Add comments on OpenSSH AES-encrypted key support, including one

mentioning that I haven't yet switched to _exporting_ OpenSSH keys
in the new style.

git-svn-id: svn://svn.tartarus.org/sgt/putty@8917 cda61777-01e9-0310-a592-d414129be87e

diff --git a/import.c b/import.c
index 17bf65b..20a77e5 100644 (file)
--- a/import.c
+++ b/import.c
@@ -529,6 +529,10 @@ struct ssh2_userkey *openssh_read(const Filename *filename, char *passphrase,
         *  - let block B equal MD5(A || passphrase || iv)
         *  - block C would be MD5(B || passphrase || iv) and so on
         *  - encryption key is the first N bytes of A || B
+        *
+        * (Note that only 8 bytes of the iv are used for key
+        * derivation, even when the key is encrypted with AES and
+        * hence there are 16 bytes available.)
         */
        struct MD5Context md5c;
        unsigned char keybuf[32];
@@ -872,6 +876,9 @@ int openssh_write(const Filename *filename, struct ssh2_userkey *key,
 
     /*
      * Encrypt the key.
+     *
+     * For the moment, we still encrypt our OpenSSH keys using
+     * old-style 3DES.
      */
     if (passphrase) {
        /*