EIP4345 - Difficulty Bomb Delay to June 2022

# Abstract

Starting with FORK_BLOCK_NUMBER the client will calculate the difficulty based on a fake block number suggesting to the client that the difficulty bomb is adjusting 10,700,000 blocks later than the actual block number.

# Motivation

Targeting for The Merge to occur before June 2022. If it is not ready by then, the bomb can be delayed further.

# Specification

# Relax Difficulty with Fake Block Number

For the purposes of calc_difficulty, simply replace the use of block.number, as used in the exponential ice age component, with the formula:

    fake_block_number = max(0, block.number - 10_700_000) if block.number >= FORK_BLOCK_NUMBER else block.number

# Rationale

The following script predicts a ~0.1 second delay to block time by June 2022 and a ~0.5 second delay by July 2022. This gives reason to address because the effect will be seen, but not so much urgency we don't have space to work around if needed.

def predict_diff_bomb_effect(current_blknum, current_difficulty, block_adjustment, months):
    '''
    Predicts the effect on block time (as a ratio) in a specified amount of months in the future.
    Vars used for predictions:
    current_blknum = 13423376 # Oct 15, 2021
    current_difficulty = 9545154427582720
    block adjustment = 10700000
    months = 7.5 # June 2022
    months = 8.5 # July 2022
    '''
    blocks_per_month = (86400 * 30) // 13.3
    future_blknum = current_blknum + blocks_per_month * months
    diff_adjustment = 2 ** ((future_blknum - block_adjustment) // 100000 - 2)
    diff_adjust_coeff = diff_adjustment / current_difficulty * 2048
    return diff_adjust_coeff


diff_adjust_coeff = predict_diff_bomb_effect(13423376,9545154427582720,10700000,7.5)
diff_adjust_coeff = predict_diff_bomb_effect(13423376,9545154427582720,10700000,8.5)

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# Backwards Compatibility

No known backward compatibility issues.

# Security Considerations

Misjudging the effects of the difficulty can mean longer blocktimes than anticipated until a hardfork is released. Wild shifts in difficulty can affect this number severely. Also, gradual changes in blocktimes due to longer-term adjustments in difficulty can affect the timing of difficulty bomb epochs. This affects the usability of the network but unlikely to have security ramifications.

In this specific instance, it is possible that the network hashrate drops considerably before The Merge, which could accelerate the timeline by which the bomb is felt in block times. The offset value chosen aimed to take this into account.