1 files changed, 282 insertions, 17 deletions

diff --git a/sshkey.c b/sshkey.c
index 379a579cf..7aa7e772c 100644
--- a/sshkey.c
+++ b/sshkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.c,v 1.75 2019/05/20 00:20:35 djm Exp $ */
+/* $OpenBSD: sshkey.c,v 1.76 2019/06/21 04:21:05 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Alexander von Gernler.  All rights reserved.
@@ -78,7 +78,15 @@
 /* Version identification string for SSH v1 identity files. */
 #define LEGACY_BEGIN            "SSH PRIVATE KEY FILE FORMAT 1.1\n"
 
-int     sshkey_private_serialize_opt(const struct sshkey *key,
+/*
+ * Constants relating to "shielding" support; protection of keys expected
+ * to remain in memory for long durations
+ */
+#define SSHKEY_SHIELD_PREKEY_LEN        (16 * 1024)
+#define SSHKEY_SHIELD_CIPHER            "aes256-ctr" /* XXX want AES-EME* */
+#define SSHKEY_SHIELD_PREKEY_HASH       SSH_DIGEST_SHA512
+
+int     sshkey_private_serialize_opt(struct sshkey *key,
     struct sshbuf *buf, enum sshkey_serialize_rep);
 static int sshkey_from_blob_internal(struct sshbuf *buf,
     struct sshkey **keyp, int allow_cert);
@@ -604,6 +612,8 @@ sshkey_free(struct sshkey *k)
         }
         if (sshkey_is_cert(k))
                 cert_free(k->cert);
+        freezero(k->shielded_private, k->shielded_len);
+        freezero(k->shield_prekey, k->shield_prekey_len);
         freezero(k, sizeof(*k));
 }
 
@@ -1869,6 +1879,218 @@ sshkey_from_private(const struct sshkey *k, struct sshkey **pkp)
         return r;
 }
 
+int
+sshkey_is_shielded(struct sshkey *k)
+{
+        return k != NULL && k->shielded_private != NULL;
+}
+
+int
+sshkey_shield_private(struct sshkey *k)
+{
+        struct sshbuf *prvbuf = NULL;
+        u_char *prekey = NULL, *enc = NULL, keyiv[SSH_DIGEST_MAX_LENGTH];
+        struct sshcipher_ctx *cctx = NULL;
+        const struct sshcipher *cipher;
+        size_t i, enclen = 0;
+        struct sshkey *kswap = NULL, tmp;
+        int r = SSH_ERR_INTERNAL_ERROR;
+
+#ifdef DEBUG_PK
+        fprintf(stderr, "%s: entering for %s\n", __func__, sshkey_ssh_name(k));
+#endif
+        if ((cipher = cipher_by_name(SSHKEY_SHIELD_CIPHER)) == NULL) {
+                r = SSH_ERR_INVALID_ARGUMENT;
+                goto out;
+        }
+        if (cipher_keylen(cipher) + cipher_ivlen(cipher) >
+            ssh_digest_bytes(SSHKEY_SHIELD_PREKEY_HASH)) {
+                r = SSH_ERR_INTERNAL_ERROR;
+                goto out;
+        }
+
+        /* Prepare a random pre-key, and from it an ephemeral key */
+        if ((prekey = malloc(SSHKEY_SHIELD_PREKEY_LEN)) == NULL) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        arc4random_buf(prekey, SSHKEY_SHIELD_PREKEY_LEN);
+        if ((r = ssh_digest_memory(SSHKEY_SHIELD_PREKEY_HASH,
+            prekey, SSHKEY_SHIELD_PREKEY_LEN,
+            keyiv, SSH_DIGEST_MAX_LENGTH)) != 0)
+                goto out;
+#ifdef DEBUG_PK
+        fprintf(stderr, "%s: key+iv\n", __func__);
+        sshbuf_dump_data(keyiv, ssh_digest_bytes(SSHKEY_SHIELD_PREKEY_HASH),
+            stderr);
+#endif
+        if ((r = cipher_init(&cctx, cipher, keyiv, cipher_keylen(cipher),
+            keyiv + cipher_keylen(cipher), cipher_ivlen(cipher), 1)) != 0)
+                goto out;
+
+        /* Serialise and encrypt the private key using the ephemeral key */
+        if ((prvbuf = sshbuf_new()) == NULL) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if (sshkey_is_shielded(k) && (r = sshkey_unshield_private(k)) != 0)
+                goto out;
+        if ((r = sshkey_private_serialize_opt(k, prvbuf,
+             SSHKEY_SERIALIZE_FULL)) != 0)
+                goto out;
+        /* pad to cipher blocksize */
+        i = 0;
+        while (sshbuf_len(prvbuf) % cipher_blocksize(cipher)) {
+                if ((r = sshbuf_put_u8(prvbuf, ++i & 0xff)) != 0)
+                        goto out;
+        }
+#ifdef DEBUG_PK
+        fprintf(stderr, "%s: serialised\n", __func__);
+        sshbuf_dump(prvbuf, stderr);
+#endif
+        /* encrypt */
+        enclen = sshbuf_len(prvbuf);
+        if ((enc = malloc(enclen)) == NULL) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if ((r = cipher_crypt(cctx, 0, enc,
+            sshbuf_ptr(prvbuf), sshbuf_len(prvbuf), 0, 0)) != 0)
+                goto out;
+#ifdef DEBUG_PK
+        fprintf(stderr, "%s: encrypted\n", __func__);
+        sshbuf_dump_data(enc, enclen, stderr);
+#endif
+
+        /* Make a scrubbed, public-only copy of our private key argument */
+        if ((r = sshkey_from_private(k, &kswap)) != 0)
+                goto out;
+
+        /* Swap the private key out (it will be destroyed below) */
+        tmp = *kswap;
+        *kswap = *k;
+        *k = tmp;
+
+        /* Insert the shielded key into our argument */
+        k->shielded_private = enc;
+        k->shielded_len = enclen;
+        k->shield_prekey = prekey;
+        k->shield_prekey_len = SSHKEY_SHIELD_PREKEY_LEN;
+        enc = prekey = NULL; /* transferred */
+        enclen = 0;
+
+        /* success */
+        r = 0;
+
+ out:
+        /* XXX behaviour on error - invalidate original private key? */
+        cipher_free(cctx);
+        explicit_bzero(enc, enclen);
+        explicit_bzero(keyiv, sizeof(keyiv));
+        explicit_bzero(&tmp, sizeof(tmp));
+        freezero(prekey, SSHKEY_SHIELD_PREKEY_LEN);
+        sshkey_free(kswap);
+        sshbuf_free(prvbuf);
+        return r;
+}
+
+int
+sshkey_unshield_private(struct sshkey *k)
+{
+        struct sshbuf *prvbuf = NULL;
+        u_char pad, *cp, keyiv[SSH_DIGEST_MAX_LENGTH];
+        struct sshcipher_ctx *cctx = NULL;
+        const struct sshcipher *cipher;
+        size_t i;
+        struct sshkey *kswap = NULL, tmp;
+        int r = SSH_ERR_INTERNAL_ERROR;
+
+#ifdef DEBUG_PK
+        fprintf(stderr, "%s: entering for %s\n", __func__, sshkey_ssh_name(k));
+#endif
+        if (!sshkey_is_shielded(k))
+                return 0; /* nothing to do */
+
+        if ((cipher = cipher_by_name(SSHKEY_SHIELD_CIPHER)) == NULL) {
+                r = SSH_ERR_INVALID_ARGUMENT;
+                goto out;
+        }
+        if (cipher_keylen(cipher) + cipher_ivlen(cipher) >
+            ssh_digest_bytes(SSHKEY_SHIELD_PREKEY_HASH)) {
+                r = SSH_ERR_INTERNAL_ERROR;
+                goto out;
+        }
+        /* check size of shielded key blob */
+        if (k->shielded_len < cipher_blocksize(cipher) ||
+            (k->shielded_len % cipher_blocksize(cipher)) != 0) {
+                r = SSH_ERR_INVALID_FORMAT;
+                goto out;
+        }
+
+        /* Calculate the ephemeral key from the prekey */
+        if ((r = ssh_digest_memory(SSHKEY_SHIELD_PREKEY_HASH,
+            k->shield_prekey, k->shield_prekey_len,
+            keyiv, SSH_DIGEST_MAX_LENGTH)) != 0)
+                goto out;
+        if ((r = cipher_init(&cctx, cipher, keyiv, cipher_keylen(cipher),
+            keyiv + cipher_keylen(cipher), cipher_ivlen(cipher), 0)) != 0)
+                goto out;
+#ifdef DEBUG_PK
+        fprintf(stderr, "%s: key+iv\n", __func__);
+        sshbuf_dump_data(keyiv, ssh_digest_bytes(SSHKEY_SHIELD_PREKEY_HASH),
+            stderr);
+#endif
+
+        /* Decrypt and parse the shielded private key using the ephemeral key */
+        if ((prvbuf = sshbuf_new()) == NULL) {
+                r = SSH_ERR_ALLOC_FAIL;
+                goto out;
+        }
+        if ((r = sshbuf_reserve(prvbuf, k->shielded_len, &cp)) != 0)
+                goto out;
+        /* decrypt */
+#ifdef DEBUG_PK
+        fprintf(stderr, "%s: encrypted\n", __func__);
+        sshbuf_dump_data(k->shielded_private, k->shielded_len, stderr);
+#endif
+        if ((r = cipher_crypt(cctx, 0, cp,
+            k->shielded_private, k->shielded_len, 0, 0)) != 0)
+                goto out;
+#ifdef DEBUG_PK
+        fprintf(stderr, "%s: serialised\n", __func__);
+        sshbuf_dump(prvbuf, stderr);
+#endif
+        /* Parse private key */
+        if ((r = sshkey_private_deserialize(prvbuf, &kswap)) != 0)
+                goto out;
+        /* Check deterministic padding */
+        i = 0;
+        while (sshbuf_len(prvbuf)) {
+                if ((r = sshbuf_get_u8(prvbuf, &pad)) != 0)
+                        goto out;
+                if (pad != (++i & 0xff)) {
+                        r = SSH_ERR_INVALID_FORMAT;
+                        goto out;
+                }
+        }
+
+        /* Swap the parsed key back into place */
+        tmp = *kswap;
+        *kswap = *k;
+        *k = tmp;
+
+        /* success */
+        r = 0;
+
+ out:
+        cipher_free(cctx);
+        explicit_bzero(keyiv, sizeof(keyiv));
+        explicit_bzero(&tmp, sizeof(tmp));
+        sshkey_free(kswap);
+        sshbuf_free(prvbuf);
+        return r;
+}
+
 static int
 cert_parse(struct sshbuf *b, struct sshkey *key, struct sshbuf *certbuf)
 {
@@ -2373,41 +2595,55 @@ sshkey_check_sigtype(const u_char *sig, size_t siglen,
 }
 
 int
-sshkey_sign(const struct sshkey *key,
+sshkey_sign(struct sshkey *key,
     u_char **sigp, size_t *lenp,
     const u_char *data, size_t datalen, const char *alg, u_int compat)
 {
+        int was_shielded = sshkey_is_shielded(key);
+        int r2, r = SSH_ERR_INTERNAL_ERROR;
+
         if (sigp != NULL)
                 *sigp = NULL;
         if (lenp != NULL)
                 *lenp = 0;
         if (datalen > SSH_KEY_MAX_SIGN_DATA_SIZE)
                 return SSH_ERR_INVALID_ARGUMENT;
+        if ((r = sshkey_unshield_private(key)) != 0)
+                return r;
         switch (key->type) {
 #ifdef WITH_OPENSSL
         case KEY_DSA_CERT:
         case KEY_DSA:
-                return ssh_dss_sign(key, sigp, lenp, data, datalen, compat);
+                r = ssh_dss_sign(key, sigp, lenp, data, datalen, compat);
+                break;
 # ifdef OPENSSL_HAS_ECC
         case KEY_ECDSA_CERT:
         case KEY_ECDSA:
-                return ssh_ecdsa_sign(key, sigp, lenp, data, datalen, compat);
+                r = ssh_ecdsa_sign(key, sigp, lenp, data, datalen, compat);
+                break;
 # endif /* OPENSSL_HAS_ECC */
         case KEY_RSA_CERT:
         case KEY_RSA:
-                return ssh_rsa_sign(key, sigp, lenp, data, datalen, alg);
+                r = ssh_rsa_sign(key, sigp, lenp, data, datalen, alg);
+                break;
 #endif /* WITH_OPENSSL */
         case KEY_ED25519:
         case KEY_ED25519_CERT:
-                return ssh_ed25519_sign(key, sigp, lenp, data, datalen, compat);
+                r = ssh_ed25519_sign(key, sigp, lenp, data, datalen, compat);
+                break;
 #ifdef WITH_XMSS
         case KEY_XMSS:
         case KEY_XMSS_CERT:
-                return ssh_xmss_sign(key, sigp, lenp, data, datalen, compat);
+                r = ssh_xmss_sign(key, sigp, lenp, data, datalen, compat);
+                break;
 #endif /* WITH_XMSS */
         default:
-                return SSH_ERR_KEY_TYPE_UNKNOWN;
+                r = SSH_ERR_KEY_TYPE_UNKNOWN;
+                break;
         }
+        if (was_shielded && (r2 = sshkey_shield_private(key)) != 0)
+                return r2;
+        return r;
 }
 
 /*
@@ -2652,7 +2888,7 @@ sshkey_certify_custom(struct sshkey *k, struct sshkey *ca, const char *alg,
 }
 
 static int
-default_key_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
+default_key_sign(struct sshkey *key, u_char **sigp, size_t *lenp,
     const u_char *data, size_t datalen,
     const char *alg, u_int compat, void *ctx)
 {
@@ -2762,15 +2998,21 @@ sshkey_format_cert_validity(const struct sshkey_cert *cert, char *s, size_t l)
 }
 
 int
-sshkey_private_serialize_opt(const struct sshkey *key, struct sshbuf *b,
+sshkey_private_serialize_opt(struct sshkey *key, struct sshbuf *buf,
     enum sshkey_serialize_rep opts)
 {
         int r = SSH_ERR_INTERNAL_ERROR;
+        int was_shielded = sshkey_is_shielded(key);
+        struct sshbuf *b = NULL;
 #ifdef WITH_OPENSSL
         const BIGNUM *rsa_n, *rsa_e, *rsa_d, *rsa_iqmp, *rsa_p, *rsa_q;
         const BIGNUM *dsa_p, *dsa_q, *dsa_g, *dsa_pub_key, *dsa_priv_key;
 #endif /* WITH_OPENSSL */
 
+        if ((r = sshkey_unshield_private(key)) != 0)
+                return r;
+        if ((b = sshbuf_new()) == NULL)
+                return SSH_ERR_ALLOC_FAIL;
         if ((r = sshbuf_put_cstring(b, sshkey_ssh_name(key))) != 0)
                 goto out;
         switch (key->type) {
@@ -2896,14 +3138,23 @@ sshkey_private_serialize_opt(const struct sshkey *key, struct sshbuf *b,
                 r = SSH_ERR_INVALID_ARGUMENT;
                 goto out;
         }
-        /* success */
+        /*
+         * success (but we still need to append the output to buf after
+         * possibly re-shielding the private key)
+         */
         r = 0;
  out:
+        if (was_shielded)
+                r = sshkey_shield_private(key);
+        if (r == 0)
+                r = sshbuf_putb(buf, b);
+        sshbuf_free(b);
+
         return r;
 }
 
 int
-sshkey_private_serialize(const struct sshkey *key, struct sshbuf *b)
+sshkey_private_serialize(struct sshkey *key, struct sshbuf *b)
 {
         return sshkey_private_serialize_opt(key, b,
             SSHKEY_SERIALIZE_DEFAULT);
@@ -3358,7 +3609,7 @@ sshkey_dump_ec_key(const EC_KEY *key)
 #endif /* WITH_OPENSSL && OPENSSL_HAS_ECC */
 
 static int
-sshkey_private_to_blob2(const struct sshkey *prv, struct sshbuf *blob,
+sshkey_private_to_blob2(struct sshkey *prv, struct sshbuf *blob,
     const char *passphrase, const char *comment, const char *ciphername,
     int rounds)
 {
@@ -3728,20 +3979,28 @@ sshkey_parse_private2(struct sshbuf *blob, int type, const char *passphrase,
 #ifdef WITH_OPENSSL
 /* convert SSH v2 key in OpenSSL PEM format */
 static int
-sshkey_private_pem_to_blob(struct sshkey *key, struct sshbuf *blob,
+sshkey_private_pem_to_blob(struct sshkey *key, struct sshbuf *buf,
     const char *_passphrase, const char *comment)
 {
+        int was_shielded = sshkey_is_shielded(key);
         int success, r;
         int blen, len = strlen(_passphrase);
         u_char *passphrase = (len > 0) ? (u_char *)_passphrase : NULL;
         const EVP_CIPHER *cipher = (len > 0) ? EVP_aes_128_cbc() : NULL;
         char *bptr;
         BIO *bio = NULL;
+        struct sshbuf *blob;
 
         if (len > 0 && len <= 4)
                 return SSH_ERR_PASSPHRASE_TOO_SHORT;
-        if ((bio = BIO_new(BIO_s_mem())) == NULL)
+        if ((blob = sshbuf_new()) == NULL)
                 return SSH_ERR_ALLOC_FAIL;
+        if ((bio = BIO_new(BIO_s_mem())) == NULL) {
+                sshbuf_free(blob);
+                return SSH_ERR_ALLOC_FAIL;
+        }
+        if ((r = sshkey_unshield_private(key)) != 0)
+                goto out;
 
         switch (key->type) {
         case KEY_DSA:
@@ -3774,6 +4033,12 @@ sshkey_private_pem_to_blob(struct sshkey *key, struct sshbuf *blob,
                 goto out;
         r = 0;
  out:
+        if (was_shielded)
+                r = sshkey_shield_private(key);
+        if (r == 0)
+                r = sshbuf_putb(buf, blob);
+        sshbuf_free(blob);
+
         BIO_free(bio);
         return r;
 }
@@ -4102,7 +4367,7 @@ sshkey_set_filename(struct sshkey *k, const char *filename)
 }
 #else
 int
-sshkey_private_serialize_maxsign(const struct sshkey *k, struct sshbuf *b,
+sshkey_private_serialize_maxsign(struct sshkey *k, struct sshbuf *b,
     u_int32_t maxsign, sshkey_printfn *pr)
 {
         return sshkey_private_serialize_opt(k, b, SSHKEY_SERIALIZE_DEFAULT);