WIP: RFC 0012 : authentication file format first draft

authentication file format RFC 0012

rfc/0012_duniterkey_authentication_file_format_v1.md

+```txt
+RFC: 12
+Title: RFC Format
+Type: Convention
+Status: Draft
+Author: vit
+Created: 2020-02-12
+Last edited: 2020-02-12
+License: GPL-3
+```
+
+# Duniterkey Authentication File Format
+
+This document serves as a reference for the `.duniterkey` authentication file format.
+
+## Limitations
+
+This format is a container format. Its main caveat is that you can have inside a data not be compatible with your application.
+
+This is the same problem as video containers. The video codec inside the container can be unreadable by your application.
+
+## File format extension
+
+The official extension is `.duniterkey`.
+
+## Text File Format
+
+This format is inspired by [the Yaml format](https://yaml.org/spec/1.2/spec.html) for human readability.
+
+The charset is utf-8 and the newline are unix style (\n).
+
+So it is a yaml formatted file containing root fields of the form:
+
+```yaml
+Type: string
+Version: int
+data_field_1: data_value_1
+[data_field_n: data_value_n]
+```
+
+## Header fields
+
+The first two fields are the header of the file. Their purpose is to know how to treat the following data fields.
+
+### Type field
+
+The first field is the `Type` field. Its value is a string id identifying the type of data in the file.
+
+Recognized values are:
+
+* `PubSec`
+* `WIF`
+* `EWIF`
+
+### Version field
+
+The second field is the `Version` field. Its value is an integer specifying a version for the following data.
+
+## Data fields
+
+After the header fields come the data fields. This number and the name of the fields depend on the type of data.
+
+### PubSec fields
+
+The PubSec fields are as follow:
+
+```yaml
+Type: PubSec
+Version: 1
+pub: base58(public_key_bytes)
+sec: base58(secret_key_bytes)
+```
+`public_key_bytes` is the public key in bytes.
+
+`secret_key_bytes` is the secret key in bytes.
+
+### WIF fields
+
+The WIF fields are as follow:
+
+```yaml
+Type: WIF
+Version: 1
+Data: base58(data_bytes)
+```
+Where 
+```shell script
+data_bytes = format_byte + seed_bytes + checksum_bytes
+```
+Where
+```shell script
+format_byte = \x01
+checksum_bytes = sha256(sha256(format_byte + seed_bytes))[0:2]
+```
+`format_byte` is one byte with value 1 for the WIF format.
+
+`seed_bytes` is the seed in bytes of the key pair.
+
+`checksum_bytes` are the two first bytes of a two pass sha256 hash of the `format_byte` concatenated to the `seed_bytes`.
+
+### EWIF fields
+
+The EWIF fields are as follow:
+
+```yaml
+Type: EWIF
+Version: 1
+Data: base58(seed_bytes + checksum_bytes)
+```
+Where 
+```shell script
+checksum_bytes = sha256(sha256(seed_bytes))[0:2]
+```
+Where 
+```shell script
+seed_bytes = \x02 + salt + encrypted_half_1 + encrypted_half_2
+```
+Where 
+```shell script
+salt = sha256(sha256(pubkey_bytes))[0:4]
+
+password_bytes = bytes(password_utf8_string)
+
+scrypt_seed = scrypt(password_bytes, salt, n=16384, r=8, p=8, length=64)
+
+derived_half_1 = scrypt_seed[0:32]
+derived_half_2 = scrypt_seed[32:64]
+
+seed1_xor_derived_half_1a = bytes(xor_bytes(original_seed_bytes[0:16], derived_half_1[0:16]))
+seed2_xor_derived_half_1b = bytes(xor_bytes(original_seed_bytes[16:32], derived_half_1[16:32]))
+
+encrypted_half_1 = aes256.encrypt(seed1_xor_derived_half_1a, key=derived_half_2)
+encrypted_half_2 = aes256.encrypt(seed2_xor_derived_half_1b, key=derived_half_2)
+
+seed_bytes = \x02 + salt + encrypted_half_1 + encrypted_half_2
+```
+`password_utf8_string` is the password string in utf-8 used to encrypt the seed.
+
+`pubkey_bytes` is the public key in bytes used to create the `salt` value.
+
+`original_seed_bytes` is the original seed in bytes of the key pair.
+
+This document can be completed and improved by Tortue document:
+
+https://tmp.tednet.fr/paperwallet/AddressFormat.html
+
+Thanks to him for his work.
+
+End of document
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