Hard Forks¶

Monero uses scheduled network upgrades (hard forks) in order to introduce changes to consensus rules. Each upgrade activates at a fixed block height, and nodes that have not upgraded to a compatible release will reject the new blocks and "fall off" of the network.

Upgrades usually come in pairs, with the first fork introducing a new format and allowing both old and new, and the second fork, roughly a day (720 blocks) later, forbidding the old format. This gives transactions which are already in the mempool time to be mined.

Mainnet¶

Dates are in the format of YYYY-MM-DD. Version 1 covers blocks 1 to 1009826.

Consensus changes¶

The changes below are the rules enforced by monerod for blocks at or above each fork's activation height. The constants in parentheses are defined in cryptonote_config.h.

v1¶

• Original CryptoNote rules
• 60 second block time (DIFFICULTY_TARGET_V1)
• CryptoNight proof of work
• 20,000 byte penalty-free block size (CRYPTONOTE_BLOCK_GRANTED_FULL_REWARD_ZONE_V1)

v2¶

• 120 second block time (DIFFICULTY_TARGET_V2)
• Minimum ring size of 3, unless spending outputs that do not have enough decoys on the chain
• Outputs of non-RingCT transactions must be valid decomposed amounts (no dust)
• 60,000 byte penalty-free block size (CRYPTONOTE_BLOCK_GRANTED_FULL_REWARD_ZONE_V2)
• Miners may claim less than the full block reward (allowed until v13). The unclaimed amount is pushed back into future emission

v3¶

• Coinbase outputs must be valid decomposed amounts
• Outputs of version 2 (RingCT) transactions must have a zero cleartext amount

v4¶

• Version 2 (RingCT) transactions are allowed
• Dynamic fees (HF_VERSION_DYNAMIC_FEE)

v5¶

• 300,000 byte penalty-free block size (CRYPTONOTE_BLOCK_GRANTED_FULL_REWARD_ZONE_V5)
• Adjusted dynamic fee algorithm

v6¶

• RingCT is required (HF_VERSION_ENFORCE_RCT). Version 1 transactions are only accepted when spending pre-RingCT outputs that do not have enough decoys
• Minimum ring size of 5 (HF_VERSION_MIN_MIXIN_4)

v7¶

• CryptoNight variant 1 (HF_VERSION_CRYPTONIGHT_VARIANT_1)
• Minimum ring size of 7 (HF_VERSION_MIN_MIXIN_6)
• Transaction inputs must be sorted by key image

v8¶

• CryptoNight variant 2
• Bulletproofs range proofs are allowed
• Ring size fixed at exactly 11 (HF_VERSION_MIN_MIXIN_10)
• Per-byte fees (HF_VERSION_PER_BYTE_FEE)
• Maximum transaction size of half the penalty-free block size

v9¶

• Borromean range proofs are forbidden. Bulletproofs are required

v10¶

• CryptoNight-R (CryptoNight variant 4)
• RCTTypeBulletproof2, a more compact RingCT format, is allowed (HF_VERSION_SMALLER_BP)
• Long-term block weight algorithm (HF_VERSION_LONG_TERM_BLOCK_WEIGHT)

v11¶

• RCTTypeBulletproof is forbidden. Only RCTTypeBulletproof2 is accepted

v12¶

• RandomX proof of work (RX_BLOCK_VERSION)
• RingCT transactions must have at least 2 outputs (HF_VERSION_MIN_2_OUTPUTS)
• Coinbase transactions must be version 2 (HF_VERSION_MIN_V2_COINBASE_TX)
• RingCT signatures in coinbase transactions are forbidden (HF_VERSION_REJECT_SIGS_IN_COINBASE)
• All inputs in a transaction must use the same ring size (HF_VERSION_SAME_MIXIN)
• Outputs cannot be spent until they are 10 blocks old (HF_VERSION_ENFORCE_MIN_AGE, CRYPTONOTE_DEFAULT_TX_SPENDABLE_AGE)
• The block reward penalty uses the effective short-term median block weight (HF_VERSION_EFFECTIVE_SHORT_TERM_MEDIAN_IN_PENALTY)

v13¶

• CLSAG ring signatures (RCTTypeCLSAG) are allowed (HF_VERSION_CLSAG)
• Coinbase transactions must claim exactly the block reward plus fees (HF_VERSION_EXACT_COINBASE)
• Time-based unlock times are checked against the blockchain's adjusted time instead of the node's local clock (HF_VERSION_DETERMINISTIC_UNLOCK_TIME)

v14¶

• MLSAG ring signatures are forbidden. Only CLSAG is accepted
  • Two MLSAG transactions that were in the mempool at the time of the fork are grandfathered in

v15¶

• Ring size of 16 (HF_VERSION_MIN_MIXIN_15). Ring size 11 is still accepted during this fork as a grace period
• Bulletproofs+ range proofs (RCTTypeBulletproofPlus) are allowed (HF_VERSION_BULLETPROOF_PLUS)
• View tags (txout_to_tagged_key) are allowed (HF_VERSION_VIEW_TAGS). All outputs in a transaction must use the same output type
• Adjusted dynamic block weight and fee algorithm (HF_VERSION_2021_SCALING)

v16¶

• Ring size fixed at exactly 16
• Bulletproofs (RCTTypeBulletproof, RCTTypeBulletproof2, RCTTypeCLSAG) are forbidden. Only Bulletproofs+ is accepted
• All outputs must have view tags

Stagenet and Testnet¶

Stagenet and testnet follow the same consensus rules as mainnet for each version, but activate them at different heights.

Sources¶

• Fork heights (src/hardforks/hardforks.cpp)
• Upgrade schedule (README.md)
• Consensus checks (src/cryptonote_core/blockchain.cpp)