Harvest now, decrypt later (HNDL) is one of the most urgent quantum threats facing cryptocurrency. The attack is simple: adversaries record encrypted blockchain transactions and wallet data today, store it, and wait until quantum computers can break the encryption — then decrypt everything at once.
Why this matters for blockchain: Unlike traditional internet traffic, blockchain transactions are permanently and publicly recorded. Every Bitcoin transaction ever made is stored on the blockchain forever. This means all historical wallet public keys are already "harvested" and waiting to be cracked.
The timeline: Nation-state actors are believed to already be collecting encrypted data for future quantum decryption. The NSA warned about this threat in 2015. The crypto space has trillions of dollars in publicly visible, permanently stored encrypted data — making it the largest target for HNDL attacks.
How BMIC protects against HNDL: BMIC uses CRYSTALS-Kyber encryption from day one. This means data encrypted with BMIC's protocol cannot be decrypted by future quantum computers — the harvest-now strategy fails because there is nothing to decrypt later.