script system introduction

rfc/0005 Duniter Protocol Rework.md

@@ -289,9 +289,8 @@ A **transaction document** describes the consumption of **sources** and the crea
 of UDs to spend. Each source or UD can be spent only once, and the
 **sum of *inputs* values must equal the sum of *output* values**.
 
-Each *output* describes spending conditions using a **script**. This *script* is defined as
-an **Abstract Syntaxic Tree** of operations which returns a boolean : can this output be used
-as an input of a new transaction. This format will be describe further in this document.
+Each *output* describes spending conditions using a **script** system which will be
+described below.
 
 | Size | Data |
 |:----:|:-----|
@@ -305,12 +304,30 @@ as an input of a new transaction. This format will be describe further in this d
 | | **For each unspent input** : |
 | *32 bytes* | Source transaction document hash |
 | *1 byte* | Source output index |
-| ... | *Unlock conditions* |
+| ... | *Unlock parameters (with alignement padding)* |
 | | **For each output** : |
 | *4 bytes* | Unsigned currency value |
 | *1 byte* | Unsigned value power base |
-| ... | *Lock script* |
+| ... | *Lock script (with alignement padding)* |
 
-### 8.X Script system
+### 8.2 Script system
+
+> This system is heavily inspired by Bitcoin script system discribed
+> [here](https://en.bitcoin.it/wiki/Script). It adds to it transaction data reflection
+> such as outputs, amounts, merkelized scripts and multiple cryptographic systems
+> support.
+
+The script system is simple, stack-based and processed from left to right. It is intentionnaly
+not Turing-complete, with no loops.
+
+A transaction is valid if nothing in the combined script triggers a failure and the top
+stack item is `true` (non-zero) when the script exits.
+
+That stacks hold byte vectors. When used as numbers, byte vectors are interpreted as
+big-endian variable-length integers with two's complement fir sign handling. 0 can also be
+represented by a null-length vector. Byte vectors are interpreted as booleans where `false`
+is represented by 0 and `true` by any other value.
+
+#### Opcodes
 
 TODO
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