[BK-2020-03.git] / unitproc / bkpoe

#!/bin/bash
#
# Date: 2020-02-18T20:06Z
#
# Author: Steven Baltakatei Sandoval (baltakatei.com)
#
# License: This bash script, 'bkpoe', is licensed under GPLv3 or
# later by Steven Baltakatei Sandoval:
#
#    'bkpoe', a file system proof of existence generator
#    Copyright (C) 2020  Steven Baltakatei Sandoval (baltakatei.com)
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    A copy of the GNU General Public License may be found at
#    <https://www.gnu.org/licenses/>.
#
# Description: This is a simple script that uses GNU Coreutils
# OpenTimestamps to generate a proof that permits a user to prove the
# existence of any individual file within a directory. A proof
# consists of:
#
#   - An OpenTimestamps 'ots' file (if '-t' option provided)
#
#   - Public proof: text file(s) containing a list of salted file
#     hashes.
#
#   - Private proof: text file(s) containing:
#
#     - A list of unsalted file hashes
#
#     - A list of nonces used to generate the list of salted file hashes.
#
#     - The list of salted file hashes
#
#     - File attributes (size, relative path)
#
#   The proof is produced by performing the following steps:
#
#   - Use 'find' and GNU Coreutils digest algorithms to create
#     numbered lists of file digests at specified directories.
#
#   - Save these numbered lists of digests into text files within a
#     proof directory.
#
#   - If more than one specified directory is provided also process
#     the files within the proof directory.
#
#   - Use OpenTimestamps to create an 'ots' timestamp file
#     for the final digest list file. (if '-t' option provided).
#
#   - Use OpenTimestamps to upgrade each 'ots' timestamp file after a
#     delay. (if '-w' option provided).
#
# Dependencies: coreutils, ots. See end of file
#
# Tested on:
#
#   - GNU/Linux Debian 10


# === VARIABLE INITIALIZATION AND FUNCTION DEFINITIONS ===

PATH="/usr/local/bin/:$PATH" # Add default OpenTimestamps path to PATH (necessary if cron used to call this script)
scriptHostname=$(hostname) # Save hostname of system running this script.
OTS_TIMEOUT="6h" # maximum time to run `ots --wait` (used via `timeout` command)

# Declare array for storing directories whose contents will be hashed.
declare -a directoriesToProcess

# Declare arrays for storing file paths, file index, file hashes, file
# hash nonces, the salted hashes, file sizes, file paths, file
# modification times, and proof file paths.
declare -a filePathsFull      # array
declare -a filePathsIndex     # array
declare -a fileHashes         # array
declare -a fileHashNonces     # array
declare -a fileHashesSalted   # array
declare -a fileSizes          # array
declare -a fileModTime        # array
declare -g PROOF_DIRECTORY    # global
declare -ag prvProofPaths     # array, global
declare -ag pubProofPaths     # array, global

# Define 'echoerr' function which outputs text to stderr
    # Note: function copied from https://stackoverflow.com/a/2990533
echoerr() {
    echo "$@" 1>&2;
}

# Define script version.
SCRIPT_VERSION="bkpoe 0.1.0"

# Save current date.
runDate=$(date +%Y%m%dT%H%M%S%z)
sleep 1 # Space out program run times by at least one second.
###echoerr "DEBUG: Current date is:"$runDate

# Save working directory
runPath=$(pwd)
###echoerr "DEBUG: Current working directory is:"$runPath

# Define proof directory basename
PROOF_DIRECTORY_BASE="$runDate""..""$scriptHostname""_bkpoe_proofs"

# Define default proof directory
PROOF_DIRECTORY="$runPath"/"$PROOF_DIRECTORY_BASE"

# Print information on how to use this bash script.
usage() {

    echo "USAGE:"
    echo "    bkpoe [ options ] DIRECTORIES"
    echo
    echo "OPTIONS:"
    echo "    -h, --help"
    echo "            Display help information."
    echo
    echo "    -r, --recursive"
    echo "            Perform recursive hashing of directories."
    echo
    echo "    -v, --verbose"
    echo "            Display debugging info."
    echo
    echo "    -a, --algorithm [ algo ]"
    echo "            Specify GNU Coreutils hash command. Options include:      "
    echo "            b2sum md5sum sha1sum sha224sum sha256sum sha384sum        "
    echo "            sha512sum"
    echo
    echo "    -m, --message [ string ]"
    echo "            Specify message to be included in filehash files."
    echo
    echo "    -d, --delimiter [ string ]"
    echo "            Specify character to serve as delimiter in proof files.   "
    echo "            (Default: ,)                                              "
    echo "    -t, --timestamp"
    echo "            Create openTimestmaps proof file."
    echo "    -w, --wait"
    echo "            Pass '--wait' option to OpenTimestamps to 'wait           "
    echo "            until a complete timestamp committed in the               "
    echo "            Bitcoin blockchain is available instead of                "
    echo "            returning immediately.                                    "
    echo "    -o, --output"
    echo "            Specify output directory to save proof. Default is working"
    echo "            directory where script was run."
}


# Check that a string matches one of GNU Coreutils hash commands.
isValidDigestAlgo() {
    # Syntax: isValidDigestAlgo [string]
    # Description: Returns 1 if [string] is a valid GNU Coreutils hash function command. Returns 0 otherwise.

    # Exit if more than one argument provided.
    ###echoerr "DEBUG: Arguments provided to isValidDigestAlgo() are:$@"
    if [[ $# -ne 1 ]]; then
	echoerr "ERROR: Illegal number of digest arguments provided."
	exit 1
    fi

    # Exit if argument contains non-alphanumeric characters
    if [[ "$@" =~ [^a-zA-Z0-9$] ]]; then
	echoerr "ERROR: Illegal characters for digest argument provided."
	exit 1
    fi
        
    local input=$1 #Save first argument provided to function as input for further processing.
    
    ###echoerr "DEBUG: Starting function to check validity of string as valid digest command."

    # Define array of valid hash algorithm commands present in by GNU coreutils package. List is current as of Debian Buster. List taken from https://packages.debian.org/buster/amd64/coreutils/filelist ).
    local gnuCoreutilsAlgos=(b2sum md5sum sha1sum sha224sum sha256sum sha384sum sha512sum)
    ###echoerr "DEBUG:Contents of \$gnuCoreutilsAlgos array is:${gnuCoreutilsAlgos[@]}"
    
    # Make input string lowercase
    #input=${input,,} # Make all letters in $1 lowercase (see https://stackoverflow.com/questions/2264428/how-to-convert-a-string-to-lower-case-in-bash ) and save as $input
    ###echoerr "DEBUG: User-specified hash algorithm is:$input"
    
    # Return true (0) if $gnuCoreutilsAlgos array contains string $input (see https://unix.stackexchange.com/a/177139 )
    for item in "${gnuCoreutilsAlgos[@]}"; do
	###echoerr "DEBUG: \$item is:$item"
	###echoerr "DEBUG: \$input is:$input"
	if [ "$input" == "$item" ]; then
	    ###echoerr "DEBUG: $input present in \$gnuCoreutilsAlgos array."
	    return 0
	fi
    done

    # Return false (1) otherwise.
    echoerr "DEBUG: $input not recognized as valid hash algorithm name."
    return 1
}

writeProofs() {
    # Syntax: writeProofs [ loopIndex ] [ dirPath ]

    # Description: Construct private and public proofs for files
    # contained within [ dirPath ]. Save file with date, [ loopIndex ],
    # and base directory name within filename.

    # Required variables:
    #  - $runDate: used in creating proof directory
    #  - $PROOF_DIRECTORY: used as directory where proof files are saved
    #  - $OPTION_ALGORITHM: used to decide which hash algorithm to use
    #  - $OPTION_DELIMITER: used to determine which char to use as a delimiter in proof files
    #  - $OPTION_MESSAGE: used to determine message included in proof files
    #  - $OPTION_RECURSIVE: used to determine if files within subdirectories under [ dir Path ] directory should be included

    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG:This is the writeProofs() function. Provided arguments are:$@"
    
    # Determine scope of 'find' file search (recursive search or not)
    if [[ $OPTION_RECURSIVE == "true" ]]; then
        [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Performing recursive file search on directory $directoryToHash"
	findMaxDepthOption=""  # Do not specify -maxdepth option for find (causes 'find' to include all files recursively within [ dirPath ]
    else
	findMaxDepthOption="-maxdepth 1" # Specify "-maxdepth 1 " as option for 'find' so only files immediately within [ dirPath ] directory are included (no subdirectories).
    fi
    
    # Save current date of loop
    proofLoopRunDate=$(date +%Y%m%dT%H%M%S%z)
    ###echoerr "DEBUG: Date and time of current loop is:"$proofLoopRunDate

    # Reset arrays.
    filePathsFull=()
    filePathsIndex=()
    fileHashes=()
    fileHashNonces=()
    fileHashesSalted=()
    fileSizes=()
    fileModTime=()

    # Pass first argument provided to function as directory index.
    local loopIndex=$1 

    # Pass second argument as directory to process
    if [[ -d $2 ]]; then
	[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Valid directory argument provided to writeProofs() function."
	local directoryToHash=$2
	## local directoryToHash=$(readlink -f $2) # Use absolutely full path (not used for privacy).
    else
	echoerr "ERROR: Invalid directory argument provided to writeProofs() function."
	exit 1
    fi
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG:Processing directory:"$directoryToHash
    local directoryToHashShort="$(basename "$directoryToHash")"
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG:Directory basename:"$directoryToHashShort

    # Populate filePathsFull array with file paths from 'find' results (see https://stackoverflow.com/a/54561526 ).
    #   Note: For creating array from output of find via readarray, see https://unix.stackexchange.com/a/263885
    #   Note: For sorting output of find, see https://unix.stackexchange.com/a/34328
    readarray -d '' filePathsFull < <(find $directoryToHash $findMaxDepthOption -readable -type f -print0 | sort -z) # Populate filePathsFull array with sorted list of files present in $directoryToHash (and subdirectories if $OPTION_RECURSIVE set to 'true'.
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#filePathsFull[@]} elements of filePathsFull array are:${filePathsFull[@]}" # Show array length (see https://www.cyberciti.biz/faq/finding-bash-shell-array-length-elements/ )

    # Construct index array from filePathsFull array for the for loops used to write proofs.
    filePathsIndex=(${!filePathsFull[@]})
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#filePathsIndex[@]} elements of filePathsIndex array are:${filePathsIndex[@]}"

    # Populate fileHashes with hashes of files listed in filePathsFull array
    # Iterate through all elements of filePathsFull array using an integer index. (see https://stackoverflow.com/a/6723516 )
    for i in "${!filePathsIndex[@]}"; do 
	###[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG:The $i th element of the filePathsFull array is:${filePathsFull[i]}"
	fileHashes[i]=$($OPTION_ALGORITHM "${filePathsFull[i]}" | awk '{ print $1 }') # Get hash value from GNU Coreutils hash command (see https://stackoverflow.com/a/3679803 )
    done
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#fileHashes[@]} elements of fileHashes array are:${fileHashes[@]}"

    # Populate fileHashNonces array with same number of elements as filePathsFull array. Each element is a random hexadecimal nonce of length matching OPTION_ALGORITHM. Hex nonce generated from 64-byte (512-bits) block from /dev/urandom.
    for i in "${!filePathsIndex[@]}"; do
	fileHashNonces[i]=$(dd bs=64 count=1 if=/dev/urandom 2>/dev/null | $OPTION_ALGORITHM | awk '{ print $1 }')
    done
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#fileHashNonces[@]} elements of fileHashNonces array are:${fileHashNonces[@]}"

    # Populate fileHashesSalted array with salted digest for each file hash corresponding nonce.
    for i in "${!filePathsIndex[@]}"; do
	fileHashesSalted[i]=$(echo -n "${fileHashes[i]}${fileHashNonces[i]}" | $OPTION_ALGORITHM | awk '{ print $1 }')
    done
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#fileHashesSalted[@]} elements of fileHashesSalted array are:${fileHashesSalted[@]}"

    # Populate fileSizes array with file sizes (in bytes).
    for i in "${!filePathsIndex[@]}"; do
	fileSizes[i]=$(wc -c "${filePathsFull[i]}" | awk '{ print $1 }')
    done
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#fileSizes[@]} elements of fileSizes array are:${fileSizes[@]}"

    # Populate fileModTime array with file modification times (in ISO-8601 format)
    for i in "${!filePathsIndex[@]}"; do
	fileModTime[i]=$(date --iso-8601=seconds -r "${filePathsFull[i]}" | awk '{ print $1 }')
    done
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#fileModTime[@]} elements of fileModTime array are:${fileModTime[@]}"

    # ==== GENERATE PROOF FILES FROM HASH LIST(S) ====

    # Define output file names and paths.
    local PROOF_PRIVATE_FILENAME=$proofLoopRunDate"_"$loopIndex"_prv.."$scriptHostname"_"$directoryToHashShort"_"$OPTION_ALGORITHM"_proof_private.txt"
    local PROOF_PUBLIC_FILENAME=$proofLoopRunDate"_"$loopIndex"_pub.."$scriptHostname"_"$directoryToHashShort"_"$OPTION_ALGORITHM"_proof_public.txt"
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: \$PROOF_PRIVATE_FILENAME is $PROOF_PRIVATE_FILENAME"
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: \$PROOF_PUBLIC_FILENAME is $PROOF_PUBLIC_FILENAME"
    PROOF_PRIVATE_FILEPATH="$PROOF_DIRECTORY"/"$PROOF_PRIVATE_FILENAME"
    PROOF_PUBLIC_FILEPATH="$PROOF_DIRECTORY"/"$PROOF_PUBLIC_FILENAME"

    # Create private proof and public proof files.
    touch "$PROOF_PRIVATE_FILEPATH"
    touch "$PROOF_PUBLIC_FILEPATH"

    # Abbreviate OPTION_DELIMITER to local variable DELIM
    local DELIM=$OPTION_DELIMITER
    
    # Define private proof first-line headers (date, version, algorithm, message)
    local PROOF_PRIVATE_HEADER1="$proofLoopRunDate$DELIM$SCRIPT_VERSION$DELIM$OPTION_ALGORITHM$DELIM$OPTION_MESSAGE"
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: \$PROOF_PRIVATE_HEADER1 is $PROOF_PRIVATE_HEADER1"
    # Define public proof first-line headers (date, version, algorithm, message)
    local PROOF_PUBLIC_HEADER1="$proofLoopRunDate$DELIM$SCRIPT_VERSION$DELIM$OPTION_ALGORITHM$DELIM$OPTION_MESSAGE"
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: \$PROOF_PUBLIC_HEADER1 is $PROOF_PUBLIC_HEADER1"

    # Define private proof second-line column labels (index, digest, nonce, salted digest, mdate, size, filepath)
    local PROOF_PRIVATE_HEADER2="index"$DELIM"digest"$DELIM"nonce"$DELIM"digest_salted"$DELIM"mdate"$DELIM"size_bytes"$DELIM"file_path"
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: \$PROOF_PRIVATE_HEADER2 is $PROOF_PRIVATE_HEADER2"
    # Define public proof second-line column labels (index, salted digest)
    local PROOF_PUBLIC_HEADER2="index"$DELIM"digest_salted"
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: \$PROOF_PUBLIC_HEADER2 is $PROOF_PUBLIC_HEADER2"

    # Write headers to proof files
    echo $PROOF_PRIVATE_HEADER1 >> "$PROOF_PRIVATE_FILEPATH"
    echo $PROOF_PRIVATE_HEADER2 >> "$PROOF_PRIVATE_FILEPATH"
    echo $PROOF_PUBLIC_HEADER1 >> "$PROOF_PUBLIC_FILEPATH"
    echo $PROOF_PUBLIC_HEADER2 >> "$PROOF_PUBLIC_FILEPATH"
    
    # Loop to append array contents.
    for i in "${!filePathsIndex[@]}"; do
	# Append to private proof: filePathsIndex[i],fileHashes[i],fileHashNonces[i],fileHashesSalted[i],fileModTime[i],fileSizes[i],filePathsFull[i]
	###[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Writing line to $PROOF_PRIVATE_FILEPATH"
        echo ${filePathsIndex[i]}$DELIM${fileHashes[i]}$DELIM${fileHashNonces[i]}$DELIM${fileHashesSalted[i]}$DELIM${fileModTime[i]}$DELIM${fileSizes[i]}$DELIM${filePathsFull[i]} >> "$PROOF_PRIVATE_FILEPATH"
	# Append to public proof: filePathsIndex[i],fileHashesSalted[i]
	[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Writing line to $PROOF_PUBLIC_FILEPATH"
	echo ${filePathsIndex[i]}$DELIM${fileHashesSalted[i]} >> $PROOF_PUBLIC_FILEPATH
    done

    # Save file paths to global variables prvProofPaths and pubProofPaths to allow other functions to manipulate files.
    prvProofPaths+=($PROOF_PRIVATE_FILEPATH)
    pubProofPaths+=($PROOF_PUBLIC_FILEPATH)
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#prvProofPaths[@]} elements of prvProofPaths array are:${prvProofPaths[@]}"
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: The ${#pubProofPaths[@]} elements of pubProofPaths array are:${pubProofPaths[@]}"

    # Reset arrays.
    filePathsFull=()
    filePathsIndex=()
    fileHashes=()
    fileHashNonces=()
    fileHashesSalted=()
    fileSizes=()
    fileModTime=()
}


# === INPUT PROCESSING ===
# Check for presence of options.
###echoerr "DEBUG: === INPUT PROCESSING START ==="

# Process initial option arguments (see https://jonalmeida.com/posts/2013/05/26/different-ways-to-implement-flags-in-bash/ and https://likegeeks.com/linux-bash-scripting-awesome-guide-part3/ )
while [ ! $# -eq 0 ]   # While number of arguments ($#) is not (!) equal to (-eq) zero (0).
do
    case "$1" in    # Check first of remaining arguments to see if it matches one of strings below.
	--help | -h)
	    # Code to run if $1 matched "--help" or "-h":
	    ###echoerr "DEBUG: This is the help information."
	    usage # Run usage function to display helpful info to user.
	    exit 1
	    ;;
	--recursive | -r)
	    # Code to run if $1 matched "--recursive" or "-r":
	    ###echoerr "DEBUG: Recursive option activated."
	    OPTION_RECURSIVE="true"
	    ;;
	--verbose | -v)
	    # Code to run if $1 matched "--verbose" or "-v":
	    ###echoerr "DEBUG: Verbose option activated."
	    OPTION_VERBOSE="true"
	    ;;
	--algorithm | -a)
	    # Code to run if $1 matched "--algorithm" or "-a":

	    ###echoerr "DEBUG: Selecting hash algorithm."
	    # Check that OPTION_ALGORITHM variable hasn't already been set.
	    # Check that OPTION_ALGORITHM contains only alphanumeric characters.
	    # Check that argument following '-a' or '--algorithm' ($2) is valid algorithm.
	    if [[ ! -v OPTION_ALGORITHM ]] && [[ ! "$2" =~ [^a-zA-Z0-9$] ]] && isValidDigestAlgo $2; then
		###echoerr "DEBUG: Valid hash algorithm provided."
		OPTION_ALGORITHM=$2 # Save argument following '-a' or '--algorithm' to $OPTION_ALGORITHM
		shift # Remove an additional argument so the additional algorithm argument $2 is properly removed at the end of the while loop.
	    else
		echoerr "ERROR: Invalid hash algorithm argument provided:""$2"
		exit 1
	    fi
	    ;;
	--message | -m)
	    # Code to run if $1 matched "--message" or "-m":
	    ###echoerr "DEBUG: Specifying header message."
	    # Check that OPTION_MESSAGE variable hasn't already been set.
	    if [[ ! -v OPTION_MESSAGE ]]; then
		OPTION_MESSAGE=$2 # Save argument following '-m' or '--message' to $OPTION_MESSAGE
		shift # Remove an additional argument so the additional algorithm argument $2 is properly removed at the end of the while loop.
	    fi
	    ;;
	--delimiter | -d)
	    # Code to run if $1 matched "--delimiter" or "-d":
	    ###echoerr "DEBUG: Specifying delimiter."
	    # Check that OPTION_DELIMITER variable hasn't already been set.
	    if [[ ! -v OPTION_DELIMITER ]]; then
		OPTION_DELIMITER=$2 # Save argument following '-d' or '--delimiter' to $OPTION_DELIMITER
		shift # Remove an additional argument so the additional delimiter argument $2 is properly removed at the end of the while loop.
	    fi
	    ;;
	--timestamp | -t)
	    # Code to run if $1 matched "--timestamp" or "-t":
	    echoerr "DEBUG: OpenTimestamps option selected."
	    # Check that ots command exists. (see https://stackoverflow.com/a/677212 )
	    if command -v ots >/dev/null 2>&1 ; then
		echoerr "DEBUG: OpenTimestampscommand ('ots') detected."
		OPTION_OPENTIMESTAMPS="true"
	    else
		echo >&2 "I require the ots (OpenTimestamps) command but it's not installed.  Aborting."
		exit 1
	    fi
	    ;;
	--wait | -w)
	    # Code to run if $1 matched "--wait" or "-w":
	    echoerr "DEBUG: OpenTimestamps '--wait' option selected."
	    OPTION_OPENTIMESTAMPS_WAIT="true"
	    ;;
	--output | -o)
	    # Code to run if $1 matched "--output" or "-o":
	    # Check that argument $2 is a directory.
	    if [[ -d $2 ]]; then
		echoerr "DEBUG: Specified ""$PROOF_DIRECTORY_BASE"" in ""$2"" as directory for saving proof files."
		PROOF_DIRECTORY="$2"/"$PROOF_DIRECTORY_BASE"
		echoerr "DEBUG: Proof Directory is:""$PROOF_DIRECTORY"
		shift # Remove an additional argument so the additional delimiter argument $2 is properly removed at the end of the while loop.
	    else
		echoerr "ERROR: Invalid argument provided as output directory for proof files:""$2"
		exit 1
	    fi
	    ;;
	*)
	    # Code to run if $1 isn't any of the above cases:
	    # Check that remaining argument is a directory.
	    if [[ -d $1 ]]; then
		###echoerr "DEBUG: Remaining argument is directory. Adding to \$directoriesToProcess array."
		# Add directory argument $1 to directory array
		directoriesToProcess+=($1)  # (see https://stackoverflow.com/a/1951523 )
	    else
		echoerr "ERROR: Remaining argument is not a directory or valid option. Exiting."
		exit 1
	    fi
	    ;;
    esac
    shift  # Remove first argument ($1) so remaining arguments can be processed on next loop.
done

# If OPTION_ALGORITHM is not set then set it to 'sha256sum' by default.
if [[ ! -v OPTION_ALGORITHM ]]; then
    echoerr "DEBUG: No hash algorithm set. Defaulting to sha256sum."
    OPTION_ALGORITHM="sha256sum"
fi

# If OPTION_DELIMITER is not set then set it to ',' by default.
if [[ ! -v OPTION_DELIMITER ]]; then
    ###echoerr "DEBUG: No delimiter set. Defaulting to ','."
    OPTION_DELIMITER=","
fi

# Exit program if directoriesToProcess array is empty.
if [[ ${#directoriesToProcess[@]} -eq 0 ]]; then
    echoerr "ERROR: No valid directory specified."
    exit 1
fi

###echoerr "DEBUG: === INPUT PROCESSING END ==="

# === MAIN PROGRAM ===
[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: === MAIN PROGRAM START ==="
[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Verbose option active."
[[ $OPTION_VERBOSE == "true" ]] && [[ $OPTION_RECURSIVE == "true" ]] && echoerr "DEBUG: Recursive option active."
[[ $OPTION_VERBOSE == "true" ]] && [[ -v OPTION_ALGORITHM ]] && echoerr "DEBUG: Selected Hash algorithm is:""$OPTION_ALGORITHM"
[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Directories to process are: ${directoriesToProcess[@]}"
[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Message to add to proof is: $OPTION_MESSAGE"
[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Proof directory is:""$PROOF_DIRECTORY"
[[ $OPTION_VERBOSE == "true" ]] && [[ $OPTION_OPENTIMESTAMPS == "true" ]] && echoerr "DEBUG: OpenTimestamps option active."
[[ $OPTION_VERBOSE == "true" ]] && [[ $OPTION_OPENTIMESTAMPS_WAIT == "true" ]] && echoerr "DEBUG: OpenTimestamps '--wait' option selected."
# Create proof directory
mkdir "$PROOF_DIRECTORY"
echoerr "Proof directory created at:""$PROOF_DIRECTORY"

## TEMP REF:
# declare -a filePathsFull      # array
# declare -a filePathsIndex     # array
# declare -a fileHashes         # array
# declare -a fileHashNonces     # array
# declare -a fileHashesSalted   # array
# declare -a fileSizes          # array
# declare -a fileModTime        # array
# declare -ag prvProofPaths     # array, global
# declare -ag pubProofPaths     # array, global

# ==== GENERATE HASH LIST(S) ====
[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: ==== GENERATING HASH LIST(S) ===="

# Assemble and write proofs to disk for all specified directories.

# Generate proofs from all provided directories.
for j in "${!directoriesToProcess[@]}"; do
    writeProofs $j "${directoriesToProcess[j]}"    
done

# Decide if superproof is required.
if [[ ${#directoriesToProcess[@]} -eq 1 ]]; then
    # If only one directory provided then no further proofs required.
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: Only 1 directory processed. No superproof required."
elif [[ ${#directoriesToProcess[@]} -gt 1 ]]; then
    # If multiple directories provided then create superproof from files in PROOF_DIRECTORY.
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: More than 1 directory processed. Proceeding to generate superproof from PROOF_DIRECTORY."
    writeProofs "S" $PROOF_DIRECTORY # Create proof using proof files which are stored in PROOF_DIRECTORY
fi

# ==== GENERATE HASH LIST(S) REPORT =====
echoerr "Proof files written to $PROOF_DIRECTORY directory:"
for i in ${!prvProofPaths[@]}; do
    echo $(basename "${prvProofPaths[i]}")
    echo $(basename "${pubProofPaths[i]}")
done

# ==== GENERATE OPENTIMESTAMPS TIMESTAMP FILE(S) ====

# Determine if OpenTimestamp actions to be performed.
if [[ $OPTION_OPENTIMESTAMPS == "true" ]]; then
    # Identify target for OpenTimeStamps script.
    otsTarget=${pubProofPaths[-1]}  # Select final element in pubProofPaths array as target for 'ots' command.
    [[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: otsTarget is:""$otsTarget"

    # Set wait option as determined by OPTION_OPENTIMESTAMPS_WAIT variable. Set timeout length.
    if [[ $OPTION_OPENTIMESTAMPS_WAIT == "true" ]]; then
	otsWaitOption="--wait" # Specify '--wait' option for ots command.
	otsWaitTimeCmd="timeout ""$OTS_TIMEOUT" # Specify timeout length (6 hours) for ots command.
	[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: OpenTimestamps '--wait' option active."
    else
	otsWaitOption=""
	otsWaitTimeCmd=""
	[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: OpenTimestamps '--wait' option not active."
    fi
    
    # Generate OpenTimeStamps proof file.
    pushd "$PROOF_DIRECTORY" 1>/dev/null 2>/dev/null # temporarily change working dir to PROOF_DIRECTORY, suppress stdout and stderr
    $otsWaitTimeCmd ots $otsWaitOption stamp $otsTarget
    echoerr "OpenTimestamps operation successful! $otsTarget created."
    echoerr "Use 'ots info [ filename ]' for more info."
    echoerr "Use 'ots upgrade' if '--wait' option not used to make .ots file independently-verifiable."
    echoerr "See https://opentimestamps.org/ for more information."
    popd 1>/dev/null 2>/dev/null # reverse temporary change to working dir, suppress stdout and stderr

fi


[[ $OPTION_VERBOSE == "true" ]] && echoerr "DEBUG: === MAIN PROGRAM END ==="
# Exit program successfully.
exit 0


# == Dependencies ==
#
# - bash, find, sort, echo, mkdir, basename, awk, wc, date, dd,
#   readlink, touch, ots,

# - GNU bash, version 5.0.3(1)-release (x86_64-pc-linux-gnu)
#   Copyright (C) 2019 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
#   This is free software; you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.

# - find (GNU findutils) 4.6.0.225-235f
#   Copyright (C) 2019 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by Eric B. Decker, James Youngman, and Kevin Dalley.
#   Features enabled: D_TYPE O_NOFOLLOW(enabled) LEAF_OPTIMISATION FTS(FTS_CWDFD) CBO(level=2) 

# - sort (GNU coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by Mike Haertel and Paul Eggert.

# - echo (GNU coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by Brian Fox and Chet Ramey.

# - mkdir (GNU coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by David MacKenzie.

# - basename (GNU coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by David MacKenzie.

# - GNU Awk 4.2.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.1.2)
#   Copyright (C) 1989, 1991-2018 Free Software Foundation.
#   This program is free software; you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation; either version 3 of the License, or
#   (at your option) any later version.
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU General Public License for more details.
#   You should have received a copy of the GNU General Public License
#   along with this program. If not, see http://www.gnu.org/licenses/.

# - wc (GNU coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by Paul Rubin and David MacKenzie.

# - date (GNU coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by David MacKenzie.

# - dd (coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by Paul Rubin, David MacKenzie, and Stuart Kemp.

# - readlink (GNU coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by Dmitry V. Levin.

# - touch (GNU coreutils) 8.30
#   Copyright (C) 2018 Free Software Foundation, Inc.
#   License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
#   This is free software: you are free to change and redistribute it.
#   There is NO WARRANTY, to the extent permitted by law.
#   Written by Paul Rubin, Arnold Robbins, Jim Kingdon,
#   David MacKenzie, and Randy Smith.

# - ots v0.7.0 ( https://github.com/opentimestamps/opentimestamps-client )
#   The OpenTimestamps Client is free software: you can redistribute it and/or
#   modify it under the terms of the GNU Lesser General Public License as published
#   by the Free Software Foundation, either version 3 of the License, or (at your
#   option) any later version.
#   The OpenTimestamps Client is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
#   or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
#   below for more details.