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PERL Crypt Function



You cannot decrypt a string that has been encrypted in this way. It's normally used one way, first to encrypt a string, and then to encrypt a password to compare against the encrypted string. If you're using it in this form, then consider supplying the encrypted password as the SALT.




PERL Crypt Function



crypt is a one-way hash function. The PLAINTEXT and SALT are turned into a short string, called a digest, which is returned. The same PLAINTEXT and SALT will always return the same string, but there is no (known) way to get the original PLAINTEXT from the hash. Small changes in the PLAINTEXT or SALT will result in large changes in the digest.


There is no decrypt function. This function isn't all that useful for cryptography (for that, look for Crypt modules on your nearby CPAN mirror) and the name "crypt" is a bit of a misnomer. Instead it is primarily used to check if two pieces of text are the same without having to transmit or store the text itself. An example is checking if a correct password is given. The digest of the password is stored, not the password itself. The user types in a password that is crypt'd with the same salt as the stored digest. If the two digests match, the password is correct.


When verifying an existing digest string you should use the digest as the salt (like crypt($plain, $digest) eq $digest). The SALT used to create the digest is visible as part of the digest. This ensures crypt will hash the new string with the same salt as the digest. This allows your code to work with the standard crypt and with more exotic implementations. In other words, assume nothing about the returned string itself nor about how many bytes of SALT may matter.


When choosing a new salt create a random two character string whose characters come from the set [./0-9A-Za-z] (like join '', ('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]). This set of characters is just a recommendation; the characters allowed in the salt depend solely on your system's crypt library, and Perl can't restrict what salts crypt accepts.


If using crypt on a Unicode string (which potentially has characters with codepoints above 255), Perl tries to make sense of the situation by trying to downgrade (a copy of) the string back to an eight-bit byte string before calling crypt (on that copy). If that works, good. If not, crypt dies with Wide character in crypt.


Crypt function in, Perl, is basically used to store sensitive data and passwords using ASCII characters as encrypted strings (this function encrypts the string). Strings can only be encrypted, they can not be decrypted in the same way as encryption is done.


We can use/include more characters other than this given set of characters, this set is just used for the purpose of recommendation. First two characters in the encrypted string are stored as the salt character which can be used for later comparisons. We can even select the characters for salt by using rand function(random selection). We can observe /see large changes in the resulting / final encrypted string, if small changes are made in the $string or $salt.Example: Below is the example to illustrate the above mentioned crypt function for Encryption.


For decryption, the encrypted password in Perl needs to be decrypted using the MIME::Base64 module. For decrypting a string we can call or use decode_base64() function. A single argument in the form of the string is taken as the input by the function in order to return the decoded or decrypted data/password. Syntax:


So the exact return value of crypt is system dependent, but it often uses an algorithm that only looks at the first 8 byte of the password. These two things combined make it a poor choice for portable password encryption. If you're using a system with a stronger encryption routine and don't try to check those passwords on incompatible systems, you're fine. But it sounds like you're using an OS with the old crappy DES routine.


I just started learning Perl and I have a task to compare user input variable with SHA-512 stored hashed password. I made below function to test. I use randomly generated salt to generate digest from real password (p2). Next, I use this digest as salt for my user entered password (p1) to be compared with digest value. This is based on description I have found here.I use crypt function to generate digest, however I am not able to display or compare it in next if step.The password should be hashed using SHA-512.I appreciate your help.


crypt is a thin wrapper around the C crypt function. Its implementation will vary from environment to environment. Here on OS X it does not take a leading $x$ to indicate which algorithm to use, it just uses DES. crypt("foo", '$6$'.$salt); results in $6A86JNndVTdM. Only the first two bytes of the salt are used, $6.


crypt and DES are inappropriate for password hashing. Its short key makes it very easy to defeat, and its salt is just two characters. SHA-512 is also not appropriate for password hashing, it's too fast. Instead, you want a dedicated password hashing function such as bcrypt or PBKDF2 and other key stretching algorithms. Some implementations of crypt can do bcrypt, many can not.


Encrypts a string exactly like the crypt(3) function in the C library(assuming that you actually have a version there that has not beenextirpated as a potential munition). This can prove useful for checkingthe password file for lousy passwords, amongst other things. Only theguys wearing white hats should do this.


Note that crypt is intended to be a one-way function, much likebreaking eggs to make an omelette. There is no (known) correspondingdecrypt function (in other words, the crypt() is a one-way hashfunction). As a result, this function isn't all that useful forcryptography. (For that, see your nearby CPAN mirror.)


When verifying an existing encrypted string you should use theencrypted text as the salt (like crypt($plain, $crypted) eq$crypted). This allows your code to work with the standard cryptand with more exotic implementations. In other words, do not assumeanything about the returned string itself, or how many bytes inthe encrypted string matter.


Traditionally the result is a string of 13 bytes: two first bytes ofthe salt, followed by 11 bytes from the set [./0-9A-Za-z], and onlythe first eight bytes of the encrypted string mattered, butalternative hashing schemes (like MD5), higher level security schemes(like C2), and implementations on non-UNIX platforms may producedifferent strings.


When choosing a new salt create a random two character string whosecharacters come from the set [./0-9A-Za-z] (like join '', ('.','/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]). This set ofcharacters is just a recommendation; the characters allowed inthe salt depend solely on your system's crypt library, and Perl can'trestrict what salts crypt() accepts.


The crypt function is unsuitable for encrypting large quantitiesof data, not least of all because you can't get the informationback. Look at the by-module/Crypt and by-module/PGP directorieson your favorite CPAN mirror for a slew of potentially usefulmodules.


If using crypt() on a Unicode string (which potentially hascharacters with codepoints above 255), Perl tries to make senseof the situation by trying to downgrade (a copy of the string)the string back to an eight-bit byte string before calling crypt()(on that copy). If that works, good. If not, crypt() dies withWide character in crypt.


I am trying to generate a unique string/id given another relatively large string(consisting of a directory path name), thought of using crypt function. However, it's not working as expected, most probably due to my inability to understand.


Deprecated since version 3.11, will be removed in version 3.13: The crypt module is deprecated(see PEP 594 for details and alternatives).The hashlib module is a potential replacement for certain use cases.


This module implements an interface to the crypt(3) routine, which isa one-way hash function based upon a modified DES algorithm; see the Unix manpage for further details. Possible uses include storing hashed passwordsso you can check passwords without storing the actual password, or attemptingto crack Unix passwords with a dictionary.


salt (either a random 2 or 16 character string, possibly prefixed with$digit$ to indicate the method) which will be used to perturb theencryption algorithm. The characters in salt must be in the set[./a-zA-Z0-9], with the exception of Modular Crypt Format whichprefixes a $digit$.


crypt is the password encryption function. It is based on the Data Encryption Standard algorithm with variations intended (among other things) to discourage use of hardware implementations of a key search.


By taking the lowest 7 bit of each character of $plaintext (filling it up to 8 characters with zeros, if needed), a 56-bit key is obtained. This 56-bit key is used to encrypt repeatedly a constant string (usually a string consisting of all zeros). The returned value points to the encrypted password, a series of 13 printable ASCII characters (the first two characters represent the salt itself).


The DES algorithm itself has a few quirks which make the use of the crypt(3) interface a very poor choice for anything other than password authentication. If you are planning on using the crypt(3) interface for a cryptography project, don't do it: get a good book on encryption and one of the widely available DES libraries.


This crypt function has some problems... all of these return the same result$returnValue = crypt('MyStringStarted', 'Fixed');$returnValue = crypt('MyStringFinished', 'Fixed');$returnValue = crypt('MyStringStarted', 'Filtered');$returnValue = crypt('MyStringFinished', 'Filtered');Basicly it only "encripts" the first 5 chars of the string with the first 2 of the salt...


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