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 ...

learn more… | top users | synonyms (1)

0
votes
0answers
66 views

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 ...
1
vote
2answers
64 views

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, ...
1
vote
1answer
78 views

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 ...
1
vote
3answers
202 views

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 ...
2
votes
1answer
97 views

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. ...
2
votes
1answer
199 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 ...
2
votes
0answers
38 views

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 ...
2
votes
2answers
275 views

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 ...
1
vote
0answers
51 views

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 ...
1
vote
2answers
161 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 ...
2
votes
1answer
176 views

Mathematical formula for switching the key for OTP?

Instead of generating the random key for the one time pad cipher over and over again, is there a mathematical formula that allows you to switch the key to a new key? The new key must be as random and ...
2
votes
1answer
103 views

Memory hard password based key derivation functions?

How are memory hard functions designed for the purpose of password based key derivation? To protect against a brute force attack from a parallel machine. What design could work well with Skein? The ...
0
votes
0answers
52 views

one complex password as a “seed” for localy generated per-service passwords

I've stumbled upon a project that suggests a way of having to remember one password, from which a “per-service password” could be generated by salting the service name using scrypt. What could be a ...
3
votes
1answer
51 views

Software interface for KDF and PBKDF?

I'm working on an implementation of Krawczyk and Eronen HKDF from RFC 5869. From Krawczyk's original paper, he identifies four inputs to a KDF in Cryptographic Extraction and Key Derivation: The HKDF ...
1
vote
1answer
237 views

Derive cipher IV and cipher Key using PBKDF2 with random salt?

It is said that cipher IV does not have to be secret and the only secret component of the encryption scheme should be a cipher key. Question: is it safe to generate IV using PBKDF2 function, which ...
2
votes
2answers
96 views

SHA256_HMAC for deriving session keys using a counter

I need to generate some session keys from a master key that was generated from an ECDH key exchange. The master key is 256 bits and I need 256 bit sessions keys. Is it safe to use SHA256_HMAC with ...
0
votes
1answer
105 views

What's wrong with an iterative (with counter) hashed salted KDF?

It seems like the brain-dead simplest KDF would have a key-stretching structure that is not substantially different from $\text{hash}(S | P | S | P |\dots|S|P)$, where $S$ is a salt and $P$ is a ...
1
vote
1answer
81 views

Differences between HMAC and HKDF in a specific case

I want to use a key derivation function to derive a key to another one. I think HKDF is the easiest solution in my case. The following picture gives a clear definition of it : ...
0
votes
4answers
731 views

Why don’t all AES encryption tools produce the same key from the same password?

Alice and Bob meet regularly. They have agreed face-to-face a 128 bit password which they want use to encrypt/decrypt emails written between them. They decide to use 256-bit AES. Alice wrote her ...
1
vote
0answers
56 views

Hardening of random number generators

Boxcryptor uses various CSPRNGs and apparently hashes the output using PBKDF2 to derive the final key. Even though the choice of ...
1
vote
1answer
81 views

Is there a tangible benefit in keeping the number of PBKDF iterations secret and not storing them with the ciphertext?

Suppose I have a local file and it is encrypted with a symmetric key derived from a strong passphrase, unique salt and $x$ number of PBKDF (e.g. Scrypt) iterations. I am interested in keeping this ...
4
votes
1answer
153 views

Yubico's take on U2F key wrapping

I've been reading up on Yubico's implementation of U2F. What I understand so far is that two things are calculated. So upon registration first you calculate a private key by $PrivateKey = ...
3
votes
1answer
135 views

Is it safe to derive two different keys with the same password and key derivation function using two different salts?

I would like to know if the following process would harm the security of a fictional system if the persisted data would be stolen: in this system a user has a single password. The password will be ...
1
vote
1answer
26 views

Key iteration count while using random keyfile larger than master key

If I were to have a 4096-bit file of random data (/dev/random) used as a keyfile for LUKS, would there be any benefit to having a key iteration count higher than 1? My reasoning is that the attacker ...
1
vote
1answer
79 views

Can a cryptographic hash be used as a cryptographic RNG?

Say I roll a six sided die 200 times (6^200 = ~2^517) and string all the results together into a long string of numbers and hash then result with SHA-512. Can I use that result for cryptographic ...
0
votes
1answer
55 views

Different keys for clients but 1 key on server

Is it possible to have different keys on alot of (embedded) devices and just have 1 key on a server (to witch all these devices connect)? The main point here being when 1 device is compromised this ...
1
vote
2answers
246 views

correct usage of keys and nonce

I've being studying up on AES, GCM, CBC, HMAC and a lot of other primitives and am somewhat ( a little bit, perhaps) familiar with them however I am still a bit weary on the use of the keys and nonce. ...
7
votes
3answers
231 views

What is a Key Derivation Function?

From Wikipedia: 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 ...
0
votes
1answer
126 views

What is the proper way to generate a fixed length key from a variable length password?

The password is entered by the user and the key is processed locally. Neither the password nor the key will be stored, only used and forgotten (but hopefully not by the user). Is SHA256 by itself ...
1
vote
1answer
260 views

KDFs for symmetric encryption master key & serial number

Let's assume that I generate a high entropy AES master key (through /dev/random for example) and I want to derive it with a fixed-length serial number (12345 for instance). The derived key is used to ...
0
votes
1answer
88 views

New to cryptology, studying key exchange

I'm just getting an overview of some of the concepts in key exchanging at the moment, and I'm a bit disoriented on a few topics, namely key stretching, key derivation functions and perfect forward ...
1
vote
1answer
113 views

chaining multiple key derivation functions together

I was looking at PBKDF2, bcrypt and scrypt as options for key derivation; and would like to try using them all together in order to get the cryptographic strength of the strongest one (which seems to ...
2
votes
1answer
596 views

Deterministically generate a RSA public/private key pair from a passphrase (with sufficient entropy)?

Is it possible to deterministically generate public/private RSA key pairs from passphrases? Would giving the (key generating) algorithm data made from key-stretching the passphrase (instead of a ...
2
votes
1answer
264 views

PBKDF2 for login key, scrypt for encryption key

I need to derive two keys from a single password client side. One for in-browser login, the other for encryption. Is the following secure ? ...
2
votes
2answers
144 views

Does key derivation with known parameters add any security?

First up: this is a question about a concept that I try to wrap my head around; it is not about the specific implementation. Anyway… I have the following scenario (simplified to show the problem I ...
0
votes
2answers
721 views

How secure is it to use password as AES key?

I am developing a steganography app where user encrypt any file into an audio file. The user can enter a password to protect the hidden data. The same password is converted as a 256 bit key and the ...
2
votes
1answer
51 views

Is it possible: Derived key based on variable number of private keys?

I have a MySQL database that I want to encrypt with AES_ENCRYPT() and have to provide access to a variable and possibly changing number of users. Is it possible to derive an encryption key based on a ...
1
vote
1answer
744 views

What is the algorithm behind PasswordDeriveBytes?

Microsoft has created an implementation of PBKDF1 in the PasswordDeriveBytes class. It can however generate more bytes than PBKDF1, which is limited to the number ...
4
votes
2answers
293 views

Share encrypted files without giving master key

Imagine I have four files I want to encrypt. I have master key, and from that master key I derive four keys, one for each file: ...
3
votes
1answer
163 views

Is the salt used with PBKDF2 secret?

I have two network endpoints that need to use the same derived key. Can the server send the salt to the client 'in the clear'?
1
vote
1answer
101 views

Many single-time use keys encryption scheme (not Shamir's Shared Secret)

I'm looking for encryption scheme with the following properties: There's a sequence of keys that can be used to decrypt the message Strictly only one key from the sequence is required to decrypt the ...
2
votes
2answers
134 views

Is it safe to salt a MAC?

Say that I define a scheme where the salt is public and is MAC-ed with the message: $k = KDF(password, salt)$ $tag = MAC_k(salt || message)$ Is it safe to salt the MAC this way? Assume that the salt ...
5
votes
2answers
349 views

Secure way to derive separate encryption and MAC keys from a single master key?

I want to derive a 256 bit encryption key and a 256 bit MAC key from a single 256 bit master key for an authenticated encryption scheme. I was considering the following construction to derive the two ...
3
votes
2answers
174 views

Does a stream cipher require a KDF when it's key is variable length?

RC4 has a variable length key. Is it still necessary to use a key derivation function, such as PBKDF2, to initialize it? Would using a single character password weaken it's output when compared to a ...
4
votes
1answer
194 views

Is it safe to derive a password from a signature provided by ssh-agent?

I'd like to use a password-based system on a remote host (accessed via SSH) without having to copy-and-paste the password and without storing it on disk. Using the system with some other form of ...
0
votes
1answer
174 views

Key management protocol for end-to-end security on Advanced Metering Infrastructure

I am currently working on a research on end-to-end security implementation for Advanced Metering Infrastructure (AMI). Pardon me if I a bit off topic or not asking the right question as I am ...
1
vote
1answer
118 views

Is it possible to 'fake' time for TOTP? (Time-based One-time Password)

TOTP (Time-based One-Time Password) Algorithm is used in Two factor authentication. I understand the algorithm and that current time is used as a variable to generate a token. Wiki page for reference: ...
3
votes
1answer
224 views

Why don't we use bcrypt and scrypt together?

Everyone is comparing bcrypt to scrypt. Bcrypt is proven, lots of cryptoanalysis and no vulnerabilities so far, but uses very low memory. While scrypt uses a lot of memory, but it's too early in its ...
0
votes
3answers
393 views

Implementing a web app where the server cannot decrypt its own data?

I'm a cryptography novice, but I think that the world needs to move towards an "encrypt everything" mentality as much as possible. As a result, I've been thinking a lot about ways to build a web app ...
2
votes
0answers
59 views

ECIES: Purpose of optional shared information?

According to Wikipedia the ECIES algorithm has two optional shared information $S_1$ and $S_2$. They are used as follows: Generate a random shared secret $Z$ according to ECIES, which will never be ...