Add Address doc. Closes: #1727.

docs/address.rst

@@ -0,0 +1,106 @@
+Address
+=======
+
+Bitmessage adresses are Base58 encoded public key hashes. An address looks like
+``BM-BcbRqcFFSQUUmXFKsPJgVQPSiFA3Xash``. All Addresses start with ``BM-``,
+however clients should accept addresses without the prefix. PyBitmessage does
+this. The reason behind this idea is the fact, that when double clicking on an
+address for copy and paste, the prefix is usually not selected due to the dash
+being a common separator.
+
+Public Key usage
+----------------
+
+Addresses may look complicated but they fulfill the purpose of verifying the
+sender. A Message claiming to be from a specific address can simply be checked by
+decoding a special field in the data packet with the public key, that represents
+the address. If the decryption succeeds, the message is from the address it
+claims to be.
+
+Length
+------
+
+Without the ``BM-`` prefix, an address is usually 32-34 chars long. Since an
+address is a hash it can be calculated by the client in a way, that the first
+bytes are zero (``\0``) and bitmessage strips these. This causes the client to do
+much more work to be lucky and find such an address. This is an optional checkbox
+in address generation dialog.
+
+Versions
+--------
+
+ * v1 addresses used a single RSA key pair
+ * v2 addresses use 2 ECC key pairs
+ * v3 addresses extends v2 addresses to allow specifying the proof of work
+   requirements. The pubkey object is signed to mitigate against
+   forgery/tampering.
+ * v4 addresses protect against harvesting addresses from getpubkey and pubkey
+   objects
+
+Address Types
+-------------
+
+There are two address types the user can generate in PyBitmessage. The resulting
+addresses have no difference, but the method how they are created differs.
+
+Random Address
+^^^^^^^^^^^^^^
+
+Random addresses are generated from a randomly chosen number. The resulting
+address cannot be regenerated without knowledge of the number and therefore the
+keys.dat should be backed up. Generating random addresses takes slightly longer
+due to the POW required for the public key broadcast.
+
+Usage
+"""""
+
+ * Generate unique addresses
+ * Generate one time addresses.
+
+
+Deterministic Address
+^^^^^^^^^^^^^^^^^^^^^
+
+For this type of Address a passphrase is required, that is used to seed the
+random generator. Using the same passphrase creates the same addresses.
+Using deterministic addresses should be done with caution, using a word from a
+dictionary or a common number can lead to others generating the same address and
+thus being able to receive messages not intended for them. Generating a
+deterministic address will not publish the public key. The key is sent in case
+somebody requests it. This saves :doc:`pow` time, when generating a bunch of
+addresses.
+
+Usage
+"""""
+
+ * Create the same address on multiple systems without the need of copying
+   keys.dat or an Address Block.
+ * create a Channel. (Use the *Join/create chan* option in the file menu instead)
+ * Being able to restore the address in case of address database corruption or
+   deletation.
+
+Address generation
+------------------
+
+ 1. Create a private and a public key for encryption and signing (resulting in
+    4 keys)
+ 2. Merge the public part of the signing key and the encryption key together.
+    (encoded in uncompressed X9.62 format) (A)
+ 3. Take the SHA512 hash of A. (B)
+ 4. Take the RIPEMD160 of B. (C)
+ 5. Repeat step 1-4 until you have a result that starts with a zero
+    (Or two zeros, if you want a short address). (D)
+ 6. Remove the zeros at the beginning of D. (E)
+ 7. Put the stream number (as a var_int) in front of E. (F)
+ 8. Put the address version (as a var_int) in front of F. (G)
+ 9. Take a double SHA512 (hash of a hash) of G and use the first four bytes as a
+    checksum, that you append to the end. (H)
+ 10. base58 encode H. (J)
+ 11. Put "BM-" in front J. (K)
+
+K is your full address
+
+ .. note:: Bitmessage's base58 encoding uses the following sequence
+	   (the same as Bitcoin's):
+	   "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".
+	   Many existing libraries for base58 do not use this ordering.

docs/index.rst

@@ -7,6 +7,7 @@ Protocol documentation
    :maxdepth: 2
 
    protocol
+   address
    encryption
    pow