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Questions tagged [md5]

MD5 is a hash function that is no longer considered secure from a cryptographic point of view. Therefore, it should only be used for backward compatibility.

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Suitable 16-bit checksum?

I am writing a toy1 transport protocol and I am trying to implement a feature whereby: A 16-bit checksum is included in every packet. This checksum can be extended to be 48-bit if the data is large, ...
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2answers
153 views

Does it matter if I publish only publish good or bad MD5 hashes after recovering from a hack?

(This question is a follow-up from another question I asked about MD5, which is why I'm insisting on using MD5 in this question as well) My imaginary Linux distribution, Sushi Linux has had a big ...
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8answers
8k views

Is there really no use for MD5 anymore?

I read an article about password schemes that makes two seemingly conflicting claims: MD5 is broken; it’s too slow to use as a general purpose hash; etc The problem is that MD5 is fast I know ...
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1answer
26 views

Is OpenSSL HMAC vulnerable to length extesion attacks when using MD5 as hash algorithm?

Given that a valid hash for a specific payload is known, would some C code like this be vulnerable to a length extension attack? ...
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0answers
62 views

Overcome MD5-RSA Signature verification

I asked this question already at the Information Security SO site, but my research on how to overcome this problem ended always on the crypto site. That's why I will try to find some help here :) I ...
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1answer
56 views

MD5: Existence of invariant (fixed point)

Is it possible to find 128 bits $B$ such that $md5(B) = B$? md5 has collisions that can be computed in acceptable time, but I did not find any papers on fixed points in md5. As pointed out in this ...
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1answer
34 views

How does MD5 divide the padded message in 16 words?

This is the image from a website that shows all the steps of the MD5 Hashing algorithm: The original message is 'Hello World!'. I don't understand where these values are coming from: For example the ...
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1answer
174 views

How did I get a nonuniform distribution of UUID4s across MD5 space?

We have a system that processes data. Each entity has an ID that is generated using uuid4() in Python. Later, that ID is used as a partition key for AWS Kinesis. ...
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2answers
77 views

Integrity check of a binary firmware file with hash function

I need to provide a mechanism that it is possible to verify the integrity of a firmware image flashed on an embedded system. The procedure should be, that if someone has doubt on the firmware’s ...
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1answer
49 views

Add string to create specific MD5?

I have a file that include a long string , I can calc the md5 of this file . Is there any way to know which string I need to add for this file so the md5 of this file will be specific md5 that I want?...
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2answers
1k views

Using a hash function as a random number generator

Using MD5 or SHA1 for instance, and applying integers (as seed so to speak) to the hash function, in sequence, and only keeping, say, the first 64 bits of the resulting hash, do we always have a ...
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1answer
64 views

What is the smallest last value of sequence of integers from 1, where there is a collision in md5? [duplicate]

Question is just out of interest. If we take md5 hash from all integers from 1 to n, what is the first n, where its md5 collides with some previous md5? Has anyone ever calculated and proved the ...
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1answer
141 views

Md5 padding bits

What is the condition if the message size in md5 increses from 448 as the 64 bits are the length and we have to make the block of 512. So what will be the bits if it increases from 448
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1answer
184 views

Practical attack on md5 hashing algorithm?

I have the following conditions: String which consist of "STRING+key+ID+key" is hashed with md5. I have a knowledge of STRING (10 chars), ID is probabilistic (int 15), key is 15 chars long (a-z A-Z 0-...
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1answer
884 views

Vulnerabilities of AES method that uses MD5 to create the key

Are there security vulnerabilities given the would a user be able to access the original text and the encrypted text with AES using an MD5 as a key? In other words, if the user had both the original ...
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1answer
592 views

MD5 - Chosen Prefix Collision Attack

Given 2 messages $m_1$ and $m_2$, in a chosen prefix attack, we want to find $s_1$ and $s_2$ such that: $\text{MD5}(m_1 || s_1) = \text{MD5}(m_2 || s_2)$ Are $s_1$ and $s_2$ found by brute force ...
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2answers
442 views

Why aren't hash values for “nothing” (empty) defined as all zeros?

Any decent hash algorithm will produce basically "random like" values for any given input including the empty input. For example MD5 produces d41d8cd98f00b204e9800998ecf8427e on an empty input. I ...
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1answer
1k views

Cracking MD5, SHA1, SHA256 hashes [closed]

Hey guys i am trying to crack some hashes and it seems to be taking longer then expected (going on 7 days now). I am using John the ripper, I cant use hash cat due to pc limitations. I used online ...
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1answer
83 views

Are MD5 possibilities really $2^{128}$? [duplicate]

I have a simple question: Are we certain that the md5 hashing algorithm can produce $2^{128}$ different outputs ? If so, how ? Note: Sorry if this has already been asked, I really couldn't find it.
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3answers
146 views

Two salts, One password

If I have two different MD5 password hashes with two different salts (the salts are known), is there any way to cryptographically deduce if the two passwords match? Other than brute force password ...
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2answers
238 views

What is the point of using a cryptographic sequence number if you're not using it as a nonce?

OSPF features the use of Auth Crypto Sequence Number however, from reading the RFC it would appear the sequence number is not being used as a nonce. In addition, ...
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2answers
331 views

MD5 hash functions to prove integrity of a download

It doesn't take a lot of time on the crypto StackExchange to realise the sentiment around MD5 hash functions is poor. My questions are: If it's such a bad idea to make use of MD5 hash functions why ...
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4answers
2k views

Can SHA or MD5 results be decrypted?

I have learned that SHA-1 and MD5 are one way hash functions, which means that it is not possible to obtain the original value by performing the reverse calculation. There however some online ...
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1answer
138 views

What are the specifics behind MD5 being weak against collisions?

I'm not very well-versed in cryptography so bare with me. One thing I see a lot on InfoSec Exchange is this phrase - MD5 is weak against collisions but what I am failing to understand is why. ...
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2answers
2k views

How many trials does it take to break HMAC-MD5?

I know that you can find collision in MD5 with 2^64 trials using Birthday paradox. Now everyone is saying that HMAC-MD5 is significantly more secure. How can I ...
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1answer
83 views

MD5 hashing Algorithm

I created a repository on github to write some of the computer security algorithms, and it's time to write MD5 Algorithm, i searched about papers/videos explain the algorithm with examples alongside ...
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2answers
557 views

Attack MD5 with partial information?

If I generate an MD5 hash from 2 pieces of information – i.e. by concatenating two strings – how easy is it to guess what that hash is, assuming an attacker has knowledge of only 1 piece of those info?...
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3answers
368 views

Using weak hash functions to construct a stream cipher

I am in the awkward position of developing a secure encryption scheme that provides data-at-rest security for a very limited embedded system. The system is only guaranteed to have 4 MiB of memory (...
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1answer
95 views

Does public-key + hashing create a security vulnerability?

The title says it all really...let's say I have a packet of data that one of my applications needs to store encrypted with a public key (RSA, say, with the private key kept elsewhere). Let's say the ...
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4answers
17k views

How can hashes be unique if they are limited in number? [duplicate]

I'm curious, how can for example SHA-256 be unique if there are only a limited number of them?! For clarification: how many MD5 hashes are there? $16^{32}$ MD5 hashes can be produced. $16^{64}$ SHA-...
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1answer
97 views

Statistical attacks on a list of MD5/SHA-1 hashes?

I have a list of MD5 and SHA-1 hashes where the input string is of the form secret1000 secret1001 … all the way up to ...
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1answer
36 views

Expanding truly random key into printable password for successive hashing

The STUN network protocol defines its client authorization in the terms of message-integrity check employing the following scheme [RFC5389, section 10.2]: $$ \DeclareMathOperator{\HMAC}{HMAC} \...
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1answer
192 views

Difficulty of generating a string “The (md5|sha1) hash of this string is (x)” that hashes to (x) vs. regular hash collision between files?

I know that collisions in md5 and sha1 have been demonstrated in particular pairs of files (by incrementing some none viewable portion of a PDF, etc). Would generating the above string be ...
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1answer
483 views

Salt and pepper at both client and server sides?

Putting aside that it may sound paranoid. I know that many users tend to use the same password on many sites. Then, from an ethical point of view, I should not only be concerned about security breaks ...
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1answer
205 views

Hash function composition - security level

When using two hash functions, g(x)=SHA-512 and f(x)=MD5 g(x) has 512 bit output (using salt) f(x) has 128 bit output. Let's say that z(x)=f(g(x)) meaning the output is 128 bit long. The Question: ...
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3answers
578 views

Sign MD5 hash with RSA [duplicate]

I have to hash a message with MD5, digitally sign it, and then verify. I have looked around, but I can't find a step-by-step example. I understand how RSA works when a message is given as number (not ...
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1answer
288 views

An iso file containing its MD5 hash?

My colleague remembers and old backup tool, packaged as a standard bootable ISO image. He thinks the file was about ~250 MB, containing a MD5SUM.txt, which included the MD5 Checksum of the entire ISO ...
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1answer
633 views

Getting the key used for HMAC given the hash and the plaintext?

I'm working on a little exercise to understand the drawbacks of poor library choices and I've been presented with the following scenario. The HMAC function in python is being used (md5). I know the ...
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1answer
1k views

Is it possible to make two files with the same size and the same MD5 and CRC32?

I have seen a lot of different files with the same MD5s. For CRC32 is quite easy to find collision. But is is it possible to make size, and two different hashes the same? I have seen many linux ...
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2answers
496 views

Reverse MD5 of a 76 character string when the first 44 characters are known

I have a situation where I would like to reverse a hash which is the MD5 of a concatenation of 76 characters. I know the first 44 characters but don't know the remaining 32 characters. A description ...
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2answers
118 views

Why does md5_crypt move bytes around?

I looked into the code for md5_crypt the other day (yes, I know it's insecure), and I noticed that after mushing up everything with strange md5 hashes, it generates a base64 string with a strange ...
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1answer
332 views

Keyspace in truncated MD5 hash?

I have identified a password hashing algorithm that uses a truncated MD5 hash to compare user passwords. This means that any password whose hash matches the same first 23 hex chars (11.5 bytes or 92 ...
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1answer
1k views

I didn't get the hash length extension attacks

I was trying to solve a cryptography challenge and the problem was about "hash length key extension". After some reading in different topics, I don't know why I still didn't solve the challenge. I ...
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1answer
5k views

Decoding an MD5 hash where I already know most of the string [closed]

Let's say my friend has made an md5 hash of an email address and sent it to me. The email address will be something like 'jessica_XXXX@gmail.com', and I know it begins with 'jessica_' and ends with '@...
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1answer
160 views

Unable to implement Client and Server Side Hashing (Validation problem)

I'm trying to implement hashing on both client and server Sides for my web/mobile Application. On the client side, I implemented the slow hashing algorithm (bcrypt) On the server side, I tried to use ...
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1answer
590 views

MD5 - What happens if message is exactly 64bit block size message?

Based on RFC 1321 after we recive a message if message size is less than 64 Byte we will append it with a 0x80 and message length + zeroes until it's 64 bit and then generate the digest. The question ...
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1answer
289 views

Would finding a Merkle-Damgård preimage that doesn't change the initial state allow an attacker to prepend it to any hashed message?

Suppose, a message M was found so that MD5(M) = S, where S is the initial state of the MD5 function (0x01234567, ...). Given a hash MD5(m), would this allow computing MD5(M∥m∥padding), where padding ...
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1answer
5k views

Could we break MD5 entirely in the future?

Even of today MD5 is (sadly) still heavyly used in some applications. Even big tools like ApacheMD5. But even today there are more then enough MD5 hashes which are still not cracked. According to ...
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1answer
28 views

Can private hashing techniques be used in MySql 2000 server ? Help me decode this? [closed]

So last night my father gave me my birthday challenge. He made a website and asked me to get admin access there. I don't have any XSS knowledge, so I started with SQL Injection. I tried using SqlMap ...
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0answers
155 views

Breaking an addition-based cipher with two ciphertexts but no known plaintext

I'm attempting to break a system which uses decryption code functionally equivalent to the following: ...