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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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 ...
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Concepts for realization in applied cryptography [on hold]

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 ...
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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 ...
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170 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 ...
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289 views

AES-CTR with ephemeral keys vs IV

Let's say that we have a key exchange of some sort, which leaves A and B sharing the long-term secret $S$. Then, A and B want to use AES-CTR for the communication, which leaves us with several ...
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69 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 ...
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104 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 ...
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40 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 ...
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320 views

Get permutations from password

Are there any "good" ways to get a permutation from a password/pass-phrase? If one, for example, wanted to get a permutation of letters from a password, how might one do that in a smart way? I would ...
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40 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 ...
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65 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 ...
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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 ...
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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 ...
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41 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 : ...
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Why is Bcrypt called a Key Derivation Function?

I am trying to understand why is bcrypt called a Key Derivation Function? I looked up the details of Ekfblowfish on Usenix article here: ...
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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 ...
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54 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 ...
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104 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 ...
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1answer
20 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 ...
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72 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 ...
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52 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 ...
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83 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. ...
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Compressing EC private keys

For reasonable security, EC private keys are typically 256-bits. Shorter EC private keys are not sufficiently secure. However, shorter symmetric keys (128-bits, for example) are comparably secure. I ...
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83 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 ...
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101 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 ...
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77 views

Key change and key derivation

There are two ways for key change: key update, and Re-keying. Which of these methods use a KDF (Key Derivation Function) for getting new keys?
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Computing IV for CBC from PBKDF2 + HKDF

Note that this question is somewhat similar to Can I use my random IV (for AES) as a salt for PBKDF2? My current encryption format computes two random PBKDF2 salts (encryption and HMAC, 8 bytes each) ...
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65 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 ...
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68 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 ...
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244 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 ...
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185 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 ...
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1answer
118 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 ? ...
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109 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 ...
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1answer
338 views

Is this key management scheme secure?

I'm designing a scheme for management of a small number of cryptographic keys (< 100 at any given time) and I had an idea: rather than storing all the keys, could I just store one master key and ...
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1answer
42 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 ...
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How does multi platform encrypted cloud storage work?

I'm really interested in end-to-end encrypted cloud storage and couldn't find out how following scenario could work: A user of a cloud provider which provides zero-knowledge-authentication (like for ...
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3answers
300 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 ...
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1answer
137 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 ...
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1answer
294 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 ...
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208 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: ...
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1answer
140 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'?
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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 ...
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122 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 ...
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260 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 ...
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1answer
831 views

Security of KDF1 and KDF2 (hash based KDF's)

It's still common to come across implementations of KDF1 and KDF2. Basically these are KDF's that simply derive multiple keys from the key seed and a counter: $K_i = KDF(K_{master}, i) = H(K_{master} ...
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2answers
162 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 ...
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1answer
99 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: ...
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40 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 ...
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86 views

Counter Mode: how to choose the nonce part of the counter? [duplicate]

Suppose: The "counter field" is about: NONCE || CTR-VALUE. I have multiples messages $M_a, M_b, M_c, \dots$ Each message can be divided into x-bits blocks ($M_{a1}, M_{a2}, M_{a3}, \dots$). Each ...
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603 views

Is it secure to derive an AES key from a MAC?

I'm working on a project where we need to encrypt a large number of files and store them on the cloud. And I'm wondering if the following process would be secure (we have a “Hardware Security Module” ...