doc: fix flaw in escape transactions.

As reported by mmeijeri on r/Bitcoin: https://www.reddit.com/r/Bitcoin/comments/3dlxw4/reaching_the_ground_with_lightning_lightning/ct80xpp As the signature doesn't cover the input itself, you could replace the secret key from the escape transaction with 0, and it will use the "A and B" branch of the output. (This also fixes a bug in the anchor output where the OP_IF consumed the secret). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
10 years ago · 73ba5acca9
6 changed files with 295 additions and 253 deletions
--- a/doc/deployable-lightning.lyx
+++ b/doc/deployable-lightning.lyx
@ -907,6 +907,9 @@ reference "fig:Secret-Revelation-by"
 \end_inset

 .
+ Note that this requires the other party to provide an alternate key (denoted
+ here using A' and B'), otherwise there is no way to force the escape transactio
+n to provide the secret.
 \end_layout

 \begin_layout Standard
@ -1169,6 +1172,22 @@ By using a dual anchor and escape transactions, channel establishment can
 Acknowlegments
 \end_layout

+\begin_layout Standard
+Thanks to mmeijeri on Reddit's r/Bitcoin for pointing out a flaw in escape
+ transactions reusing the same A and B keys as the commitment transaction
+\begin_inset Foot
+status collapsed
+
+\begin_layout Plain Layout
+https://www.reddit.com/r/Bitcoin/comments/3dlxw4/reaching_the_ground_with_lightnin
+g_lightning/ct80xpp
+\end_layout
+
+\end_inset
+
+.
+\end_layout
+
 \begin_layout Standard
 Thanks to Joseph Poon for designing the escape/fast-escape dual-anchor method,
 as well as finding a flaw in my original formulation of the dual anchor
@ -1233,11 +1252,6 @@ Anchor Output Redeemscript
 The anchor output is a pay to script hash, with a redeemscript as follows:
 \end_layout

-\begin_layout Description
-OP_IF They put a non-zero here if they're supplying the secret
-\end_layout
-
-\begin_deeper
 \begin_layout Description
 OP_HASH
 \begin_inset space ~
@ -1247,24 +1261,43 @@ OP_HASH
 \begin_inset space ~
 \end_inset

-OP_EQUALVERIFY Check secret is correct.
+OP_EQUAL If the secret is supplied,
 \end_layout

-\end_deeper
 \begin_layout Description
-OP_ENDIF
+OP_IF
 \end_layout

+\begin_deeper
 \begin_layout Description
 2
 \begin_inset space ~
 \end_inset

-<KEY-A>
+<KEY-B'> Should be signed by B's escape key.
+\end_layout
+
+\end_deeper
+\begin_layout Description
+OP_ELSE
+\end_layout
+
+\begin_deeper
+\begin_layout Description
+2
 \begin_inset space ~
 \end_inset

-<KEY-B>
+<KEY-B> Should be signed by B's commitment key.
+\end_layout
+
+\end_deeper
+\begin_layout Description
+OP_ENDIF
+\end_layout
+
+\begin_layout Description
+<KEY-A>
 \begin_inset space ~
 \end_inset

@ -1293,7 +1326,7 @@ Escape Input Script
 \begin_inset space ~
 \end_inset

-<SIG-B>
+<SIG-B'>
 \begin_inset space ~
 \end_inset

@ -1423,7 +1456,7 @@ This is identical to the normal escape input script.
 \begin_inset space ~
 \end_inset

-<SIG-B>
+<SIG-B'>
 \begin_inset space ~
 \end_inset

--- a/doc/deployable-lightning.pdf
+++ b/doc/deployable-lightning.pdf
--- a/doc/dual-anchor-diag4.eps
+++ b/doc/dual-anchor-diag4.eps
@ -1,10 +1,10 @@
 %!PS-Adobe-3.0 EPSF-3.0
 %%Creator: cairo 1.14.2 (http://cairographics.org)
-%%CreationDate: Tue Jul 14 15:49:50 2015
+%%CreationDate: Sun Jul 19 13:19:35 2015
 %%Pages: 1
 %%DocumentData: Clean7Bit
 %%LanguageLevel: 2
-%%BoundingBox: 12 -1 552 434
+%%BoundingBox: 12 -1 555 434
 %%EndComments
 %%BeginProlog
 save
@ -71,6 +71,7 @@ save
 0 1 255 { Encoding exch /.notdef put } for
 Encoding 32 /space put
 Encoding 38 /ampersand put
+Encoding 39 /quotesingle put
 Encoding 45 /hyphen put
 Encoding 65 /A put
 Encoding 66 /B put
@ -99,7 +100,7 @@ Encoding 114 /r put
 Encoding 115 /s put
 Encoding 116 /t put
 Encoding 120 /x put
-/CharStrings 31 dict dup begin
+/CharStrings 32 dict dup begin
 /.notdef 0 def
 /A 1 def
 /n 2 def
@ -124,19 +125,20 @@ Encoding 120 /x put
 /I 21 def
 /G 22 def
 /ampersand 23 def
-/R 24 def
-/hyphen 25 def
-/O 26 def
-/P 27 def
-/underscore 28 def
-/V 29 def
-/M 30 def
+/quotesingle 24 def
+/R 25 def
+/hyphen 26 def
+/O 27 def
+/P 28 def
+/underscore 29 def
+/V 30 def
+/M 31 def
 end readonly def
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