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BOLT 04: increase max size of onion payload messages (#227)

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* BOLT 04: increase max size of onion payload messages

This commit increases the max size of the encapsulated onion error
messages. This is a follow up change to the recent change that added a
`chain_hash` field to the `channel_update` message. With the addition of
this field, the largest payload encoded within the onion errors has
expanded to 138 bytes:

  * msat_amount || 2_byte_len || channel_update.

As a result, the old fixed limit (including padding) is now
insufficient. We use 256 bytes here in order to give us room for future
message expansions.
This commit is contained in:
Olaoluwa Osuntokun 2017-08-21 17:07:02 -07:00 committed by Rusty Russell
parent eb30bedbb9
commit 876b93151f
1 changed files with 2 additions and 2 deletions
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04-onion-routing.md
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@ -426,8 +426,8 @@ The node returning the message builds a return packet consisting of the followin
Where `hmac` is an HMAC authenticating the remainder of the packet, with a key using the above key generation with key type "_um_", `failuremsg` is defined below, and `pad` as extra bytes to conceal length. Where `hmac` is an HMAC authenticating the remainder of the packet, with a key using the above key generation with key type "_um_", `failuremsg` is defined below, and `pad` as extra bytes to conceal length.
The node SHOULD set `pad` such that the `failure_len` plus `pad_len` is equal to 128. The node SHOULD set `pad` such that the `failure_len` plus `pad_len` is equal to 256.
This is 28 bytes longer than then the longest currently-defined message. This is 118 bytes longer than then the longest currently-defined message.
The node then generates a new key, using the key type `ammag`. The node then generates a new key, using the key type `ammag`.
This key is then used to generate a pseudo-random stream, which is then applied to the packet using `XOR`. This key is then used to generate a pseudo-random stream, which is then applied to the packet using `XOR`.