Account numbers

Account names on a psibase network are able to compress to 64-bit numbers. To achieve this, psibase uses a reimplementation of the CACM87 arithmetic coding technique. Arithmetic coding uses fewer bits to encode frequently-seen symbols and more bits to encode rarely-seen symbols. For the psibase implementation, the model used to calibrate character and substring frequency was calculated using the set of publicly known Reddit account names.

The benefit of using an entropy-encoding technique is that psibase account names can be up to 18 characters long. The following rules for account names must be adhered to:

• Name length is between 0 and 18 characters
• Names may only include the following character: a-z, 0-9, and - (hyphen)
• Non-empty names must begin with a letter
• A hyphen may not be the last character in an account name

To get 64-bit values out of 18-character names, some names will necessarily fail to compress down to 64 bits. The probability that a name will fail to compress increases as the length of the name increases and also as the number of rarely-seen characters and substrings increases. The compression algorithm prefers names that are more likely to appear in user handles, and less likely to compress names that look non-human (e.g. no vowels).

Note: For more details, see the code for the account number encoding C++ reference implementation.

Custom rules

Account names will frequently appear in subdomains of psibase network nodes. Therefore, the usage of the AccountNumber type for network accounts imposes the additional restriction that a hyphen may not be the first character in an account name. This is to comply with standard DNS rules.

Furthermore, an account may not begin with the subsequence "x-" because it would have a subdomain which overshadows the subdomains reserved for use by infrastructure providers.