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prop224: Implement encoding of superencrypted HS descriptor.

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Also, relaxed the checks of encrypted_data_length_is_valid() since now
only one encrypted section has padding requirements and we don't
actually care to check that all the padding is there.

Consider starting code review from function encode_superencrypted_data().
This commit is contained in:
George Kadianakis
2017-02-08 14:43:43 +02:00
parent bb602f6197
commit b2e37b87a7
2 changed files with 245 additions and 69 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/or/hs_descriptor.c
+242 -53
View File
@@ -554,8 +554,8 @@ compute_padded_plaintext_length(size_t plaintext_len)
tor_assert(plaintext_len <=
(SIZE_T_CEILING - HS_DESC_PLAINTEXT_PADDING_MULTIPLE));
/* Get the extra length we need to add. For example, if srclen is 234 bytes,
* this will expand to (2 * 128) == 256 thus an extra 22 bytes. */
/* Get the extra length we need to add. For example, if srclen is 10200
* bytes, this will expand to (2 * 10k) == 20k thus an extra 9800 bytes. */
plaintext_padded_len = CEIL_DIV(plaintext_len,
HS_DESC_PLAINTEXT_PADDING_MULTIPLE) *
HS_DESC_PLAINTEXT_PADDING_MULTIPLE;
@@ -697,20 +697,89 @@ encrypt_descriptor_data(const hs_descriptor_t *desc, const char *plaintext,
return final_blob_len;
}
/* Take care of encoding the encrypted data section and then encrypting it
* with the descriptor's key. A newly allocated NUL terminated string pointer
* containing the encrypted encoded blob is put in encrypted_blob_out. Return
* 0 on success else a negative value. */
static int
encode_encrypted_data(const hs_descriptor_t *desc,
char **encrypted_blob_out)
/* Create and return a string containing a fake client-auth entry. It's the
* responsibility of the caller to free the returned string. This function will
* never fail. */
static char *
get_fake_auth_client_str(void)
{
int ret = -1;
char *encoded_str, *encrypted_blob;
smartlist_t *lines = smartlist_new();
char *auth_client_str = NULL;
/* We are gonna fill these arrays with fake base64 data. They are all double
* the size of their binary representation to fit the base64 overhead. */
char client_id_b64[8*2];
char iv_b64[16*2];
char encrypted_cookie_b64[16*2];
int retval;
tor_assert(desc);
tor_assert(encrypted_blob_out);
/* This is a macro to fill a field with random data and then base64 it. */
#define FILL_WITH_FAKE_DATA_AND_BASE64(field) STMT_BEGIN \
crypto_rand((char *)field, sizeof(field)); \
retval = base64_encode_nopad(field##_b64, sizeof(field##_b64), \
field, sizeof(field)); \
tor_assert(retval > 0); \
STMT_END
{ /* Get those fakes! */
uint8_t client_id[8]; /* fake client-id */
uint8_t iv[16]; /* fake IV (initialization vector) */
uint8_t encrypted_cookie[16]; /* fake encrypted cookie */
FILL_WITH_FAKE_DATA_AND_BASE64(client_id);
FILL_WITH_FAKE_DATA_AND_BASE64(iv);
FILL_WITH_FAKE_DATA_AND_BASE64(encrypted_cookie);
}
/* Build the final string */
tor_asprintf(&auth_client_str, "%s %s %s %s", str_desc_auth_client,
client_id_b64, iv_b64, encrypted_cookie_b64);
#undef FILL_WITH_FAKE_DATA_AND_BASE64
return auth_client_str;
}
/** How many lines of "client-auth" we want in our descriptors; fake or not. */
#define CLIENT_AUTH_ENTRIES_BLOCK_SIZE 16
/** Create the "client-auth" part of the descriptor and return a
* newly-allocated string with it. It's the responsibility of the caller to
* free the returned string. */
static char *
get_fake_auth_client_lines(void)
{
/* XXX: Client authorization is still not implemented, so all this function
does is make fake clients */
int i = 0;
smartlist_t *auth_client_lines = smartlist_new();
char *auth_client_lines_str = NULL;
/* Make a line for each fake client */
const int num_fake_clients = CLIENT_AUTH_ENTRIES_BLOCK_SIZE;
for (i = 0; i < num_fake_clients; i++) {
char *auth_client_str = get_fake_auth_client_str();
tor_assert(auth_client_str);
smartlist_add(auth_client_lines, auth_client_str);
}
/* Join all lines together to form final string */
auth_client_lines_str = smartlist_join_strings(auth_client_lines,
"\n", 1, NULL);
/* Cleanup the mess */
SMARTLIST_FOREACH(auth_client_lines, char *, a, tor_free(a));
smartlist_free(auth_client_lines);
return auth_client_lines_str;
}
/* Create the inner layer of the descriptor (which includes the intro points,
* etc.). Return a newly-allocated string with the layer plaintext, or NULL if
* an error occured. It's the responsibility of the caller to free the returned
* string. */
static char *
get_inner_encrypted_layer_plaintext(const hs_descriptor_t *desc)
{
char *encoded_str = NULL;
smartlist_t *lines = smartlist_new();
/* Build the start of the section prior to the introduction points. */
{
@@ -751,31 +820,159 @@ encode_encrypted_data(const hs_descriptor_t *desc,
* then encrypt it. */
encoded_str = smartlist_join_strings(lines, "", 0, NULL);
/* Encrypt the section into an encrypted blob that we'll base64 encode
* before returning it. */
{
char *enc_b64;
ssize_t enc_b64_len, ret_len, enc_len;
err:
SMARTLIST_FOREACH(lines, char *, l, tor_free(l));
smartlist_free(lines);
enc_len = encrypt_descriptor_data(desc, encoded_str, &encrypted_blob);
tor_free(encoded_str);
/* Get the encoded size plus a NUL terminating byte. */
enc_b64_len = base64_encode_size(enc_len, BASE64_ENCODE_MULTILINE) + 1;
enc_b64 = tor_malloc_zero(enc_b64_len);
/* Base64 the encrypted blob before returning it. */
ret_len = base64_encode(enc_b64, enc_b64_len, encrypted_blob, enc_len,
BASE64_ENCODE_MULTILINE);
/* Return length doesn't count the NUL byte. */
tor_assert(ret_len == (enc_b64_len - 1));
tor_free(encrypted_blob);
*encrypted_blob_out = enc_b64;
return encoded_str;
}
/* Create the middle layer of the descriptor, which includes the client auth
* data and the encrypted inner layer (provided as a base64 string at
* <b>layer2_b64_ciphertext</b>). Return a newly-allocated string with the
* layer plaintext, or NULL if an error occured. It's the responsibility of the
* caller to free the returned string. */
static char *
get_outer_encrypted_layer_plaintext(const hs_descriptor_t *desc,
const char *layer2_b64_ciphertext)
{
char *layer1_str = NULL;
smartlist_t *lines = smartlist_new();
/* XXX: Disclaimer: This function generates only _fake_ client auth
* data. Real client auth is not yet implemented, but client auth data MUST
* always be present in descriptors. In the future this function will be
* refactored to use real client auth data if they exist (#20700). */
(void) *desc;
/* Specify auth type */
smartlist_add_asprintf(lines, "%s %s\n", str_desc_auth_type, "x25519");
{ /* Create fake ephemeral x25519 key */
char fake_key_base64[CURVE25519_BASE64_PADDED_LEN + 1];
curve25519_keypair_t fake_x25519_keypair;
if (curve25519_keypair_generate(&fake_x25519_keypair, 0) < 0) {
goto done;
}
if (curve25519_public_to_base64(fake_key_base64,
&fake_x25519_keypair.pubkey) < 0) {
goto done;
}
smartlist_add_asprintf(lines, "%s %s\n",
str_desc_auth_key, fake_key_base64);
/* No need to memwipe any of these fake keys. They will go unused. */
}
{ /* Create fake auth-client lines. */
char *auth_client_lines = get_fake_auth_client_lines();
tor_assert(auth_client_lines);
smartlist_add(lines, auth_client_lines);
}
/* create encrypted section */
{
smartlist_add_asprintf(lines,
"%s\n"
"-----BEGIN MESSAGE-----\n"
"%s"
"-----END MESSAGE-----",
str_encrypted, layer2_b64_ciphertext);
}
layer1_str = smartlist_join_strings(lines, "", 0, NULL);
done:
SMARTLIST_FOREACH(lines, char *, a, tor_free(a));
smartlist_free(lines);
return layer1_str;
}
/* Encrypt <b>encoded_str</b> into an encrypted blob and then base64 it before
* returning it. <b>desc</b> is provided to derive the encryption
* keys. <b>is_superencrypted_layer</b> is set if <b>encoded_str</b> is the
* middle (superencrypted) layer of the descriptor. It's the responsibility of
* the caller to free the returned string. */
static char *
encrypt_desc_data_and_base64(const hs_descriptor_t *desc,
const char *encoded_str,
int is_superencrypted_layer)
{
char *enc_b64;
ssize_t enc_b64_len, ret_len, enc_len;
char *encrypted_blob = NULL;
enc_len = encrypt_descriptor_data(desc, encoded_str, &encrypted_blob,
is_superencrypted_layer);
/* Get the encoded size plus a NUL terminating byte. */
enc_b64_len = base64_encode_size(enc_len, BASE64_ENCODE_MULTILINE) + 1;
enc_b64 = tor_malloc_zero(enc_b64_len);
/* Base64 the encrypted blob before returning it. */
ret_len = base64_encode(enc_b64, enc_b64_len, encrypted_blob, enc_len,
BASE64_ENCODE_MULTILINE);
/* Return length doesn't count the NUL byte. */
tor_assert(ret_len == (enc_b64_len - 1));
tor_free(encrypted_blob);
return enc_b64;
}
/* Generate and encode the superencrypted portion of <b>desc</b>. This also
* involves generating the encrypted portion of the descriptor, and performing
* the superencryption. A newly allocated NUL-terminated string pointer
* containing the encrypted encoded blob is put in encrypted_blob_out. Return 0
* on success else a negative value. */
static int
encode_superencrypted_data(const hs_descriptor_t *desc,
char **encrypted_blob_out)
{
int ret = -1;
char *layer2_str = NULL;
char *layer2_b64_ciphertext = NULL;
char *layer1_str = NULL;
char *layer1_b64_ciphertext = NULL;
tor_assert(desc);
tor_assert(encrypted_blob_out);
/* Func logic: We first create the inner layer of the descriptor (layer2).
* We then encrypt it and use it to create the middle layer of the descriptor
* (layer1). Finally we superencrypt the middle layer and return it to our
* caller. */
/* Create inner descriptor layer */
layer2_str = get_inner_encrypted_layer_plaintext(desc);
if (!layer2_str) {
goto err;
}
/* Encrypt and b64 the inner layer */
layer2_b64_ciphertext = encrypt_desc_data_and_base64(desc, layer2_str, 0);
if (!layer2_b64_ciphertext) {
goto err;
}
/* Now create middle descriptor layer given the inner layer */
layer1_str = get_outer_encrypted_layer_plaintext(desc,layer2_b64_ciphertext);
if (!layer1_str) {
goto err;
}
/* Encrypt and base64 the middle layer */
layer1_b64_ciphertext = encrypt_desc_data_and_base64(desc, layer1_str, 1);
if (!layer1_b64_ciphertext) {
goto err;
}
/* Success! */
ret = 0;
err:
SMARTLIST_FOREACH(lines, char *, l, tor_free(l));
smartlist_free(lines);
tor_free(layer1_str);
tor_free(layer2_str);
tor_free(layer2_b64_ciphertext);
*encrypted_blob_out = layer1_b64_ciphertext;
return ret;
}
@@ -828,7 +1025,7 @@ desc_encode_v3(const hs_descriptor_t *desc,
/* Build the superencrypted data section. */
{
char *enc_b64_blob=NULL;
if (encode_encrypted_data(desc, &enc_b64_blob) < 0) {
if (encode_superencrypted_data(desc, &enc_b64_blob) < 0) {
goto err;
}
smartlist_add_asprintf(lines,
@@ -868,6 +1065,13 @@ desc_encode_v3(const hs_descriptor_t *desc,
encoded_str = smartlist_join_strings(lines, "\n", 1, NULL);
*encoded_out = encoded_str;
if (strlen(encoded_str) >= hs_cache_get_max_descriptor_size()) {
log_warn(LD_GENERAL, "We just made an HS descriptor that's too big (%d)."
"Failing.", (int)strlen(encoded_str));
tor_free(encoded_str);
goto err;
}
/* XXX: Trigger a control port event. */
/* Success! */
@@ -1095,30 +1299,15 @@ cert_parse_and_validate(tor_cert_t **cert_out, const char *data,
STATIC int
encrypted_data_length_is_valid(size_t len)
{
/* Check for the minimum length possible. */
if (len < HS_DESC_ENCRYPTED_MIN_LEN) {
/* Make sure there is enough data for the salt and the mac. The equality is
there to ensure that there is at least one byte of encrypted data. */
if (len <= HS_DESC_ENCRYPTED_SALT_LEN + DIGEST256_LEN) {
log_warn(LD_REND, "Length of descriptor's encrypted data is too small. "
"Got %lu but minimum value is %d",
(unsigned long)len, HS_DESC_ENCRYPTED_MIN_LEN);
(unsigned long)len, HS_DESC_ENCRYPTED_SALT_LEN + DIGEST256_LEN);
goto err;
}
/* Encrypted data has the salt and MAC concatenated to it so remove those
* from the validation calculation. */
len -= HS_DESC_ENCRYPTED_SALT_LEN + DIGEST256_LEN;
/* Check that it's aligned on the block size of the crypto algorithm. */
if (len % HS_DESC_PLAINTEXT_PADDING_MULTIPLE) {
log_warn(LD_REND, "Length of descriptor's encrypted data is invalid. "
"Got %lu which is not a multiple of %d.",
(unsigned long) len, HS_DESC_PLAINTEXT_PADDING_MULTIPLE);
goto err;
}
/* XXX: Check maximum size. Will strongly depends on the maximum intro point
* allowed we decide on and probably if they will all have to use the legacy
* key which is bigger than the ed25519 key. */
return 1;
err:
return 0;
src/or/hs_descriptor.h
+3 -16
View File
@@ -41,24 +41,11 @@
* the secret IV and MAC key length which is the length of H() output. */
#define HS_DESC_ENCRYPTED_KDF_OUTPUT_LEN \
CIPHER256_KEY_LEN + CIPHER_IV_LEN + DIGEST256_LEN
/* We need to pad the plaintext version of the encrypted data section before
* encryption and it has to be a multiple of this value. */
#define HS_DESC_PLAINTEXT_PADDING_MULTIPLE 128
/* XXX: Let's make sure this makes sense as an upper limit for the padded
* plaintext section. Then we should enforce it as now only an assert will be
* triggered if we are above it. */
/* Once padded, this is the maximum length in bytes for the plaintext. */
#define HS_DESC_PADDED_PLAINTEXT_MAX_LEN 8192
/* Minimum length in bytes of the encrypted portion of the descriptor. */
#define HS_DESC_ENCRYPTED_MIN_LEN \
HS_DESC_ENCRYPTED_SALT_LEN + \
HS_DESC_PLAINTEXT_PADDING_MULTIPLE + DIGEST256_LEN
/* Pad plaintext of superencrypted data section before encryption so that its
* length is a multiple of this value. */
#define HS_DESC_SUPERENC_PLAINTEXT_PAD_MULTIPLE 10000
/* Maximum length in bytes of a full hidden service descriptor. */
#define HS_DESC_MAX_LEN 50000 /* 50kb max size */
/* The minimum amount of fields a descriptor should contain. The parsing of
* the fields are version specific so the only required field, as a generic
* view of a descriptor, is 1 that is the version field. */
#define HS_DESC_PLAINTEXT_MIN_FIELDS 1
/* Key length for the descriptor symmetric encryption. As specified in the
* protocol, we use AES-256 for the encrypted section of the descriptor. The