Agata buzzed wearily; at least she wouldn’t be debating Pio. ‘Have your own family taken positions?’

‘Gineto against, Serena for, Vala undecided.’ Medoro didn’t seem too worried by the split. ‘But they all gave me grief that I didn’t go public.’

‘That’s unfair,’ Agata protested. ‘Ramiro had it all laid out for him. We were just guessing – it would have been irresponsible to start a rumour when we weren’t even sure of the facts.’

‘Hmm.’ Medoro sounded unconvinced, so Agata let the subject drop.

She said, ‘But now Ramiro is courage personified, and I have to stand in front of a crowd of his admirers and tell them he’s wrong.’

‘I’m sure you’ll have admirers too,’ Medoro teased her.

‘For what? My theorems on sectional curvature?’

‘Why not? Any idiot can set himself on fire.’ Medoro rearranged himself on the guide rope. ‘Anyway, you don’t need to attack Ramiro. His arguments aren’t unreasonable: of course there could be drawbacks if the system is abused. But that doesn’t mean we can’t minimise the risks.’

‘I was going to start with a few practical benefits,’ Agata said. ‘Suppose we learn that a new crop disease shows up three years from now. We can’t prevent it arising altogether – or we’d never hear about it – but we can still take early quarantine measures and ensure that the outbreak is limited.’

‘Boring but sensible,’ Medoro declared approvingly. ‘Exactly the kind of thing people want the Council to be doing. Throw in a reference to the Great Holin Shortage, and you’ll have won over half the women in the room. What about averted collisions?’

Agata said, ‘No – in most realistic cases we would have had plenty of warning by conventional means.’

Medoro was disappointed. ‘You don’t want to go for the frisson of danger? Message: “Thanks for starting a sideways swerve when you read this, it just paid off and saved the whole mountain”?’

‘I could raise it briefly,’ Agata decided. ‘Almost as a joke, so Ramiro can’t go too hard on the implausibility.’

‘What else?’ Medoro pressed her.

‘Next, reassurances about privacy, validation and containment. Everything can be encrypted and signed, in exactly the same way as with the ordinary network. So there’ll be no chance of anyone else reading a message intended for you personally, and no chance of the sender convincing you that they’re someone they’re not.’

Medoro said, ‘I can check a message that purports to be from you because you’ve published a validation key – and you’re here to complain loudly if someone else tries to distribute a different key and claim that it’s yours. But if I get a message from someone who claims to be my grand-niece . . . how do I authenticate that?’

‘You just need a chain of trust,’ Agata explained. ‘You get a message from your niece, signed with a key that you’ll give her personally when she’s old enough. Her message gives you a key for authenticating her daughter’s message.’