Cloud storage · Security guide
There is no honest universal “most secure” winner. Proton Drive is our leading documentation-supported privacy fit, Tresorit is our leading secure team fit, and other choices make more sense for Linux, recoverability, selective vaults, or provider independence.
Evidence and volatile product facts checked July 13, 2026. Recommendations were finalized independently of monetization availability.
Leading privacy fit
Broad documented end-to-end encryption with unusually clear field-level privacy documentation.
Tradeoff: No current public audit of the entire service was verified, and collaboration is lighter than mainstream suites.
Leading secure team fit
A documentation-supported fit for teams that need encrypted collaboration, policy, and administration.
Tradeoff: Its latest public security evidence is a scoped vendor summary, not a complete public audit report.
Open and Linux-friendly contenders
Filen offers account-wide encrypted storage; Koofr adds an open-source encrypted vault to a broader Linux-capable service.
Tradeoff: Their architectures and workflows differ, and neither earned a categorical security win on current independent evidence.
Recovery-oriented contender
Documented sharing and recovery controls can suit users who prioritize recoverability.
Tradeoff: The 2024 ETH findings and email-reset key-access model must remain central to the decision.
Provider-independent option
Encrypt a vault locally before storing it with a provider you already use.
Tradeoff: You take on more key, recovery, preview, search, sharing, and workflow responsibility.
Choose Proton Drive when reducing provider access to file contents and names is the priority. Choose Tresorit when encrypted team workflows and administration matter more. Consider Filen or Koofr Vault for open/Linux-oriented workflows, Sync for qualified recovery needs, pCloud Crypto for a selected-files vault, or Cryptomator when you want encryption independent of the storage provider.
“Secure” is incomplete without a threat model. A service that reduces provider access may still be a poor choice for account recovery, collaborative work, ransomware resilience, or a compromised laptop.
Prefer client-side or end-to-end encryption, then inspect which names, sizes, timestamps, recipients, and events remain visible.
Prioritize MFA, recovery design, session controls, sharing discipline, and a separate backup—not encryption marketing alone.
Independent cryptographic analysis matters because a server may send altered data or keys to a client.
Cloud encryption cannot protect an unlocked endpoint that can already read decrypted files.
Version history may help, but retention and file-type limits vary. Keep an independent tested backup.
Managed recovery, ownership, export, offboarding, and administrator access can change the privacy boundary.
A secure vault becomes a different system once files are shared. Link secrets, recipient identity, permissions, and revocation matter.
Prefer conventional file formats and test exports. Versions, comments, permissions, links, and cloud-native files may not migrate cleanly.
This table compares architecture and evidence boundaries, not speed or ease of use. Those practical behaviors were not tested.
Swipe horizontally to compare all columns.
| Option | Best fit | Encryption scope | Metadata boundary | Independent evidence | CBT position |
|---|---|---|---|---|---|
| Proton Drive | Privacy-conscious personal storage | Account-wide documented E2EE | Names and thumbnails documented as encrypted; operational fields remain | No current full-service public audit verified | Documentation-based leading privacy fit |
| Tresorit | Encrypted team collaboration | E2EE architecture with managed-business controls | Metadata and administrator boundaries still matter | Scoped 2025 vendor summary; full report not public | Leading secure team fit |
| Filen | Open clients and Linux | Account-wide documented E2EE | Provider documentation says metadata is encrypted | No current public cryptographic audit verified | Technical contender, not independently proven |
| Koofr Vault | Free selective encrypted vault | Client-side encrypted Vault add-on | Ordinary Koofr storage is not encrypted the same way | No current public Vault audit verified | Selective-vault contender |
| Sync.com | Controlled sharing and recovery | Provider-documented E2EE | Email reset can change the key-access model | SOC evidence plus unresolved ETH/remediation conflict | Qualified recovery-oriented contender |
| pCloud Encryption | Selected sensitive files and Linux | Paid Crypto folder, not whole-account E2EE | Ordinary storage and Crypto differ | 2024 ETH findings; no complete independent retest verified | Qualified selective-vault contender |
| Cryptomator | Adding encryption to another provider | Local client-side encrypted vault | Provider still sees encrypted objects and account activity | Open code; public audit evidence is dated | Provider-independent alternative |
Security scope, storage, billing, bundles, add-ons, recovery, and business controls are packaged differently. We rechecked the official plan structures on July 13, 2026, but did not use price to determine the recommendations because regional checkout, promotions, taxes, renewal, and encrypted-feature paywalls were not normalized well enough for a durable value ranking.
Compare the total plan you would actually use—not only cost per terabyte. A cheaper ordinary-storage plan is not equivalent to account-wide E2EE, and a lifetime payment does not remove provider, account, continuity, or recovery risk.
Plan shape: Free, Drive-specific, ecosystem bundles, Duo, Family, and business structures
Check before paying: Storage and member allocations differ; displayed checkout and renewal terms can be regional or dynamic.
Plan shape: Free account plus personal, professional, and business subscriptions
Check before paying: The secure-team fit may cost more than a consumer needs; verify seats, storage, trial conversion, administration, and renewal.
Plan shape: Free eligibility plus monthly, annual, lifetime, and stackable paid structures
Check before paying: Displayed prices, promotions, renewal context, and included storage can change; do not choose it on headline cost alone.
Plan shape: Vault is included as a free add-on within Koofr plans
Check before paying: Ordinary Koofr storage and Vault have different encryption scope, so a low price does not make the whole account equivalent.
Plan shape: Free and paid personal/team tiers
Check before paying: Sharing, recovery, history, and promotion terms vary; the research did not normalize a stable value winner.
Plan shape: Subscription or lifetime storage plus potentially separate Crypto pricing
Check before paying: Read the definition of lifetime, promotion terms, Crypto inclusion, recovery, and extended-history costs before paying.
Plan shape: Desktop application plus platform-specific mobile licensing; storage is purchased separately
Check before paying: Total cost includes the underlying provider and the operational cost of managing your own vault and recovery.
Current official plan pages are linked in the visible evidence section below. Verify the checkout total, renewal treatment, currency, tax, refund, storage, user limits, and encryption scope immediately before purchase.
We compared encryption scope, exposed metadata, key and recovery design, sharing, account controls, platform support, audit scope, independent research, incident and remediation evidence, portability, backup boundaries, business administration, and plan restrictions.
Architecture documents, privacy policies, support pages, terms, plan documentation, source repositories, and scoped audit reports.
Academic cryptographic analysis, public vulnerability records, independent reports, and dated provider responses kept separate from validation.
Untested speed, reliability, usability, migration quality, support, cancellation friction, or recovery success.
Proton documents end-to-end encryption for file contents, filenames, folder names, and thumbnails. Its privacy policy also makes clear that operational fields can remain available, including timestamps, permissions, uploader information, link activity, and an encrypted size value. That combination of broad encryption and unusually specific documentation earns the leading privacy fit—not a universal security crown.
You want the provider to have less access to stored contents and names, accept the Proton ecosystem, and can maintain independent backups.
You need the deepest office collaboration, a native Linux GUI sync workflow, or current public independent validation of the complete service.
The public Securitum reports we found covered mobile clients in 2022. Open source and scoped audits are useful evidence, but neither proves the whole 2026 service. Read the field-by-field analysis in our Proton Drive Review.
Tresorit's architecture, sharing, policy, and administration documentation make it the strongest fit here for organizations that need encrypted collaboration rather than personal storage alone. Managed recovery and administrator controls are features for a business, but they also change who may be able to restore or access managed data.
A December 2025 vendor summary describes a commissioned gray-box test of selected SecureCloud and Engage components plus E2EE, web, mobile, and desktop areas. The public source did not expose the full report or auditor identity, so we treat it as scoped vendor-reported evidence—not blanket validation.
Teams that can verify plan-specific administration, recovery, ownership, offboarding, export, legal, and retention requirements before rollout. Price-sensitive personal users may find its business orientation unnecessary.
Filen documents account-wide E2EE, encrypted metadata, open clients, versions, and native Linux support. It also says its published whitepaper is slightly outdated, and we did not verify a current public cryptographic audit.
Fit: technical users who prioritize open clients and Linux and accept a smaller independent evidence base.
Koofr Vault is a free, open-source client-side encrypted add-on within Koofr. Ordinary storage is not encrypted by the client in the same way, and Vault's workflow differs from an account-wide encrypted sync service.
Fit: users who want a selected encrypted vault inside a Linux-capable broader service and accept thin independent validation.
The evidence does not support calling either one the universal best open-source or Linux option. Their encryption scope, interface, recovery, and integration tradeoffs are different.
Sync documents sharing controls, versions, recovery, and security-control evidence. It also documents that email-based password reset gives automated systems temporary access to the account's encryption keys; the option is enabled by default on paid plans and cannot be disabled on Teams.
The 2024 ETH study reported confidentiality, link-sharing, integrity, metadata, and injection attacks. Sync later said the link issue was fixed and other fixes were being fast-tracked. We did not verify a complete independent current retest. That makes Sync a qualified recovery-oriented contender, not a broad security or value winner.
pCloud separates ordinary storage from its paid Crypto folder. That can suit a Linux user who wants selected files in a distinct vault, but it is not default whole-account E2EE. Lost Crypto credentials create recovery risk, and the 2024 ETH findings remain part of the record.
Cryptomator encrypts a local vault before another provider synchronizes it. This separates encryption from the storage company, but makes you responsible for keys, recovery, compatible clients, and a workflow with fewer previews, searches, and collaboration features.
Neither approach wins universally. pCloud offers a provider-integrated selected-files workflow; Cryptomator is more provider-independent. Both require recovery planning and an independent backup.
The ETH Zurich / ACM CCS research matters because it examined a malicious-server threat model rather than accepting E2EE labels at face value. It reported severe vulnerabilities in the analyzed Sync, pCloud, Icedrive, and Seafile designs, plus conditional key-substitution and metadata-integrity risks for Tresorit.
This guide does not freeze dated findings as permanent current facts. It preserves the original research, later provider responses, claimed fixes, and the limits of independent retesting separately. A provider saying it fixed an issue is useful status information; it is not the same as independent validation.
MEGA has a separate 2022–2023 research and hardening chronology. We retained it as an evidence-rich alternative rather than presenting later mitigation claims as a complete current independent revalidation.
Broad documented platform support and public Securitum/SOC evidence, but fast-changing claims and scoped evidence keep it conditional.
An important encrypted-storage service with consequential 2022–2023 cryptographic research and an incompletely independently revalidated hardening story.
A local-plus-cloud encryption candidate with a thinner current independent evidence base than the leading fits.
Evaluated but excluded from the shortlist because the 2024 ETH integrity findings and remediation conflict remain material.
Excluded while its April 2026 release remains an invite-only closed beta rather than a broadly assessable service.
A separate self-hosted or managed-server category where administrator configuration and update discipline are part of the threat model.
A backup-first alternative for data-loss protection, not a like-for-like secure collaboration and sync recommendation.
Useful baselines for ecosystem, collaboration, recovery, and administration; standard consumer configurations should not be relabeled as universal E2EE storage.
For a mainstream ecosystem decision rather than a threat-model-first security ranking, read Best Cloud Storage for Beginners, Google Drive vs Dropbox, or iCloud vs Google Drive.
Standard iCloud protection and optional Advanced Data Protection are not the same architecture. Eligible users can enable ADP to extend end-to-end encryption to categories including iCloud Drive, but it is opt-in, changes recovery responsibility, has device and regional qualifications, and can interact differently with some sharing workflows.
An Apple household may reasonably prefer iCloud with ADP for ecosystem continuity and expanded content confidentiality. A Google, Microsoft, Dropbox, or standard-iCloud workflow may still be the better practical choice when live collaboration, assisted recovery, integrations, administration, or mixed-device compatibility matters more than making stored content provider-blind. “More E2EE” is not automatically “better for every workflow.”
There is no defensible universal winner. Proton Drive is the leading documentation-supported privacy fit in this review, while Tresorit is the leading secure team-collaboration fit. Your answer changes with the threat model, recovery needs, platforms, and sharing workflow.
No. E2EE can reduce provider access to content, but account data, billing, device information, timestamps, permissions, sharing activity, recipients, and other operational fields may remain visible. Recipients and unlocked devices can also expose decrypted files.
It is our leading documentation-supported privacy fit, not a universal winner. It is less compelling when deep office collaboration, a native Linux GUI sync workflow, or mature business administration matters more.
The evidence does not support a universal head-to-head security winner. Tresorit is the stronger documented fit for encrypted team administration; Proton is the stronger documented personal privacy fit. Both have audit-scope and workflow qualifications.
Sync remains a qualified contender, but the 2024 academic findings and provider-reported remediation must be visible. We did not verify a complete independent current retest, so this guide does not treat the issue as conclusively closed.
Not necessarily. Its Linux-capable service and Crypto folder can fit a selected-files vault workflow, but ordinary storage and Crypto differ, Crypto costs extra, recovery responsibility is high, and the 2024 findings remain relevant.
We did not verify a current public cryptographic audit. Filen documents encrypted metadata, open clients, and Linux support, but those facts do not equal independent validation.
Koofr Vault is a free, open-source client-side encrypted add-on available within Koofr plans. Ordinary Koofr storage is not encrypted by the client in the same way, and current independent cryptographic validation was not verified.
Cryptomator can encrypt a vault locally before synchronized files reach a provider. It does not hide the cloud account itself, all traffic patterns, or endpoint activity, and it reduces browser preview, search, collaboration, and assisted recovery.
No. Open code can improve inspectability, but security also depends on protocol design, builds, deployment, update practices, recovery, endpoints, and whether independent experts have reviewed the relevant version and scope.
No. An audit is evidence tied to a date, scope, methodology, and tested version. SOC reports assess controls, penetration tests inspect selected systems, and cryptographic reviews examine different questions. None is a permanent guarantee.
Synchronization is not automatically an independent backup. Deletions, corruption, and ransomware changes can propagate. Version history may help within its limits, but irreplaceable files still need a separate tested backup.
Filen documents a native Linux client. Koofr and pCloud document Linux support for their broader services, but their encrypted-vault workflows differ. Proton documents a command-line interface rather than the same native GUI sync workflow available on Windows and macOS.
Tresorit is the leading documentation-supported secure team fit in this review. Businesses must still verify administrator access, managed recovery, ownership, offboarding, export, legal requirements, and current plan terms.
It was evaluated, but the 2024 ETH research reported integrity-related attacks and the public remediation record remains conflicted. We did not verify a complete independent current retest that justified a shortlist recommendation.
Tuta described Drive as invite-only closed beta in April 2026. A closed beta is not yet a broadly available, independently assessable recommendation for mainstream readers.
Jurisdiction matters, but it does not replace architecture, implementation, recovery, metadata, audits, incidents, sharing, and endpoint security. A favorable location cannot repair a weak cryptographic design.
In a true user-controlled design, losing the only working recovery method can permanently destroy access. Set up supported recovery, protect codes or keys separately, and test recovery before trusting the system with irreplaceable data.
Not while malware or another user can access files after decryption. Use device encryption, updates, screen locking, malware defenses, account MFA, and separate backups alongside cloud encryption.
Recheck before purchase and after meaningful changes to architecture, ownership, audits, incidents, plans, platforms, recovery, or sharing. This guide's volatile claims were checked July 13, 2026.
These visible sources support the main architecture, incident, audit-scope, and category-boundary claims. The internal research record contains the complete 44-claim ledger, conflicts, qualifications, and refresh triggers.
Final recommendation
Proton Drive is the leading documentation-supported privacy fit. Tresorit is the leading secure team fit. Filen and Koofr Vault serve different open/Linux workflows; Sync is a qualified recovery-oriented contender; pCloud Crypto and Cryptomator offer different selected-vault strategies. None removes the need for endpoint security, careful sharing, tested recovery, and an independent backup.
Editorial independence: affiliate and commercial opportunities did not determine the candidate set, exclusions, labels, evidence treatment, or verdict. No tracked product link or commercial CTA was added to this article.
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