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sphinx: Simplify the filler generation code

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Just some reorganizations and clarifications before we add the multi-frame
support.

Signed-off-by: Christian Decker <decker.christian@gmail.com>
This commit is contained in:
Christian Decker
2019-02-18 13:22:07 +01:00
committed by Rusty Russell
parent 6831db62f7
commit 75c0160c08
1 changed files with 31 additions and 17 deletions
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48
common/sphinx.c
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@@ -22,6 +22,8 @@
#define NUM_STREAM_BYTES (2*ROUTING_INFO_SIZE)
#define ONION_REPLY_SIZE 256
#define RHO_KEYTYPE "rho"
struct hop_params {
u8 secret[SHARED_SECRET_SIZE];
u8 blind[BLINDING_FACTOR_SIZE];
@@ -268,27 +270,40 @@ static bool generate_key(void *k, const char *t, u8 tlen, const u8 *s)
return compute_hmac(k, s, KEY_LEN, t, tlen);
}
static bool generate_header_padding(
void *dst, size_t dstlen,
const size_t hopsize,
const char *keytype,
size_t keytypelen,
const u8 numhops,
struct hop_params *params
)
static bool generate_header_padding(void *dst, size_t dstlen,
const struct sphinx_path *path,
struct hop_params *params)
{
int i;
u8 cipher_stream[(NUM_MAX_FRAMES + 1) * FRAME_SIZE];
u8 stream[2 * ROUTING_INFO_SIZE];
u8 key[KEY_LEN];
size_t fillerStart, fillerEnd, fillerSize;
memset(dst, 0, dstlen);
for (i = 1; i < numhops; i++) {
if (!generate_key(&key, keytype, keytypelen, params[i - 1].secret))
for (int i = 0; i < tal_count(path->hops) - 1; i++) {
if (!generate_key(&key, RHO_KEYTYPE, strlen(RHO_KEYTYPE),
params[i].secret))
return false;
generate_cipher_stream(cipher_stream, key, sizeof(cipher_stream));
int pos = ((NUM_MAX_FRAMES - i) + 1) * hopsize;
xorbytes(dst, dst, cipher_stream + pos, sizeof(cipher_stream) - pos);
generate_cipher_stream(stream, key, sizeof(stream));
/* Sum up how many bytes have been used by previous hops,
* that gives us the start in the stream */
fillerSize = 0;
for (int j = 0; j < i; j++)
fillerSize += FRAME_SIZE; /* Currently constant, will change
with multi-frame hops */
fillerStart = ROUTING_INFO_SIZE - fillerSize;
/* The filler will dangle off of the end by the current
* hop-size, we'll make sure to copy it into the correct
* position in the next step. */
/* TODO: This'll change with multi-frame hops */
fillerEnd = ROUTING_INFO_SIZE + FRAME_SIZE;
/* Apply the cipher-stream to the part of the filler that'll
* be added by this hop */
xorbytes(dst, dst, stream + fillerStart,
fillerEnd - fillerStart);
}
return true;
}
@@ -463,8 +478,7 @@ struct onionpacket *create_onionpacket(
memset(nexthmac, 0, HMAC_SIZE);
memset(packet->routinginfo, 0, ROUTING_INFO_SIZE);
generate_header_padding(filler, sizeof(filler), FRAME_SIZE,
"rho", 3, num_hops, params);
generate_header_padding(filler, sizeof(filler), sp, params);
for (i = num_hops - 1; i >= 0; i--) {
memcpy(sp->hops[i].hmac, nexthmac, HMAC_SIZE);