The Password-Based Key Derivation Function 2 (PBKDF2) is a method of securely deriving encryption keys from a passphrase entered by a user. It features an iteration count that can be deliberately adjusted (key stretching) to slow down brute force password guessing attacks.

learn more… | top users | synonyms

3
votes
1answer
245 views

PBKDF2 Salt and Password Ordering

I am currently reading about PBKDF2, and understand that the salt is used only once, while the password is used multiple times in the computation of the final key (see this question). How would the ...
2
votes
1answer
236 views

PBKDF2-SHA256+SHA256 for password storage

I recently came across an interesting paper detailing the use of hardened session cookies. Each cookie includes a preimage of the password hash, and the preimage is hashed once more and compared to ...
2
votes
2answers
466 views

Maximum password length in PBKDF2

Haven't found any clear cut answer in Google so its up to you guys: DK = PBKDF2(PRF, Password, Salt, c, dkLen) Here, what is the upper limit of password length? ...
7
votes
2answers
4k views

What is the difference between Scrypt and PBKDF2?

After reading these two resources I am wondering am I getting all the differences between Scrypt and PBKDF2. As far as I understood, the similarity is: both are password-based key derivation ...
1
vote
1answer
347 views

Importance of salt when deriving an encryption key

I'm very curious to know this and a bit confuses too: Suppose, I have two files encrypted using AES-128bit with keys PBKDF2-derived from the same password and the same salt. If an attacker does ...
3
votes
2answers
2k views

How long does it take to crack PBKDF2?

How much time will it take to crack PBKDF2 while using a 9 character password? I'm not specifying any specific system or platform. If a brute force attack is made using the best ever super computer ...
3
votes
1answer
126 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“, ...
2
votes
2answers
314 views

Password-based encrypted key storage?

RFC 5959 specifies the encrypted storage of private keys based on PBKDF2-HMAC-SHA-256 and AES encryption (in ECB mode). Is there a particular reason AES is used, instead of simply XORing the key ...
5
votes
1answer
443 views

Is SHA256 good enough to shrink a key?

I have a key that is the combination of two shorter keys generated by PBKDF2, which together are long more or less 64 bytes. Now I need to shrink it down to 32 bytes and I'm not sure what to use to do ...
3
votes
2answers
240 views

Using PBKDF2 twice with different argument order

I'm pretty sure this is a really bad approach (in theory), but one of my clients is doing this and I was wondering… How bad it is to perform pbkdf-2 in this way (with 2000 iterations)? ...
2
votes
1answer
196 views

User-specified PBKDF2 password, salt, and iterations limits

For a decentralized login where a user is left to select the password, salt, and iterations, what minimums for each should be enforced? In other words, because none are ever stored by the ...
4
votes
3answers
1k views

Hash function in PBKDF2

From this excellent answer I learned (correct me if I am wrong) that when writing a block cipher with say key size 128 bit, one has to pad the password given (variable size) so that it becomes exactly ...
6
votes
2answers
3k views

Is PBKDF2-HMAC-SHA1 really broken?

I just read through this article which demonstrates practical (and seemingly trivial) collisions in PBKDF2-HMAC-SHA1, and provides a few examples of collisions. Am I missing something here? Is PBKDF2-...
1
vote
1answer
357 views

What is the “purpose” byte in Crypto++ PBKDF2?

Does anyone know the purpose of the "purpose" byte in the PBKDF2 implementation in Crypto++? It appears that the PBKDF2 does not use this byte, but I want to make sure I am not setting the option to ...
2
votes
1answer
525 views

Right usage of PBKDF2 and login system questions

I'm developing the login part of my application and I was asking myself how to do it right. My application stores some users' data server-side that must be inaccessible from us, so all the content ...
3
votes
1answer
520 views

Rfc2898DeriveBytes - password length

Trying to find related answer for a long time, but not convinced yet. What I am trying is to encrypt using RijndaelManaged. To create Key, I am passing password, ...
2
votes
2answers
3k views

OpenSSL PBKDF2 documentation

I'm using OpenSSL 0.9.8 on OSX Maverick, and I want to use a PBKDF but I can't find any doc/man about it on OpenSSL's website. I'm working on QCA, an OpenSSL wrapper for Qt, and when I arrived there ...
3
votes
1answer
273 views

Derive both MAC and AES keys from same PBKDF2?

When doing password-based encryption, is it OK to create one instance of PBKDF2 from the password, and then use it to create both the AES key and the MAC key? (Or should a new instance of PBKDF2 be ...
2
votes
1answer
374 views

Strange Password Hashing

I know about PBKDF2, bcrypt, scrypt, etc. and while I'm not a crypt professional, I think I understand why are they better than just "hash(pass+salt)". But a colleague of mine surprised me with the ...
1
vote
2answers
597 views

pbkdf2 password validation

My question is related to PBKDF2. I am unsure how to validate user entered password with already existing hashes and salts. I have heard of the so called "length-constant" comparison which basically ...
1
vote
1answer
646 views

Encrypting a payload for transmission over HTTP. AES256 with PBKDF2

I've done some reading about implementing AES256 and deriving a key from a password. If I understand correctly: I want to generate a new salt (for the key) and a new IV (for the encrypted message) ...
3
votes
2answers
422 views

Best way to get 32 bytes from PBKDF2

Use the PBKDF2 output as an HMAC key, hashing two different inputs - once for 20 bytes and once for 12 : ...
2
votes
1answer
333 views

Using KDF output for password validation

I am currently revising an AES data format. I would like to determine whether a provided password/key is incorrect. Previously this was done by validating the HMAC, but this makes it impossible to ...
1
vote
1answer
352 views

What's wrong with my security model - or how can it be attacked?

I'm working on a little personal project where security is very important, and I've thought for a while about the best way to do this. Now I am looking for a little outside help on good practices. The ...
3
votes
1answer
142 views

Calculate entropy of key derived from PBKF2 function

I am using PBKF2 to derive a encryption key from a password. suppose entropy of my password is y and my PBKF2 function has x number of iterations. So how to calculate the entropy of finale key derived ...
4
votes
1answer
114 views

Are IVs and salts the same and usable for each other uses?

I'm new in the crypto world and I've just discovered PBKDF (I used to use typed passeword as symmetric key). When using some crypto mode, you're required to ...
5
votes
2answers
806 views

Encryption Key derivation from numeric PIN?

I want to store data encrypted within an Android application. Keeping an encryption key safe outside the app is not an option so I looked into password derived key algorithms. I found a nice example ...
2
votes
1answer
524 views

A key-derivation function that is as strong as the stronger of PBKDF2 and scrypt

I want a key stretching system that's as strong as the stronger of scrypt and PBKDF2. The consensus now is that scrypt is by far the better system, but that might change if in the future, a weakness ...
2
votes
2answers
869 views

Is scrypt a hashing function, encryption, or PBKDF?

I have installed a python implementation of scrypt and noticed it has several functions, both an encrypt and hash function. Yet Wikipedia lists it as being used for PBKDF instead of PBKDF2. Is scrypt ...
2
votes
3answers
522 views

Can PBKDF2 be used to create an XOR cipher key to encrypt random plaintext?

I want to encrypt a truly random plaintext (a key file) based on a user password. I'll use PBKDF2-HMAC-SHA256 to generate an encryption key from the password, but I'm wondering if I even need to ...
2
votes
1answer
1k views

Proper way of doing encryption and authentication (PBKDF2 + AES)

I'm currently in the planning phase of an authentication and storage-ish service. The client needs a file ("ENCFILE") which he will work with. This file will be encrypted with AES256, and stored on ...
3
votes
2answers
393 views

bcrypt and pbkdf2 double hashing

If I want to protect myself from implementation of algorithm issues and inherent design flaws of algorithms in password hashing, what would be most secure way to combine two hashes? bcrypt(pbkdf2(pw)...
2
votes
3answers
497 views

Can I dynamically calculate an appropriate number of iterations for PBKDF2 based on the system time, rather than using a fixed value?

Could you choose the number of PBKDF2 iterations based upon the system time? I've heard a few people recommend that the number of iterations for PBKDF2 should be doubled every two years (starting ...
2
votes
2answers
370 views

PBKDF2 uses HMAC-SHA1 to generate keys, but what is the key for the HMAC?

I was reading up on PBKDF2 and noted the following: DK = PBKDF2(PRF, Password, Salt, c, dkLen) PRF is a keyed HMAC, but I can't seem to find out what they use ...
6
votes
1answer
1k views

KDF and number of iterations for GPG

I gather, from reading the GPG manual, that symmetric encryption based on a password uses one of a variety of Key Derivation Functions (KDF). Although not explicitly mentioned I assume that PBKDF2 is ...
4
votes
2answers
282 views

How to use salt when there is only one user

I am encrypting files for storage in an untrusted location, using a custom Java program to do that. There is only one user, but there are many files. I am using AES in CBC mode with PKCS5 padding, and ...
4
votes
1answer
228 views

Securely generating passwords based on a secret and a public identifier

I'm trying to create a good scheme for generating passwords in my systems management scripts. What I'd like to do is have a secret key (let's say hello123), which I ...
3
votes
1answer
886 views

Is a PBKDF2-derived master key easier cracked if very many Data Protection Keys are derived from it?

I'm referring the NIST document about PBKDF2, NIST Special Publication 800-132, Recommendation for Password-Based Key Derivation, Part 1: Storage Applications, Page 8 and 9, section 5.4 Using the ...
3
votes
2answers
146 views

KDF with low-entropy salts

I need to derive a key from a username and a password. These are the only two things I have access to. What I thought is using PBKDF2 with username as the salt and password as the master password. ...
0
votes
1answer
91 views

PKCS#11: Which CKK_types are supported by CKM_PKCS5_PBKD2?

On Solaris there's a function pkcs11_PasswdToKey() which is a wrapper of C_GenerateKey(). I made a simple test and it turned out ...
4
votes
1answer
459 views

Injecting salt into PyCrypto KDF - useful?

I have noted some sources indicate that when using a KDF like PBKDF2 (alternatively) some advocate injecting the salt at the time of execution - like this: ...
10
votes
2answers
591 views

How to derive two keys from one password

What is the best way to generate two independent symmetric keys from one user-entered password or passphrase? Would using both scrypt and pbkdf2 achieve this?
1
vote
1answer
115 views

PBKDF2 when dkLen and hLen have the same size

I was reading RFC 2898 and something is not clear to me. When I use PBKDF2 with SHA-256 and I want a derived key with length 32 bytes (the same length as my hash function output), your derived key ...
8
votes
2answers
3k views

Should I salt an AES password at each encryption?

I saw a sample code where the same password is salted with a different value (using PBKDF2) for each encryption. That means that the salt must be stored for each encrypted message. I don't understand ...
6
votes
2answers
486 views

AES encrypting multiple files

So if I want to encrypt all the files in a folder with AES (same password) I take each file and generate the key schedule using PBKDF2. As the PBKDF2 algorithm takes in a salt then this salt should ...
4
votes
1answer
745 views

Can I use my random IV (for AES) as a salt for PBKDF2?

Also, where do I store my salt (can I just store it at the beginning of the encrypted file)?
8
votes
4answers
11k views

PBKDF2 and salt

I want to ask some questions about the PBKDF2 function and generally about the password-based derivation functions. Actually we use the derivation function together with the salt to provide ...
11
votes
2answers
822 views

Why is the salt used only once in PBKDF2, while the password is used often?

The purpose of PBKDF2 is to create a derived key (DK) from a master password (PW) and a salt, often using a function like HMAC-SHA256. I have read that the salt should be as random as possible. But ...
5
votes
3answers
908 views

Can I use PBKDF2 for authentication and decryption?

I want to store a hash for authenticating a password. I also want to use the same password for decryption. Can I use PBKDF2 for both? (I plan to use different salts for the authentication and the ...
3
votes
1answer
273 views

Is there a known vulnerability when using identical key and salt with PBKDF2?

For optimum security, a random salt should be chosen for PBKDF2. I came across a scenario where I produce a hash of a random file that serves as the "password". Due to the nature of files, this has ...