tracy (01/13/83)
.TH CYPHER 1 Local .SH NAME cypher - guard against routine mail eavesdropping .SH SYNOPSIS \fBcypher\fR [-er] [-k key] [file . . .] .SH DESCRIPTION \fBCypher\fR will read text from the named file (or if no file is named from standard input) and encrypt it placing the result on the standard output. .PP Only printing characters (including \fIspace\fR and excluding \fInewline\fR and \fItilde\fR are encrypted. All others pass unmolested. Characters are only encrypted into this set of printable characters. The maximum length of any input line is 512 bytes including the \fInewline\fR. .PP The cypher algorithm is its own inverse. One decrypts by encrypting again with the same key. The algorithm is an enigma machine similar to crypt(1) but with four 94 element rotors. .PP The program has two modes: \fBencrypting\fR and \fBnonencrypting\fR. It starts in the nonencrypting mode. It may be switched between the two modes by placing the commands "[cypher]" (start encrypting) and "[clear]" (stop encrypting) at the beginning of any line. The command and the remaining text on the line is not encrypted. .PP In order to avoid confusing mailers, \fBcypher\fR will prepend a tilde to any line beginning "From " that it produces while encrypting. The resulting line cannot be longer than 512 bytes. .PP The "-r" option will cause cypher to replace the file(s) specified with their encrypted form. This is useful for mail. Any number of files may be specified. If the first character of the name of the file \fBcypher\fR is invoked from is "r" the "-r" flag is turned on. The original file is only unlinked if there were no errors. .PP The "-e" flag forces \fBcypher\fR to start in encryption mode. .PP A key may be supplied using the "-k key" option. .SH USE WITH \fBMail(1)\fR It is quite easy to set up Mail to interface with \fBcypher\fR. Set either your MAILER or VISUAL environment variable to the name of a \fBcypher\fR binary that starts with "r". (Example: Include the line "setenv VISUAL /usr/frodo/bin/rcypher" in your .login file. (This presupposes that that file contains a \fBcypher\fR binary.)) .PP When sending mail, type your message using the "[cypher]" command where you would like encryption to start (usually at the beginning). Before sending, type the appropriate tilde escape (~v or ~e). This will invoke \fBcypher\fR which will ask you for your key (it will verify it) and will then replace the original temp file with the encrypted version. .PP When receiving, use the appropriate editor command (e or v) to recover the text. The header will not be affected. .PP This program behaves the same on PDP 11/44 UNIX* and VAX 11/780 4.1BSD UNIX*. .SH AUTHOR Tracy Tims .SH BUGS Not incredibly portable. Will work on PDP11's and VAX/11's and should work on most machines with 32 bit (or greater) longs. Requires crypt(3) for password encryption. .PP No warranty of any kind is made concerning any use of this program. The author assumes no responsibility for it's use or for any problems arising from it's use by any recipient. .SH NECESSARY DETAIL * UNIX is a trademark of Bell Laboratories.