How the UK’s centralised Covid-19 app differs from decentralised apps

The UK’s centralised NHS app

 

Once data has been uploaded, the NHS knows which phones have seen which other phones, and can use that information to understand how rapidly Covid-19 is being spread

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1

A person’s phone sends out a randomised signal over Bluetooth, and listens for the same from others, recording every signal. Their signal changes periodically, so they can't be tracked

NHS

2

If the person contracts Covid-19, they upload a list of randomised signals their phone has heard while they were infectious to the NHS

3

The NHS contacts the users on the list, and tells them ‘a random user tells us they met you while infectious. Self-isolate for seven days’

Decentralised apps

 

The public health authority does not know which phones have seen which other phones, as it is only told the signals that a given phone was broadcasting

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1

A person’s phone sends out a randomised signal over Bluetooth, and listens for the same from others, recording every signal. Their signal changes periodically, so they can't be tracked

2

If the person contracts Covid-19, they upload a list of randomised signals their phone sent out while they were infectious

3

The PHA sends that list to every other phone, with a warning ‘if you heard any of these random signals before, you have been exposed to Covid-19. Self-isolate for seven days

The UK’s centralised NHS app

 

Once data has been uploaded, the NHS knows which phones have seen which other phones, and can use that information to understand how rapidly Covid-19 is being spread

Decentralised apps

 

The public health authority does not know which phones have seen which other phones, as it is only told the signals that a given phone was broadcasting

95Sdvb

YhZa23

Gnbv71

lMkq81

1

1

A person’s phone sends out a randomised signal over Bluetooth, and listens for the same from others, recording every signal. Their signal changes periodically, so they can't be tracked

A person’s phone sends out a randomised signal over Bluetooth, and listens for the same from others, recording every signal. Their signal changes periodically, so they can't be tracked

NHS

2

2

If the person contracts Covid-19, they upload a list of randomised signals their phone has heard while they were infectious to the NHS

If the person contracts Covid-19, they upload a list of randomised signals their phone sent out while they were infectious

3

3

The NHS contacts the users on the list, and tells them ‘a random user tells us they met you while infectious. Self-isolate for seven days’

The PHA sends that list to every other phone, with a warning ‘if you heard any of these random signals before, you have been exposed to Covid-19. Self-isolate for seven days