On Thu, 23 Jan 2020, Damien Miller wrote:
> On Thu, 16 Jan 2020, Jakub Jelen wrote:
>
> > > Thanks for this - it seems to work okay with OpenSSL when patched to
> > > -current, but when I adapt it for OpenBSD/LibreSSL the encryption is
> > > broken and the connection fails right after KEX.
>
> I've worked with the LibreSSL developers and they should land a fix
> for EVP_chacha20 soon. Hopefully this will happen soon enough to get
> this committed before the looming OpenSSH release.
Here's the working patches BTW. I've separated the libcrypto chacha/poly
implementation to its own file for clarity.
-d
From 741027d3663db1f93f1ccd06d4e8ca96446fdc6b Mon Sep 17 00:00:00 2001
From: Damien Miller <djm@xxxxxxxxxxx>
Date: Wed, 22 Jan 2020 18:51:50 +1100
Subject: [PATCH 1/2] refactor chachapoly AEAD to use an opaque struct
---
cipher-chachapoly.c | 23 ++++++++++++++++++-----
cipher-chachapoly.h | 9 ++++-----
cipher.c | 16 +++++++++-------
3 files changed, 31 insertions(+), 17 deletions(-)
diff --git a/cipher-chachapoly.c b/cipher-chachapoly.c
index 0899c5ad5..a638c3416 100644
--- a/cipher-chachapoly.c
+++ b/cipher-chachapoly.c
@@ -28,15 +28,28 @@
#include "ssherr.h"
#include "cipher-chachapoly.h"
-int
-chachapoly_init(struct chachapoly_ctx *ctx,
- const u_char *key, u_int keylen)
+struct chachapoly_ctx {
+ struct chacha_ctx main_ctx, header_ctx;
+};
+
+struct chachapoly_ctx *
+chachapoly_new(const u_char *key, u_int keylen)
{
+ struct chachapoly_ctx *ctx;
+
if (keylen != (32 + 32)) /* 2 x 256 bit keys */
- return SSH_ERR_INVALID_ARGUMENT;
+ return NULL;
+ if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
+ return NULL;
chacha_keysetup(&ctx->main_ctx, key, 256);
chacha_keysetup(&ctx->header_ctx, key + 32, 256);
- return 0;
+ return ctx;
+}
+
+void
+chachapoly_free(struct chachapoly_ctx *cpctx)
+{
+ freezero(cpctx, sizeof(*cpctx));
}
/*
diff --git a/cipher-chachapoly.h b/cipher-chachapoly.h
index b7072be7d..21636bee6 100644
--- a/cipher-chachapoly.h
+++ b/cipher-chachapoly.h
@@ -24,13 +24,12 @@
#define CHACHA_KEYLEN 32 /* Only 256 bit keys used here */
-struct chachapoly_ctx {
- struct chacha_ctx main_ctx, header_ctx;
-};
+struct chachapoly_ctx;
-int chachapoly_init(struct chachapoly_ctx *cpctx,
- const u_char *key, u_int keylen)
+struct chachapoly_ctx *chachapoly_new(const u_char *key, u_int keylen)
__attribute__((__bounded__(__buffer__, 2, 3)));
+void chachapoly_free(struct chachapoly_ctx *cpctx);
+
int chachapoly_crypt(struct chachapoly_ctx *cpctx, u_int seqnr,
u_char *dest, const u_char *src, u_int len, u_int aadlen, u_int authlen,
int do_encrypt);
diff --git a/cipher.c b/cipher.c
index 25f98ba8e..daec5d955 100644
--- a/cipher.c
+++ b/cipher.c
@@ -59,7 +59,7 @@ struct sshcipher_ctx {
int plaintext;
int encrypt;
EVP_CIPHER_CTX *evp;
- struct chachapoly_ctx cp_ctx; /* XXX union with evp? */
+ struct chachapoly_ctx *cp_ctx;
struct aesctr_ctx ac_ctx; /* XXX union with evp? */
const struct sshcipher *cipher;
};
@@ -262,7 +262,8 @@ cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,
cc->cipher = cipher;
if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
- ret = chachapoly_init(&cc->cp_ctx, key, keylen);
+ cc->cp_ctx = chachapoly_new(key, keylen);
+ ret = cc->cp_ctx != NULL ? 0 : SSH_ERR_INVALID_ARGUMENT;
goto out;
}
if ((cc->cipher->flags & CFLAG_NONE) != 0) {
@@ -339,7 +340,7 @@ cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,
const u_char *src, u_int len, u_int aadlen, u_int authlen)
{
if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
- return chachapoly_crypt(&cc->cp_ctx, seqnr, dest, src,
+ return chachapoly_crypt(cc->cp_ctx, seqnr, dest, src,
len, aadlen, authlen, cc->encrypt);
}
if ((cc->cipher->flags & CFLAG_NONE) != 0) {
@@ -402,7 +403,7 @@ cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,
const u_char *cp, u_int len)
{
if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
- return chachapoly_get_length(&cc->cp_ctx, plenp, seqnr,
+ return chachapoly_get_length(cc->cp_ctx, plenp, seqnr,
cp, len);
if (len < 4)
return SSH_ERR_MESSAGE_INCOMPLETE;
@@ -415,9 +416,10 @@ cipher_free(struct sshcipher_ctx *cc)
{
if (cc == NULL)
return;
- if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)
- explicit_bzero(&cc->cp_ctx, sizeof(cc->cp_ctx));
- else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
+ if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {
+ chachapoly_free(cc->cp_ctx);
+ cc->cp_ctx = NULL;
+ } else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)
explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));
#ifdef WITH_OPENSSL
EVP_CIPHER_CTX_free(cc->evp);
--
2.25.0.341.g760bfbb309-goog
From 2b48f39cc8753c996f0df01e480b56dbc1b7d224 Mon Sep 17 00:00:00 2001
From: Damien Miller <djm@xxxxxxxxxxx>
Date: Wed, 22 Jan 2020 19:51:33 +1100
Subject: [PATCH 2/2] chacha20-poly1305 AEAD using libcrypto EVP_chacha20
Based on patch from Yuriy M. Kaminskiy
---
Makefile.in | 2 +-
cipher-chachapoly-libcrypto.c | 163 ++++++++++++++++++++++++++++++++
cipher-chachapoly.c | 3 +
openbsd-compat/openssl-compat.h | 7 ++
4 files changed, 174 insertions(+), 1 deletion(-)
create mode 100644 cipher-chachapoly-libcrypto.c
diff --git a/Makefile.in b/Makefile.in
index 963f99fb5..d6fcfe2c3 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -103,7 +103,7 @@ LIBSSH_OBJS=${LIBOPENSSH_OBJS} \
ssh-ed25519-sk.o ssh-rsa.o dh.o \
msg.o progressmeter.o dns.o entropy.o gss-genr.o umac.o umac128.o \
ssh-pkcs11.o smult_curve25519_ref.o \
- poly1305.o chacha.o cipher-chachapoly.o \
+ poly1305.o chacha.o cipher-chachapoly.o cipher-chachapoly-libcrypto.o \
ssh-ed25519.o digest-openssl.o digest-libc.o \
hmac.o sc25519.o ge25519.o fe25519.o ed25519.o verify.o hash.o \
kex.o kexdh.o kexgex.o kexecdh.o kexc25519.o \
diff --git a/cipher-chachapoly-libcrypto.c b/cipher-chachapoly-libcrypto.c
new file mode 100644
index 000000000..ad2be45bf
--- /dev/null
+++ b/cipher-chachapoly-libcrypto.c
@@ -0,0 +1,163 @@
+/*
+ * Copyright (c) 2013 Damien Miller <djm@xxxxxxxxxxx>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* $OpenBSD: cipher-chachapoly.c,v 1.8 2016/08/03 05:41:57 djm Exp $ */
+
+#include "includes.h"
+
+#if defined(WITH_OPENSSL) && !defined(INCOMPAT_EVP_CHACHA)
+
+#include <sys/types.h>
+#include <stdarg.h> /* needed for log.h */
+#include <string.h>
+#include <stdio.h> /* needed for misc.h */
+
+#include <openssl/evp.h>
+
+#include "log.h"
+#include "sshbuf.h"
+#include "ssherr.h"
+#include "cipher-chachapoly.h"
+
+struct chachapoly_ctx {
+ EVP_CIPHER_CTX *main_evp, *header_evp;
+};
+
+struct chachapoly_ctx *
+chachapoly_new(const u_char *key, u_int keylen)
+{
+ struct chachapoly_ctx *ctx;
+
+ if (keylen != (32 + 32)) /* 2 x 256 bit keys */
+ return NULL;
+ if ((ctx = calloc(1, sizeof(*ctx))) == NULL)
+ return NULL;
+ if ((ctx->main_evp = EVP_CIPHER_CTX_new()) == NULL ||
+ (ctx->header_evp = EVP_CIPHER_CTX_new()) == NULL)
+ goto fail;
+ if (!EVP_CipherInit(ctx->main_evp, EVP_chacha20(), key, NULL, 1))
+ goto fail;
+ if (!EVP_CipherInit(ctx->header_evp, EVP_chacha20(), key + 32, NULL, 1))
+ goto fail;
+ if (EVP_CIPHER_CTX_iv_length(ctx->header_evp) != 16)
+ goto fail;
+ return ctx;
+ fail:
+ chachapoly_free(ctx);
+ return NULL;
+}
+
+void
+chachapoly_free(struct chachapoly_ctx *cpctx)
+{
+ if (cpctx == NULL)
+ return;
+ EVP_CIPHER_CTX_free(cpctx->main_evp);
+ EVP_CIPHER_CTX_free(cpctx->header_evp);
+ freezero(cpctx, sizeof(*cpctx));
+}
+
+/*
+ * chachapoly_crypt() operates as following:
+ * En/decrypt with header key 'aadlen' bytes from 'src', storing result
+ * to 'dest'. The ciphertext here is treated as additional authenticated
+ * data for MAC calculation.
+ * En/decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'. Use
+ * POLY1305_TAGLEN bytes at offset 'len'+'aadlen' as the authentication
+ * tag. This tag is written on encryption and verified on decryption.
+ */
+int
+chachapoly_crypt(struct chachapoly_ctx *ctx, u_int seqnr, u_char *dest,
+ const u_char *src, u_int len, u_int aadlen, u_int authlen, int do_encrypt)
+{
+ u_char seqbuf[16]; /* layout: u64 counter || u64 seqno */
+ int r = SSH_ERR_INTERNAL_ERROR;
+ u_char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
+
+ /*
+ * Run ChaCha20 once to generate the Poly1305 key. The IV is the
+ * packet sequence number.
+ */
+ memset(seqbuf, 0, sizeof(seqbuf));
+ POKE_U64(seqbuf + 8, seqnr);
+ memset(poly_key, 0, sizeof(poly_key));
+ if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
+ EVP_Cipher(ctx->main_evp, poly_key,
+ poly_key, sizeof(poly_key)) < 0) {
+ r = SSH_ERR_LIBCRYPTO_ERROR;
+ goto out;
+ }
+
+ /* If decrypting, check tag before anything else */
+ if (!do_encrypt) {
+ const u_char *tag = src + aadlen + len;
+
+ poly1305_auth(expected_tag, src, aadlen + len, poly_key);
+ if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
+ r = SSH_ERR_MAC_INVALID;
+ goto out;
+ }
+ }
+
+ /* Crypt additional data */
+ if (aadlen) {
+ if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 1) ||
+ EVP_Cipher(ctx->header_evp, dest, src, aadlen) < 0) {
+ r = SSH_ERR_LIBCRYPTO_ERROR;
+ goto out;
+ }
+ }
+
+ /* Set Chacha's block counter to 1 */
+ seqbuf[0] = 1;
+ if (!EVP_CipherInit(ctx->main_evp, NULL, NULL, seqbuf, 1) ||
+ EVP_Cipher(ctx->main_evp, dest + aadlen, src + aadlen, len) < 0) {
+ r = SSH_ERR_LIBCRYPTO_ERROR;
+ goto out;
+ }
+
+ /* If encrypting, calculate and append tag */
+ if (do_encrypt) {
+ poly1305_auth(dest + aadlen + len, dest, aadlen + len,
+ poly_key);
+ }
+ r = 0;
+ out:
+ explicit_bzero(expected_tag, sizeof(expected_tag));
+ explicit_bzero(seqbuf, sizeof(seqbuf));
+ explicit_bzero(poly_key, sizeof(poly_key));
+ return r;
+}
+
+/* Decrypt and extract the encrypted packet length */
+int
+chachapoly_get_length(struct chachapoly_ctx *ctx,
+ u_int *plenp, u_int seqnr, const u_char *cp, u_int len)
+{
+ u_char buf[4], seqbuf[16];
+
+ if (len < 4)
+ return SSH_ERR_MESSAGE_INCOMPLETE;
+ memset(seqbuf, 0, sizeof(seqbuf));
+ POKE_U64(seqbuf + 8, seqnr);
+ if (!EVP_CipherInit(ctx->header_evp, NULL, NULL, seqbuf, 0))
+ return SSH_ERR_LIBCRYPTO_ERROR;
+ if (EVP_Cipher(ctx->header_evp, buf, (u_char *)cp, sizeof(buf)) < 0)
+ return SSH_ERR_LIBCRYPTO_ERROR;
+ *plenp = PEEK_U32(buf);
+ return 0;
+}
+#endif /* defined(WITH_OPENSSL) && !defined(INCOMPAT_EVP_CHACHA) */
diff --git a/cipher-chachapoly.c b/cipher-chachapoly.c
index a638c3416..af5295524 100644
--- a/cipher-chachapoly.c
+++ b/cipher-chachapoly.c
@@ -18,6 +18,8 @@
#include "includes.h"
+#if !defined(WITH_OPENSSL) || defined(INCOMPAT_EVP_CHACHA)
+
#include <sys/types.h>
#include <stdarg.h> /* needed for log.h */
#include <string.h>
@@ -130,3 +132,4 @@ chachapoly_get_length(struct chachapoly_ctx *ctx,
*plenp = PEEK_U32(buf);
return 0;
}
+#endif /* !defined(WITH_OPENSSL) || defined(INCOMPAT_EVP_CHACHA) */
diff --git a/openbsd-compat/openssl-compat.h b/openbsd-compat/openssl-compat.h
index abdcb8763..98a974763 100644
--- a/openbsd-compat/openssl-compat.h
+++ b/openbsd-compat/openssl-compat.h
@@ -55,6 +55,13 @@ void ssh_libcrypto_init(void);
# define LIBCRYPTO_EVP_INL_TYPE size_t
#endif
+/* LibreSSL < 3.1.0 has an incompatible EVP_chacha20() */
+#ifdef LIBRESSL_VERSION_NUMBER
+# if LIBRESSL_VERSION_NUMBER < 0x3010000fL
+# define INCOMPAT_EVP_CHACHA
+# endif
+#endif
+
#ifndef OPENSSL_RSA_MAX_MODULUS_BITS
# define OPENSSL_RSA_MAX_MODULUS_BITS 16384
#endif
--
2.25.0.341.g760bfbb309-goog
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