gistfile1.txt

#!/usr/bin/env bash

set -e -o pipefail

dev=${1:?usage: $0 <device name>}

dir="/sys/block/$dev"
if ! [[ -d "$dir" ]]; then
    echo "$dev probably is not a block device (no $dir)" >&2
    exit 1
fi

if ! [[ -b "/dev/$dev" ]]; then
    echo "$dev probably is not a block device (no /dev/$dev)" >&2
    exit 1
fi
dev="/dev/$dev"

sectors=$(cat "$dir/size")
bsize=$((64 * 1024 * 1024))

blocks=$((sectors * 512 / $bsize))
dd=(dd "bs=$bsize" "count=$blocks" iflag=fullblock)

for pass in {1..3}; do
    key="key$RANDOM"
    enc=(openssl enc -aes-128-ctr -pass "pass:$key" -nosalt)

    "${dd[@]}" if=/dev/zero | "${enc[@]}" | "${dd[@]}" "of=$dev"
    sync; echo 3 > /proc/sys/vm/drop_caches
    cmp <("${dd[@]}" if=/dev/zero | "${enc[@]}") <("${dd[@]}" "if=$dev")
done

dd if=/dev/zero of="$dev" bs=1M count=1