From the Coldcard $70 million air heist, see how institutional-level assets are secured with HSM

At the end of July 2026, the cryptocurrency industry experienced a hacking incident that disrupted public safety perceptions: the well-known Bitcoin hardware wallet Coldcard, which emphasizes "physical isolation and private keys never leaving the device," was subjected to a mass hacking attack.

In just 41 minutes, attackers directly stole over 1,080 Bitcoins from 1,196 Coldcard wallet addresses, resulting in losses of up to $70 million to $88.6 million. Shockingly, the attackers never had physical contact with any device throughout the process, and many of the stolen wallets had been offline and stored in safes for years.

This painful case once again proves that the underlying defense of digital asset security does not depend on whether the device is connected to the internet, but rather on the physical randomness (entropy) of the private key at the time of generation and whether the keys have financial-grade hardware isolation during storage and approval.

1. Incident Review: "41 Minutes of Offline Cracking" Caused by Firmware Configuration Oversight

Many investors blindly believe that "as long as the private key exists in an offline hardware device, the assets are completely safe." However, the root cause of the Coldcard heist lies in the fact that the fate of the private key was determined from the moment of its generation.

According to an in-depth review by the Block engineering team and on-chain security agencies, the vulnerability originated from a configuration logic oversight in the Coldcard firmware update in March 2021 [1]:

1. Random Number Generator (RNG) Downgrade: The underlying logic for hardware wallets to generate private keys is to extract physical noise to produce high-entropy true random numbers (TRNG). However, the flawed Coldcard firmware accidentally skipped the hardware random number generator when generating the root random number (Seed), falling back to a software pseudo-random number generator (PRNG) based on firmware code calculations.

2. Entropy Collapse: The pseudo-random algorithm relied solely on the device's fixed serial number and initialization time register, causing the private key generation space, which should have had 2\^{256} (unimaginably vast, astronomical numbers), to collapse to only about 2\^{32} (approximately 4 billion possibilities).

3. Offline Exhaustion and Network-wide Calculation: For hackers, the solution space transformed from "finding a needle in a haystack" to "billions of simple enumerations." Attackers only needed to quickly run through these 4 billion mnemonic combinations offline on their computing devices, derive the corresponding public key addresses, and compare them against the blockchain ledger. Once a match was found, they could directly broadcast the transaction on-chain, transferring the assets from the offline wallet in one go.

Just like the Profanity vanity address vulnerability that resulted in a loss of $160 million [2] and the Lubian mining pool losing 127,000 BTC (approximately $15 billion) due to weak randomness [3], the lack of algorithmic entropy is the most insidious and deadly poison in the crypto world.

2. The Life Starting Point of the Private Key: From True Random Numbers to Source Security

In cryptography, random numbers are the cornerstone of all security rules. The private key of a blockchain is derived from a mnemonic phrase, which entirely depends on the entropy of the initially generated random number.

Ordinary software pseudo-random algorithms (PRNG) are derived from deterministic mathematical formulas; as long as the initial seed or variable is known, the subsequent "random sequence" can be completely predicted. In contrast, true security must rely on true random number generators (TRNG), which extract pure "physical entropy" by capturing unpredictable physical phenomena such as quantum micro-noise, circuit thermal noise, or atomic decay.

HSM Private Key Generation Paradigm

To eliminate any risk of entropy collapse caused by logical computation defects from the physical source, Cactus Custody refuses to use any software pseudo-random models.

In Cactus Custody's architecture, both the private key and seed are generated directly within a hardware security module (HSM) that has been certified to the highest security levels. The HSM is equipped with an industrial-grade physical entropy source generator (TRNG), which produces irregular and unpredictable true random numbers through physical thermal noise, ensuring that the private key generation space possesses complete cryptographic strength, mathematically sealing off any possibility of offline cracking or reverse engineering.

3. Key Custody Paradigm: Consumer-grade Cold Wallet vs. Institutional-grade HSM Hardware Base

In addition to the entropy issues during the generation phase, there is also a fundamental generational gap in the storage mechanisms between consumer-grade hardware wallets and institutional-grade custody.

Natural Limitations of Consumer-grade Hardware Wallets

Ordinary consumer-grade hardware wallets (such as Ledger, Trezor, or Coldcard) primarily function to prevent private keys from being directly stolen by malware on connected computers. However, to facilitate ordinary users in backing up and migrating, the private keys and 12/24 mnemonic phrases in these devices can essentially be exported or backed up on paper. Once the mnemonic phrases are written down, photographed, or physically accessed, hackers can replicate the private key on any device.

Financial-grade HSM Physical Protection

As a professional institutional digital asset custody service provider, Cactus Custody employs Thales hardware security modules (HSM) that are universally used by top financial institutions and central banks as the underlying defense.

【Consumer-grade Cold Wallet】

Private key generation ──► Stored in consumer-grade chip ──► Mnemonic phrases can be exported/backed up ──► Facing risks of physical access leakage/exhaustion

【Cactus Custody Institutional-grade HSM Architecture】

TRNG physical true random generation ──► Locked inside Thales HSM ──► Strongly marked as "non-exportable" ──► Physical disassembly self-destruction

1. Non-exportable: In the Thales HSM, once the private key is generated inside the chip, it is forcibly marked as non-exportable. The private key can never physically leave the secure boundary of the HSM from its birth to its use.

2. Closed-in Chip Signing: All transaction signatures are completed within the secure area of the HSM, with only legitimate signature results broadcasted externally. Attackers cannot access the private key itself through remote networks or firmware extraction.

3. Physical Tamper Resistance and Self-destruction Mechanism: The Thales HSM features military-grade physical protection casing. Any attempt to physically disassemble, micro-probe scan, or attack the HSM through environmental anomalies will instantly trigger the physical protection circuit, automatically clearing and physically destroying all keys stored inside the chip, preventing any physical key theft.

4. Multi-signature Architecture: A multi-signature governance architecture is employed, where a single private key cannot independently allocate cold storage funds, eliminating single-point decision-making and significantly reducing the risks of single-point failure and internal malfeasance.

5. Random Private Key Generation: Each address's private key is independently generated by the hardware true random number generator (TRNG) built into the HSM, compliant with FIPS 140-2/3 and NIST SP 800-90 standards, without using master seed derivation (such as BIP32/44 HD Wallet) architecture. The keys have no mathematical correlation with each other, eliminating the batch risk of "one point being compromised, the entire system failing," fundamentally removing single-point failure.

Conclusion

As renowned cryptography expert Bruce Schneier said, "Security is a process, not a product." For digital asset custody, no single wallet or technology is omnipotent; layered defense, multi-signature, and risk diversification are the true endpoints of security.

From blind signing attacks (such as the Bybit $1.5 billion incident) to the Coldcard entropy collapse incident, the facts repeatedly prove that as attackers' methods evolve towards offline computational cracking, supply chain poisoning, and high-dimensional social engineering, relying on retail-level consumer-grade cold wallets for large asset management is increasingly inadequate to meet current security challenges.

Digital asset governance is accelerating towards an institutional era. Cactus Custody will continue to provide an unshakeable top-tier asset protection barrier for global Web3 institutions, funds, and high-net-worth clients by combining physical HSM hardware with a compliant trust framework and dual audit systems of SOC/ISO.