The Dagger (XDAG) cryptocurrency
- Community site: https://xdag.io
- The Main net was launched January 5, 2018 at 22:45 GMT
- Directed acyclic graph (DAG), not blockchain
- Block = transaction = address
- Original idea and implementation
- Mineable, no premine, no ICO
- Mining new money every 64 seconds
Main chain idea:
Every block in DAG has up to 15 links to another blocks (inputs and outputs). Block B is referenced by another block A if we can reach B from A by following the links. Chain is a sequence of blocks each of which is referenced by the previous block. Chain is called distinct if every its block belongs to separate 64-seconds interval. Difficulty_of_block is 1/hash where hash is sha256(sha256(block)) regarded as little-endian number. Difficulty_of_chain is sum of difficulties of blocks. Main_chain is the distinct chain with maximum difficulty. Blocks in main chain are called main_blocks.
Daggers are mined in every main block. For first 4 years 1024 XDAG are mined in each main block. For second 4 years - 512 XDAG, and so on. So, maximum XDAG supply is approximately power(2,32). Each dagger is equal to power(2,32) cheatoshino. Transaction is valid if it is referenced by a main block. Valid transactions are strictly ordered depending on main chain and links order. Double spending is prohibited because only first concurrent transaction (by this order) is applied.
Structure of block:
The on-disk format will change in the future. Consider this the network protocol. Each block has a fixed size of 512 bytes. Block consists of 16 fields each of which has length 32 bytes. Field 0 is header, it consists of 4 quadwords:
- transport-layer header
- types of all 16 fields, 4 bits for one type
- timestamp of the block, in seconds from Unix era * 1024
- block fee in cheatoshi
Types of fields:
- transaction input: 24 lower bytes of block hash and 8 bytes of input amount
- transaction output, structure is the same as input
- half of block signature; ECDSA number r or s; digest for signature is hash of (block concate public key)
- half of output signature; only owner of this key can use this block as input
- public key (x) with even y
- public key with odd y
- header of testnet
- ... 15. are reserved for future usage.
The dnet network is used as transport layer. A new transport layer will come in the future.