A hash algorithm is a function which takes a variable size input and produces a fixed size output. The algorithm tries to make it difficult to predict the output for a given input, find two inputs with the same output, or reconstruct the input from the output.

learn more… | top users | synonyms (1)

5
votes
3answers
2k views

HMACSHA512 versus Rfc2898DeriveBytes for password hash

We are currently using HMACSHA512 in .net, with a 128Char (64byte) validation key The salt is 64 char randomly generated string. We allocated 2048 length on the database for the hashed base64 string ...
5
votes
1answer
189 views

Is the execution time for bcrypt independent of the length of the input string?

Is the execution time for bcrypt independent of the length of the input string? i.e. Should the execution time of bcrypt.hashpw('input_string', bcrypt.gensalt(12)) and ...
1
vote
1answer
914 views

How secure is my private key in the Windows Digital Certificate store?

Many files we download don't have digital signatures. Files may get infected or someone may intentionally modify them on our hard disk. So I wrote a simple file hashing program in c# that creates a ...
0
votes
3answers
315 views

Why one time passwords using nested hash chain are not used?

I am wondering, why web sites do not use one-time passwords generated by hash chain. By that I mean that a client chooses a secret and after being salted, he applies some secure hash function F() on ...
0
votes
2answers
109 views

Does hash solve passwords in parts?

From an answer this earlier question: Does adding dictionary words to passwords weaken them? "...you have no way to recognize it as a password before testing it (against a hash or an online ...
3
votes
1answer
112 views

Are there any uses of having a non-deterministic salt value for hashes?

So I've been toying with the idea of having non-deterministic salt values for hashes. Let me explain what I mean: Basically, I applied some properties from Bitcoin including a "difficulty" (ie, ...
2
votes
1answer
222 views

Hash extension(padding) attack

I recently came across this website talking about sha1 padding attack. http://www.vnsecurity.net/2010/03/codegate_challenge15_sha1_padding_attack/ After reading here are some of my doubts: How ...
3
votes
1answer
240 views

How to determine hashes/second in password cryptanalysis

I'm working on my dissertation concerning cryptanalysis on password hashes. As part of my research, I aim to crack a number of passwords with John the Ripper and rainbowcrack-mt. I'd like to ...
4
votes
2answers
610 views

Truncating the output of SHA256 to 128 bits

suppose we need/prefer 128 bit hash output. for example to generate a 128 bit encryption key or, in other applications (e.g. file integrity verifications), to consume less storage space. i don't know ...
11
votes
1answer
363 views

“Please Enter Nth Character” without HSM

This question has been asked a few times, but always in the format "How does examplewebsite.com implement their 'please enter xth yth and zth characters of your password' function?" And the ...
0
votes
4answers
136 views

multiple hash values in a single malware file

Can a malware file have multiple "Hash values"?
7
votes
3answers
459 views

Is Using MD5 Sufficient Reason to Reject This Payment Processor?

I'm evaluating a credit card processor[1], and I noticed they are using MD5 as part of a salted hash algorithm to protect a secret key. Since I know MD5 is generally considered broken, this feels like ...
7
votes
3answers
9k views

With ASIC bitcoin miners, should SHA256 be considered insecure for password hashing?

I'm sure everyone here has seen the rise and further rise of bitcoin. The process used for mining bitcoin is basically "let's brute force an SHA256 hash that is less than this amount" That being ...
1
vote
1answer
280 views

what does GUID have that a whirlpool, md5 or sha2 hash dont

I'm trying to understand the use of GUID and what has always left me wondering is what's so special about them that I should consider using them instead of rolling my own type of unique id. In other ...
2
votes
1answer
108 views

Securely store two values per user in SQL

I have come across the need in my web app to store two values for each user. These values would need to be retrievable from a value stored in a URL. I would prefer to store neither of the values in ...
30
votes
5answers
5k views

How does hashing work?

I have been interested in Information Security. I was recently introduced to the idea of hashing. What I currently understand about hashing is that it takes the password a user enters. Then it ...
11
votes
4answers
991 views

Handling passwords in a web application

I am trying to learn how a secure web application is developed. Particularly, I am unsure of how passwords are sent from the client to the server. For a typical user/password login form. If the client ...
6
votes
1answer
179 views

Encrypting short identifiers?

I am developing a webapp that does not reveal record count, because it hides the primary key. I am looking for a better way to do this. My favorite idea is to encrypt the ID itself with a block ...
4
votes
5answers
322 views

Expanding/Inverse Hash function

First off, before I ask my question, let me explain what I am NOT asking. I am NOT asking for a way/method to reverse a hash output; by definition, a hashing function is one-way. Is there such a ...
8
votes
2answers
372 views

PINsentry PRNG and Bank Cards

My bank provides me with a device similar to this: The device is essentially a PRNG, presumably based on the date/time of it's internal clock, synchronized with the bank servers. To generate a pin ...
1
vote
1answer
291 views

Use brute force to mitigate brute force

Just an idea I had, and I am sure there is a lot of material about this subject, so I am looking for a pointer as to where I can find more information. My idea is this... When storing a password in ...
28
votes
8answers
2k views

Why improvising your own Hash function out of existing hash functions is so bad

I'm afraid I'll have tomatoes thrown at me for asking this old question, but here goes. After reading that cooking up your own password hash out of existing hashing functions is dangerous over and ...
20
votes
4answers
1k views

When hashing passwords, is it ok to use the hashed password as the salt?

I don't like this idea. But I can not come up with a technical argument against it. Can somebody explain it to me? The basic idea is: $passwd = 'foo'; $salt = hash($passwd); $finalHash = hash($passwd ...
5
votes
3answers
374 views

NTLMv2 resistance to bruteforcing

I have a question regarding NTLMv2 resistance to password bruteforcing. I know that some modern graphic processors (like Radeon 6990) are able to calculate billions hashes per second and crack NTLM ...
10
votes
4answers
1k views

Is there a length beyond which increasing password length provides no additional security?

Assuming that the password is stored hashed and salted, and that it is a string of random characters, is there a point where adding to password length doesn't add security? Since the hash will have a ...
1
vote
1answer
57 views

Parameters in output of password hashing function

A number of encryption functions include their tuning parameters in the output. For example, SCrypt, which I've been considering for an app I'm building, outputs in the following format: ...
4
votes
4answers
933 views

What security purpose do hashes of files serve?

Many websites offering downloads also provide the MD5 or SHA1 hashes of the files which are available for download. An example- What is the security purpose behind providing such a facility to the ...
11
votes
7answers
1k views

Why does some popular software still use md5?

Nowadays no one dares to defend md5 for any use, and of course they should not! However, much popular software still uses md5 in applications such as password hashing (although it's not simple/plain ...
4
votes
1answer
489 views

Reducing password length with hash function

Suppose I would like to use a very long string as a password. As an example we can just say this string is 100 characters in length. However, suppose the application for which I would like to use ...
12
votes
2answers
8k views

Why are GPUs so good at cracking passwords?

What is it about GPUs that lets them crack passwords so quickly? It seems like the driving force behind adopting good key-derivation functions for passwords (bcrpyt, PBKDF2, scrypt) instead of ...
2
votes
2answers
441 views

Does it make any difference of the order Hashing and Encrypting in terms of security?

I am implementing a password vault program with java. I have programmed a triple DES for encryption and a SHA256 for hashing. My question is would it make any difference if I first hash the raw data ...
6
votes
3answers
314 views

Increase the security of an already stored password hash

Right now we're using 1024 byte PBKDF2 with 256 byte user-specific salt and variable iterations. However, I would much prefer to be able to, perhaps once every year or two, to be able to flat out ...
1
vote
2answers
133 views

Should hashing hashed hashes colide or not?

Since key stretching basically boils down to hashing hashes over and over again (where salt, pepper and password individualize the hash function, but the principle remains the same), I wonder about ...
2
votes
1answer
364 views

Improving Digest Authentication using PBKDF2

For a variety of reasons, I need to use digest authentication for a REST server that I have created. I have come up with an "improvement" that I believe strengthens the algorithm against MD5 attacks ...
3
votes
2answers
412 views

what is the difference between a mac and a digital signiture

I understand that a MAC algorithm takes a message and a private key as input and hashes them to a value. I understand that senders and receivers often use MACs to authenticate a message and check the ...
4
votes
3answers
315 views

Hashing a key: less entropy than the key itself

A web API needs to store a 'key' for authentication, in much the same fashion as a password but at 128 characters. My concern is that the salted SHA1 hash for the key has less entropy than the key ...
3
votes
3answers
330 views

Client-Side Hashing to decrease value of password guessing heuristics

Yes, this is 'yet another client-side hashing' question. But, don't leave yet, I think there is some value here. I'd like to do something to mitigate the affect on the community as a whole when my ...
2
votes
3answers
605 views

Why we use GPG signatures for file verification instead of hash values?

for example here they put a gpg signature to verify what you download is what they really made. but why they just don't put a SHA256 hash value ? because its much more faster to check it and sometimes ...
1
vote
2answers
266 views

How high is the entropy of this salt-generating code? (No code-reading actually necessary)

What is the best method? Assumption: I have a function that generates a number of medium-high entropy bytes Step1: I generate 3 of these medium-high entropy bytes. Step2: I hash these bytes using a ...
3
votes
1answer
670 views

Key length and hash function in PBKDF2

On this page: http://www.ruby-doc.org/stdlib-2.0/libdoc/openssl/rdoc/OpenSSL/PKCS5.html they make a statement that strikes me as rather weird: Key Length Specifies the length in bytes of ...
3
votes
2answers
2k views

File security when encrypting files directly with the openssl command / and what about SHA1 hashing password first?

I've been using this command to encrypt files for a while now: openssl aes-256-cbc -a -salt -in secrets.txt -out secrets.txt.enc Then I type in a password. Can someone tell me, roughly speaking, ...
2
votes
1answer
184 views

Legality and ethics of cryptanalysis on password hashes

I'm working on my dissertation concerning cryptanalysis on password hashes. I'd like to delve into the legal and ethical aspects of cryptanalysis, however, seeing as I'n not at all well versed in law ...
7
votes
2answers
445 views

How to proceed if a new hash algorithm for passwords is introduced?

I have an e-mail address at a certain institution. A few days ago they sent me an e-mail (in German), which I'd like to paraphrase without revealing the institution: Dear Madams and Sirs, a ...
7
votes
5answers
1k views

Can I determine which algorithm was used if I know the matching hash of a given input?

If I know original text "12345" which encodes to "Tut0nlFFZ9sLVhPE5x81lQ==", how I can identify hashing algorithm?
2
votes
1answer
73 views

What is the purpose of the hashcode used in Exchange OWA HTTP requests?

This blog describes the URLs that are used in OWA and webservices. It also says that there is a hashcode that is used in conjunction with the throttling policy. Is this hashcode responsible for ...
3
votes
2answers
199 views

Confidentiality and integrity for web session

When the client authenticates with our service, he is issued an opaque "token". This token includes the information, that identifies the client and some other information about the client ("payload"). ...
3
votes
5answers
712 views

The security level in hash function

What is the difference in security between using part of message digest hash function or all the message digest hash function? and is there any equation can calculate the security for part or whole ...
19
votes
5answers
1k views

What is the point of hashing passwords?

Even when following strict security protocols, and what the user typed is (in this hypothetical situation) completely impossible to derive, the key that the server needs to compare to is still there. ...
12
votes
3answers
4k views

Cracking MS-CACHE v2 hashes using GPU

As most people here will know, Windows caches domain/AD credentials in a format known as MS-Cache v2. Obviously, these would be excellent passwords to gain during a penetration test when local access ...
3
votes
2answers
1k views

Why doesn't Microsoft implement salt on users passwords in Windows?

Pretty straightforward - So we use rainbow tables to get passwords of users out of hashes. So why won't Microsoft implement salt on the passwords in Windows to be hash(password+salt)? Won't this ...