[R] Encrypt/decrypt in R

[Carl Witthoft]

 > Hi all,
 >
 > Does any one know of any encryption/decryption algorithms in R? I'm
 > not looking for anything robust - I want some way of printing output
 > to the screen that the user can't read immediately, but can decrypt a
 > little later. The main thing I don't want to the user to see is a
 > number, so (e.g.) ROT13 isn't appropriate.

Nobody seems to have asked what you mean by "don't want the user to see 
a number."
Do you mean that there should be no numbers in the output (impossible 
unless you stir in ten non-alpha characters), or simply that numbers 
should be translated (at least some of the time) into alpha?


Anyway,  here's a toy I wrote for my own amusement back when learning R:


# rotrw -- a func to read from a file, rot, and write to
# a new file
# file: name of source file
# rot:  number to rot by
# field: ascii or alpha, selects what characters to rot thru
#		 If select alpha, only alphas are rotted.
#		 If select ascii, all ascii chars are rotted

rotrw<-function(file,rot=13,field=ascii)
{
	readLines(file)->fin
	if(field=='alpha')
		{
		rot13(fin,rot)->tempf	
		}
	else if(field=='ascii')
		{
		rotit(fin,rot)->tempf
		}
	else
		{
		stop("Error: ",field,' is unknown type.\n')
		}
#	strip the .extension so can get  file name and build
#	output name 'file'[rot].ext
	strsplit(file,split='\\.')->splitfil# to get file name alone
	unlist(splitfil)->unfil # makes it a char vector,
	# so unlist[1] is name, unlist[2] is ext
	paste(unfil[1],rot,field,'.',unfil[2],sep="")->outname
	writeLines(tempf,con=outname)
	}
	
rot13 <- function(string,rot=13){
   cstr<-as.character(string)
   #get fancy: force ROT into 0-25, by shifting negative values and
   # taking a modulus:
   rtm<-(rot+(rot<0)*26)%%26
   old<-paste(c(letters,LETTERS),collapse="")
   shift<-c(rtm+1,26,1,rtm)
    	 
new<-paste(c(letters[shift[1]:shift[2]],letters[shift[3]:shift[4]],LETTERS[shift[1]:shift[2]],LETTERS[shift[3]:shift[4]]),collapse="")
   rotted<-chartr(old = old, new = new, x = string)
   return(rotted)
}

rotit <- function(string,rot=13){
	library(sfsmisc) #needed for chars8bit()
   cstr<-as.character(string)
   #get fancy: force ROT into 0-95, by shifting negative values and
   # taking a modulus:
   rtm<-(rot+(rot<0)*95)%%95
   # OLD is full baseline ASCII char set. Note that it's a vector
   old<-c(chars8bit(seq(32,126)))
   shift<-c(rtm+1,95,1,rtm)
   new<-paste(c(old[shift[1]:shift[2]],old[shift[3]:shift[4]]),collapse="")
   rotted<-chartr(old = paste(old,collapse=""), new = new, x = string)
   return(rotted)
}