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.


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.


  • 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.


  • 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 Proof of work time, when generating a bunch of addresses.


  • 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


Bitmessage’s base58 encoding uses the following sequence (the same as Bitcoin’s): “123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz”. Many existing libraries for base58 do not use this ordering.