1  Address
  2  =======
  3  
  4  Bitmessage adresses are Base58 encoded public key hashes. An address looks like
  5  ``BM-BcbRqcFFSQUUmXFKsPJgVQPSiFA3Xash``. All Addresses start with ``BM-``,
  6  however clients should accept addresses without the prefix. PyBitmessage does
  7  this. The reason behind this idea is the fact, that when double clicking on an
  8  address for copy and paste, the prefix is usually not selected due to the dash
  9  being a common separator.
 10  
 11  Public Key usage
 12  ----------------
 13  
 14  Addresses may look complicated but they fulfill the purpose of verifying the
 15  sender. A Message claiming to be from a specific address can simply be checked by
 16  decoding a special field in the data packet with the public key, that represents
 17  the address. If the decryption succeeds, the message is from the address it
 18  claims to be.
 19  
 20  Length
 21  ------
 22  
 23  Without the ``BM-`` prefix, an address is usually 32-34 chars long. Since an
 24  address is a hash it can be calculated by the client in a way, that the first
 25  bytes are zero (``\0``) and bitmessage strips these. This causes the client to do
 26  much more work to be lucky and find such an address. This is an optional checkbox
 27  in address generation dialog.
 28  
 29  Versions
 30  --------
 31  
 32   * v1 addresses used a single RSA key pair
 33   * v2 addresses use 2 ECC key pairs
 34   * v3 addresses extends v2 addresses to allow specifying the proof of work
 35     requirements. The pubkey object is signed to mitigate against
 36     forgery/tampering.
 37   * v4 addresses protect against harvesting addresses from getpubkey and pubkey
 38     objects
 39  
 40  Address Types
 41  -------------
 42  
 43  There are two address types the user can generate in PyBitmessage. The resulting
 44  addresses have no difference, but the method how they are created differs.
 45  
 46  Random Address
 47  ^^^^^^^^^^^^^^
 48  
 49  Random addresses are generated from a randomly chosen number. The resulting
 50  address cannot be regenerated without knowledge of the number and therefore the
 51  keys.dat should be backed up. Generating random addresses takes slightly longer
 52  due to the POW required for the public key broadcast.
 53  
 54  Usage
 55  """""
 56  
 57   * Generate unique addresses
 58   * Generate one time addresses.
 59  
 60  
 61  Deterministic Address
 62  ^^^^^^^^^^^^^^^^^^^^^
 63  
 64  For this type of Address a passphrase is required, that is used to seed the
 65  random generator. Using the same passphrase creates the same addresses.
 66  Using deterministic addresses should be done with caution, using a word from a
 67  dictionary or a common number can lead to others generating the same address and
 68  thus being able to receive messages not intended for them. Generating a
 69  deterministic address will not publish the public key. The key is sent in case
 70  somebody requests it. This saves :doc:`pow` time, when generating a bunch of
 71  addresses.
 72  
 73  Usage
 74  """""
 75  
 76   * Create the same address on multiple systems without the need of copying
 77     keys.dat or an Address Block.
 78   * create a Channel. (Use the *Join/create chan* option in the file menu instead)
 79   * Being able to restore the address in case of address database corruption or
 80     deletation.
 81  
 82  Address generation
 83  ------------------
 84  
 85   1. Create a private and a public key for encryption and signing (resulting in
 86      4 keys)
 87   2. Merge the public part of the signing key and the encryption key together.
 88      (encoded in uncompressed X9.62 format) (A)
 89   3. Take the SHA512 hash of A. (B)
 90   4. Take the RIPEMD160 of B. (C)
 91   5. Repeat step 1-4 until you have a result that starts with a zero
 92      (Or two zeros, if you want a short address). (D)
 93   6. Remove the zeros at the beginning of D. (E)
 94   7. Put the stream number (as a var_int) in front of E. (F)
 95   8. Put the address version (as a var_int) in front of F. (G)
 96   9. Take a double SHA512 (hash of a hash) of G and use the first four bytes as a
 97      checksum, that you append to the end. (H)
 98   10. base58 encode H. (J)
 99   11. Put "BM-" in front J. (K)
100  
101  K is your full address
102  
103   .. note:: Bitmessage's base58 encoding uses the following sequence
104  	   (the same as Bitcoin's):
105  	   "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".
106  	   Many existing libraries for base58 do not use this ordering.