support PKCS8 as an optional format for storage of private keys,

enabled via "ssh-keygen -m PKCS8" on operations that save private
keys to disk.

The OpenSSH native key format remains the default, but PKCS8 is a
superior format to PEM if interoperability with non-OpenSSH software
is required, as it may use a less terrible KDF (IIRC PEM uses a single
round of MD5 as a KDF).

adapted from patch by Jakub Jelen via bz3013; ok markus

5 files changed, 86 insertions, 41 deletions

diff --git a/usr.bin/ssh/authfile.c b/usr.bin/ssh/authfile.c
index 5a2f41d6db1..d6b03a4d77b 100644
--- a/usr.bin/ssh/authfile.c
+++ b/usr.bin/ssh/authfile.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: authfile.c,v 1.132 2019/06/28 13:35:04 deraadt Exp $ */
+/* $OpenBSD: authfile.c,v 1.133 2019/07/15 13:16:29 djm Exp $ */
 /*
  * Copyright (c) 2000, 2013 Markus Friedl.  All rights reserved.
  *
@@ -72,7 +72,7 @@ sshkey_save_private_blob(struct sshbuf *keybuf, const char *filename)
 int
 sshkey_save_private(struct sshkey *key, const char *filename,
     const char *passphrase, const char *comment,
-    int force_new_format, const char *new_format_cipher, int new_format_rounds)
+    int format, const char *openssh_format_cipher, int openssh_format_rounds)
 {
 	struct sshbuf *keyblob = NULL;
 	int r;
@@ -80,7 +80,7 @@ sshkey_save_private(struct sshkey *key, const char *filename,
 	if ((keyblob = sshbuf_new()) == NULL)
 		return SSH_ERR_ALLOC_FAIL;
 	if ((r = sshkey_private_to_fileblob(key, keyblob, passphrase, comment,
-	    force_new_format, new_format_cipher, new_format_rounds)) != 0)
+	    format, openssh_format_cipher, openssh_format_rounds)) != 0)
 		goto out;
 	if ((r = sshkey_save_private_blob(keyblob, filename)) != 0)
 		goto out;
diff --git a/usr.bin/ssh/ssh-keygen.1 b/usr.bin/ssh/ssh-keygen.1
index f42127c60ca..8184a1797ec 100644
--- a/usr.bin/ssh/ssh-keygen.1
+++ b/usr.bin/ssh/ssh-keygen.1
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: ssh-keygen.1,v 1.160 2019/05/20 06:01:59 jmc Exp $
+.\"	$OpenBSD: ssh-keygen.1,v 1.161 2019/07/15 13:16:29 djm Exp $
 .\"
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -35,7 +35,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: May 20 2019 $
+.Dd $Mdocdate: July 15 2019 $
 .Dt SSH-KEYGEN 1
 .Os
 .Sh NAME
@@ -419,11 +419,12 @@ The supported key formats are:
 .Dq RFC4716
 (RFC 4716/SSH2 public or private key),
 .Dq PKCS8
-(PEM PKCS8 public key)
+(PKCS8 public or private key)
 or
 .Dq PEM
 (PEM public key).
-The default conversion format is
+By default OpenSSH will write newly-generated private keys in its own
+format, but when converting public keys for export the default format is
 .Dq RFC4716 .
 Setting a format of
 .Dq PEM
diff --git a/usr.bin/ssh/ssh-keygen.c b/usr.bin/ssh/ssh-keygen.c
index 7f09a922002..bc999415079 100644
--- a/usr.bin/ssh/ssh-keygen.c
+++ b/usr.bin/ssh/ssh-keygen.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-keygen.c,v 1.335 2019/07/05 07:32:01 djm Exp $ */
+/* $OpenBSD: ssh-keygen.c,v 1.336 2019/07/15 13:16:29 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1994 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -140,11 +140,11 @@ static char *key_type_name = NULL;
 /* Load key from this PKCS#11 provider */
 static char *pkcs11provider = NULL;
 
-/* Use new OpenSSH private key format when writing SSH2 keys instead of PEM */
-static int use_new_format = 1;
+/* Format for writing private keys */
+static int private_key_format = SSHKEY_PRIVATE_OPENSSH;
 
 /* Cipher for new-format private keys */
-static char *new_format_cipher = NULL;
+static char *openssh_format_cipher = NULL;
 
 /*
  * Number of KDF rounds to derive new format keys /
@@ -1027,7 +1027,8 @@ do_gen_all_hostkeys(struct passwd *pw)
 		snprintf(comment, sizeof comment, "%s@%s", pw->pw_name,
 		    hostname);
 		if ((r = sshkey_save_private(private, prv_tmp, "",
-		    comment, use_new_format, new_format_cipher, rounds)) != 0) {
+		    comment, private_key_format, openssh_format_cipher,
+		    rounds)) != 0) {
 			error("Saving key \"%s\" failed: %s",
 			    prv_tmp, ssh_err(r));
 			goto failnext;
@@ -1370,7 +1371,7 @@ do_change_passphrase(struct passwd *pw)
 
 	/* Save the file using the new passphrase. */
 	if ((r = sshkey_save_private(private, identity_file, passphrase1,
-	    comment, use_new_format, new_format_cipher, rounds)) != 0) {
+	    comment, private_key_format, openssh_format_cipher, rounds)) != 0) {
 		error("Saving key \"%s\" failed: %s.",
 		    identity_file, ssh_err(r));
 		explicit_bzero(passphrase1, strlen(passphrase1));
@@ -1459,7 +1460,7 @@ do_change_comment(struct passwd *pw, const char *identity_comment)
 	}
 
 	if (private->type != KEY_ED25519 && private->type != KEY_XMSS &&
-	    !use_new_format) {
+	    private_key_format != SSHKEY_PRIVATE_OPENSSH) {
 		error("Comments are only supported for keys stored in "
 		    "the new format (-o).");
 		explicit_bzero(passphrase, strlen(passphrase));
@@ -1493,7 +1494,8 @@ do_change_comment(struct passwd *pw, const char *identity_comment)
 
 	/* Save the file using the new passphrase. */
 	if ((r = sshkey_save_private(private, identity_file, passphrase,
-	    new_comment, use_new_format, new_format_cipher, rounds)) != 0) {
+	    new_comment, private_key_format, openssh_format_cipher,
+	    rounds)) != 0) {
 		error("Saving key \"%s\" failed: %s",
 		    identity_file, ssh_err(r));
 		explicit_bzero(passphrase, strlen(passphrase));
@@ -2503,11 +2505,12 @@ main(int argc, char **argv)
 			}
 			if (strcasecmp(optarg, "PKCS8") == 0) {
 				convert_format = FMT_PKCS8;
+				private_key_format = SSHKEY_PRIVATE_PKCS8;
 				break;
 			}
 			if (strcasecmp(optarg, "PEM") == 0) {
 				convert_format = FMT_PEM;
-				use_new_format = 0;
+				private_key_format = SSHKEY_PRIVATE_PEM;
 				break;
 			}
 			fatal("Unsupported conversion format \"%s\"", optarg);
@@ -2545,7 +2548,7 @@ main(int argc, char **argv)
 			add_cert_option(optarg);
 			break;
 		case 'Z':
-			new_format_cipher = optarg;
+			openssh_format_cipher = optarg;
 			break;
 		case 'C':
 			identity_comment = optarg;
@@ -2892,7 +2895,7 @@ passphrase_again:
 
 	/* Save the key with the given passphrase and comment. */
 	if ((r = sshkey_save_private(private, identity_file, passphrase1,
-	    comment, use_new_format, new_format_cipher, rounds)) != 0) {
+	    comment, private_key_format, openssh_format_cipher, rounds)) != 0) {
 		error("Saving key \"%s\" failed: %s",
 		    identity_file, ssh_err(r));
 		explicit_bzero(passphrase1, strlen(passphrase1));
diff --git a/usr.bin/ssh/sshkey.c b/usr.bin/ssh/sshkey.c
index 597bd281ca8..e814f6e917f 100644
--- a/usr.bin/ssh/sshkey.c
+++ b/usr.bin/ssh/sshkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.c,v 1.79 2019/07/07 01:05:00 dtucker Exp $ */
+/* $OpenBSD: sshkey.c,v 1.80 2019/07/15 13:16:29 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Alexander von Gernler.  All rights reserved.
@@ -3915,10 +3915,10 @@ sshkey_parse_private2(struct sshbuf *blob, int type, const char *passphrase,
 
 
 #ifdef WITH_OPENSSL
-/* convert SSH v2 key in OpenSSL PEM format */
+/* convert SSH v2 key to PEM or PKCS#8 format */
 static int
-sshkey_private_pem_to_blob(struct sshkey *key, struct sshbuf *buf,
-    const char *_passphrase, const char *comment)
+sshkey_private_to_blob_pem_pkcs8(struct sshkey *key, struct sshbuf *buf,
+    int format, const char *_passphrase, const char *comment)
 {
 	int was_shielded = sshkey_is_shielded(key);
 	int success, r;
@@ -3928,30 +3928,47 @@ sshkey_private_pem_to_blob(struct sshkey *key, struct sshbuf *buf,
 	char *bptr;
 	BIO *bio = NULL;
 	struct sshbuf *blob;
+	EVP_PKEY *pkey = NULL;
 
 	if (len > 0 && len <= 4)
 		return SSH_ERR_PASSPHRASE_TOO_SHORT;
 	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;
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+	if (format == SSHKEY_PRIVATE_PKCS8 && (pkey = EVP_PKEY_new()) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
 	}
 	if ((r = sshkey_unshield_private(key)) != 0)
 		goto out;
 
 	switch (key->type) {
 	case KEY_DSA:
-		success = PEM_write_bio_DSAPrivateKey(bio, key->dsa,
-		    cipher, passphrase, len, NULL, NULL);
+		if (format == SSHKEY_PRIVATE_PEM) {
+			success = PEM_write_bio_DSAPrivateKey(bio, key->dsa,
+			    cipher, passphrase, len, NULL, NULL);
+		} else {
+			success = EVP_PKEY_set1_DSA(pkey, key->dsa);
+		}
 		break;
 	case KEY_ECDSA:
-		success = PEM_write_bio_ECPrivateKey(bio, key->ecdsa,
-		    cipher, passphrase, len, NULL, NULL);
+		if (format == SSHKEY_PRIVATE_PEM) {
+			success = PEM_write_bio_ECPrivateKey(bio, key->ecdsa,
+			    cipher, passphrase, len, NULL, NULL);
+		} else {
+			success = EVP_PKEY_set1_EC_KEY(pkey, key->ecdsa);
+		}
 		break;
 	case KEY_RSA:
-		success = PEM_write_bio_RSAPrivateKey(bio, key->rsa,
-		    cipher, passphrase, len, NULL, NULL);
+		if (format == SSHKEY_PRIVATE_PEM) {
+			success = PEM_write_bio_RSAPrivateKey(bio, key->rsa,
+			    cipher, passphrase, len, NULL, NULL);
+		} else {
+			success = EVP_PKEY_set1_RSA(pkey, key->rsa);
+		}
 		break;
 	default:
 		success = 0;
@@ -3961,6 +3978,13 @@ sshkey_private_pem_to_blob(struct sshkey *key, struct sshbuf *buf,
 		r = SSH_ERR_LIBCRYPTO_ERROR;
 		goto out;
 	}
+	if (format == SSHKEY_PRIVATE_PKCS8) {
+		if ((success = PEM_write_bio_PrivateKey(bio, pkey, cipher,
+		    passphrase, len, NULL, NULL)) == 0) {
+			r = SSH_ERR_LIBCRYPTO_ERROR;
+			goto out;
+		}
+	}
 	if ((blen = BIO_get_mem_data(bio, &bptr)) <= 0) {
 		r = SSH_ERR_INTERNAL_ERROR;
 		goto out;
@@ -3973,8 +3997,9 @@ sshkey_private_pem_to_blob(struct sshkey *key, struct sshbuf *buf,
 		r = sshkey_shield_private(key);
 	if (r == 0)
 		r = sshbuf_putb(buf, blob);
-	sshbuf_free(blob);
 
+	EVP_PKEY_free(pkey);
+	sshbuf_free(blob);
 	BIO_free(bio);
 	return r;
 }
@@ -3984,29 +4009,38 @@ sshkey_private_pem_to_blob(struct sshkey *key, struct sshbuf *buf,
 int
 sshkey_private_to_fileblob(struct sshkey *key, struct sshbuf *blob,
     const char *passphrase, const char *comment,
-    int force_new_format, const char *new_format_cipher, int new_format_rounds)
+    int format, const char *openssh_format_cipher, int openssh_format_rounds)
 {
 	switch (key->type) {
 #ifdef WITH_OPENSSL
 	case KEY_DSA:
 	case KEY_ECDSA:
 	case KEY_RSA:
-		if (force_new_format) {
-			return sshkey_private_to_blob2(key, blob, passphrase,
-			    comment, new_format_cipher, new_format_rounds);
-		}
-		return sshkey_private_pem_to_blob(key, blob,
-		    passphrase, comment);
+		break; /* see below */
 #endif /* WITH_OPENSSL */
 	case KEY_ED25519:
 #ifdef WITH_XMSS
 	case KEY_XMSS:
 #endif /* WITH_XMSS */
 		return sshkey_private_to_blob2(key, blob, passphrase,
-		    comment, new_format_cipher, new_format_rounds);
+		    comment, openssh_format_cipher, openssh_format_rounds);
 	default:
 		return SSH_ERR_KEY_TYPE_UNKNOWN;
 	}
+
+#ifdef WITH_OPENSSL
+	switch (format) {
+	case SSHKEY_PRIVATE_OPENSSH:
+		return sshkey_private_to_blob2(key, blob, passphrase,
+		    comment, openssh_format_cipher, openssh_format_rounds);
+	case SSHKEY_PRIVATE_PEM:
+	case SSHKEY_PRIVATE_PKCS8:
+		return sshkey_private_to_blob_pem_pkcs8(key, blob,
+		    format, passphrase, comment);
+	default:
+		return SSH_ERR_INVALID_ARGUMENT;
+	}
+#endif /* WITH_OPENSSL */
 }
 
 
diff --git a/usr.bin/ssh/sshkey.h b/usr.bin/ssh/sshkey.h
index 8a682cf6bb4..0655b14ba4b 100644
--- a/usr.bin/ssh/sshkey.h
+++ b/usr.bin/ssh/sshkey.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshkey.h,v 1.32 2019/06/21 04:21:05 djm Exp $ */
+/* $OpenBSD: sshkey.h,v 1.33 2019/07/15 13:16:29 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -82,6 +82,13 @@ enum sshkey_serialize_rep {
 	SSHKEY_SERIALIZE_INFO = 254,
 };
 
+/* Private key disk formats */
+enum sshkey_private_format {
+	SSHKEY_PRIVATE_OPENSSH = 0,
+	SSHKEY_PRIVATE_PEM = 1,
+	SSHKEY_PRIVATE_PKCS8 = 2,
+};
+
 /* key is stored in external hardware */
 #define SSHKEY_FLAG_EXT		0x0001
 
@@ -215,7 +222,7 @@ int	sshkey_private_deserialize(struct sshbuf *buf,  struct sshkey **keyp);
 /* private key file format parsing and serialisation */
 int	sshkey_private_to_fileblob(struct sshkey *key, struct sshbuf *blob,
     const char *passphrase, const char *comment,
-    int force_new_format, const char *new_format_cipher, int new_format_rounds);
+    int format, const char *openssh_format_cipher, int openssh_format_rounds);
 int	sshkey_parse_private_fileblob(struct sshbuf *buffer,
     const char *passphrase, struct sshkey **keyp, char **commentp);
 int	sshkey_parse_private_fileblob_type(struct sshbuf *blob, int type,