Tagged Questions

Passwords are secret keys which human beings can memorize.

learn more… | top users | synonyms (1)

3
votes
1answer
236 views

What's the most secure way to derive a key from a password repeatably?

I'm trying to write a cloud storage application where everything the user uploads is unreadable by the server, encrypted client-side before being sent. Currently, the flow looks like this: User ...
2
votes
0answers
107 views

Jumblar: Using map locations as passwords

I had the idea of converting map locations into passwords. Basically Jumblar takes a hash of the user's location and stores this as a comment on the PGP network. The 'stored-hash'(Vague-Hash) ...
4
votes
3answers
137 views

using elliptic curve point multiplication as a key stretching method

My friend came up with the following idea: assuming we agreed on curve parameters, use the following algorithm for key stretching/derivation from user-entered password. Pad the ascii representation ...
1
vote
1answer
156 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 ...
2
votes
1answer
67 views

How does the possible attack on passwords and salts mentioned in PKCS#5 v2.1 work?

From PKCS#5 v2.1, 4.1 Salt (page 6, emphasis by me), also in v2.0, RFC 2898: In password-based encryption, the party encrypting a message can gain assurance that these benefits are realized ...
2
votes
2answers
404 views

Is rainbow table attack applicable to any hash?

Typically when rainbow tables are discussed MD5 hash is used as an example. It's not quite clear whether this attack is specific just to MD5 or to a certain subset of hashes or to just any hash ...
1
vote
0answers
71 views

Password checking algorithm

I'm trying to reverse engineer key exchange protocol and faced with the following problem: Protocol is based on Diffie-Hellman key exchange method: g - generator m - modulus Alice: a - private key $A ...
0
votes
1answer
131 views

Trying to finalize my understanding about password storing

am sorry, an a beginner, so please forgive me if i make mistakes, so here is what I understood: PBKDF2: uses HMAC, so, the message is the password, and the key that crypts the message is the salt? or ...
5
votes
4answers
2k views

How does Scrypt use Salsa?

Bcrypt uses Blowfish to encrypt a derived key from the passphrase, and Blowfish is a cryptographic algorithm, but here it is said that: Note that Salsa20/8 Core is not a cryptographic hash ...
2
votes
1answer
2k views

Bcrypt VS Scrypt, Again?

I found this article on SO, but the answer was short, and the subject was closed, What i don't understand, is: Which one of the two limits memory usage to avoid custom Hardware to break the password? ...
4
votes
1answer
117 views

Which version(s) of SRP are in ISO/IEC 11770-4:2006?

I am on the impression that SRP emerges as the least uncommon and best analyzed protocol for authentication and key agreement based on a short password. This states that SRP is part of IEC 11770-4, ...
8
votes
5answers
930 views

Encrypt a file once with 50 characters password or twice with 25 characters?

What better Encrypt the file once with 50 characters password or encrypt it twice each time with 25 characters password.
6
votes
1answer
849 views

Using an MD5 hash as a password

Suppose Alice is using a password prompt that only accepts up to 32 characters for any particular password. Memorization of long strings of random characters is not one of Alice's strengths, so she ...
4
votes
1answer
524 views

Recommended way of adding a pepper/secret key to password before hashing?

There have been several questions regarding password hashing here and on Security.SE. A "pepper" is sometimes mentioned – an application-specific secret key. The canonical answer on password hashing ...
1
vote
1answer
183 views

Password verification

I'm looking for feedback on whether or not this is the proper way to approach password verification without transmitting the actual password. Are there any problems with this scheme. We are working ...
1
vote
2answers
274 views

Using salted hash as password for easy memorization without reuse?

I had an idea earlier: Secure passwords are a) long, and b) unpredictable. A hash is both of these. Would it be safe to reuse a key between sites, and include the site's name as a salt? For example: ...
6
votes
1answer
293 views

Single-purpose symmetric encryption scheme for single files

I'm writing a simple password manager program that will encrypt/decrypt a single file (it's size will most likely stay under a few K). This is my initial file format design: ...
2
votes
2answers
239 views

It is reasonably safe to leave a SSH private key with a 30+ character passphrase public?

I'm curious about exploring uses for a distributing a single RSA private key with a passphrase instead of trying to secure the private key and distribute the public key. With the private key (and ...
2
votes
2answers
265 views

Assymetric password encryption - Viable? Which algorithm?

We have an application that requires cleartext passwords for user authentication because of the authentication mechanism in use (RADIUS/CHAP), which unfortunately we cannot change. Since we don't want ...
6
votes
4answers
252 views

Could a very long password theoretically eliminate the need for a slow hash?

Before I provide details, I want to clarify that I am not looking to implement this practically, but I'm only asking to get a better understanding. The way I currently understand it, we use slow ...
1
vote
1answer
182 views

Sensible usecase for restricting special characters in passwords? [closed]

Please See Why Not Allow Special Characters In a Password on Security. Several websites I've come across limit the allowed special characters for a password. My thought was, it should all be ...
0
votes
2answers
629 views

Deriving HMAC key and cipher key from passphrase? [duplicate]

I'm encrypting a file with AES-256 in CBC mode. I needed to add an HMAC for authentication and validation of the file contents and passphrase, so I used a SHA-256 HMAC over chunks of my file ...
4
votes
1answer
259 views

Why does the SRP-6 calculation of B include a multiplier k = 3?

In SRP-6 $B$ is calculated as $B=kv+ g^b, k=3$. What is the purpose of $k$, and why was it fixed as $3$? (In SRP-6a, this value $3$ is replaced by $k = H(N,g)$, but this question is about SRP-6.)
5
votes
2answers
155 views

Can the hash of one message be used to make it easier to find the hash of a very similar message?

Background: I am trying to get an understanding of using a hash of a passphrase as a secret. Example: ...
4
votes
2answers
302 views

Commutativity of keyed hashes

Definition ${H_1}^{K_1}(X)$ means data $X$ hashed by keyed hashing algorithm $H_1$ with key $K_1$. Short question Is $H_1^{K_1}(H_2^{K_2}(X))$ equal to $H_2^{K_2}(H_1^{K_1}(X))$? Is ...
1
vote
1answer
140 views

How can encryption software accept password lengths which are not one of the AES key lengths?

AES comes with key sizes of 128, 192, and 256 bit. But in Truecrypt or other crypto software we can use passwords of different length, even less than 128 bit or more than 256 bit. How is this ...
4
votes
1answer
573 views

Hashing passwords with a salt - why use different salt for everyone?

Given a database where we have usernames and passwords, we want to secure users' passwords by hashing them. We should not use only username and passwords in this hash, as someone having data from ...
6
votes
3answers
566 views

Initialize a PRNG with a password

Let's assume that we have a secure PRNG. Is it "safe" to initialize it with password, or seed based on a password like SHA256(password)? If yes, is it "safe" to generate an RSA or DSA key from it? ...
5
votes
1answer
135 views

How to generate a key using any m passwords out of total n?

My application requires an AES-256 key K for some secure operation. In order to avoid saving this key in application, I have implemented following scheme: There ...
7
votes
4answers
224 views

Encrypting or HMACing password digests

Assuming I'm using bcrypt to digest passwords, is any additional security gained by either encrypting or HMACing the resulting digests? By requiring a key to compare password hashes, I would expect ...
3
votes
1answer
532 views

estimate of time required to crack sha512crypt password with JtR + OpenCL

OK, I have a shadow file with a password that I know, it is 4 letters followed by two numbers. Using John The Ripper with OpenCL support, on a laptop with AMD Radeon Mobility graphics, how long would ...
1
vote
2answers
168 views

Where can I learn basic cryptography to know more about passwords and Bitcoin?

Basically my knowledge in passwords consist of setting up a Diceware master password back then, and I know hashes are not convertible back to the original password. Some basic question I want to know ...
3
votes
2answers
312 views

Crypto USB Devices - where is the PIN/Password stored?

I am currently looking at the security of cryto USB drives for storing x509 certificates. I have one in possession currently. It can be read/written to using the Microsoft Crypto APIs. Anytime one ...
3
votes
1answer
803 views

Ideal passphrase length: old diceware method (5 words) vs. your Bitcoin wallet.dat passphrase lenght (8 words) and doubling passwords?

I made a cool 5 word passphrase back then using the old Diceware method and use it as a master password. The question is as computing power increases will we need to add more and more words to our ...
5
votes
1answer
1k views

A single password manager vs password generator/hash

I have been wondering about the options available for managing passwords. However, they all seem to fail if the master password is compromised (which isn't a big surprise). On one hand you have ...
4
votes
1answer
426 views

Exhausting the entropy of a hash function

In the case of password storage, consider the following: I have an idea that one can exhaust the entropy of input to the MD5 function by using a 128 bit random value as the password (indeed, any hash ...
1
vote
2answers
107 views

What can a master password also be called?

When having a company computer that is full disk encrypted, it is common that the boss have a master password / backdoor, so the data always can be decrypted. I have heard some call this for "scrow" ...
0
votes
1answer
159 views

Pseudo-random Number generation for Passwords

I am looking for a good pseudo-random number generation algorithm for passwords. My scenario is that I have to generate 5K pseudo-random bits from a user-supplied password (6 characters). What are ...
3
votes
1answer
212 views

Seed a PRNG with random data and a password

I'd like to combine a random key file with a password to generate a secure seed for a CSPRNG. The key file is assumed to have very high entropy, but the password will be whatever the user provides. ...
1
vote
1answer
325 views

password entropy calculation

I have the following password with a prescribed format: it starts with a fixed value of 111, followed by 2 random lower case letters and then lastly a random digit: "111""2 Random lowercase ...
3
votes
1answer
636 views

What happens to the entropy of a password when you hash it?

For example, if the entropy of a password is 30 bits, what is the entropy of the password when you hash it with MD5?
5
votes
4answers
352 views

How is it possible to parallelize a hashing function to crack an iteratively hashed password?

Suppose I have an algorithm that relies on multiple iterations of a hash function like SHA1 to slow down an attacker trying to bruteforce a hash. ...
5
votes
3answers
296 views

Stretching passwords for encrypting small files

I would like to know how to store a sensitive file; a credential of sorts. I want to password-protect it, obviously. It would be appropriate - in my application - to prompt the user for the password ...
11
votes
2answers
561 views

Do I have to have a different salt for each password?

Should I use a different salt for each password? In my system, there are no user names, only passwords. When a user logins in, he types in one or more passwords and the server compares the results ...
8
votes
2answers
2k views

Is there a way to make RC4 (ARCFOUR) secure, or is it completely broken?

I need a method to authenticate a process with another in order to establish interprocess communication between them, to prevent malicious processes from trying to hook onto the system. Currently I ...
8
votes
1answer
3k views

How do I store encrypted files on a web server and decrypt them locally?

I want to store files (images) on a public webserver and let users see them if they know a password. The server shouldn't have the unecrypted files and the server can only serve files, not perform ...
7
votes
1answer
416 views

Why does SRP-6a use k = H(N, g) instead of the k = 3 in SRP-6?

I've been reading up on the Secure Remote Pasword protocol (SRP). There are a couple different versions of the protocol (the original published version being designated SRP-3, with two subsequent ...
5
votes
2answers
260 views

Do MD5's weaknesses affect Oplop?

Oplop is an algorithm that generates account-specific passwords from a master password and user-chosen nickname (typically username@domain). From the website: Concatenate the master password with ...
1
vote
2answers
192 views

Is stretching hash several times basically the same as bcrypt?

As I understand it, the main advantage of bcrypt is stretching so it becomes slower to crack overtime. But, is using a "good enough" algorithm (e.g., SHA-2 family) then stretching until it's slow ...
6
votes
2answers
535 views

Can I use a key-derivation-function as the hash function H in SRP?

In the Secure Remote Password Protocol, the verifier must be stored on the server. In the case of a server compromise, an attacker could obtain these verifiers. If nobody reused passwords, this ...