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Created page with "In Unix computing, '''crypt''' is a utility program used for encryption. Due to the ease of breaking it, it is considered to be obsolete. ==History==..."

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In [[Unix]] computing, '''crypt''' is a [[utility software|utility program]] used for encryption. Due to the ease of breaking it, it is considered to be obsolete.

==History==
[[Robert Morris (cryptographer)|Robert Morris]] wrote <tt>crypt</tt>, which first appeared in [[Version 3 Unix]], to encourage codebreaking experiments; Morris himself broke <tt>crypt</tt> by hand. [[Dennis M. Ritchie]] automated decryption with a method by James Reeds, and an improved version appeared in [[Version 7 Unix|Version 7]] which Reeds and [[Peter J. Weinberger]] also broke.

== Relationship to password hash function ==
There is also a Unix [[password hash]] function with the same name, [[Crypt (C)|crypt]]. Though both are used for encrypting data in some sense, they are otherwise essentially unrelated. To distinguish between the two, writers often refer to the utility program as '''''crypt(1)''''', because it is documented in section 1 of the Unix [[Manual page (Unix)|manual pages]], and refer to the password hash function as '''''crypt(3)''''', because its documentation is in manual section 3.

== Command filter ''crypt(1)'' ==
''crypt(1)'' is a simple command to encrypt or decrypt data. Usually this is used as a [[filter (Unix)|filter]], and it has traditionally been implemented using an [[algorithm]] based on the [[Enigma machine]]. It is considered to be far too [[cryptography|cryptographically]] weak to provide any security against [[Brute-force attack|brute force attacks]] by modern, commodity [[personal computer]]s.

Some versions of Unix shipped with an even weaker version of the ''crypt(1)'' command in order to comply with contemporaneous laws and regulations, which limited the exportation of cryptographic software (for example by classifying them as [[munition]]s). Some of these were simply implementations of the [[Caesar cipher]] (effectively no more secure than [[ROT13]], which is implemented as a Caesar cipher with a well known key).

=== ''crypt(1)'' under Linux ===

[[Linux distribution]]s generally do not include a Unix compatible version of the ''crypt'' command. This is largely due to a combination of three major factors:

# ''crypt'' is relatively obscure and rarely used for e-mail attachments nor as a file format
# ''crypt'' is considered far too cryptographically weak to withstand [[brute force attack]]s by modern computing systems (Linux systems generally ship with [[GNU Privacy Guard]] which is considered to be reasonably secure by modern standards)
# During the early years of Linux development and adoption there was some concern that even as weak as the algorithm used by ''crypt'' was, that it might still run afoul of [[ITAR]]'s export controls; so mainstream distribution developers in the [[United States]] generally excluded it (and left their customers to fetch GnuPG or other strong cryptographic software from international sites, sometimes providing packages or scripts to automate that process).

The source code to several old versions of the ''crypt'' command is available in The Unix Heritage Society's [http://www.tuhs.org/archive_sites.html Unix Archive].

The recent crypt source code is available in the [[OpenSolaris]] project.

Enhanced [[Symmetric-key algorithm|symmetric encryption]] utilities are available for Linux (and should also be [[Software portability|portable]] to any other [[Unix-like]] system) including [[mcrypt]] and [[ccrypt]]. While these provide support for much more sophisticated and modern algorithms, they can be used to encrypt and decrypt files which are compatible with the traditional ''crypt(1)'' command by providing the correct command line options.

=== Breaking crypt(1) encryption ===

Programs for breaking crypt(1) encryption are widely available. Bob Baldwin's Crypt Breaker's Workbench, which was written in 1984-1985, is an interactive tool that provides successive plaintext guesses that must be corrected by the user. Peter Selinger's unixcrypt-breaker uses a simple statistical model to guess plausible plaintexts, and does not require user interaction.

==Source==

[http://wikipedia.org/ http://wikipedia.org/]
[[Category:Cryptography]]
[[Category:Cryptographic algorithms]]

Crypt (Unix) - Revision history

Admin: Created page with "In Unix computing, '''crypt''' is a utility program used for encryption. Due to the ease of breaking it, it is considered to be obsolete. ==History==..."