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Fix replay attack from reordering ext IDs

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AdamSLevy committed Nov 24, 2018
1 parent 759c81e commit b62ef5ef2f7c422e3e820707a76e80124e05b759
Showing with 8 additions and 3 deletions.
  1. +8 −3 fatips/0.md
@@ -342,9 +342,14 @@ attacks.
- T.2.1: The entry hash of the transaction entry must be unique among all
transactions belonging to this token.
- T.3.1: If `i` is odd then the `i`th External ID must be the raw data of a
valid signature of the raw bytes of the chain id bytes prepended to the raw
bytes of the content of the entry, verified against the public key stored in
the last 32 bytes of the RCD in the `i-1`th External ID.
valid signature verified against the public key stored in the last 32 bytes
of the RCD in the `i-1`th External ID. The signed message shall be the
following three things concatenated in order:
1. The shortest (no leading "0") decimal string representation of int(i/2)
2. The raw bytes of the chain id
3. The raw bytes of the content of the entry
The first prevents replay attacks from reordering External IDs, and the second
prevents replay attacks across FAT token chains.

##### N.x Requirements for normal account-to-account transactions

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