---
eip: 3554
title: Difficulty Bomb Delay to December 2021
author: James Hancock (@madeoftin)
discussions-to: https://ethereum-magicians.org/t/eip-3554-ice-age-delay-targeting-december-2021/6188
status: Final
type: Standards Track
category: Core
created: 2021-05-06
---

## Simple Summary
Delays the difficulty bomb to show effect the first week of December 2021.

## 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 9,700,000 blocks later than the actual block number.

## Motivation
Targeting for the Shanghai upgrade and/or the Merge to occur before December 2021. Either the bomb can be readjusted at that time, or removed all together.

## 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:
```py
    fake_block_number = max(0, block.number - 9_700_000) if block.number >= FORK_BLOCK_NUMBER else block.number
```
## Rationale

The following script predicts a .1 second delay to blocktime the first week of december and a 1 second delay by the end of the month. 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.

```python
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 in last prediction:
    current_blknum = 12382958
    current_difficulty = 7393633000000000
    block adjustment = 9700000
    months = 6
    '''
    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(12382958,7393633000000000,9700000,6)
```

## 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.

## Copyright
Copyright and related rights waived via [CC0](../LICENSE.md).