Google previews MPC custody service as Fireblocks library flaw surfaces

What happened

Google is previewing an institutional crypto security service built on multi-party computation, or MPC, and is aiming for commercial availability in early 2027. Crypto.news, citing a CoinDesk report, said the service is in private testing with several major financial institutions ahead of Google's first digital assets symposium in New York. Google has not identified those institutions, said which assets Alphabet holds through the system or published pricing. Alphabet, Google's parent company, has begun using the technology to secure unspecified digital assets on Ethereum and Solana.

Under the proposed design, control of a private key is divided among independent participants rather than held in one place. Institutions could place signing shares on their own equipment, on Google Cloud and on competing cloud providers, then require a set number of approvals before a transaction is signed; the reports give two-of-three and five-of-seven as examples. Transaction policies would run inside Google's Confidential Space environment and could restrict destination addresses, set transfer limits or demand extra approvals. Google plans to support ECDSA and Ed25519 signing at general availability and has not announced a date for post-quantum upgrades.

The preview coincided with new scrutiny of an existing MPC implementation. Cryptonews.com reported that CERT/CC published advisory VU#701544 on October 26, assigning CVE-2026-90975 to a flaw in Fireblocks' mpc-lib library. The advisory concerns BIP32 hardened key derivation when a required private parent key is missing: the library can use a zero-filled buffer instead of rejecting the operation. If an attacker also obtains a compromised descendant signer share and its chain code, the attacker may recover ancestor shares within that party's key hierarchy. CERT/CC said the issue does not expose a complete, spendable private key, and no vendor fix was available when the advisory was published.

Why it matters

The two developments put attention on how MPC custody is implemented, not just on whether keys are split. Google's entry would place its cloud infrastructure alongside specialized providers such as Fireblocks, Fordefi and BitGo, and it is aimed at banks that want to keep direct control of custody operations without transferring ownership of their keys to Google. The Fireblocks advisory shows that splitting a key does not remove risk from the software that handles shares. Derivation logic, access controls, approval policies and recovery procedures all affect the security of the overall system.

Losses from compromised credentials remain a major concern. Crypto.news cited a Chainalysis estimate that private-key compromises accounted for 43.8% of cryptocurrency stolen in 2024. It also pointed to a June incident at Humanity Protocol, where an attacker obtained seven private keys stored on a developer's computer and used them to reach administrative controls across Ethereum and BNB Smart Chain. Humanity Protocol said the attack used valid signatures generated with compromised keys rather than a flaw in its blockchain contracts. Crypto.news noted that distributing credentials does not eliminate operational risk when signing participants share administrative privileges or recovery systems.

What the data shows

Reported figures and dates frame the shift. Google's target is early 2027, with private testing under way and no precise launch date beyond that window. The service is designed for threshold approvals such as two-of-three or five-of-seven, and it is set to support ECDSA and Ed25519 at general availability. Post-quantum support has no announced release date.

The Fireblocks advisory was published on October 26. CERT/CC's identifier is VU#701544, and the CVE is CVE-2026-90975. The flaw affects hardened derivation in mpc-lib when a private parent key is absent, and the advisory says exploitation requires a compromised descendant signer share plus its chain code. CERT/CC recommended keeping chain codes confidential and avoiding reliance on hardened derivation to isolate signer shares until the implementation is corrected.

Background

Google has worked on related infrastructure before. In April 2023 it published technical guidance on building distributed-signing systems with Confidential Space, which uses confidential computing and hardware-backed attestation. The proposed service combines similar capabilities with signing policies and recovery tools. Google Cloud already offers Key Management Service and Cloud HSM for key protection, but the new offering is focused on the authorization and recovery requirements of digital assets, where a completed blockchain transaction generally cannot be reversed.

The custody market is also evolving. In September, UniCredit was exploring digital asset custody and brokerage infrastructure as European banks developed services for cryptocurrencies and tokenized securities, according to Crypto.news. Fireblocks has supplied wallet and tokenization technology to the Qivalis banking consortium. Google has not disclosed performance benchmarks comparing its system with commercial products.

What is still unclear

Several details remain undisclosed. Google has not named the financial institutions testing the service, the assets Alphabet secures with it, the price of the service or the first institutions expected to adopt it after the preview. There are no public benchmarks against existing custody platforms. The reports also do not establish that AI caused higher crypto losses or that MPC would have prevented the schemes cited. On the Fireblocks side, the reports do not say whether a fix has since been released or whether the flaw has been exploited in the wild.

What to watch

Watch for Google to identify testing partners and pricing, and for Fireblocks to publish remediation guidance for mpc-lib. Institutions evaluating either system will need to show how signing shares are separated, who controls administrators and recovery, and whether approval policies are enforced independently of the devices that hold shares. Those operational questions will matter as much as the cryptographic design.

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