Preparation for AEAD cipher modes, which also have to authenticate the
opcode and peer-id of packets. To supply that information to
openvpn_encrypt(), I want to simply write those to the work buffer
before calling openvpn_encrypt(). That however requires that
openvpn_encrypt() never prepends something to the work buffer.
Signed-off-by: Steffan Karger <stef...@karger.me>
---
src/openvpn/crypto.c | 55 ++++++++++++++++++++++++++++++----------------------
1 file changed, 32 insertions(+), 23 deletions(-)
diff --git a/src/openvpn/crypto.c b/src/openvpn/crypto.c
index db52182..e92125e 100644
--- a/src/openvpn/crypto.c
+++ b/src/openvpn/crypto.c
@@ -93,6 +93,8 @@ openvpn_encrypt (struct buffer *buf, struct buffer work,
if (buf->len > 0 && opt)
{
const struct key_ctx *ctx = &opt->key_ctx_bi.encrypt;
+ uint8_t *mac_out = NULL;
+ const uint8_t *hmac_start = NULL;
/* Do Encrypt from buf -> work */
if (ctx->cipher)
@@ -102,6 +104,17 @@ openvpn_encrypt (struct buffer *buf, struct buffer work,
const cipher_kt_t *cipher_kt = cipher_ctx_get_cipher_kt (ctx->cipher);
int outlen;
+ /* initialize work buffer with FRAME_HEADROOM bytes of prepend
capacity */
+ ASSERT (buf_init (&work, FRAME_HEADROOM (frame)));
+
+ /* Reserve space for HMAC */
+ if (ctx->hmac)
+ {
+ mac_out = buf_write_alloc (&work, hmac_ctx_size(ctx->hmac));
+ ASSERT (mac_out);
+ hmac_start = BEND(&work);
+ }
+
if (cipher_kt_mode_cbc(cipher_kt))
{
CLEAR (iv_buf);
@@ -137,12 +150,12 @@ openvpn_encrypt (struct buffer *buf, struct buffer work,
ASSERT (0);
}
- /* initialize work buffer with FRAME_HEADROOM bytes of prepend
capacity */
- ASSERT (buf_init (&work, FRAME_HEADROOM (frame)));
-
/* set the IV pseudo-randomly */
if (opt->flags & CO_USE_IV)
- dmsg (D_PACKET_CONTENT, "ENCRYPT IV: %s", format_hex (iv_buf,
iv_size, 0, &gc));
+ {
+ ASSERT (buf_write(&work, iv_buf, iv_size));
+ dmsg (D_PACKET_CONTENT, "ENCRYPT IV: %s", format_hex (iv_buf,
iv_size, 0, &gc));
+ }
dmsg (D_PACKET_CONTENT, "ENCRYPT FROM: %s",
format_hex (BPTR (buf), BLEN (buf), 80, &gc));
@@ -165,27 +178,16 @@ openvpn_encrypt (struct buffer *buf, struct buffer work,
}
/* Encrypt packet ID, payload */
- ASSERT (cipher_ctx_update (ctx->cipher, BPTR (&work), &outlen, BPTR
(buf), BLEN (buf)));
+ ASSERT (cipher_ctx_update (ctx->cipher, BEND (&work), &outlen, BPTR
(buf), BLEN (buf)));
ASSERT (buf_inc_len(&work, outlen));
/* Flush the encryption buffer */
- ASSERT (cipher_ctx_final(ctx->cipher, BPTR (&work) + outlen,
&outlen));
+ ASSERT (cipher_ctx_final(ctx->cipher, BEND (&work), &outlen));
ASSERT (buf_inc_len(&work, outlen));
/* For all CBC mode ciphers, check the last block is complete */
ASSERT (cipher_kt_mode (cipher_kt) != OPENVPN_MODE_CBC ||
outlen == iv_size);
-
- /* prepend the IV to the ciphertext */
- if (opt->flags & CO_USE_IV)
- {
- uint8_t *output = buf_prepend (&work, iv_size);
- ASSERT (output);
- memcpy (output, iv_buf, iv_size);
- }
-
- dmsg (D_PACKET_CONTENT, "ENCRYPT TO: %s",
- format_hex (BPTR (&work), BLEN (&work), 80, &gc));
}
else /* No Encryption */
{
@@ -195,22 +197,29 @@ openvpn_encrypt (struct buffer *buf, struct buffer work,
packet_id_alloc_outgoing (&opt->packet_id.send, &pin, BOOL_CAST
(opt->flags & CO_PACKET_ID_LONG_FORM));
ASSERT (packet_id_write (&pin, buf, BOOL_CAST (opt->flags &
CO_PACKET_ID_LONG_FORM), true));
}
+ if (ctx->hmac)
+ {
+ hmac_start = BPTR(buf);
+ ASSERT (mac_out = buf_prepend (buf, hmac_ctx_size(ctx->hmac)));
+ }
+ buf_write_prepend(buf, BPTR(&work), BLEN(&work));
work = *buf;
}
/* HMAC the ciphertext (or plaintext if !cipher) */
if (ctx->hmac)
{
- uint8_t *output = NULL;
-
hmac_ctx_reset (ctx->hmac);
- hmac_ctx_update (ctx->hmac, BPTR(&work), BLEN(&work));
- output = buf_prepend (&work, hmac_ctx_size(ctx->hmac));
- ASSERT (output);
- hmac_ctx_final (ctx->hmac, output);
+ hmac_ctx_update (ctx->hmac, hmac_start, BEND(&work) - hmac_start);
+ hmac_ctx_final (ctx->hmac, mac_out);
+ dmsg (D_PACKET_CONTENT, "ENCRYPT HMAC: %s",
+ format_hex (mac_out, hmac_ctx_size(ctx->hmac), 80, &gc));
}
*buf = work;
+
+ dmsg (D_PACKET_CONTENT, "ENCRYPT TO: %s",
+ format_hex (BPTR (&work), BLEN (&work), 80, &gc));
}
gc_free (&gc);
--
2.5.0
