India, Oct. 26 -- In espionage, time has traditionally worked against stolen intelligence. Military plans expire, diplomatic positions change, and the value of a confidential conversation diminishes as events overtake it. An intercepted message that cannot be deciphered today might be worthless by the time someone finds a way to read it.

Quantum computing threatens to disturb that calculation. Some information may remain politically or strategically valuable long after the mathematics protecting it has become obsolete.

There is something peculiar about this possibility. The attack could take place in 2026, the decryption in 2040, and the consequences reach back to decisions made decades earlier. A confidential diplomatic exchange could ...