# String#crypt first 8 characters

**URL:** <https://www.ruby-forum.com/t/string-crypt-first-8-characters/78388>\
**Category:** Ruby\
**Created:** [December 5, 2006, 2:09pm UTC](https://www.ruby-forum.com/t/string-crypt-first-8-characters/78388 "2006-12-05T14:09:08Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![pjpatten](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e47c2d/32.png) [@pjpatten](https://www.ruby-forum.com/u/pjpatten)\
**Post date:** [December 5, 2006, 2:09pm UTC](https://www.ruby-forum.com/t/string-crypt-first-8-characters/78388/1 "2006-12-05T14:09:08Z")

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Hello,

i had a problem with str.crypt - i got every time the same result. The  
problem is, that this method only use the first 8 characters of the  
string:

irb(main):022:0\> “1234567”.crypt(‘aa’)  
=\> “aaOK9MRbwVNmQ”  
irb(main):023:0\> “12345678”.crypt(‘aa’)  
=\> “aaNN3X.PL2piw”  
irb(main):024:0\> “123456789”.crypt(‘aa’)  
=\> “aaNN3X.PL2piw”

If it is a feature not a bug, it should not be an undocumented feature  
😉 . [ruby-doc.org](http://ruby-doc.org) doesn’t told me about this behaviour.

Have a nice day,  
Patrick

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<div class="post-metadata">

**Author:** ![pjpatten](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e47c2d/32.png) [@pjpatten](https://www.ruby-forum.com/u/pjpatten)\
**Post date:** [December 5, 2006, 2:47pm UTC](https://www.ruby-forum.com/t/string-crypt-first-8-characters/78388/2 "2006-12-05T14:47:11Z")

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----- Original Message -----  
From: Patrick P.   
Date:  
Tuesday, December 5, 2006 2:09 pm  
Subject: String#crypt first 8  
characters  
To: removed\_email\_address@domain.invalid (ruby-talk ML)  
\>  
irb(main):022:0\> “1234567”.crypt(‘aa’)  
\> =\> “aaOK9MRbwVNmQ”  
\>  
irb(main):023:0\> “12345678”.crypt(‘aa’)  
\> =\> “aaNN3X.PL2piw”  
\>  
irb(main):024:0\> “123456789”.crypt(‘aa’)  
\> =\> “aaNN3X.PL2piw”  
\>  
  
\> If it is a feature not a bug, it should not be an undocumented  
  
\> feature   
\> 😉 . [ruby-doc.org](http://ruby-doc.org) doesn’t told me about this  
behaviour.  
  
 String.crypt is a wrapper around Unix standard C  
function crypt, used to encrypt passwords. From man crypt,   
  
By  
taking the lowest 7 bits of each of the first eight characters of the  
key, 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  
return value points to static data whose content is overwritten by  
each  
 call.  
  
 There goes your explanation. But that  
should be documented, I agree with you. My opinion is that you should  
use crypt if you plan to interface somehow with Unix password database.  
If you want one way cryptography, try MD5:  
  
 require  
‘digest/md5’  
 digest = Digest::MD5.hexdigest(“Hello World\n”)  
  
puts digest  
  
 Cheers,  
  
 Vince

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**Author:** ![pjpatten](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e47c2d/32.png) [@pjpatten](https://www.ruby-forum.com/u/pjpatten)\
**Post date:** [December 5, 2006, 5:25pm UTC](https://www.ruby-forum.com/t/string-crypt-first-8-characters/78388/3 "2006-12-05T17:25:47Z")

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On Dec 5, 8:08 am, Patrick P.  
…

> i had a problem with str.crypt - i got every time the same result. The  
> problem is, that this method only use the first 8 characters of the string:

…

A little googling on ‘C standard library crypt’ led me to :  
[http://bama.ua.edu/cgi-bin/man-cgi?crypt\_unix+5](http://bama.ua.edu/cgi-bin/man-cgi?crypt_unix+5)

It turns out the default crypt functionality only uses the first 8  
chars, silently ignoring the rest.

Suggest looking into a “real” cryptographic lib. Googling for ‘ruby  
crypt’ gave up:  
[http://crypt.rubyforge.org/](http://crypt.rubyforge.org/)

cheers

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**Author:** ![pjpatten](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e47c2d/32.png) [@pjpatten](https://www.ruby-forum.com/u/pjpatten)\
**Post date:** [December 5, 2006, 5:55pm UTC](https://www.ruby-forum.com/t/string-crypt-first-8-characters/78388/4 "2006-12-05T17:55:59Z")

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Le 05 décembre à 14:08, Patrick P. a écrit :

> Hello,
> 
> i had a problem with str.crypt - i got every time the same result. The  
> problem is, that this method only use the first 8 characters of the string:

There are workarounds, but I think that’s dependent on the OS.

For instance, the \*BSD variants usually allow to use the notation  
$n$salt in the salt part of the crypt to choose another algorythm (n=1  
-\> MD5, n=2 -\> Blowfish, n=3 -\>NT-Hash, at least on FreeBSD) :

> > “abcdefghijklmnop”.crypt("$1$8aezq78a")  
> > =\> “$1$8aezq78a$reWMwf7b8UtEUWK0LM7pZ/”
> 
> > “abcdefghijklmnopr”.crypt("$1$8aezq78a")  
> > =\> “$1$8aezq78a$frgoGqHZ6bRujQt7qQeSP.”

It seems to give the same results on some Linuxes and FreeBSD, but I  
don’t know exactly how portable it is.

Fred

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**Author:** ![pjpatten](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e47c2d/32.png) [@pjpatten](https://www.ruby-forum.com/u/pjpatten)\
**Post date:** [December 7, 2006, 11:50am UTC](https://www.ruby-forum.com/t/string-crypt-first-8-characters/78388/5 "2006-12-07T11:50:22Z")

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Thanks for all the ideas and suggestions. I understand how crypt works  
and now I use an other method.

Patrick