outside observer but can always be reconstructed from a single root key, also: Neither private ...
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How is a public/private key pair generated from a Diffe-Hellman key exchange?

I very well understand the DH key exchange. But what is the public key and private key at the end of the exchange. For example: Alice and Bob agree to use a modulus $p = 23$ and base $g = 5$ (which ...
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Practical benefit of using a KDF?

I see that KDFs should be used in systems that rely on PSKs, but what practical benefit does it provide? For instance, suppose the system relies on a shared secret for AES encryption and decryption. ...
221 views

Obtain 384 bits from a 256bit MasterSecret

I'm currently implementing, with crypto++, and AES tranmsission system, whose key is based on a previous ...
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How does FileVault2 Recovery actually work?

I'm a crypto-enthusiast but no expert at all, that'll explain why i didn't understand. Also please consider english isn't my native language :) I am about to enable FileVault2 FDE on the new macbook ...
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How to derive a symmetric key from ECDH shared secret?

I am trying to implement the internal primitives of ECDH. Currently I'm able to multiply the receiver's public EC point with the sender's private key to arrive at the shared EC point. Next step is to ...
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Concepts for realization in applied cryptography [closed]

I'm a computer science student (not a mathematican) and I'm gonna to write a master degree diploma on applied cryptography. Specifically, I'd like to create a realization of some cryptographic stuff ...
165 views

Is entropy being lost when the hash of a secret has a specific format?

Bitcoin's mini private key format works by brute forcing random data to produce a secret so that when appending ? and then hashing with sha256 it will produce a ...