Google Cloud KMS now generally supports post-quantum digital signatures using ML-DSA and SLH-DSA. The signing algorithms can help protect the authenticity and integrity of software, firmware, documents, and other data expected to remain verifiable for years. They do not make every Cloud KMS key, certificate chain, or application quantum-safe: the change covers signing, not every part of a customer’s cryptographic system.
What Google added, and when
Google announced general availability of quantum-safe digital signatures and post-quantum key encapsulation in Cloud KMS on July 28, 2026. The release notes date general availability of the post-quantum signing algorithms to July 16, 2026. The algorithms were first available in public preview on February 21, 2025, with ML-DSA-65 and SLH-DSA-SHA2-128s. See Google’s announcement and the Cloud KMS release notes.
The announcement also covers ML-KEM, but that algorithm serves a different purpose: key encapsulation for establishing shared secrets. This article focuses on the new signing options, which let a verifier check whether signed data came from the expected signer and has remained unchanged.
Which signing algorithms are available?
Google identifies ML-DSA as the algorithm standardized in FIPS 204 and SLH-DSA as the algorithm standardized in FIPS 205. Cloud KMS lists these eight GA signing identifiers:
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PQ_SIGN_ML_DSA_44andPQ_SIGN_ML_DSA_44_EXTERNAL_MUPQ_SIGN_ML_DSA_65andPQ_SIGN_ML_DSA_65_EXTERNAL_MUPQ_SIGN_ML_DSA_87andPQ_SIGN_ML_DSA_87_EXTERNAL_MUPQ_SIGN_SLH_DSA_SHA2_128SandPQ_SIGN_HASH_SLH_DSA_SHA2_128S_SHA256
The ML-DSA choices are parameter sets 44, 65, and 87, each with a pure and an external-μ variant. SLH-DSA-SHA2-128s is available in a pure form and a pre-hash form. Check the Cloud KMS key-purpose and algorithm reference and the digital-signatures documentation when selecting an identifier and integrating it with an application; the verifier must support the format and variant you choose.
How large are the keys and signatures?
Google Cloud’s digital-signatures documentation publishes the following implementation sizes. The page does not state a publication year.
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| Algorithm | Private key | Public key | Signature |
|---|---|---|---|
| SLH-DSA-SHA2-128s | 64 bytes | 32 bytes | 7,856 bytes |
| ML-DSA-44 | 2,560 bytes | 1,312 bytes | 2,420 bytes |
| ML-DSA-65 | 4,032 bytes | 1,952 bytes | 3,309 bytes |
| ML-DSA-87 | 4,896 bytes | 2,592 bytes | 4,627 bytes |
These are documented parameter sizes, not performance benchmarks. In practice, the larger signatures—particularly the 7,856-byte SLH-DSA-SHA2-128s signature—can matter for bandwidth, storage, and systems that repeatedly process signature chains. The effect on any specific workload depends on how that system stores, transports, and verifies signatures; the documentation figures alone do not establish a particular speed or cost penalty.
What can you use a post-quantum signature for?
A signature can help preserve trust in an artifact that must be checked later, including when the original signing event is far in the past. Google’s examples include validating binary builds and creating new post-quantum roots of trust for software, firmware, and documents. In binary validation, a verifier checks the binary against the corresponding public key; an invalid signature indicates the binary may have been altered or corrupted. Google discusses these use cases in its guidance on preparing for a quantum-safe future.
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For a real deployment, signing is only one part of the verification path. The system that consumes the artifact needs to understand the chosen signature format and algorithm, and the verifier needs access to the appropriate public key. A signing key in Cloud KMS does not automatically update a device, build pipeline, document reader, identity provider, certificate authority, or other relying system.
What Cloud KMS does not make quantum-safe
The GA announcement should not be read as a blanket conversion of Cloud KMS or customer infrastructure to quantum-safe cryptography. The signing algorithms protect signatures they create; ML-KEM is for key establishment. Neither step by itself replaces classical asymmetric keys elsewhere in an environment or updates applications that use them.
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- WORKS WITH 1000+ ACCOUNTS: Compatible with Google, Microsoft, and Apple. A single Security Key NFC secures 100 of your favorite accounts, including email, password managers, and more.
- FAST & CONVENIENT LOGIN: Plug in your Security Key NFC via USB-A and tap it, or tap it against your phone (NFC) to authenticate. No batteries, no internet connection, and no extra fees required.
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Google’s documentation supports standalone post-quantum signatures. It states: “Due to the lack of a standard for hybridization of post-quantum and classical digital signatures, only the standalone implementations are supported.” That means the documented KMS interface does not provide a native hybrid signature combining a classical signature and a post-quantum signature. Organizations that require a transition period with both kinds of signature need to assess their own application and verification design rather than assume KMS will generate the hybrid format.
Certificate, identity, hardware, and key-import capabilities are also separate migration concerns. In an August 11, 2026 roadmap post, Google said Cloud KMS had reached GA for standardized ML-KEM, ML-DSA, and SLH-DSA, while quantum-safe key import was still in progress. Other roadmap milestones extending through 2028 are Google targets, not confirmation that those capabilities are currently delivered. See Google Cloud’s PQC roadmap.
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- WORKS WITH 1000+ ACCOUNTS: Compatible with popular accounts like Google, Microsoft, and Apple. A single YubiKey 5 secures 100+ of your favorite accounts, including email, password managers, and more.
- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5 via USB and tap it to authenticate. No batteries, no internet connection, and no extra fees required.
- MOST SECURE PASSKEY: Supports FIDO2/WebAuthn, FIDO U2F, Yubico OTP, OATH-TOTP/HOTP, Smart card (PIV), and OpenPGP. That means it’s versatile, working almost anywhere you need it.
- BUILT TO LAST: Made from tough, waterproof, and crush-resistant materials. Manufactured in Sweden and programmed in the USA with the highest security standards.
How to plan a signing-key migration
Google’s PQC insights guidance recommends creating new keys with a post-quantum algorithm and updating applications. An existing key’s purpose cannot be changed, so moving a workflow to post-quantum signing can require a new key or key version as well as application changes. Use the asymmetric PQC insights to inventory asymmetric keys and distinguish classical algorithms such as RSA and ECC from post-quantum options.
- Inventory the signing path. Identify which keys sign software, firmware, documents, or other long-lived data, and which services or devices verify those signatures.
- Choose an algorithm and variant. Compare the parameter set and signature size with the supported formats of the signer and every verifier. Confirm whether the workflow can accept a standalone post-quantum signature.
- Create a new post-quantum key. Do not expect to change the purpose of an existing key to turn it into a signing key with a different algorithm.
- Update and test applications. Ensure signing, distribution, storage, and verification components all handle the selected format and public key.
- Plan dependencies beyond KMS. Account for certificate, identity, hardware, and key-import requirements separately; a successful Cloud KMS signing operation does not establish that the full trust chain has migrated.
Google notes that symmetric keys are generally considered resistant to quantum-computer attacks and are not included in its asymmetric-key insights chart; it identifies HMAC-SHA1 as an exception. That chart is an inventory aid, not a declaration that every asymmetric key has already been replaced or that every workflow is ready for PQC.
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