Merge pull request #527 from Narrat/optim/kdf

Improve KDF handling

Author: jaromil

doc/tomb.1

@@ -49,8 +49,10 @@ more recipient GPG ids can be indicated (comma separated). The default cipher
 to protect the key is AES256, a custom one can be specified using the \fI-o\fR
 option, for a list of supported ciphers use \fI-v\fR. For additional protection
 against dictionary attacks on keys, the \fI--kdf\fR option can be used when
-forging a key, making sure that the binaries in \fIextras/kdf\fR were compiled
-and installed on the system.
+forging a key. Two KDF are currently supported: \fIargon2\fR and \fIpbkdf2\fR.
+\fIpbkdf2\fR is available from \fIextras/kdf\fR and needs to be compiled and
+installed on the system. \fIargon2\fR is generally available from distribution
+repositories.
 
 .B
 .IP "lock"
@@ -283,24 +285,45 @@ Provide a new set of recipient(s) to encrypt a tomb key. \fIgpg_ids\fR
 can be one or more GPG key ID, comma separated. All GPG keys must be
 trusted keys in GPG.
 .B
-.IP "--kdf \fI<itertime>\fR"
-Activate the KDF feature against dictionary attacks when creating a key: forces
-a delay of \fI<itertime>\fR times every time this key is used.  The actual time
-to wait depends on the CPU speed (default) or the RAM size (argon2) of the
-computer where the key is used.  Using 5 or 10 is a sane amount for modern
-computers, the value is multiplied by 1 million.
-.B
-.IP "--kdftype \fIargon2 | pbkdf2\fR"
-Adopt the \fIargon2\fR algorithm for KDF, stressing the RAM capacity rather
-than the CPU speed of the computer decrypting the tomb. Requires the
-\fIargon2\fR binary by P-H-C to be installed, as packaged by most distros.
+.IP "--kdf \fI[argon2 | pbkdf2]\fR"
+Enable the KDF feature against dictionary attacks when creating a key.
+The required argument currently allows to choose between \fIargon2\fR
+or \fIpbkdf2\fR.
+\fIargon2\fR is using a mix of RAM capacity, number of threads and
+iterations to achieve a time cost.
+\fIpbkdf2\fR is only about calculation speed to achieve a time cost.
+Due to a low memory footprint and no restrictions regarding threads, this
+time cost can be somewhat negated due to parallelization. Especially on
+GPUs with their high number of cores.
+\fIargon2\fR requires the respective binary by P-H-C to be installed, as
+packaged by most distros. \fIpbkdf2\fR is available from the \fItomb\fR
+sources and is a custom implementation of the algorithm.
 Default is \fIpbkdf2\fR.
 .B
+.IP "--kdfiter \fI<itertime>\fR"
+Available for \fIargon2\fR and \fIpbkdf2\fR. In general this controls how
+often the algorithm will be run. In case of \fIpbkdf2\fR the argument will
+be interpret as an interval in seconds. The actual number of iterations to
+achieve this delay will be calculated with \fItomb-kdb-pbkdf2-getiter\fR,
+which needs to available (normally installed alongside tomb's pbkdf2 tools).
+Reason being that the actual time to wait depends on the CPU speed.
+OWASP recommendations from 2023 suggest a minimal iteration count of 600000
+for \fIpbkdf2\fR, which should be achieved with the current default value.
+Default is 3 (based on the \fIargon2\fR default).
+.B
 .IP "--kdfmem \fI<memory>\fR"
 In case of \fIargon2\fR KDF algorithm, this value specifies the size of RAM
 used: it consists of a number which is the elevated power of two in kilobytes.
 Default is 18 which is 250 MiB (2^18 = 262,144 kilobytes).
 .B
+.IP "--kdfpar \fI<# of threads>\fR"
+In case of \fIargon2\fR KDF algorithm, this value specifies the number of
+threads that should be used. This helps to remedy the effects of an increased
+time cost for your system whereas setups of ASICs or GPUs don't profit. Only
+increase if memory or iteration got increased that much, that key decryption
+takes massively longer on regular systems.
+Default is 1 thread (based on the \fIargon2\fR default).
+.B
 .IP "--sudo \fI<executable>\fR"
 Select a different tool than sudo for privilege escalation.
 Alternatives supported so far are: pkexec, doas, sup, sud. For any

extras/test/30_kdf-pbkdf2.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env zsh
+
+export test_description="Testing tomb with pbkdf2 KDF key"
+
+source ./setup
+
+if test_have_prereq KDF; then
+    test_export "kdf"
+    test_expect_success 'Testing pbkdf2 KDF: tomb creation' '
+        tt_dig -s 20 &&
+        tt_forge --tomb-pwd $DUMMYPASS --kdf pbkdf2 &&
+        print $DUMMYPASS \
+            | gpg --batch --passphrase-fd 0 --no-tty --no-options -d $tomb_key \
+            | xxd &&
+        tt_lock --tomb-pwd $DUMMYPASS
+        '
+
+    test_expect_success 'Testing pbkdf2 KDF: tomb passwd' '
+        tt passwd -k $tomb_key \
+            --unsafe --tomb-old-pwd $DUMMYPASS --tomb-pwd $DUMMYPASSNEW &&
+        tt passwd -k $tomb_key \
+            --unsafe --tomb-old-pwd $DUMMYPASSNEW --tomb-pwd $DUMMYPASS
+        '
+
+    test_expect_success 'Testing pbkdf2 KDF: tomb open & close' '
+        tt_open --tomb-pwd $DUMMYPASS &&
+        tt_close
+        '
+fi
+
+test_done

extras/test/30_kdf.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env zsh
+
+export test_description="Testing tomb with argon2 KDF key"
+
+source ./setup
+
+if test_have_prereq ARGON; then
+    test_export "argon"
+    test_expect_success 'Testing argon2 KDF: tomb creation' '
+        tt_dig -s 20 &&
+        tt_forge --tomb-pwd $DUMMYPASS --kdf argon2 &&
+        print $DUMMYPASS \
+            | gpg --batch --passphrase-fd 0 --no-tty --no-options -d $tomb_key \
+            | xxd &&
+        tt_lock --tomb-pwd $DUMMYPASS
+        '
+
+    test_expect_success 'Testing argon2 KDF: tomb passwd' '
+        tt passwd -k $tomb_key --kdf argon2 \
+            --unsafe --tomb-old-pwd $DUMMYPASS --tomb-pwd $DUMMYPASSNEW &&
+        tt passwd -k $tomb_key --kdf argon2 \
+            --unsafe --tomb-old-pwd $DUMMYPASSNEW --tomb-pwd $DUMMYPASS
+        '
+
+    test_expect_success 'Testing argon2 KDF: tomb open & close' '
+        tt_open --tomb-pwd $DUMMYPASS &&
+        tt_close
+        '
+fi
+
+test_done

extras/test/31_kdf-argon2.sh

@@ -50,6 +50,7 @@ MEDIA="/media"
 command -v steghide > /dev/null && test_set_prereq STEGHIDE
 command -v e2fsck resize2fs > /dev/null && test_set_prereq RESIZER
 command -v tomb-kdb-pbkdf2 > /dev/null && test_set_prereq KDF
+command -v argon2 > /dev/null && test_set_prereq ARGON
 command -v qrencode > /dev/null && test_set_prereq QRENCODE
 command -v lsof > /dev/null && test_set_prereq LSOF
 command -v python3 > /dev/null && test_set_prereq PYTHON3

extras/test/setup

@@ -66,6 +66,7 @@ typeset -i RECOLL=1
 typeset -i QRENCODE=1
 typeset -i LSOF=1
 typeset -i ACL=1
+typeset -i ARGON2=1
 
 # Default mount options
 typeset		 MOUNTOPTS="rw,noatime,nodev"
@@ -749,8 +750,13 @@ usage() {
 	_print " -R           provide GnuPG hidden recipients (separated by comma)"
 	_print " --sudo       super user exec alternative to sudo (doas or none)"
 
-	[[ $KDF == 1 ]] && {
-		_print " --kdf        forge keys armored against dictionary attacks"
+	[[ $KDF == 1 ]] || [[ $ARGON2 == 1 ]] && {
+		_print " --kdf        forge keys armored against dictionary attacks (pbkdf2, argon2)"
+		_print " --kdfiter    Number of iterations (meaning depending on KDF algorithm) (pbkdf2, argon2)"
+	}
+	[[ $ARGON2 == 1 ]] && {
+		_print " --kdfmem     memory to be used (argon2)"
+		_print " --kdfpar     number of threads (argon2)"
 	}
 
 	echo
@@ -1225,11 +1231,14 @@ get_lukskey() {
 				kdf_salt="${firstline[(ws:_:)3]}"
 				kdf_ic="${firstline[(ws:_:)4]}"
 				kdf_mem="${firstline[(ws:_:)5]}"
+				kdf_par="${firstline[(ws:_:)6]}"
+				# ToDo also parse kdf_len?
 				_message "Unlocking KDF key protection (::1 kdf::)" $kdf_hash
 				_verbose "KDF salt: $kdf_salt"
 				_verbose "KDF ic: $kdf_ic"
 				_verbose "KDF mem: $kdf_mem"
-				_password=$(argon2 $kdf_salt -m $kdf_mem -t $kdf_ic -l 64 -r 2>/dev/null <<<$_password)
+				_verbose "KDF # threads: $kdf_par"
+				_password=$(argon2 $kdf_salt -m $kdf_mem -t $kdf_ic -p $kdf_par -l 64 -r 2>/dev/null <<<$_password)
 				;;
 
 			*)
@@ -1470,50 +1479,58 @@ gen_key() {
 		fi
 
 		header=""
-		[[ $KDF == 1 ]] && {
+		[[ $KDF == 1 ]] || [[ $ARGON2 == 1 ]] && {
 			{ option_is_set --kdf } && {
-				# KDF is a new key strengthening technique against brute forcing
+				# KDF is a key strengthening technique against brute forcing
 				# see: https://github.com/dyne/Tomb/issues/82
-				itertime="`option_value --kdf`"
-				# removing support of floating points because they can't be type checked well
-				# if [[ "$itertime" != <-> ]]; then
-				# 	unset tombpass
-				# 	unset tombpasstmp
-				# 	_warning "Wrong argument for --kdf: must be an integer number (iteration seconds)."
-				# 	_failure "Depending on the speed of machines using this tomb, use 1 to 10, or more"
-				# 	return 1
-				# fi
-				# # --kdf takes one parameter: iter time (on present machine) in seconds
-
-				kdftype="`option_value --kdftype`"
-				kdftype=${kdftype:-pbkdf2}
+				# Two KDF are currently supported:
+				# * pbkdf2 (time restrictive)
+				# * argon2 (memory, parallelismn restrictive and through those time)
+
+				# --kdfiter takes one integer value as parameter
+				# argon2: # of iterations (default of 3);
+				# pbkdf2: calculates # of iterations to reach this as time cost in seconds
+				itertime="`option_value --kdfiter`"
+				itertime=${itertime:-3}
+
+				# Generating salt (either via tomb-kdb-pbkdf2 or a shell fallback)
+				if $(command -v tomb-kdb-pbkdf2-gensalt 1>/dev/null 2>/dev/null); then
+					kdfsalt=`tomb-kdb-pbkdf2-gensalt`
+				else
+					kdfsalt=$(LC_CTYPE=C tr -cd 'a-f0-9' < /dev/random | head -c 64)
+				fi
+				_message "kdf salt: ::1 kdfsalt::" $kdfsalt
+
+				# --kdf takes one parameter: what KDF
+				kdftype="`option_value --kdf`"
 				case ${kdftype} in
-				    pbkdf2)
+				pbkdf2)
 					local -i microseconds
 					microseconds=$(( itertime * 1000000 ))
-					_success "Using KDF, iteration time: ::1 microseconds::" $microseconds
-					_message "generating salt"
-					pbkdf2_salt=`tomb-kdb-pbkdf2-gensalt`
-					_message "calculating iterations"
+					_success "Using pbkdf2 as KDF"
+					_message "iteration time: ::1 microseconds::" $microseconds
 					pbkdf2_iter=`tomb-kdb-pbkdf2-getiter $microseconds`
-					_message "encoding the password"
+					_message "iterations: ::1 pbkdf2_iter::" $pbkdf2_iter
 					# We use a length of 64bytes = 512bits (more than needed!?)
-					tombpass=`tomb-kdb-pbkdf2 $pbkdf2_salt $pbkdf2_iter 64 <<<"${tombpass}"`
-
-					header="_KDF_pbkdf2sha1_${pbkdf2_salt}_${pbkdf2_iter}_64\n"
+					tombpass=`tomb-kdb-pbkdf2 $kdfsalt $pbkdf2_iter 64 <<<"${tombpass}"`
+					header="_KDF_pbkdf2sha1_${kdfsalt}_${pbkdf2_iter}_64\n"
 					;;
-				    argon2)
-					_success "Using KDF Argon2"
+				argon2)
+					_success "Using Argon2 as KDF"
+					_message "iterations: ::1 kdfiterations::" $itertime
 					kdfmem="`option_value --kdfmem`"
 					kdfmem=${kdfmem:-18}
 					_message "memory used: 2^::1 kdfmemory::" $kdfmem
-          itertime="`option_value --kdf`"
-          itertime=${itertime:-3}
-					kdfsalt=`tomb-kdb-pbkdf2-gensalt`
-					_message "kdf salt: ::1 kdfsalt::" $kdfsalt
-					_message "kdf iterations: ::1 kdfiterations::" $itertime
-					tombpass=`argon2 $kdfsalt -m $kdfmem -t $itertime -l 64 -r <<<"${tombpass}"`
-					header="_KDF_argon2_${kdfsalt}_${itertime}_${kdfmem}_64\n"
+					kdfpar="`option_value --kdfpar`"
+					kdfpar=${kdfpar:-1}
+					_message "parallelismn: ::1 kdfparallel::" $kdfpar
+					tombpass=`argon2 $kdfsalt -m $kdfmem -t $itertime -p $kdfpar -l 64 -r <<<"${tombpass}"`
+					header="_KDF_argon2_${kdfsalt}_${itertime}_${kdfmem}_${kdfpar}_64\n"
+					;;
+				*)
+					_warning "unrecognized KDF ::1::" $kdftype
+					_warning "key won\'t be protected via a KDF implementation"
+					_warning "only pbkdf2 and argon2 are valid arguments"
 					;;
 				esac
 			}
@@ -1976,7 +1993,7 @@ forge_key() {
 			 $destkey $algo
 
 	[[ $KDF == 1 ]] && { ! option_is_set -g } && {
-		_message "Using KDF to protect the key password (`option_value --kdf` rounds)"
+		_message "Using KDF to protect the key password"
 	}
 
 	TOMBKEYFILE="$destkey"	  # Set global variable
@@ -3129,19 +3146,19 @@ main() {
 	main_opts=(q -quiet=q D -debug=D h -help=h v -version=v f -force=f -tmp: U: G: T: -no-color -unsafe g -gpgkey=g -sudo:)
 	subcommands_opts[__default]=""
 	# -o in open and mount is used to pass alternate mount options
-	subcommands_opts[open]="n -nohook=n k: -kdf: -kdftype: -kdfmem: o: -ignore-swap -tomb-pwd: r: R: p -preserve-ownership=p"
+	subcommands_opts[open]="n -nohook=n k: o: -ignore-swap -tomb-pwd: r: R: p -preserve-ownership=p"
 	subcommands_opts[mount]=${subcommands_opts[open]}
 
 	subcommands_opts[create]="" # deprecated, will issue warning
 
 	# -o in forge and lock is used to pass an alternate cipher.
-	subcommands_opts[forge]="-ignore-swap k: -kdf: -kdftype: -kdfmem: o: -tomb-pwd: -use-random r: R: "
+	subcommands_opts[forge]="-ignore-swap k: -kdf: -kdfiter: -kdfmem: -kdfpar: o: -tomb-pwd: -use-random r: R: "
 	subcommands_opts[dig]="-ignore-swap s: -size=s "
-	subcommands_opts[lock]="-ignore-swap k: -kdf: -kdftype: -kdfmem: o: -tomb-pwd: r: R: -filesystem: "
-	subcommands_opts[setkey]="k: -ignore-swap -kdf: -kdftype: -kdfmem: -tomb-old-pwd: -tomb-pwd: r: R: "
+	subcommands_opts[lock]="-ignore-swap k: o: -tomb-pwd: r: R: -filesystem: "
+	subcommands_opts[setkey]="k: -ignore-swap -tomb-old-pwd: -tomb-pwd: r: R: "
 	subcommands_opts[engrave]="k: "
 
-	subcommands_opts[passwd]="k: -ignore-swap -kdf: -kdftype: -kdfmem: -tomb-old-pwd: -tomb-pwd: r: R: "
+	subcommands_opts[passwd]="k: -ignore-swap -kdf: -kdfiter: -kdfmem: -kdfpar: -tomb-old-pwd: -tomb-pwd: r: R: "
 	subcommands_opts[close]=""
 	subcommands_opts[help]=""
 	subcommands_opts[slam]=""