How Bitcoin Custody Works & Breaking Down The Coldcard Incident

— Cold Card hardware wallet suffered a catastrophic bug post-March 2021: seeds generated were vulnerable to theft because the device fell back to weak 40-bit entropy instead of proper 256-bit randomness when its secure RNG failed silently.

— Bitcoin security fundamentally depends on one thing: generating a sufficiently large and random private key (secret number). The ledger only cares about math; it cannot distinguish a legitimate owner from an attacker who recreates that secret.

— Single-signature vs. multi-signature custody: single-sig requires only one compromised key to lose funds; multi-sig (e.g., 2-of-3) requires multiple keys, providing redundancy. Multi-sig trades complexity for resilience but risks permanent loss if set up incorrectly.

— Self-custody is not dead; the incident reflects one company's failure to implement basic cryptographic best practices, not an inherent flaw in storing secrets offline or in hardware wallets.

— Custody is a stack: key generation (where Cold Card failed), key protection (sharding, geography), multi-sig, operations, and recovery. All layers matter; no single solution solves custody alone.

— Strike's custody model uses geographically distributed multi-sig and has deployed AI-based code review tools to detect vulnerabilities daily; the platform absorbed hundreds of millions in Bitcoin deposits over 36 hours post-incident.

— Immediately move any Bitcoin stored in a Cold Card wallet generated post-March 2021 to a new wallet, multi-sig setup, or a custodial service like Strike. The vulnerability is ongoing and exploitable in minutes on weaker seeds.

— Educate yourself on the difference between single-sig and multi-sig custody, and consider multi-sig (such as 2-of-3) if you self-custody large amounts. This prevents total loss if one key is compromised, though setup must be done carefully to avoid accidental lock-out.

— Understand that Bitcoin custody success depends on proper randomness during key generation and keeping that secret private—not on any single product or service. Verify that any wallet or custody provider uses cryptographically sound RNG (Bitcoin Core and Trezor/Ledger have strong track records; Cold Card did not).