[RFC17] reworf presentation and add example values

rfc/0017_transaction_comment_encryption.md

@@ -37,14 +37,15 @@ The symmetric encryption key `k` is obtained as follows:
 
 With following parameters for scrypt:
 
-```txt
-password = R
-Salt = s
-N = 1024
-r = 8
-p = 1
-dkLen = message length
-```
+| Parameter | Value |
+|:-----------:|:-------:|
+|**password** | R |
+|**Salt** | s |
+|**N** | 1024 |
+|**r** | 8 |
+|**p** | 1 |
+|**dkLen** | message length |
+
 
 ## Encrypt with XOR cipher
 
@@ -52,9 +53,21 @@ Encrypt bit per bit with XOR cipher.
 
 ## Serialize encrypted message with meta data
 
-| Magic value | Version | Message type | Nonce    | Real message length | Encrypted UTF8 message | Random extra bytes |
-|:-----------:|:-------:|:------------:|:--------:|:-------------------:|:----------------------:|:------------------:|
-| `0x27b6`    | `0x01`  | 1 byte       | 16 bytes | 1 byte (encrypted)  | Any bytes              | Any bytes          |
+| Metadata | Encrypted Data |
+| ------   | -------------- |
+| 20 bytes | max. 171 bytes |
+
+### Metadata
+
+| Magic value | Version | Message type | Nonce    |
+|:-----------:|:-------:|:------------:|:--------:|
+| `0x27b6`    | `0x01`  | 1 byte       | 16 bytes |
+
+### Encrypted Data
+
+| Real message length | UTF8 message | Random extra bytes |
+|:-------------------:|:------------:|:------------------:|
+| 1 byte              | Any byte     | Any bytes          |
 
 The message must be encoded in UTF8.
 
@@ -75,6 +88,10 @@ Future versions of the present format must increment this byte.
 | 0x00 | For a human     |
 | 0x01 | For a machine   |
 
+### Nonce
+
+An sequence of 16 random bytes to use as scrypt salt
+
 ### Real message length
 
 Indicates the real size of the message in bytes. That is, the number of bytes that should be interpreted as an UTF8 string. There may be extra bytes, the extra bytes should be ignored (see section "Random extra bytes").
@@ -100,7 +117,7 @@ There are at least 21 bytes of metadata, so the maximum size of a message is **1
 Let `m` the user message bytes encoded in UTF8.
 Let `t` the message type.
 
-1. Generate 16 random bytes a stores them in a byte array `nonce`.
+1. Generate 16 random bytes and stores them in a byte array `nonce`.
 1. Compute `l = m.lenght`
 1. Generate a random integer `x` between `0` and `170 - l`
 1. Generate `x` random bytes and add them at end of `m`.
@@ -124,7 +141,7 @@ Let `t` the message type.
 
 Let `source` a base64 string read from comment field of a transaction document.
 
-1. compute `b = base64.decode(source)`
+1. Compute `b = base64.decode(source)`
 1. Ensure that `b.length >= 3`
 1. Ensure that `b[0] = 0x27` and `b[1] = 0xb6` (magic value check)
 1. Ensure that `b[2] = 0x01` (version check)
@@ -133,14 +150,29 @@ Let `source` a base64 string read from comment field of a transaction document.
 1. compute `Sr'` and `Pi'`.
 1. Compute `R = crypto_box_beforenm(Sr', Pi')`
 1. compute `L = b.length - 20`
-1. Let `nonce` a bytes array from  `b[4]` to `b[19]`
+1. Read `nonce`: the bytes array from `b[4]` to `b[19]`
 1. Generate symmetric encryption key `k = scrypt(R, salt: nonce, N: 1024, r: 8, p: 1, dkLen: L)`
-1. Let `encryptedMessage` a bytes array from  `b[20]` to `b[b.length -1]`
-1. compute `m = encryptedMessage ^ k`
+1. Read `encryptedMessage`: the bytes array from `b[20]` to `b[b.length -1]`
+1. Compute `m = encryptedMessage ^ k`
 1. Read `l = m[0]`
 1. Ensure that `m.length > l`
 1. Interpret bytes `m[1]` to `m[l]` as an UTF8 string
 
+## Example
+
+| Parameter | Value |
+| --------- | ----- |
+|Sender Public Key| EVfy1VoZwbuN7L69kYiHxeosJLh5azkHV8G6TaSLy94r |
+|Sender Seed |0x0c6a15d0004d24a40f6503300d4971032fb057ff7dc229d651683b413c96a216 |
+|Receiver Public Key| 8txjWNFZhMJbKPijvnFybeksN1QpKaKJrM4jW8HhnFsX |
+|Receiver Seed| 0x214955b558c7793268589e557eda2ab69b5293b73d3907f82c82e12d69c47221 |
+|Comment| My taylor is rich ? Isn't it ? Un été 42...|
+|Nonce| 0x16740285721adeb10da04106c9eb9e34 |
+|Extra Bytes| 0x17968f2f344679fe23ef483a53adcaa18ecd753036dd2cdab1 |
+|Scrypt Password| 0xe63c31edb6e9e4fa04142cd73f30423aa7fb09e404fb60f154dcc913a7e3657c|
+|XOR Key| 0x691114edf5f3da4f4c04b77842da44a4fa97cd59fee742c98244441897e91532de8bcf883d279d4cf4ab3715014cf417a309c979ee4058613668698e1f0df8edf4ac556868e64f|
+|Encrypted comment| J7YBABZ0AoVyGt6xDaBBBsnrnjREXG3NgZKjIyN2lxEx+jbNmf/tZt6uMaelMGRx48kqEovl70uUU17l1J8FOy9i44EsJv0/l757jn5SOiPVrHYggZxjtUQ8/g|
+
 [crypto_box_beforenm]: https://nacl.cr.yp.to/box.html
 [Null character]: https://en.wikipedia.org/wiki/Null_character
 [XOR cipher]: https://en.wikipedia.org/wiki/XOR_cipher