Internalize transcrypt crypt functions

At the moment, the crypt functions are initialized and permanently set
to whatever the version of transcrypt the user is using contains. This
means updates to these scripts are never propagated out to existing
users.

This commit moves the crypt functions into transcrypt itself, which
should allow for more transparent updates to the scripts to be
propagated out to users.

Author: apeschel

sensitive_file

@@ -1,40 +1,93 @@
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transcrypt

@@ -268,92 +268,68 @@ stage_rekeyed_files() {
 	fi
 }
 
-# save helper scripts under the repository's git directory
-save_helper_scripts() {
-	mkdir -p "${GIT_DIR}/crypt"
-
-	# The `decryption -> encryption` process on an unchanged file must be
-	# deterministic for everything to work transparently. To do that, the same
-	# salt must be used each time we encrypt the same file. An HMAC has been
-	# proven to be a PRF, so we generate an HMAC-SHA256 for each decrypted file
-	# (keyed with a combination of the filename and transcrypt password), and
-	# then use the last 16 bytes of that HMAC for the file's unique salt.
-
-	cat <<-'EOF' >"${GIT_DIR}/crypt/clean"
-		#!/usr/bin/env bash
-		filename=$1
-		# ignore empty files
-		if [[ -s $filename ]]; then
-		  # cache STDIN to test if it's already encrypted
-		  tempfile=$(mktemp 2>/dev/null || mktemp -t tmp)
-		  trap 'rm -f "$tempfile"' EXIT
-		  tee "$tempfile" &>/dev/null
-		  # the first bytes of an encrypted file are always "Salted" in Base64
-		  read -n 8 firstbytes <"$tempfile"
-		  if [[ $firstbytes == "U2FsdGVk" ]]; then
-		    cat "$tempfile"
-		  else
-		    cipher=$(git config --get --local transcrypt.cipher)
-		    password=$(git config --get --local transcrypt.password)
-		    salt=$(openssl dgst -hmac "${filename}:${password}" -sha256 "$filename" | tr -d '\r\n' | tail -c 16)
-		    ENC_PASS=$password openssl enc -$cipher -md MD5 -pass env:ENC_PASS -e -a -S "$salt" -in "$tempfile"
-		  fi
-		fi
-	EOF
-
-	cat <<-'EOF' >"${GIT_DIR}/crypt/smudge"
-		#!/usr/bin/env bash
+# The `decryption -> encryption` process on an unchanged file must be
+# deterministic for everything to work transparently. To do that, the same
+# salt must be used each time we encrypt the same file. An HMAC has been
+# proven to be a PRF, so we generate an HMAC-SHA256 for each decrypted file
+# (keyed with a combination of the filename and transcrypt password), and
+# then use the last 16 bytes of that HMAC for the file's unique salt.
+crypt_clean() {
+	filename=$1
+	# ignore empty files
+	if [[ -s $filename ]]; then
+		# cache STDIN to test if it's already encrypted
 		tempfile=$(mktemp 2>/dev/null || mktemp -t tmp)
 		trap 'rm -f "$tempfile"' EXIT
-		cipher=$(git config --get --local transcrypt.cipher)
-		password=$(git config --get --local transcrypt.password)
-		tee "$tempfile" | ENC_PASS=$password openssl enc -$cipher -md MD5 -pass env:ENC_PASS -d -a 2>/dev/null || cat "$tempfile"
-	EOF
-
-	cat <<-'EOF' >"${GIT_DIR}/crypt/textconv"
-		#!/usr/bin/env bash
-		filename=$1
-		# ignore empty files
-		if [[ -s $filename ]]; then
-		  cipher=$(git config --get --local transcrypt.cipher)
-		  password=$(git config --get --local transcrypt.password)
-		  ENC_PASS=$password openssl enc -$cipher -md MD5 -pass env:ENC_PASS -d -a -in "$filename" 2>/dev/null || cat "$filename"
+		tee "$tempfile" &>/dev/null
+		# the first bytes of an encrypted file are always "Salted" in Base64
+		read -r -n 8 firstbytes <"$tempfile"
+		if [[ $firstbytes == "U2FsdGVk" ]]; then
+			cat "$tempfile"
+		else
+			cipher=$(git config --get --local transcrypt.cipher)
+			password=$(git config --get --local transcrypt.password)
+			salt=$(openssl dgst -hmac "${filename}:${password}" -sha256 "$filename" | tr -d '\r\n' | tail -c 16)
+			ENC_PASS=$password openssl enc "-${cipher}" -md MD5 -pass env:ENC_PASS -e -a -S "$salt" -in "$tempfile"
 		fi
-	EOF
+	fi
+}
 
-	# make scripts executable
-	for script in {clean,smudge,textconv}; do
-		chmod 0755 "${GIT_DIR}/crypt/${script}"
-	done
+crypt_smudge() {
+	tempfile=$(mktemp 2>/dev/null || mktemp -t tmp)
+	trap 'rm -f "$tempfile"' EXIT
+	cipher=$(git config --get --local transcrypt.cipher)
+	password=$(git config --get --local transcrypt.password)
+	tee "$tempfile" | ENC_PASS=$password openssl enc "-${cipher}" -md MD5 -pass env:ENC_PASS -d -a 2>/dev/null || cat "$tempfile"
+}
+
+crypt_textconv() {
+	filename=$1
+	# ignore empty files
+	if [[ -s $filename ]]; then
+	  cipher=$(git config --get --local transcrypt.cipher)
+	  password=$(git config --get --local transcrypt.password)
+	  ENC_PASS=$password openssl enc "-${cipher}" -md MD5 -pass env:ENC_PASS -d -a -in "$filename" 2>/dev/null || cat "$filename"
+	fi
 }
 
 # write the configuration to the repository's git config
 save_configuration() {
-	save_helper_scripts
+	# This directory is used by transcrypt as a working directory.
+	mkdir -p "${GIT_DIR}/crypt"
 
 	# write the encryption info
 	git config transcrypt.version "$VERSION"
 	git config transcrypt.cipher "$cipher"
 	git config transcrypt.password "$password"
 
 	# write the filter settings
-	if [[ -d $(git rev-parse --git-common-dir) ]]; then
-		# this allows us to support multiple working trees via git-worktree
-		# ...but the --git-common-dir flag was only added in November 2014
-		# shellcheck disable=SC2016
-		git config filter.crypt.clean '"$(git rev-parse --git-common-dir)"/crypt/clean %f'
-		# shellcheck disable=SC2016
-		git config filter.crypt.smudge '"$(git rev-parse --git-common-dir)"/crypt/smudge'
-		# shellcheck disable=SC2016
-		git config diff.crypt.textconv '"$(git rev-parse --git-common-dir)"/crypt/textconv'
-	else
-		# shellcheck disable=SC2016
-		git config filter.crypt.clean '"$(git rev-parse --git-dir)"/crypt/clean %f'
-		# shellcheck disable=SC2016
-		git config filter.crypt.smudge '"$(git rev-parse --git-dir)"/crypt/smudge'
-		# shellcheck disable=SC2016
-		git config diff.crypt.textconv '"$(git rev-parse --git-dir)"/crypt/textconv'
-	fi
+	# shellcheck disable=SC2016
+	git config filter.crypt.clean "$0 --crypt-clean %f"
+	# shellcheck disable=SC2016
+	git config filter.crypt.smudge "$0 --crypt-smudge"
+	# shellcheck disable=SC2016
+	git config diff.crypt.textconv "$0 --crypt-textconv"
 	git config filter.crypt.required 'true'
 	git config diff.crypt.cachetextconv 'true'
 	git config diff.crypt.binary 'true'
@@ -466,6 +442,8 @@ uninstall_transcrypt() {
 		clean_gitconfig
 
 		# remove helper scripts
+		# This is obsolete, but we should keep it to clean up these
+		# scripts from old versions of transcrypt.
 		for script in {clean,smudge,textconv}; do
 			[[ ! -f "${GIT_DIR}/crypt/${script}" ]] || rm "${GIT_DIR}/crypt/${script}"
 		done
@@ -800,6 +778,21 @@ while [[ "${1:-}" != '' ]]; do
 	--import-gpg=*)
 		gpg_import_file=${1#*=}
 		;;
+	--crypt-clean)
+		shift
+		crypt_clean "$1"
+		exit 0
+		;;
+	--crypt-smudge)
+		shift
+		crypt_smudge
+		exit 0
+		;;
+	--crypt-textconv)
+		shift
+		crypt_textconv "$1"
+		exit 0
+		;;
 	-v | --version)
 		printf 'transcrypt %s\n' "$VERSION"
 		exit 0