static bool
tls_crypt_v2_wrap_client_key(struct buffer *wkc,
const struct key2 *src_key,
const struct buffer *src_metadata,
struct key_ctx *server_key, struct gc_arena *gc)
{
cipher_ctx_t *cipher_ctx = server_key->cipher;
struct buffer work = alloc_buf_gc(TLS_CRYPT_V2_MAX_WKC_LEN
+ cipher_ctx_block_size(cipher_ctx), gc);
/* Calculate auth tag and synthetic IV */
uint8_t *tag = buf_write_alloc(&work, TLS_CRYPT_TAG_SIZE);
if (!tag)
{
msg(M_WARN, "ERROR: could not write tag");
return false;
}
uint16_t net_len = htons(sizeof(src_key->keys) + BLEN(src_metadata)
+ TLS_CRYPT_V2_TAG_SIZE + sizeof(uint16_t));
hmac_ctx_t *hmac_ctx = server_key->hmac;
hmac_ctx_reset(hmac_ctx);
hmac_ctx_update(hmac_ctx, (void *)&net_len, sizeof(net_len));
hmac_ctx_update(hmac_ctx, (void *)src_key->keys, sizeof(src_key->keys));
hmac_ctx_update(hmac_ctx, BPTR(src_metadata), BLEN(src_metadata));
hmac_ctx_final(hmac_ctx, tag);
dmsg(D_CRYPTO_DEBUG, "TLS-CRYPT WRAP TAG: %s",
format_hex(tag, TLS_CRYPT_TAG_SIZE, 0, gc));
/* Use the 128 most significant bits of the tag as IV */
ASSERT(cipher_ctx_reset(cipher_ctx, tag));
/* Overflow check (OpenSSL requires an extra block in the dst buffer) */
if (buf_forward_capacity(&work) < (sizeof(src_key->keys)
+ BLEN(src_metadata)
+ sizeof(net_len)
+ cipher_ctx_block_size(cipher_ctx)))
{
msg(M_WARN, "ERROR: could not crypt: insufficient space in dst");
return false;
}
/* Encrypt */
int outlen = 0;
ASSERT(cipher_ctx_update(cipher_ctx, BEND(&work), &outlen,
(void *)src_key->keys, sizeof(src_key->keys)));
ASSERT(buf_inc_len(&work, outlen));
ASSERT(cipher_ctx_update(cipher_ctx, BEND(&work), &outlen,
BPTR(src_metadata), BLEN(src_metadata)));
ASSERT(buf_inc_len(&work, outlen));
ASSERT(cipher_ctx_final(cipher_ctx, BEND(&work), &outlen));
ASSERT(buf_inc_len(&work, outlen));
ASSERT(buf_write(&work, &net_len, sizeof(net_len)));
return buf_copy(wkc, &work);
}
/*
* force a null termination even it requires
* truncation of the last char.
*/
void
buf_null_terminate (struct buffer *buf)
{
char *last = (char *) BLAST (buf);
if (last && *last == '\0') /* already terminated? */
return;
if (!buf_safe (buf, 1)) /* make space for trailing null */
buf_inc_len (buf, -1);
buf_write_u8 (buf, 0);
}
bool
status_read(struct status_output *so, struct buffer *buf)
{
bool ret = false;
if (so && so->fd >= 0 && (so->flags & STATUS_OUTPUT_READ))
{
ASSERT(buf_defined(&so->read_buf));
ASSERT(buf_defined(buf));
while (true)
{
const int c = buf_read_u8(&so->read_buf);
/* read more of file into buffer */
if (c == -1)
{
int len;
ASSERT(buf_init(&so->read_buf, 0));
len = read(so->fd, BPTR(&so->read_buf), BCAP(&so->read_buf));
if (len <= 0)
{
break;
}
ASSERT(buf_inc_len(&so->read_buf, len));
continue;
}
ret = true;
if (c == '\r')
{
continue;
}
if (c == '\n')
{
break;
}
buf_write_u8(buf, c);
}
buf_null_terminate(buf);
}
return ret;
}
/*
* Remove trailing \r and \n chars and ensure
* null termination.
*/
void
buf_chomp (struct buffer *buf)
{
while (true)
{
char *last = (char *) BLAST (buf);
if (!last)
break;
if (char_class (*last, CC_CRLF|CC_NULL))
{
if (!buf_inc_len (buf, -1))
break;
}
else
break;
}
buf_null_terminate (buf);
}
void
tls_crypt_v2_write_client_key_file(const char *filename,
const char *b64_metadata,
const char *server_key_file,
const char *server_key_inline)
{
struct gc_arena gc = gc_new();
struct key_ctx server_key = { 0 };
struct buffer client_key_pem = { 0 };
struct buffer dst = alloc_buf_gc(TLS_CRYPT_V2_CLIENT_KEY_LEN
+ TLS_CRYPT_V2_MAX_WKC_LEN, &gc);
struct key2 client_key = { 2 };
if (!rand_bytes((void *)client_key.keys, sizeof(client_key.keys)))
{
msg(M_FATAL, "ERROR: could not generate random key");
goto cleanup;
}
ASSERT(buf_write(&dst, client_key.keys, sizeof(client_key.keys)));
struct buffer metadata = alloc_buf_gc(TLS_CRYPT_V2_MAX_METADATA_LEN, &gc);
if (b64_metadata)
{
if (TLS_CRYPT_V2_MAX_B64_METADATA_LEN < strlen(b64_metadata))
{
msg(M_FATAL,
"ERROR: metadata too long (%d bytes, max %u bytes)",
(int)strlen(b64_metadata), TLS_CRYPT_V2_MAX_B64_METADATA_LEN);
}
ASSERT(buf_write(&metadata, &TLS_CRYPT_METADATA_TYPE_USER, 1));
int decoded_len = openvpn_base64_decode(b64_metadata, BPTR(&metadata),
BCAP(&metadata));
if (decoded_len < 0)
{
msg(M_FATAL, "ERROR: failed to base64 decode provided metadata");
goto cleanup;
}
ASSERT(buf_inc_len(&metadata, decoded_len));
}
else
{
int64_t timestamp = htonll((uint64_t)now);
ASSERT(buf_write(&metadata, &TLS_CRYPT_METADATA_TYPE_TIMESTAMP, 1));
ASSERT(buf_write(&metadata, ×tamp, sizeof(timestamp)));
}
tls_crypt_v2_init_server_key(&server_key, true, server_key_file,
server_key_inline);
if (!tls_crypt_v2_wrap_client_key(&dst, &client_key, &metadata, &server_key,
&gc))
{
msg(M_FATAL, "ERROR: could not wrap generated client key");
goto cleanup;
}
/* PEM-encode Kc || WKc */
if (!crypto_pem_encode(tls_crypt_v2_cli_pem_name, &client_key_pem, &dst,
&gc))
{
msg(M_FATAL, "ERROR: could not PEM-encode client key");
goto cleanup;
}
if (!buffer_write_file(filename, &client_key_pem))
{
msg(M_FATAL, "ERROR: could not write client key file");
goto cleanup;
}
/* Sanity check: load client key (as "client") */
struct key_ctx_bi test_client_key;
struct buffer test_wrapped_client_key;
msg(D_GENKEY, "Testing client-side key loading...");
tls_crypt_v2_init_client_key(&test_client_key, &test_wrapped_client_key,
filename, NULL);
free_key_ctx_bi(&test_client_key);
/* Sanity check: unwrap and load client key (as "server") */
struct buffer test_metadata = alloc_buf_gc(TLS_CRYPT_V2_MAX_METADATA_LEN,
&gc);
struct key2 test_client_key2 = { 0 };
free_key_ctx(&server_key);
tls_crypt_v2_init_server_key(&server_key, false, server_key_file,
server_key_inline);
msg(D_GENKEY, "Testing server-side key loading...");
ASSERT(tls_crypt_v2_unwrap_client_key(&test_client_key2, &test_metadata,
test_wrapped_client_key, &server_key));
secure_memzero(&test_client_key2, sizeof(test_client_key2));
free_buf(&test_wrapped_client_key);
cleanup:
secure_memzero(&client_key, sizeof(client_key));
free_key_ctx(&server_key);
buf_clear(&client_key_pem);
buf_clear(&dst);
gc_free(&gc);
}
bool
tls_crypt_v2_extract_client_key(struct buffer *buf,
struct tls_wrap_ctx *ctx,
const struct tls_options *opt)
{
if (!ctx->tls_crypt_v2_server_key.cipher)
{
msg(D_TLS_ERRORS,
"Client wants tls-crypt-v2, but no server key present.");
return false;
}
msg(D_HANDSHAKE, "Control Channel: using tls-crypt-v2 key");
struct buffer wrapped_client_key = *buf;
uint16_t net_len = 0;
if (BLEN(&wrapped_client_key) < sizeof(net_len))
{
msg(D_TLS_ERRORS, "failed to read length");
}
memcpy(&net_len, BEND(&wrapped_client_key) - sizeof(net_len),
sizeof(net_len));
size_t wkc_len = ntohs(net_len);
if (!buf_advance(&wrapped_client_key, BLEN(&wrapped_client_key) - wkc_len))
{
msg(D_TLS_ERRORS, "Can not locate tls-crypt-v2 client key");
return false;
}
struct key2 client_key = { 0 };
ctx->tls_crypt_v2_metadata = alloc_buf(TLS_CRYPT_V2_MAX_METADATA_LEN);
if (!tls_crypt_v2_unwrap_client_key(&client_key,
&ctx->tls_crypt_v2_metadata,
wrapped_client_key,
&ctx->tls_crypt_v2_server_key))
{
msg(D_TLS_ERRORS, "Can not unwrap tls-crypt-v2 client key");
secure_memzero(&client_key, sizeof(client_key));
return false;
}
/* Load the decrypted key */
ctx->mode = TLS_WRAP_CRYPT;
ctx->cleanup_key_ctx = true;
ctx->opt.flags |= CO_PACKET_ID_LONG_FORM;
memset(&ctx->opt.key_ctx_bi, 0, sizeof(ctx->opt.key_ctx_bi));
tls_crypt_v2_load_client_key(&ctx->opt.key_ctx_bi, &client_key, true);
secure_memzero(&client_key, sizeof(client_key));
/* Remove client key from buffer so tls-crypt code can unwrap message */
ASSERT(buf_inc_len(buf, -(BLEN(&wrapped_client_key))));
if (opt && opt->tls_crypt_v2_verify_script)
{
return tls_crypt_v2_verify_metadata(ctx, opt);
}
return true;
}
static bool
tls_crypt_v2_unwrap_client_key(struct key2 *client_key, struct buffer *metadata,
struct buffer wrapped_client_key,
struct key_ctx *server_key)
{
const char *error_prefix = __func__;
bool ret = false;
struct gc_arena gc = gc_new();
/* The crypto API requires one extra cipher block of buffer head room when
* decrypting, which nicely matches the tag size of WKc. So
* TLS_CRYPT_V2_MAX_WKC_LEN is always large enough for the plaintext. */
uint8_t plaintext_buf_data[TLS_CRYPT_V2_MAX_WKC_LEN] = { 0 };
struct buffer plaintext = { 0 };
dmsg(D_TLS_DEBUG_MED, "%s: unwrapping client key (len=%d): %s", __func__,
BLEN(&wrapped_client_key), format_hex(BPTR(&wrapped_client_key),
BLEN(&wrapped_client_key),
0, &gc));
if (TLS_CRYPT_V2_MAX_WKC_LEN < BLEN(&wrapped_client_key))
{
CRYPT_ERROR("wrapped client key too big");
}
/* Decrypt client key and metadata */
uint16_t net_len = 0;
const uint8_t *tag = BPTR(&wrapped_client_key);
if (BLEN(&wrapped_client_key) < sizeof(net_len))
{
CRYPT_ERROR("failed to read length");
}
memcpy(&net_len, BEND(&wrapped_client_key) - sizeof(net_len),
sizeof(net_len));
if (ntohs(net_len) != BLEN(&wrapped_client_key))
{
dmsg(D_TLS_DEBUG_LOW, "%s: net_len=%u, BLEN=%i", __func__,
ntohs(net_len), BLEN(&wrapped_client_key));
CRYPT_ERROR("invalid length");
}
buf_inc_len(&wrapped_client_key, -(int)sizeof(net_len));
if (!buf_advance(&wrapped_client_key, TLS_CRYPT_TAG_SIZE))
{
CRYPT_ERROR("failed to read tag");
}
if (!cipher_ctx_reset(server_key->cipher, tag))
{
CRYPT_ERROR("failed to initialize IV");
}
buf_set_write(&plaintext, plaintext_buf_data, sizeof(plaintext_buf_data));
int outlen = 0;
if (!cipher_ctx_update(server_key->cipher, BPTR(&plaintext), &outlen,
BPTR(&wrapped_client_key),
BLEN(&wrapped_client_key)))
{
CRYPT_ERROR("could not decrypt client key");
}
ASSERT(buf_inc_len(&plaintext, outlen));
if (!cipher_ctx_final(server_key->cipher, BEND(&plaintext), &outlen))
{
CRYPT_ERROR("cipher final failed");
}
ASSERT(buf_inc_len(&plaintext, outlen));
/* Check authentication */
uint8_t tag_check[TLS_CRYPT_TAG_SIZE] = { 0 };
hmac_ctx_reset(server_key->hmac);
hmac_ctx_update(server_key->hmac, (void *)&net_len, sizeof(net_len));
hmac_ctx_update(server_key->hmac, BPTR(&plaintext),
BLEN(&plaintext));
hmac_ctx_final(server_key->hmac, tag_check);
if (memcmp_constant_time(tag, tag_check, sizeof(tag_check)))
{
dmsg(D_CRYPTO_DEBUG, "tag : %s",
format_hex(tag, sizeof(tag_check), 0, &gc));
dmsg(D_CRYPTO_DEBUG, "tag_check: %s",
format_hex(tag_check, sizeof(tag_check), 0, &gc));
CRYPT_ERROR("client key authentication error");
}
if (buf_len(&plaintext) < sizeof(client_key->keys))
{
CRYPT_ERROR("failed to read client key");
}
memcpy(&client_key->keys, BPTR(&plaintext), sizeof(client_key->keys));
ASSERT(buf_advance(&plaintext, sizeof(client_key->keys)));
if (!buf_copy(metadata, &plaintext))
{
CRYPT_ERROR("metadata too large for supplied buffer");
}
ret = true;
error_exit:
if (!ret)
{
secure_memzero(client_key, sizeof(*client_key));
}
buf_clear(&plaintext);
gc_free(&gc);
return ret;
}
bool
tls_crypt_unwrap(const struct buffer *src, struct buffer *dst,
struct crypto_options *opt)
{
static const char error_prefix[] = "tls-crypt unwrap error";
const struct key_ctx *ctx = &opt->key_ctx_bi.decrypt;
struct gc_arena gc;
gc_init(&gc);
ASSERT(opt);
ASSERT(src->len > 0);
ASSERT(ctx->cipher);
ASSERT(packet_id_initialized(&opt->packet_id)
|| (opt->flags & CO_IGNORE_PACKET_ID));
dmsg(D_PACKET_CONTENT, "TLS-CRYPT UNWRAP FROM: %s",
format_hex(BPTR(src), BLEN(src), 80, &gc));
if (buf_len(src) < TLS_CRYPT_OFF_CT)
{
CRYPT_ERROR("packet too short");
}
/* Decrypt cipher text */
{
int outlen = 0;
/* Buffer overflow check (should never fail) */
if (!buf_safe(dst, BLEN(src) - TLS_CRYPT_OFF_CT + TLS_CRYPT_BLOCK_SIZE))
{
CRYPT_ERROR("potential buffer overflow");
}
if (!cipher_ctx_reset(ctx->cipher, BPTR(src) + TLS_CRYPT_OFF_TAG))
{
CRYPT_ERROR("cipher reset failed");
}
if (!cipher_ctx_update(ctx->cipher, BPTR(dst), &outlen,
BPTR(src) + TLS_CRYPT_OFF_CT, BLEN(src) - TLS_CRYPT_OFF_CT))
{
CRYPT_ERROR("cipher update failed");
}
ASSERT(buf_inc_len(dst, outlen));
if (!cipher_ctx_final(ctx->cipher, BPTR(dst), &outlen))
{
CRYPT_ERROR("cipher final failed");
}
ASSERT(buf_inc_len(dst, outlen));
}
/* Check authentication */
{
const uint8_t *tag = BPTR(src) + TLS_CRYPT_OFF_TAG;
uint8_t tag_check[TLS_CRYPT_TAG_SIZE] = { 0 };
dmsg(D_PACKET_CONTENT, "TLS-CRYPT UNWRAP AD: %s",
format_hex(BPTR(src), TLS_CRYPT_OFF_TAG, 0, &gc));
dmsg(D_PACKET_CONTENT, "TLS-CRYPT UNWRAP TO: %s",
format_hex(BPTR(dst), BLEN(dst), 80, &gc));
hmac_ctx_reset(ctx->hmac);
hmac_ctx_update(ctx->hmac, BPTR(src), TLS_CRYPT_OFF_TAG);
hmac_ctx_update(ctx->hmac, BPTR(dst), BLEN(dst));
hmac_ctx_final(ctx->hmac, tag_check);
if (memcmp_constant_time(tag, tag_check, sizeof(tag_check)))
{
dmsg(D_CRYPTO_DEBUG, "tag : %s",
format_hex(tag, sizeof(tag_check), 0, &gc));
dmsg(D_CRYPTO_DEBUG, "tag_check: %s",
format_hex(tag_check, sizeof(tag_check), 0, &gc));
CRYPT_ERROR("packet authentication failed");
}
}
/* Check replay */
if (!(opt->flags & CO_IGNORE_PACKET_ID))
{
struct packet_id_net pin;
struct buffer tmp = *src;
ASSERT(buf_advance(&tmp, TLS_CRYPT_OFF_PID));
ASSERT(packet_id_read(&pin, &tmp, true));
if (!crypto_check_replay(opt, &pin, error_prefix, &gc))
{
CRYPT_ERROR("packet replay");
}
}
gc_free(&gc);
return true;
error_exit:
crypto_clear_error();
dst->len = 0;
gc_free(&gc);
return false;
}
bool
tls_crypt_wrap(const struct buffer *src, struct buffer *dst,
struct crypto_options *opt)
{
const struct key_ctx *ctx = &opt->key_ctx_bi.encrypt;
struct gc_arena gc;
/* IV, packet-ID and implicit IV required for this mode. */
ASSERT(ctx->cipher);
ASSERT(ctx->hmac);
ASSERT(packet_id_initialized(&opt->packet_id));
ASSERT(hmac_ctx_size(ctx->hmac) == 256/8);
gc_init(&gc);
dmsg(D_PACKET_CONTENT, "TLS-CRYPT WRAP FROM: %s",
format_hex(BPTR(src), BLEN(src), 80, &gc));
/* Get packet ID */
if (!packet_id_write(&opt->packet_id.send, dst, true, false))
{
msg(D_CRYPT_ERRORS, "TLS-CRYPT ERROR: packet ID roll over.");
goto err;
}
dmsg(D_PACKET_CONTENT, "TLS-CRYPT WRAP AD: %s",
format_hex(BPTR(dst), BLEN(dst), 0, &gc));
/* Buffer overflow check */
if (!buf_safe(dst, BLEN(src) + TLS_CRYPT_BLOCK_SIZE + TLS_CRYPT_TAG_SIZE))
{
msg(D_CRYPT_ERRORS, "TLS-CRYPT WRAP: buffer size error, "
"sc=%d so=%d sl=%d dc=%d do=%d dl=%d", src->capacity, src->offset,
src->len, dst->capacity, dst->offset, dst->len);
goto err;
}
/* Calculate auth tag and synthetic IV */
{
uint8_t *tag = NULL;
hmac_ctx_reset(ctx->hmac);
hmac_ctx_update(ctx->hmac, BPTR(dst), BLEN(dst));
hmac_ctx_update(ctx->hmac, BPTR(src), BLEN(src));
ASSERT(tag = buf_write_alloc(dst, TLS_CRYPT_TAG_SIZE));
hmac_ctx_final(ctx->hmac, tag);
dmsg(D_PACKET_CONTENT, "TLS-CRYPT WRAP TAG: %s",
format_hex(tag, TLS_CRYPT_TAG_SIZE, 0, &gc));
/* Use the 128 most significant bits of the tag as IV */
ASSERT(cipher_ctx_reset(ctx->cipher, tag));
}
/* Encrypt src */
{
int outlen = 0;
ASSERT(cipher_ctx_update(ctx->cipher, BEND(dst), &outlen,
BPTR(src), BLEN(src)));
ASSERT(buf_inc_len(dst, outlen));
ASSERT(cipher_ctx_final(ctx->cipher, BPTR(dst), &outlen));
ASSERT(buf_inc_len(dst, outlen));
}
dmsg(D_PACKET_CONTENT, "TLS-CRYPT WRAP TO: %s",
format_hex(BPTR(dst), BLEN(dst), 80, &gc));
gc_free(&gc);
return true;
err:
crypto_clear_error();
dst->len = 0;
gc_free(&gc);
return false;
}
void
openvpn_encrypt (struct buffer *buf, struct buffer work,
const struct crypto_options *opt,
const struct frame* frame)
{
struct gc_arena gc;
gc_init (&gc);
if (buf->len > 0 && opt->key_ctx_bi)
{
struct key_ctx *ctx = &opt->key_ctx_bi->encrypt;
/* Do Encrypt from buf -> work */
if (ctx->cipher)
{
uint8_t iv_buf[OPENVPN_MAX_IV_LENGTH];
const int iv_size = cipher_ctx_iv_length (ctx->cipher);
const cipher_kt_t *cipher_kt = cipher_ctx_get_cipher_kt (ctx->cipher);
int outlen;
if (cipher_kt_mode_cbc(cipher_kt))
{
CLEAR (iv_buf);
/* generate pseudo-random IV */
if (opt->flags & CO_USE_IV)
prng_bytes (iv_buf, iv_size);
/* Put packet ID in plaintext buffer or IV, depending on cipher mode */
if (opt->packet_id)
{
struct packet_id_net pin;
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));
}
}
else if (cipher_kt_mode_ofb_cfb(cipher_kt))
{
struct packet_id_net pin;
struct buffer b;
ASSERT (opt->flags & CO_USE_IV); /* IV and packet-ID required */
ASSERT (opt->packet_id); /* for this mode. */
packet_id_alloc_outgoing (&opt->packet_id->send, &pin, true);
memset (iv_buf, 0, iv_size);
buf_set_write (&b, iv_buf, iv_size);
ASSERT (packet_id_write (&pin, &b, true, false));
}
else /* We only support CBC, CFB, or OFB modes right now */
{
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));
dmsg (D_PACKET_CONTENT, "ENCRYPT FROM: %s",
format_hex (BPTR (buf), BLEN (buf), 80, &gc));
/* cipher_ctx was already initialized with key & keylen */
ASSERT (cipher_ctx_reset(ctx->cipher, iv_buf));
/* Buffer overflow check */
if (!buf_safe (&work, buf->len + cipher_ctx_block_size(ctx->cipher)))
{
msg (D_CRYPT_ERRORS, "ENCRYPT: buffer size error, bc=%d bo=%d bl=%d wc=%d wo=%d wl=%d cbs=%d",
buf->capacity,
buf->offset,
buf->len,
work.capacity,
work.offset,
work.len,
cipher_ctx_block_size (ctx->cipher));
goto err;
}
/* Encrypt packet ID, payload */
ASSERT (cipher_ctx_update (ctx->cipher, BPTR (&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 (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 */
{
if (opt->packet_id)
{
struct packet_id_net pin;
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));
}
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);
}
*buf = work;
}
gc_free (&gc);
return;
err:
crypto_clear_error();
buf->len = 0;
gc_free (&gc);
return;
}
/*
* If (opt->flags & CO_USE_IV) is not NULL, we will read an IV from the packet.
*
* Set buf->len to 0 and return false on decrypt error.
*
* On success, buf is set to point to plaintext, true
* is returned.
*/
bool
openvpn_decrypt (struct buffer *buf, struct buffer work,
const struct crypto_options *opt,
const struct frame* frame)
{
static const char error_prefix[] = "Authenticate/Decrypt packet error";
struct gc_arena gc;
gc_init (&gc);
if (buf->len > 0 && opt->key_ctx_bi)
{
struct key_ctx *ctx = &opt->key_ctx_bi->decrypt;
struct packet_id_net pin;
bool have_pin = false;
/* Verify the HMAC */
if (ctx->hmac)
{
int hmac_len;
uint8_t local_hmac[MAX_HMAC_KEY_LENGTH]; /* HMAC of ciphertext computed locally */
hmac_ctx_reset(ctx->hmac);
/* Assume the length of the input HMAC */
hmac_len = hmac_ctx_size (ctx->hmac);
/* Authentication fails if insufficient data in packet for HMAC */
if (buf->len < hmac_len)
CRYPT_ERROR ("missing authentication info");
hmac_ctx_update (ctx->hmac, BPTR (buf) + hmac_len, BLEN (buf) - hmac_len);
hmac_ctx_final (ctx->hmac, local_hmac);
/* Compare locally computed HMAC with packet HMAC */
if (memcmp_constant_time (local_hmac, BPTR (buf), hmac_len))
CRYPT_ERROR ("packet HMAC authentication failed");
ASSERT (buf_advance (buf, hmac_len));
}
/* Decrypt packet ID + payload */
if (ctx->cipher)
{
const int iv_size = cipher_ctx_iv_length (ctx->cipher);
const cipher_kt_t *cipher_kt = cipher_ctx_get_cipher_kt (ctx->cipher);
uint8_t iv_buf[OPENVPN_MAX_IV_LENGTH];
int outlen;
/* initialize work buffer with FRAME_HEADROOM bytes of prepend capacity */
ASSERT (buf_init (&work, FRAME_HEADROOM_ADJ (frame, FRAME_HEADROOM_MARKER_DECRYPT)));
/* use IV if user requested it */
CLEAR (iv_buf);
if (opt->flags & CO_USE_IV)
{
if (buf->len < iv_size)
CRYPT_ERROR ("missing IV info");
memcpy (iv_buf, BPTR (buf), iv_size);
ASSERT (buf_advance (buf, iv_size));
}
/* show the IV's initial state */
if (opt->flags & CO_USE_IV)
dmsg (D_PACKET_CONTENT, "DECRYPT IV: %s", format_hex (iv_buf, iv_size, 0, &gc));
if (buf->len < 1)
CRYPT_ERROR ("missing payload");
/* ctx->cipher was already initialized with key & keylen */
if (!cipher_ctx_reset (ctx->cipher, iv_buf))
CRYPT_ERROR ("cipher init failed");
/* Buffer overflow check (should never happen) */
if (!buf_safe (&work, buf->len + cipher_ctx_block_size(ctx->cipher)))
CRYPT_ERROR ("potential buffer overflow");
/* Decrypt packet ID, payload */
if (!cipher_ctx_update (ctx->cipher, BPTR (&work), &outlen, BPTR (buf), BLEN (buf)))
CRYPT_ERROR ("cipher update failed");
ASSERT (buf_inc_len(&work, outlen));
/* Flush the decryption buffer */
if (!cipher_ctx_final (ctx->cipher, BPTR (&work) + outlen, &outlen))
CRYPT_ERROR ("cipher final failed");
ASSERT (buf_inc_len(&work, outlen));
dmsg (D_PACKET_CONTENT, "DECRYPT TO: %s",
format_hex (BPTR (&work), BLEN (&work), 80, &gc));
/* Get packet ID from plaintext buffer or IV, depending on cipher mode */
{
if (cipher_kt_mode_cbc(cipher_kt))
{
if (opt->packet_id)
{
if (!packet_id_read (&pin, &work, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM)))
CRYPT_ERROR ("error reading CBC packet-id");
have_pin = true;
}
}
else if (cipher_kt_mode_ofb_cfb(cipher_kt))
{
struct buffer b;
ASSERT (opt->flags & CO_USE_IV); /* IV and packet-ID required */
ASSERT (opt->packet_id); /* for this mode. */
buf_set_read (&b, iv_buf, iv_size);
if (!packet_id_read (&pin, &b, true))
CRYPT_ERROR ("error reading CFB/OFB packet-id");
have_pin = true;
}
else /* We only support CBC, CFB, or OFB modes right now */
{
ASSERT (0);
}
}
}
else
{
work = *buf;
if (opt->packet_id)
{
if (!packet_id_read (&pin, &work, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM)))
CRYPT_ERROR ("error reading packet-id");
have_pin = !BOOL_CAST (opt->flags & CO_IGNORE_PACKET_ID);
}
}
if (have_pin)
{
packet_id_reap_test (&opt->packet_id->rec);
if (packet_id_test (&opt->packet_id->rec, &pin))
{
packet_id_add (&opt->packet_id->rec, &pin);
if (opt->pid_persist && (opt->flags & CO_PACKET_ID_LONG_FORM))
packet_id_persist_save_obj (opt->pid_persist, opt->packet_id);
}
else
{
if (!(opt->flags & CO_MUTE_REPLAY_WARNINGS))
msg (D_REPLAY_ERRORS, "%s: bad packet ID (may be a replay): %s -- see the man page entry for --no-replay and --replay-window for more info or silence this warning with --mute-replay-warnings",
error_prefix, packet_id_net_print (&pin, true, &gc));
goto error_exit;
}
}
*buf = work;
}
gc_free (&gc);
return true;
error_exit:
crypto_clear_error();
buf->len = 0;
gc_free (&gc);
return false;
}