RFC13: add aes256 key derivation instructions

rfc/0013_Duniter_Encrypted_Wallet_Import_Format.md

@@ -45,6 +45,14 @@ This base64 string encodes a sequence of bytes whose structure is defined below.
 
 Symmetric encryption algorithm : aes256
 
+aes256 key : scrypt of user passphrase with the following parameters:
+Seed generated from scrypt with the following parameters:
+password: passphrase
+salt: sha256("dewif" ++ passphrase)
+N : 4096
+r: 16
+p: 1
+
 Encrypted datas :
 
 | seed(32 bytes) | public key(32bytes) |
@@ -76,6 +84,14 @@ DUWIF base 64 string (with zeroing aes key):
 
 Symmetric encryption algorithm : aes256
 
+aes256 key : scrypt of user passphrase with the following parameters:
+Seed generated from scrypt with the following parameters:
+password: passphrase
+salt: sha256("dewif" ++ passphrase)
+N : 4096
+r: 16
+p: 1
+
 Encrypted datas :
 
 | seed1(32 bytes) | public key1(32bytes) | seed2(32 bytes) | public key2(32bytes) |