How do I read an encrypted file from disk with R

I have a sensitive data set that should never be stored unencrypted on disk. Can R deal with this or is full disk encryption my only option?

I have a feeling there's an easier way to do this, but the digest package, which does AES encryption, is the closest thing I came across to what you are asking for. This should get you started.

# write encrypted data frame to file
write.aes <- function(df,filename, key) {
  require(digest)
  zz <- textConnection("out","w")
  write.csv(df,zz, row.names=F)
  close(zz)
  out <- paste(out,collapse="\n")
  raw <- charToRaw(out)
  raw <- c(raw,as.raw(rep(0,16-length(raw)%%16)))
  aes <- AES(key,mode="ECB")
  aes$encrypt(raw)
  writeBin(aes$encrypt(raw),filename)  
}
# read encypted data frame from file
read.aes <- function(filename,key) {
  require(digest)
  dat <- readBin(filename,"raw",n=1000)
  aes <- AES(key,mode="ECB")
  raw <- aes$decrypt(dat, raw=TRUE)
  txt <- rawToChar(raw[raw>0])
  read.csv(text=txt)
}   
# sample data
set.seed(1)     # for reproducible example
data <- data.frame(x=rnorm(10),y=rpois(10,1),
                   z=letters[1:10],w=sample(T:F,10,replace=T))    

set.seed(123581321)
key <- as.raw(sample(1:32,32))
write.aes(data,"encrypted.dat",key)
result <- read.aes("encrypted.dat",key)  
# did it work?
all.equal(data,result)
# [1] TRUE

This uses ECB mode AES encryption. Obviously you need to use the same key to encrypt and decrypt. write.aes(...) converts the data frame to a csv-formatted text string, converts that to raw (which is required for AES), pads the raw vector out to a multiple of 16 bytes (also required for AES), encrypts, and writes to a binary file. read.aes(...) basically reverses the process.

This is just an example, intended to be modified to suit your needs. For instance, this saves the data frame without row names, which might or might not be a problem.