INCOMPATIBLE CHANGE to the SSH2 private key file format. There is

now a passphrase-keyed MAC covering _all_ important data in the
file, including the public blob and the key comment. Should
conclusively scupper any attacks based on nobbling the key file in
an attempt to sucker the machine that decrypts it. MACing the
comment field also protects against a key-substitution attack (if
someone's worked out a way past our DSA protections and can extract
the private key from a signature, swapping key files and
substituting comments might just enable them to get the signature
they need to do this. Paranoid, but might as well).

[originally from svn r1413]

plink.c

@@ -162,6 +162,25 @@ void askcipher(char *ciphername, int cs)
     }
 }
 
+/*
+ * Warn about the obsolescent key file format.
+ */
+void old_keyfile_warning(void)
+{
+    static const char message[] =
+	"You are loading an SSH 2 private key which has an\n"
+	"old version of the file format. This means your key\n"
+	"file is not fully tamperproof. Future versions of\n"
+	"PuTTY may stop supporting this private key format,\n"
+	"so we recommend you convert your key to the new\n"
+	"format.\n"
+	"\n"
+	"Once the key is loaded into PuTTYgen, you can perform\n"
+	"this conversion simply by saving it again.\n";
+
+    fputs(message, stderr);
+}
+
 HANDLE inhandle, outhandle, errhandle;
 DWORD orig_console_mode;