Fintech & Digital Assets
PCI DSS v4: what changed for merchants and acquirers
The requirements that were "best practice" until March 2025 are now mandatory. Most of them land on payment pages, authentication and the way risk is documented.
Fintech & Digital Assets
Digital asset custody: hot, warm and cold, and the controls between them
Losses at exchanges and custodians rarely come from broken cryptography. They come from weak controls around keys, approvals and withdrawals.
Whoever controls the private key controls the asset. Every custody design is therefore an answer to one question: who can move funds, under what conditions, and how quickly. The answer is never a single wallet.
Three tiers, three purposes
- Hot wallets are online and sign automatically. They hold only what is needed for normal withdrawals over a short period.
- Warm wallets are online but require human approval, often with a delay. They refill the hot wallet.
- Cold storage keeps keys offline, in hardware security modules or air-gapped devices, and is used for most client assets.
The split between tiers should follow withdrawal patterns, reviewed regularly, not a fixed percentage chosen at launch.
Keys: multisig or MPC
Multi-signature wallets require several keys to sign a transaction on the blockchain itself. Multi-party computation splits one key into shares held by different parties, which sign together without ever rebuilding the key. Both remove the single point of failure. MPC works across more blockchains and keeps policies off-chain; multisig makes approvals visible on-chain. Either way, key shares must sit in different places, with different people, and a documented ceremony for creating and recovering them.
The policy engine is the real control
- quorum approvals that scale with the amount;
- whitelisted withdrawal addresses, with a waiting period for new ones;
- velocity limits per client, per asset and per day;
- separation between the people who request, approve and release a transfer;
- alerts on any change to policies themselves.
Proving the assets are there
Client assets should be segregated from the company's own funds and reconciled against on-chain balances every day. Many platforms now publish proof of reserves, which lets clients check that their balance is included in the liabilities the platform has attested to. It is not a full audit, but it builds trust that a quarterly statement alone cannot.
Our fintech team designs custody architecture with HSM and MPC providers, and our cybersecurity team tests the approval paths the way an attacker would.
