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.

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Hash/Digest of string; multiple clients and reverse lookup must be impossible

Ok so i need a technique (could be a system or just an algorithm) to generate a hash/digest of a string on a client app without me (admin of a server app) being able to determine what the original ...
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68 views

Save Password length after hash to minimize calculation

Reading this topic How critical is it to keep your password length secret? following scenario comes to my mind: Assume I've a web application (PHP written using password_hash()) using salted password ...
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Is it important to use a slow hash in htpasswd?

It's my understanding that the purpose of .htpasswd files is to restrict access to some files in the server filesystem. If an attacker gains access to it, he probably has access to everything else ...
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NTLM/LM Hashes on Domain Controller

I've noticed that when extracting password hashes from a domain controller (using Elcomsoft proactive password auditor) sometimes I'll get LM and NTLM hashes and other times I'll only get NTLM hashes. ...
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212 views

Keyed-hashing a password with a hash of the password + salt as the key, is it safe?

I was looking at our authentication system which hashes passwords differently than I was taught. The salt is a constant byte array and it uses the password + the salt as a key for the password hashing ...
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312 views

Why do some passwords not allow certain types of characters?

Is there any programing related reason why some password cannot have certain characters? If the idea in storing a password is to store it's hash, since a hashing function can take any input (ok at ...
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722 views

What is the collision chance of a 128-bit hashing function if it is always fed with 256-bits of data?

I mean "normal" collisions not based on any attack. How do i calculate it?
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442 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 ...
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Using John the Ripper to crack SHA hash w/ partial knowledge

Group, I have a SHA1 hash that I would like to brute-force. I have knowledge of several characters before and after the password (ie, if the hash is derived from "xxxpasswordyyy", I know both xxx and ...
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Proper hash_hmac key creation

I'm looking for, but unable to find, some definitive information on how long to make the secret and what characters are useable in creating a HMAC signature in PHP using SHA256. I found some ...
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1answer
703 views

What kind of hashing is generally used in log-in modules?

Do operating systems hash the log-in password? What hash function is used in Windows XP, 7, 8,Linux Ubuntu, Debian, MAC Lion OS X ,...? Where should I look to know these security considerations of an ...
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Fingerprinting Hash Function

For the purpose of fingerprinting data with the least chance of collision will combining the length (as a 32 bit unsigned integer stored in addition to the hash) of the input data and/or sampling a ...
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109 views

What is the meaning of 'adaptative' and 'over time it can be made slower' in the context of the bcrypt algorithm?

I'm reading the wikipedia definition about bcrypt but I don't understand the meaning of 'adaptative' and 'over time it can be made slower'. Can someone explain what they mean in this situation?
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78 views

What is the difference between a hash table and a rainbow table, and how are they both used?

Is there much of a difference between the two tables? Can you get one from the other? (i.e. hash -> rainbow) How do they work? Are there different variables (in reference to speed, strength, ...
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3answers
214 views

How can two parties compare whether a simple (5 letter) shared word matches, without disclosing their word to each other?

I'm having some trouble with this scenario, some advice would be great. The context is that a group of people have each been give a simple 5 letter word - for example: Alice: ACTOR Bob: JEANS Dan: ...
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1answer
94 views

Securely storing passwords using PHP5

Starting note: After going through some articles and answers posted on SO related to storing secured passwords I'm still not sure whether my way of thinking is applicable to todays reality. I'm ...
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100 views

Truncating hash output for a unique ID

This seems like a common question, but my knowledge on hashing is very limited, so I'm looking for a more ELI5-type answer. I would appreciate if someone could help me with my questions Some ...
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1answer
134 views

PBKDF2 strong salt for client-side hashing

What should I use as a secure/strong salt for PBKDF2 hashing when salt is not available to use before login as it will be client-side javascript to hash user+pass with PBKDF2 ? I'm going to use ...
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394 views

Can password_verify() be used to identify password after database breach?

I am a newbie to PHP and password hashing. I am following the instructions provided here to hash my user password before storing. My questions are: PHP recommends password_hash() method as a ...
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402 views

How Windows Server 2008 Stores Local Users Passwords?

It is not clear to me how Windows Srver 2008 R8 stores local account passwords. Is there any salt added or just NT hash is computed and stored. The following article describes all the methods used by ...
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174 views

Is it ever safe to publish hashed data?

I'm having a friendly debate with someone who thinks that a website can safely make public sensitive data about it's users as long as that data is hashed (don't ask why, it's a long and hypothetical ...
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2answers
85 views

Should security phrases be hashed?

I didn't think of this before but today I just realised that in soke sites, pw recovery is possible if you know the answers to security questions like What is your mother's maiden name? In this ...
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1answer
2k views

Cracking MD5 passwords with the same salt

How long would it take to crack passwords up to 10 letters long if you knew the hashes were MD5 with a salt (that you know)?
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240 views

Any reason I shouldn't be salting and hashing before putting through bCrypt?

I've been reading up on password storage and such, and have come to the conclusion that I need to be using bCrypt. I've got an implementation working correctly, but I'm wondering the best way to move ...
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359 views

Keepass Dictionary Attack Protection Strategy

Though pretty interested, I'm everything but an expert in Information Security, please redirect me to any helpful resources if my question is stupid or correct me if my assumptions are wrong. When ...
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1answer
135 views

What to do with the extra bytes in ECDHE-RSA-AES-GCM-SHA?

I'm trying to implement, as an exercise, a protocol based on the cipher suite ECDHE-RSA-AES256-GCM-SHA384. As I understand things, ECDHE is used for the key exchange, RSA for the authenticity of the ...
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Finding out whether a website uses unsalted MD5 for password hashing

I'm working on a project where websites are analyzed and rated according to password security (factors like min/max password length, alphabet size and more are then calculated into a score). A great ...
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903 views

Password authentication using DynamoDB

I'm working on a Mac app. I have users stored using DynamoDB. Authentication is needed to enforce access control on system-internal operations, such as uploading files to Amazon S3. Of course, I ...
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1answer
179 views

Security of re-encryption with a list of pre-computed password based keys

I have a problem where an encrypted file stored on a server needs to be decrypted through a precomputed list of passwords that are used one time only - OTP applied to encryption basically. The file is ...
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3answers
715 views

Differences between brute forcing access versus decrypting password files or databases

I was just reading about how it's better to use bcrypt to protect passwords instead of saving password hashes in databases, and that got me thinking about other aspects that hackers work on that I had ...
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When to use the different types of Encryption / hash algorithm?

I'm studying for CISSP and know they will ask what type of encryption to use in different situations. Does such a list exist or is there a general rule of thumb to use?
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727 views

Time needed to generate an RSA signature of a document

How does the length of the RSA key and the size of the document affect the time it takes to sign a document using SHA-1 and RSA? I used CrypTool to check it, but the time does not appear to be larger ...
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1answer
87 views

Is there a benefit of using stateless JWT over SHA256 hash for API tokens?

Does it make sense to use stateless JWT (without persistent storage) over plain SHA256? Example scenario: User logs in User token generated as follows: a. JWT.encode(userId, 'secret') or b. ...
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97 views

Hashing algorithm for cryptsetup

I will encrypt my SSD using cryptsetup and I would like to know which hashing algprithm to use. First of all, cryptsetup benchmark: PBKDF2-sha256 262144 iterations per second PBKDF2-sha512 ...
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Reducing hash output length [duplicate]

I am using output of (keyed) hash function to make sure the input was not modified, I store it along with input. Now output of SHA-1 is 20 bytes. Say I want to reduce the output. And have it output 10 ...
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179 views

How can Alice and Bob prove that they share a file?

Carl asks Alice and Bob if they have a file f such that for a secure cryptographic hash function h, h(f) = K. Both claim to have f, but they can't show the file. Carl doesn't believe them. He can ...
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Virus - by-pass with binairies repackaging

Why don’t « hackers » (or more accurately, « virus maker ») just do repackaging over their malware to by-pass antivirus software? Because it resolves the issue of the virus signature (kind of hash), ...
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83 views

HMACs that have the same key and message

im using HMACSHA256 to generate the hash of password and store it. the objective here is to just authenticate users, i.e - save their hashed passwords, and validate users whenever needed using the ...
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770 views

TrueCrypt VS LUKS Bruteforce Resilience

I have been researching LUKS vs TrueCrypt topics -- my only concern is security, but most of the discussions I see focus around usability / interoperability . I know TrueCrypt has a bunch of nice ...
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152 views

Identical lanman hashes on AD accounts?

I ran metasploit's smart_hashdump module against my (2008r2) domain controllers, trying to find any accounts that may still have lanman hashes in place. These should have been disabled long ago. I'm ...
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326 views

PRF, IKE and hash function

The term PRF is mentioned in the documentation of the IKE (Internet Key Exchange) protocol. What is a PRF? What is the difference between a PRF and a hash function? What PRFs are used in the IKE ...
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184 views

How difficult it is to solve a salt if knowing the original data and the hash output that uses the SHA-2 algorithm

I am reading the documentation for Kentico where it describes using hashes to validate query strings ...
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821 views

Time Memory Trade-Off Attacks

Given, we want to crack a password. With Time Memory Trade-Off Attacks one tries to find the right balance between time to compute hashes for all possible passwords. And the used memory to store all ...
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1answer
102 views

Is it possible to hash bcrypt passwords more securely?

I'm wondering if it's possible to increase the work factor of an already encrypted bcrypt password. e.g. I have a password that was encrypted with a work factor of 5, is it possible to increase the ...
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273 views

Does sending two different hashes of the same password reduce security?

I'm updating a login system. The password is sent to the server as SHA512(password + long_string). I want to switch this to something like SHA512(username + password) in the future. By doing that I ...
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1answer
503 views

What key to use in HMAC

I need to use HMAC on a certain message to guarantee integrity, but I cannot figure out what are the requirements for the key to be given as input to the hashing algorithm. In particular I have to ...
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1answer
88 views

MITM vs. data leakage

We are designing a web API - accessible via https only - but two schools of thought seem to have arisen among our team: Group 1 wants to adopt an approach that is more concerned about data leakage ...
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How do I generate a blowfish password hash in Ubuntu?

What's the command line to generate a blowfish password hash? I can't seem to figure this out at all. Apache's htpasswd only supports bcrypt, and openssl passwd doesn't even do blowfish hahes (but it ...
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115 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 ...
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322 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 ...