added shred_file.sh

bin/shred_file.sh

@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+#  vim:ts=4:sts=4:sw=4:et
+#
+#  Author: Hari Sekhon
+#  Date: 2023-05-20 10:41:18 +0100 (Sat, 20 May 2023)
+#
+#  https://github.com/HariSekhon/DevOps-Bash-tools
+#
+#  License: see accompanying Hari Sekhon LICENSE file
+#
+#  If you're using my code you're welcome to connect with me on LinkedIn and optionally send me feedback to help steer this or other code I publish
+#
+#  https://www.linkedin.com/in/HariSekhon
+#
+
+set -euo pipefail
+[ -n "${DEBUG:-}" ] && set -x
+srcdir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+# shellcheck disable=SC1090,SC1091
+. "$srcdir/lib/utils.sh"
+
+# shellcheck disable=SC2034,SC2154
+usage_description="
+Overwrites a given file using dd to prevent recovery of sensitive information
+
+WARNING: you should only do this on old HDD, not SSD, hard drives which have a limited number of writes - you may shorten an SSD's lifespan if you over use this
+
+Use this only if you've accidentally written some credential / sensitive data to disk and then already deleted it, leaving the file data on disk
+without a filename to inode pointer to overwrite just the file
+
+This prevents file recovery tools from stealing your sensitive data, credentials etc. because otherwise
+the file data is still there on disk without a filename inode pointer and file recovery tools may be able to recover and steal it
+
+Your disk should also be encrypted anyway for security best practices, in which case you shouldn't need to do this
+
+Works by writing random data into a large file in the \$PWD until the disk is full and then deletes the file. This is an old trick from the 2000s
+
+See also:
+
+On Mac:
+
+    rm -P   overwrites file 3 times before deleting it (-P switch is available on BSD 'rm' variant only)
+
+on Linux:
+
+    srm     from secure-delete package
+    shred
+    wipe
+
+    sfill   works similar to this script except does 2 overwrites - DoD secure standard is 7 overwrites
+
+    sswap   overwrites your swap device
+
+    sdmem   overwrites your RAM to prevent warm boot attacks retrieving sensitive credentials or data
+"
+
+# used by usage() in lib/utils.sh
+# shellcheck disable=SC2034
+usage_args=" [<filename> <passes>]"
+
+help_usage "$@"
+
+max_args 2 "$@"
+
+file="${1:-.}"
+passes="${2:-7}"
+
+if ! [ -f "$file" ]; then
+    die "File '$file' does not exit"
+fi
+
+filesize="$(du "$file" | awk '{print $1}')"
+
+timestamp "Overwriting file '$file'"
+for (( i = 0; i < passes; i++ )); do
+    timestamp "overwrite pass 1..."
+    dd bs="$filesize" count=1 if=/dev/urandom of="$file"
+done
+
+timestamp "Removing file:"
+rm -fv "$file"