Is it possible to decrypt MD5 hashes

Question

Someone told me that he has seen software systems that    retrieve MD5 encrypted passwords from other systems  decrypt the encrypted passwords and store the passwords in the database of the system using the systems own algorithm    Is that possible  I thought that it wasn t possible   feasible to decrypt MD5 hashes   I know there are MD5 dictionaries  but is there an actual decryption algorithm

User · Answer

Decryption  directly getting the the plain text from the hashed value  in an algorithmic way   no   There are  however  methods that use what is known as a rainbow table  It is pretty feasible if your passwords are hashed without a salt

User · Answer

No  MD5 is not encryption  though it may be used as part of some encryption algorithms   it is a one way hash function  Much of the original data is actually  lost  as part of the transformation    Think about this  An MD5 is always 128 bits long  That means that there are 2128 possible MD5 hashes  That is a reasonably large number  and yet it is most definitely finite  And yet  there are an infinite number of possible inputs to a given hash function  and most of them contain more than 128 bits  or a measly 16 bytes   So there are actually an infinite number of possibilities for data that would hash to the same value  The thing that makes hashes interesting is that it is incredibly difficult to find two pieces of data that hash to the same value  and the chances of it happening by accident are almost 0   A simple example for a  very insecure  hash function  and this illustrates the general idea of it being one-way  would be to take all of the bits of a piece of data  and treat it as a large number  Next  perform integer division using some large  probably prime  number n and take the remainder  see  Modulus   You will be left with some number between 0 and n  If you were to perform the same calculation again  any time  on any computer  anywhere   using the exact same string  it will come up with the same value  And yet  there is no way to find out what the original value was  since there are an infinite number of numbers that have that exact remainder  when divided by n   That said  MD5 has been found to have some weaknesses  such that with some complex mathematics  it may be possible to find a collision without trying out 2128 possible input strings  And the fact that most passwords are short  and people often use common values  like  password  or  secret   means that in some cases  you can make a reasonably good guess at someone s password by Googling for the hash or using a Rainbow table  That is one reason why you should always  salt  hashed passwords  so that two identical values  when hashed  will not hash to the same value   Once a piece of data has been run through a hash function  there is no going back

User · Answer

MD5 has its weaknesses  see Wikipedia   so there are some projects  which try to precompute Hashes  Wikipedia does also hint at some of these projects  One I know of  and respect  is ophrack  You can not tell the user their own password  but you might be able to tell them a password that works  But i think  Just mail thrm a new password in case they forgot

User · Answer

No  you can not decrypt reverse the md5 as it is a one-way hash function till you can not found a extensive vulnerabilities in the MD5   Another way is there are some website has a large amount of set of password database  so you can try online to decode your MD5 or SHA1 hash string  I tried a website like http   www mycodemyway com encrypt-and-decrypt md5 and its working fine for me but this totally depends on your hash if that hash is stored in that database then you can get the actual string

User · Answer

You can find online tools that use a dictionary to retrieve the original message   In some cases  the dictionary method might just be useless    if the message is hashed using a SALT message if the message is hash more than once   For example  here is one MD5 decrypter online tool

User · Answer

MD5 is considered broken  not because you can get back the original content from the hash  but because with work  you can craft two messages that hash to the same hash   You cannot un-hash an MD5 hash

User · Answer

You can t revert a md5 password  in any language   But you can   give to the user a new one   check in some rainbow table to maybe retrieve the old one

User · Answer

MD5 is a cryptographic  one-way  hash function  so there is no direct way to decode it  The entire purpose of a cryptographic hash function is that you can t undo it   One thing you can do is a brute-force strategy  where you guess what was hashed  then hash it with the same function and see if it matches  Unless the hashed data is very easy to guess  it could take a long time though

User · Answer

No  it is not possible to reverse a hash function such as MD5  given the output hash value it is impossible to find the input message unless enough information about the input message is known   Decryption is not a function that is defined for a hash function  encryption and decryption are functions of a cipher such as AES in CBC mode  hash functions do not encrypt nor decrypt  Hash functions are used to digest an input message  As the name implies there is no reverse algorithm possible by design     MD5 has been designed as a cryptographically secure  one-way hash function  It is now easy to generate collisions for MD5 - even if a large part of the input message is pre-determined  So MD5 is officially broken and MD5 should not be considered a cryptographically secure hash anymore  It is however still impossible to find an input message that leads to a hash value  find X when only H X  is known  and X doesn t have a pre-computed structure with at least one 128 byte block of precomputed data   There are no known pre-image attacks against MD5    It is generally also possible to guess passwords using brute force or  augmented  dictionary attacks  to compare databases or to try and find password hashes in so called rainbow tables  If a match is found then it is computationally certain that the input has been found  Hash functions are also secure against collision attacks  finding X  so that H X     H X  given H X   So if an X is found it is computationally certain that it was indeed the input message  Otherwise you would have performed a collision attack after all  Rainbow tables can be used to speed up the attacks and there are specialized internet resources out there that will help you find a password given a specific hash   It is of course possible to re-use the hash value H X  to verify passwords that were generated on other systems  The only thing that the receiving system has to do is to store the result of a deterministic function F that takes H X  as input  When X is given to the system then H X  and therefore F can be recalculated and the results can be compared  In other words  it is not required to decrypt the hash value to just verify that a password is correct  and you can still store the hash as a different value     Instead of MD5 it is important to use a password hash or PBKDF  password based key derivation function  instead  Such a function specifies how to use a salt together with a hash  That way identical hashes won t be generated for identical passwords  from other users or within other databases   Password hashes for that reason also do not allow rainbow tables to be used as long as the salt is large enough and properly randomized    Password hashes also contain a work factor  sometimes configured using an iteration count  that can significantly slow down attacks that try to find the password given the salt and hash value  This is important as the database with salts and hash values could be stolen  Finally  the password hash may also be memory-hard so that a significant amount of memory is required to calculate the hash  This makes it impossible to use special hardware  GPU s  ASIC s  FPGA s etc   to allow an attacker to speed up the search  Other inputs or configuration options such as a pepper or the amount of parallelization may also be available to a password hash   It will however still allow anybody to verify a password given H X  even if H X  is a password hash  Password hashes are still deterministic  so if anybody has knows all the input and the hash algorithm itself then X can be used to calculate H X  and - again - the results can be compared   Commonly used password hashes are bcrypt  scrypt and PBKDF2  There is also Argon2 in various forms which is the winner of the reasonably recent password hashing competition  Here on CrackStation is a good blog post on doing password security right     It is possible to make it impossible for adversaries to perform the hash calculation verify that a password is correct  For this a pepper can be used as input to the password hash  Alternatively  the hash value can of course be encrypted using a cipher such as AES and a mode of operation such as CBC or GCM  This however requires the storage of a secret   key independently and with higher access requirements than the password hash

User · Answer

MD5 is a hashing algorithm  you can not revert the hash value   You should add  change password feature   where the user gives another password  calculates the hash and store it as a new password

User · Answer

The MD5 Hash algorithm is not reversible  so MD5 decode in not possible  but some website have bulk set of password match  so you can try online for decode MD5 hash   Try online     MD5 Decrypt  md5online  md5decrypter

User · Answer

Technically  it s  possible   but under very strict conditions  rainbow tables  brute forcing based on the very small possibility that a user s password is in that hash database     But that doesn t mean it s    Viable or Secure   You don t want to  reverse  an MD5 hash  Using the methods outlined below  you ll never need to   Reversing  MD5 is actually considered malicious - a few websites offer the ability to  crack  and bruteforce MD5 hashes - but all they are are massive databases containing dictionary words  previously submitted passwords and other words  There is a very small chance that it will have the MD5 hash you need reversed  And if you ve salted the MD5 hash - this won t work either        The way logins with MD5 hashing should work is  During Registration  User creates password -  Password is hashed using MD5 -  Hash stored in database  During Login  User enters username and password -   Username checked  Password is hashed using MD5 -  Hash is compared with stored hash in database  When  Lost Password  is needed  2 options    User sent a random password to log in  then is bugged to change it on first login    or   User is sent a link to change their password  with extra checking if you have a security question etc  and then the new password is hashed and replaced with old password in database

User · Answer

See all other answers here about how and why it s not reversible and why you wouldn t want to anyway   For completeness though  there are rainbow tables which you can look up possible matches on  There is no guarantee that the answer in the rainbow table will be the original password chosen by your user so that would confuse them greatly   Also  this will not work for salted hashes  Salting is recommended by many security experts

User · Answer

In theory it is not possible to decrypt a hash value but you have some dirty techniques for getting the original plain text back    Bruteforcing  All computer security algorithm suffer bruteforcing  Based on this idea today s GPU employ the idea of parallel programming using which it can get back the plain text by massively bruteforcing it using any graphics processor  This tool hashcat does this job  Last time I checked the cuda version of it  I was able to bruteforce a 7 letter long character within six minutes  Internet search  Just copy and paste the hash on Google and see If you can find the corresponding plaintext there  This is not a solution when you are pentesting something but it is definitely worth a try  Some websites maintain the hash for almost all the words in the dictionary

User · Answer

It is not yet possible to put in a hash of a password into an algorithm and get the password back in plain text because hashing is a one way thing  But what people have done is to generate hashes and store it in a big table so that when you enter a particular hash  it checks the table for the password that matches the hash and returns that password to you  An example of a site that does that is  http   www md5online org    Modern password storage system counters this by using a salting algorithm such that when you enter the same password into a password box during registration different hashes are generated

User · Answer

You can t - in theory  The whole point of a hash is that it s one way only  This means that if someone manages to get the list of hashes  they still can t get your password  Additionally it means that even if someone uses the same password on multiple sites  yes  we all know we shouldn t  but     anyone with access to the database of site A won t be able to use the user s password on site B   The fact that MD5 is a hash also means it loses information  For any given MD5 hash  if you allow passwords of arbitrary length there could be multiple passwords which produce the same hash  For a good hash it would be computationally infeasible to find them beyond a pretty trivial maximum length  but it means there s no guarantee that if you find a password which has the target hash  it s definitely the original password  It s astronomically unlikely that you d see two ASCII-only  reasonable-length passwords that have the same MD5 hash  but it s not impossible   MD5 is a bad hash to use for passwords    It s fast  which means if you have a  target  hash  it s cheap to try lots of passwords and see whether you can find one which hashes to that target  Salting doesn t help with that scenario  but it helps to make it more expensive to try to find a password matching any one of multiple hashes using different salts  I believe it has known flaws which make it easier to find collisions  although finding collisions within printable text  rather than arbitrary binary data  would at least be harder    I m not a security expert  so won t make a concrete recommendation beyond  Don t roll your own authentication system   Find one from a reputable supplier  and use that  Both the design and implementation of security systems is a tricky business

User · Answer

No  it cannot be done  Either you can use a dictionary  or you can try hashing different values until you get the hash that you are seeking  But it cannot be  decrypted

User · Answer

No  he must have been confused about the MD5 dictionaries   Cryptographic hashes  MD5  etc     are one way and you can t get back to the original message with only the digest unless you have some other information about the original message  etc  that you shouldn t

User · Answer

Not directly  Because of the pigeonhole principle  there is  likely  more than one value that hashes to any given MD5 output  As such  you can t reverse it with certainty  Moreover  MD5 is made to make it difficult to find any such reversed hash  however there have been attacks that produce collisions - that is  produce two values that hash to the same result  but you can t control what the resulting MD5 value will be    However  if you restrict the search space to  for example  common passwords with length under N  you might no longer have the irreversibility property  because the number of MD5 outputs is much greater than the number of strings in the domain of interest   Then you can use a rainbow table or similar to reverse hashes

User · Answer

Yes  exactly what you re asking for is possible  It is not possible to  decrypt  an MD5 password without help  but it is possible to re-encrypt an MD5 password into another algorithm  just not all in one go   What you do is arrange for your users to be able to logon to your new system using the old MD5 password  At the point that they login they have given your login program an unhashed version of the password that you prove matches the MD5 hash that you have  You can then convert this unhashed password to your new hashing algorithm   Obviously  this is an extended process because you have to wait for your users to tell you what the passwords are  but it does work    NB  seven years later  oh well hopefully someone will find it useful

User · Answer

There s no easy way to do it   This is kind of the point of hashing the password in the first place      One thing you should be able to do is set a temporary password for them manually and send them that   I hesitate to mention this because it s a bad idea  and it s not guaranteed to work anyway   but you could try looking up the hash in a rainbow table like milw0rm to see if you can recover the old password that way

User · Answer

Not possible  at least not in a reasonable amount of time   The way this is often handled is a password  reset    That is  you give them a new  random  password and send them that in an email

User · Answer

There is no way of  reverting  a hash function in terms of finding the inverse function for it  As mentioned before  this is the whole point of having a hash function  It should not be reversible and it should allow for fast hash value calculation  So the only way to find an input string which yields a given hash value is to try out all possible combinations  This is called brute force attack for that reason   Trying all possible combinations takes a lot of time and this is also the reason why hash values are used to store passwords in a relatively safe way  If an attacker is able to access your database with all the user passwords inside  you loose in any case  If you have hash values and  idealistically speaking  strong passwords  it will be a lot harder to get the passwords out of the hash values for the attacker   Storing the hash values is also no performance problem because computing the hash value is relatively fast  So what most systems do is computing the hash value of the password the user keyed in  which is fast  and then compare it to the stored hash value in their user database

User · Answer

The only thing that can be work is  if we mention that the passwords are just hashed  without adding any kind of salt to prevent the replay attacks  if it is so you must know the salt by the way  get an dictionary attack tool  the files of many words  numbers etc  then create  two rows  one row is word number  in dictionary  the other one is hash of the word  and compare the hashes if matches you get it     that s the only way  without going into cryptanalysis

[hash] Is it possible to decrypt MD5 hashes?

Examples related to hash

Examples related to cryptography

Examples related to md5

Examples related to encryption