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script: add check for 32-byte preimage.

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We need to enforce this onchain as we do in the protocol off-chain,
otherwise we can have an onchain redemption we can't redeem upstream
via the protocol.  While Laolu points out there's a 520 byte limit on
witness stack element, that can still make for a larger tx and make
problems for the steal tx case.

The downside is that even the timeout transaction, which used to spend
the HTLC with an empty 'secret', now needs a 32-byte secret, making it
a little larger.  We create a 'bitcoin_witness_htlc' helper for this
case.

See: http://lists.linuxfoundation.org/pipermail/lightning-dev/2016-May/000529.html

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2016-05-03 11:24:56 +09:30
parent 02593059cd
commit 1245ffaae3
2 changed files with 31 additions and 0 deletions
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25
bitcoin/script.c
View File

@@ -300,6 +300,11 @@ u8 *bitcoin_redeem_htlc_send(const tal_t *ctx,
u8 *script = tal_arr(ctx, u8, 0);
struct ripemd160 ripemd;
/* Must be 32 bytes long. */
add_op(&script, OP_SIZE);
add_number(&script, 32);
add_op(&script, OP_EQUALVERIFY);
add_op(&script, OP_HASH160);
add_op(&script, OP_DUP);
/* Did they supply HTLC R value? */
@@ -348,6 +353,10 @@ u8 *bitcoin_redeem_htlc_recv(const tal_t *ctx,
u8 *script = tal_arr(ctx, u8, 0);
struct ripemd160 ripemd;
add_op(&script, OP_SIZE);
add_number(&script, 32);
add_op(&script, OP_EQUALVERIFY);
add_op(&script, OP_HASH160);
add_op(&script, OP_DUP);
@@ -477,6 +486,22 @@ u8 **bitcoin_witness_secret(const tal_t *ctx,
return witness;
}
u8 **bitcoin_witness_htlc(const tal_t *ctx,
const struct sha256 *htlc_or_revocation_preimage,
const struct bitcoin_signature *sig,
const u8 *witnessscript)
{
static const struct sha256 no_preimage;
/* Use 32 zeroes if no preimage. */
if (!htlc_or_revocation_preimage)
htlc_or_revocation_preimage = &no_preimage;
return bitcoin_witness_secret(ctx, htlc_or_revocation_preimage,
sizeof(*htlc_or_revocation_preimage), sig,
witnessscript);
}
bool scripteq(const u8 *s1, size_t s1len, const u8 *s2, size_t s2len)
{
memcheck(s1, s1len);

6
bitcoin/script.h
View File

@@ -87,6 +87,12 @@ u8 **bitcoin_witness_secret(const tal_t *ctx,
const struct bitcoin_signature *sig,
const u8 *witnessscript);
/* Create a witness which spends bitcoin_redeeem_htlc_recv/send */
u8 **bitcoin_witness_htlc(const tal_t *ctx,
const struct sha256 *htlc_or_revocation_preimage,
const struct bitcoin_signature *sig,
const u8 *witnessscript);
/* Is this a pay to script hash? */
bool is_p2sh(const u8 *script, size_t script_len);