upstream: Add protection for private keys at rest in RAM against

speculation and memory sidechannel attacks like Spectre, Meltdown, Rowhammer
and Rambleed. This change encrypts private keys when they are not in use with
a symmetic key that is derived from a relatively large "prekey" consisting of
random data (currently 16KB).

Attackers must recover the entire prekey with high accuracy before
they can attempt to decrypt the shielded private key, but the current
generation of attacks have bit error rates that, when applied
cumulatively to the entire prekey, make this unlikely.

Implementation-wise, keys are encrypted "shielded" when loaded and then
automatically and transparently unshielded when used for signatures or
when being saved/serialised.

Hopefully we can remove this in a few years time when computer
architecture has become less unsafe.

been in snaps for a bit already; thanks deraadt@

ok dtucker@ deraadt@

OpenBSD-Commit-ID: 19767213c312e46f94b303a512ef8e9218a39bd4

1 files changed, 15 insertions, 6 deletions

diff --git a/sshkey.h b/sshkey.h
index a91e60436..41d159a1b 100644
--- a/sshkey.h
+++ b/sshkey.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.h,v 1.31 2019/01/20 22:51:37 djm Exp $ */
+/* $OpenBSD: sshkey.h,v 1.32 2019/06/21 04:21:05 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -123,6 +123,10 @@ struct sshkey {
         u_char  *xmss_sk;
         u_char  *xmss_pk;
         struct sshkey_cert *cert;
+        u_char  *shielded_private;
+        size_t  shielded_len;
+        u_char  *shield_prekey;
+        size_t  shield_prekey_len;
 };
 
 #define ED25519_SK_SZ   crypto_sign_ed25519_SECRETKEYBYTES
@@ -146,6 +150,11 @@ u_int		 sshkey_size(const struct sshkey *);
 
 int              sshkey_generate(int type, u_int bits, struct sshkey **keyp);
 int              sshkey_from_private(const struct sshkey *, struct sshkey **);
+
+int              sshkey_is_shielded(struct sshkey *);
+int              sshkey_shield_private(struct sshkey *);
+int              sshkey_unshield_private(struct sshkey *);
+
 int      sshkey_type_from_name(const char *);
 int      sshkey_is_cert(const struct sshkey *);
 int      sshkey_type_is_cert(int);
@@ -161,7 +170,7 @@ int	 sshkey_check_cert_sigtype(const struct sshkey *, const char *);
 
 int      sshkey_certify(struct sshkey *, struct sshkey *, const char *);
 /* Variant allowing use of a custom signature function (e.g. for ssh-agent) */
-typedef int sshkey_certify_signer(const struct sshkey *, u_char **, size_t *,
+typedef int sshkey_certify_signer(struct sshkey *, u_char **, size_t *,
     const u_char *, size_t, const char *, u_int, void *);
 int      sshkey_certify_custom(struct sshkey *, struct sshkey *, const char *,
     sshkey_certify_signer *, void *);
@@ -192,7 +201,7 @@ int	 sshkey_puts_opts(const struct sshkey *, struct sshbuf *,
 int      sshkey_plain_to_blob(const struct sshkey *, u_char **, size_t *);
 int      sshkey_putb_plain(const struct sshkey *, struct sshbuf *);
 
-int      sshkey_sign(const struct sshkey *, u_char **, size_t *,
+int      sshkey_sign(struct sshkey *, u_char **, size_t *,
     const u_char *, size_t, const char *, u_int);
 int      sshkey_verify(const struct sshkey *, const u_char *, size_t,
     const u_char *, size_t, const char *, u_int);
@@ -204,8 +213,8 @@ void	sshkey_dump_ec_point(const EC_GROUP *, const EC_POINT *);
 void    sshkey_dump_ec_key(const EC_KEY *);
 
 /* private key parsing and serialisation */
-int     sshkey_private_serialize(const struct sshkey *key, struct sshbuf *buf);
-int     sshkey_private_serialize_opt(const struct sshkey *key, struct sshbuf *buf,
+int     sshkey_private_serialize(struct sshkey *key, struct sshbuf *buf);
+int     sshkey_private_serialize_opt(struct sshkey *key, struct sshbuf *buf,
     enum sshkey_serialize_rep);
 int     sshkey_private_deserialize(struct sshbuf *buf,  struct sshkey **keyp);
 
@@ -231,7 +240,7 @@ int	 sshkey_set_filename(struct sshkey *, const char *);
 int      sshkey_enable_maxsign(struct sshkey *, u_int32_t);
 u_int32_t sshkey_signatures_left(const struct sshkey *);
 int      sshkey_forward_state(const struct sshkey *, u_int32_t, sshkey_printfn *);
-int      sshkey_private_serialize_maxsign(const struct sshkey *key, struct sshbuf *buf,
+int      sshkey_private_serialize_maxsign(struct sshkey *key, struct sshbuf *buf,
     u_int32_t maxsign, sshkey_printfn *pr);
 
 #ifdef SSHKEY_INTERNAL