Concatenate the symmetric keys instead of using HMAC-SHA256

There is no point trying to KDF here. Gocryptfs does its own KDF anyway
(https://nuetzlich.net/gocryptfs/forward_mode_crypto/), and a leaked
gocryptfs password is not really in our security model (because that
compromises the entire storage in any case).

README.md

@@ -25,7 +25,7 @@ of the original password store (`gocrypt/`), and all read operations from `pass`
 without any special care (other than remembering to unlock the subtree first). The encrypted subdirectory is stored in the original
 password store under `.gocrypt/`, and can be managed by `git` just like how it was without encryption.
 
-The biggest caveat of this is that write operations (such as `edit` and `generate`) **has** to be prefixed by the `gocrypt` subcommand
+The biggest caveat of this is that write operations (such as `edit` and `generate`) **have** to be prefixed by the `gocrypt` subcommand
 to ensure compatibility when the outer password store is a git repository. Without the prefix, git commits that are normally created
 automatically by `pass` will not be generated during a write. See the Usage section of this document for examples.
 
@@ -41,7 +41,6 @@ Dependencies:
 
 - pass
 - bash
-- perl
 - gocryptfs
 
 Usage

gocrypt.bash

@@ -9,7 +9,6 @@ readonly gocrypt_needs_passphrase_marker=".gocrypt-needs-passphrase"
 
 gocrypt_sys_check() {
     which gocryptfs > /dev/null || gocrypt_die "gocryptfs not found in PATH"
-    which perl > /dev/null || gocrypt_die "perl not found in PATH"
 }
 
 gocrypt_env_check() {
@@ -36,13 +35,6 @@ _cmd_git() {
     [ -d '.git' ] && cmd_git "$@"
 }
 
-gocrypt_derive_password() {
-    local data="$1"
-    local key="$2"
-
-    perl <<< "use Digest::SHA qw(hmac_sha256_hex);\$digest=hmac_sha256_hex(\"$data\n\", \"$key\");print(\$digest);"
-}
-
 gocrypt_init() {
     local needs_passphrase=false
     local passphrase=""
@@ -67,7 +59,6 @@ gocrypt_init() {
     if $needs_passphrase; then
         echo -n "Enter passphrase: "
         read -s passphrase
-        [[ "$passphrase" =~ [^a-zA-Z0-9\ ] ]] && gocrypt_die "Only alphanumeric characters are allowed for now"
         local passphrase_confirm=""
         echo
         echo -n "Confirm passphrase: "
@@ -84,7 +75,7 @@ gocrypt_init() {
     mkdir "$gocrypt_dir"
     if $needs_passphrase; then
         touch "$gocrypt_needs_passphrase_marker"
-        gocrypt_passwd="$(gocrypt_derive_password "$gocrypt_passwd" "$passphrase")"
+        gocrypt_passwd="$gocrypt_passwd$passphrase"
     fi
     gocryptfs -passfile /dev/stdin -init "$gocrypt_dir" <<< "$gocrypt_passwd" || gocrypt_die "Unable to initialize gocryptfs"
 
@@ -121,7 +112,7 @@ gocrypt_open() {
             local passphrase=""
             echo -n "Enter passphrase: "
             read -s passphrase
-            gocrypt_passwd="$(gocrypt_derive_password "$gocrypt_passwd" "$passphrase")"
+            gocrypt_passwd="$gocrypt_passwd$passphrase"
         fi
     fi
 
@@ -169,10 +160,11 @@ usage
 
         You can optionally use an extra piece of symmetric passphrase to encrypt the subdirectory, by
         passing the argument -p or --passphrase when invoking this command to initialize. In this case,
-        the passphrase you input will be used along with the generated password to derive a new master
-        password for gocryptfs. This second piece of passphrase will not be stored in the password store,
-        and you will be asked for it every time you invoke \`$PROGRAM gocrypt open\`. This mode adds an
-        extra layer of protection in case the gpg-encrypted master password is somehow compromised.
+        the passphrase you input will be used along with the generated password to derive the encryption
+        key (KEK) of the master key of gocryptfs. This second piece of passphrase will not be stored in
+        the password store, and you will be asked for it every time you invoke \`$PROGRAM gocrypt open\`.
+        This mode adds an extra layer of protection in case the gpg-encrypted master password is somehow
+        compromised.
 
     $PROGRAM gocrypt open
         Mount the encrypted subdirectory to \$PASSWORD_STORE_DIR/$gocrypt_dec_dir.