HNDL (Harvest-Now-Decrypt-Later)

Also known as: Store-Now-Decrypt-Later, SNDL

HNDL is the threat model where an adversary passively collects encrypted traffic today with the expectation of decrypting it later once a cryptanalytically-relevant quantum computer (CRQC) is available. It drives PQC/hybrid migration priorities: long-lived secrets (LI content, subscriber identifiers, PKI roots) and roaming/interconnect traffic with 10+ year confidentiality requirements are prioritized first.

Categories: SignalingRoaming and InterconnectThreats and Attacks

HNDL in context

Signaling protocols carry the control-plane instructions that set up calls, register subscribers, hand over sessions and route SMS. SS7, Diameter, GTP-C and SIP are the four dominant families, and interconnect exposure of any of them is treated by GSMA FS.11 / FS.19 / FS.20 as a top-tier telecom risk.

Roaming and interconnect are where two operators, often with an IPX or GRX carrier in between, exchange signaling and user-plane traffic. Trust boundaries here are the primary attack surface for location tracking, SMS interception and fraud, which is why GSMA now mandates SEPP with PRINS on 5G interconnect.

To place HNDL in the wider telecom-security picture, review NetFlow / IPFIX / sFlow, BGP Hijack, ISUP, Traffic Baselining, Behavioral Signaling Detection and Roaming.

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