system: remove DES password encoding

DES is long dead, it is insecure as hell, and virtually all known
crypt(3) implementations now all support at least md5.

Besides, the character-space of DES-encoded passwords are a sub-set
of the character-space for a clear-text password, so we can't easily
differentiate between the two. Since we're going to change the root
password prompt to support setting encoded passwords (as well as
clear-text passwords), we can't keep DES or we'd be unable to decide
whether we'd need to encode the password or not.

Remove DES encoding altogether (and add a legacy entry). The default is
still md5, and thus there's no backward-compatibility 'select' to add.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Lorenzo Catucci <lorenzo@sancho.ccd.uniroma2.it>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Config.in.legacy

@@ -101,6 +101,13 @@ endif
 ###############################################################################
 comment "Legacy options removed in 2015.05"
 
+config BR2_TARGET_GENERIC_PASSWD_DES
+	bool "Encoding passwords with DES has been removed"
+	select BR2_LEGACY
+	help
+	  Paswords can now only be encoded with either of md5, sha256 or sha512.
+	  The default is md5, which is stronger that DES (but still pretty weak).
+
 config BR2_PACKAGE_GTK2_THEME_HICOLOR
 	bool "hicolor (default theme) is a duplicate"
 	select BR2_LEGACY

system/Config.in

@@ -27,14 +27,6 @@ choice
 
 	  Note: this is used at build-time, and *not* at runtime.
 
-config BR2_TARGET_GENERIC_PASSWD_DES
-	bool "des"
-	help
-	  Use standard 56-bit DES-based crypt(3) to encode passwords.
-
-	  Old, wildly available, but also the weakest, very susceptible to
-	  brute-force attacks.
-
 config BR2_TARGET_GENERIC_PASSWD_MD5
 	bool "md5"
 	help
@@ -67,7 +59,6 @@ endchoice # Passwd encoding
 
 config BR2_TARGET_GENERIC_PASSWD_METHOD
 	string
-	default "des"       if BR2_TARGET_GENERIC_PASSWD_DES
 	default "md5"       if BR2_TARGET_GENERIC_PASSWD_MD5
 	default "sha-256"   if BR2_TARGET_GENERIC_PASSWD_SHA256
 	default "sha-512"   if BR2_TARGET_GENERIC_PASSWD_SHA512