A browser tab as an encrypted archive for external files
A recent academic study has introduced an innovative system called Safecloud, which transforms browser tabs into nodes of decentralized storage for encrypted files. The research, conducted by Gregory Magarshak of IENYC, proposes a unique architecture where storage nodes only see encrypted data and routing nodes do not hold decryption keys.
How the system fragments and hides files
Safecloud adopts an innovative approach to file management. Each file is divided into fixed-size fragments and encrypted on the owner's device before distribution. These encrypted fragments are then distributed across two types of nodes:
- Drops: operate within normal browser tabs and store the encrypted fragments in IndexedDB, the built-in storage space in web browsers.
- Jets: are routing servers that match fragments to Drops and manage retrieval requests.
The file owner, called "Cloud," holds the master secret and has the ability to decrypt the contents.
Key derivation and deduplication
Each key in the system is derived from a 32-byte master secret through a standard derivation function. This feature allows the network to maintain a single copy of duplicate data, reducing the required storage space. However, deduplication is limited within a single owner's master secret, ensuring that two owners encrypting the same file produce different addresses.
The address used to locate each fragment is calculated on the encrypted bytes, allowing storage nodes to confirm the correctness of the fragment without accessing the content or keys.
Data structures and integrity verification
Safecloud maintains three structures that share an addressing scheme:
- Public Merkle tree: covers the integrity of the fragments.
- Key derivation tree: covers confidentiality.
- Access tree: covers authorization.
A single path simultaneously locates the integrity proof of a fragment, its decryption key, and its access authorization. A consumer retrieving a fragment can verify the returned bytes against a public root, detecting any replaced or corrupted fragments.
Streaming and access control
The same key hierarchy is used to enable multimedia content streaming. A player holding the key for a track can derive the key for the next segment in one step from a key already possessed. This allows access to any point in a video with a single derivation calculation and a single retrieval.
Video tracks, audio tracks, and subtitles of a file are placed in separate branches and can be unlocked individually. An owner can grant access to a range of segments, such as a preview or a rented chapter, by providing a single key for that range.
Magarshak presents this combination of streamable, randomly decryptable access with per-segment access control as a novelty among encrypted storage networks.
Limitations and access revocation
One limitation of the design is that once a range key reaches a beneficiary, revoking that access requires key rotation for that range, as the beneficiary retains what has been derived.
The economic level
Drops earn a token called Safebux for maintaining and serving fragments, while Jets earn for routing. Payment is made through a signed request that authorizes up to a growing maximum on a numbered line, allowing providers to demonstrate what is owed to them and preventing payers from reproducing an old authorization.
Storage honesty is based on a challenge where a Jet asks a Drop to sign a new content address and a nonce. A Drop that no longer holds the fragment fails, and repeated failures lead to a reduction in stake and the fragment being reproduced.
Magarshak argues that this design has a lower cost than the sealing used by Filecoin, where a provider proves storage through slow encoding that takes tens of minutes per sector and proves separate physical replication from confidentiality.
Current status and threats
Currently, the working parts include encryption, fragmentation, content addressing, Merkle integrity tree, and delegation construction. The payment level and proof of storage are specified and partially connected.
The system's threat model is broad: an adversary can run any number of Drops, run Jets, monitor all network traffic, and collude between nodes. However, it cannot break encryption or signature schemes and does not control the owner's device, which holds the keys and plaintext data.
Under these conditions, a storage node learns nothing from the encrypted text, a node cannot return altered bytes without being detected, and a node claiming to store data it does not possess fails the challenge.
The connection with Safebox
Safecloud can be used together with a separate system called Safebox. Magarshak emphasizes that the two systems are independent: "Safecloud is completely independent of Safebox. The phases of encryption, storage, routing, and payment can be audited without relying on Safebox."
A browser tab as an encrypted archive for external files
A recent academic study has introduced an innovative system called Safecloud, which transforms browser tabs into nodes of decentralized storage for encrypted files. The research, conducted by Gregory Magarshak of IENYC, proposes a unique architecture where storage nodes only see encrypted data and routing nodes do not hold decryption keys.
How the system fragments and hides files
Safecloud adopts an innovative approach to file management. Each file is divided into fixed-size fragments and encrypted on the owner's device before distribution. These encrypted fragments are then distributed across two types of nodes:
- Drops: operate within normal browser tabs and store the encrypted fragments in IndexedDB, the built-in storage space in web browsers.
- Jets: are routing servers that match fragments to Drops and manage retrieval requests.
The file owner, called "Cloud," holds the master secret and has the ability to decrypt the contents.
Key derivation and deduplication
Each key in the system is derived from a 32-byte master secret through a standard derivation function. This feature allows the network to maintain a single copy of duplicate data, reducing the required storage space. However, deduplication is limited within a single owner's master secret, ensuring that two owners encrypting the same file produce different addresses.
The address used to locate each fragment is calculated on the encrypted bytes, allowing storage nodes to confirm the correctness of the fragment without accessing the content or keys.
Data structures and integrity verification
Safecloud maintains three structures that share an addressing scheme:
- Public Merkle tree: covers the integrity of the fragments.
- Key derivation tree: covers confidentiality.
- Access tree: covers authorization.
A single path simultaneously locates the integrity proof of a fragment, its decryption key, and its access authorization. A consumer retrieving a fragment can verify the returned bytes against a public root, detecting any replaced or corrupted fragments.
Streaming and access control
The same key hierarchy is used to enable multimedia content streaming. A player holding the key for a track can derive the key for the next segment in one step from a key already possessed. This allows access to any point in a video with a single derivation calculation and a single retrieval.
Video tracks, audio tracks, and subtitles of a file are placed in separate branches and can be unlocked individually. An owner can grant access to a range of segments, such as a preview or a rented chapter, by providing a single key for that range.
Magarshak presents this combination of streamable, randomly decryptable access with per-segment access control as a novelty among encrypted storage networks.
Limitations and access revocation
One limitation of the design is that once a range key reaches a beneficiary, revoking that access requires key rotation for that range, as the beneficiary retains what has been derived.
The economic level
Drops earn a token called Safebux for maintaining and serving fragments, while Jets earn for routing. Payment is made through a signed request that authorizes up to a growing maximum on a numbered line, allowing providers to demonstrate what is owed to them and preventing payers from reproducing an old authorization.
Storage honesty is based on a challenge where a Jet asks a Drop to sign a new content address and a nonce. A Drop that no longer holds the fragment fails, and repeated failures lead to a reduction in stake and the fragment being reproduced.
Magarshak argues that this design has a lower cost than the sealing used by Filecoin, where a provider proves storage through slow encoding that takes tens of minutes per sector and proves separate physical replication from confidentiality.
Current status and threats
Currently, the working parts include encryption, fragmentation, content addressing, Merkle integrity tree, and delegation construction. The payment level and proof of storage are specified and partially connected.
The system's threat model is broad: an adversary can run any number of Drops, run Jets, monitor all network traffic, and collude between nodes. However, it cannot break encryption or signature schemes and does not control the owner's device, which holds the keys and plaintext data.
Under these conditions, a storage node learns nothing from the encrypted text, a node cannot return altered bytes without being detected, and a node claiming to store data it does not possess fails the challenge.
The connection with Safebox
Safecloud can be used together with a separate system called Safebox. Magarshak emphasizes that the two systems are independent: "Safecloud is completely independent of Safebox. The phases of encryption, storage, routing, and payment can be audited without relying on Safebox."
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