Crypt (Unix)

Crypt was created by Robert Morris and first appeared in Version 3 Unix with the goal of encouraging crypto cracking; eventually Morris himself hacked crypt . Dennis Ritchie managed to automate the decryption process using the method proposed by James Reeds, and an improved version of the crypt algorithm appeared in Version 7 Unix , which Reeds and Peter Weinberger also hacked. ^[1] .

There is also a cryptographic hash function of the same name - crypt . Although both the crypt utility and the crypt function are used to encrypt data, there is nothing in common between them. To distinguish between them, they usually refer to the system utility as crypt (1) , since it is documented in section 1 of the UNIX manual , and to the cryptographic hash function as crypt (3) , since it is documented in section 3.

crypt (1) is a simple data encryption / decryption utility. As a rule, it is used as a filter program (a program that receives a string and returns another string), and which is traditionally based on the algorithm used in the Enigma machine . The algorithm is considered overly cryptographically vulnerable to provide protection against full enumeration of keys by a modern household personal computer .

Some versions of UNIX came with an even more vulnerable version of the crypt (1) command to enforce modern laws restricting the export of cryptographic software. Some of the crypt implementations were in fact Caesar's cipher implementations.

crypt (1) on Linux

Linux distributions usually do not include a UNIX-compatible version of crypt for several reasons:

1. crypt is considered to be very unprotected by the method of exhaustive search (the distribution usually includes GnuPG , which is quite cryptographically resistant by modern standards).
2. In the early stages of Linux, there were concerns that crypt might not meet the ITAR requirements for exporting cryptographic software; for this reason, the utility was excluded from most distributions developed in the USA (developers offer users to download GnuPG or similar software on their own, sometimes providing scripts to automate the installation process).

The source code for several older versions of crypt is available from The Unix Heritage Society.

The latest version of the code is available in the OpenSolaris project .

Enhanced symmetric cryptosystems are currently available on Linux (they are also portable to any other UNIX-like operating system ), including mcrypt and ccrypt . ^[2] Despite the fact that these programs allow the use of very complex encryption algorithms, using the command line options you can set them an operating mode compatible with the classic crypt (1) .

Hacking crypt (1)

Crypt hacking software (1) is widely available. In 1984-1985, Bob Baldwin created the Crypt Breaker's Workbench program ^[3] , which is an interactive utility that provides the user with consistent “guesses” about the password, and the user must choose the most suitable one from them. Peter Selinger's Unixcrypt-breaker ^[4] uses a simple statistical model to filter out inappropriate passwords and does not require user intervention.

• Source code for crypt (1) from OpenSolaris (published after easing export restrictions)
• Source code for crypt (1) from Version 7 Unix
• Source code for crypt (1) from Version 6 Unix (implementation of a cryptosystem based on the M-209 machine created by Boris Hagelin )
• Sample code SHA-512, bash script and its description .