A simple and naive example of using the NIST Randomness Beacon in R (https://beacon.nist.gov/home)

nist-beacon-response.R

require(RCurl)
require(XML)

# Let's make a special class
NISTBeaconResponse <- function (ts) {
    if(!is.integer(ts) &
       !inherits(ts, "POSIXct") &
       !inherits(ts, "POSIXlt")) {
        stop("We expected a unix timestamp as an integer or a POSIXct or POSIXlt value")
    }
    tsval <- ifelse(inherits(ts, "POSIXct") | inherits(ts, "POSIXlt"),
                    as.integer(ts), ts)
    url <- paste0("https://beacon.nist.gov/rest/record/", tsval)
    headers <- basicTextGatherer()  # might be a good idea to use this to check the HTTP status code
    response <- getURL(url, headerfunction=headers$update)
    # use the following line instead, if you get cert validation errors
    # response <- getURL(url, .opts = list(ssl.verifypeer = FALSE), headerfunction=headers$update)
    beacon <- structure(as.data.frame(xmlToList(xmlParse(response, asText=TRUE))),
                        class="NISTBeaconResponse")
    beacon$frequency <- as.integer(beacon$frequency)
    beacon$timeStamp <- as.integer(beacon$timeStamp)
    beacon$statusCode <- as.integer(beacon$statusCode)
    beacon
}

# and a way to print it
print.NISTBeaconResponse <- function(response) {
    if(!inherits(response, "NISTBeaconResponse")) {
       stop("An object of type NISTBeaconResponse was expected")
    }
    breakline <- function(longline) {
        lines <- gsub('(.{1,50})', '\\1\n', longline)
        lines <- gsub('\n', '\n\t\t\t', lines, fixed=TRUE)
        lines
    }
    output <- "\tNIST Randomness Beacon Response\n\t===============================\n\n"
    output <- paste0(output, "\t* version:\t", response$version, "\n")
    output <- paste0(output, "\t* frequency:\t", response$frequency, " seconds\n")
    output <- paste0(output, "\t* seed:\t\t", breakline(response$seedValue), "\n")
    output <- paste0(output, "\t* status:\t", response$statusCode, "\n")
    output <- paste0(output, "\t* timestamp:\t", as.POSIXct(response$timeStamp, origin="1970-01-01"),
                     " (", response$timeStamp,")\n")
    output <- paste0(output, "\t* output:\t", breakline(response$outputValue), "\n")
    output <- paste0(output, "\t* prev value:\t", breakline(response$previousOutputValue), "\n")
    output <- paste0(output, "\t* signature:\t", breakline(response$signatureValue), "\n")
    cat(output)
}

# test the code
ts <- Sys.time()
beacon <- NISTBeaconResponse(ts)
print(beacon)

Check your RCurl or curl configuration. The error message seems to originate with a problem related to the trusted certs. The solution described in http://stackoverflow.com/questions/17411313/ssl-verification-causes-rcurl-and-httr-to-break-on-a-website-that-should-be-le might help you.

On Ubuntu 12.04 LTS and 14.04 LTS (64-bit, both) which is what I use, could not reproduce your error.

For those that for unknown reasons do not have the local certs needed to validate the HTTPS connection to NIST, try replacing line #15 above with:

    response <- getURL(url, .opts = list(ssl.verifypeer = FALSE), headerfunction=headers$update)

Note: Updated the gist with a comment to include this modification

Here's the link to that site's certificate:
https://beacon.nist.gov/certificate/beacon.cer

It could probably be explicitly added to the function somehow.