upstream: chacha20-poly1305 AEAD using libcrypto EVP_chacha20

Based on patch from Yuriy M. Kaminskiy. ok + lots of assistance along the
way at a2k20 tb@

OpenBSD-Commit-ID: 5e08754c13d31258bae6c5e318cc96219d6b10f0

1 files changed, 160 insertions, 0 deletions

diff --git a/cipher-chachapoly-libcrypto.c b/cipher-chachapoly-libcrypto.c
new file mode 100644
index 000000000..960ac14cf
--- /dev/null
+++ b/cipher-chachapoly-libcrypto.c
@@ -0,0 +1,160 @@
+/*
+ * Copyright (c) 2013 Damien Miller <djm@mindrot.org>
+ *
+ * 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-libcrypto.c,v 1.1 2020/04/03 04:32:21 djm Exp $ */
+
+#include "includes.h"
+
+#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;
+}