Detached Signature

The core feature is the physical separation of the signature from the signed data. This allows the original data (e.g., a transaction, document, or message) to be handled, stored, or transmitted independently of its proof of authenticity. The signature is a standalone cryptographic proof that can be verified against the data at any later time.

Detached signatures provide cryptographic proof that a specific entity, possessing the corresponding private key, approved the exact data. This prevents the signer from later denying their involvement (non-repudiation) and guarantees the data has not been altered since signing (integrity). Verification involves hashing the original data and checking it against the decrypted signature.

By separating the signature, systems can transmit or store only the essential components. For example:

• A blockchain node can broadcast a transaction without its signature for initial validation checks.
• Archival systems can store data compactly, attaching signatures only when needed for audit.
• Light clients can request signatures on-demand rather than downloading them for every piece of data.

Detached signatures enable advanced verification schemes. Batch verification allows a verifier to check multiple signatures against multiple data points simultaneously, improving performance. Signature aggregation, used in schemes like BLS, allows multiple signatures on different pieces of data to be combined into a single, compact proof, drastically reducing on-chain storage and computation costs.

This pattern is fundamental in blockchain and applied cryptography:

• Bitcoin/ECDSA: The signature (r, s) is an output separate from the transaction data it signs.
• GPG/PGP: Used for signing emails and software releases, where the .sig file is separate from the payload.
• Zero-Knowledge Proofs: The proof is a detached attestation to the validity of a private statement.
• Document Signing: Legal and compliance workflows where the signature is a metadata attachment.

The decoupling allows for flexible trust models and verification workflows. Third parties can verify authenticity without needing direct access to the signing system. Auditors can cryptographically verify historical data long after it was signed. Systems can implement lazy verification, where signatures are only checked under specific conditions (e.g., dispute resolution), optimizing for performance in trusted environments.

In Layer 2 scaling solutions like ZK-Rollups, a prover generates a single cryptographic proof (a detached signature) that attests to the validity of hundreds of transactions processed off-chain. This proof is then submitted to the main chain (Layer 1), where a verifier contract checks it. This allows the network to inherit security from Ethereum while drastically reducing on-chain data and gas costs.

• Key Benefit: Enables high throughput and low fees.
• Example: StarkNet and zkSync use this model.

Detached signatures enable data availability sampling and secure off-chain data storage. Protocols like Celestia or EigenDA can attest to the availability of large data blobs (like transaction data for a rollup) by having validators sign a Merkle root commitment. Light clients or other chains only need to verify these signatures and sample small chunks of data to be confident the entire dataset is available, separating data publication from consensus.

Cross-chain bridges and interoperability protocols rely on detached signatures for attestation. A set of oracles or validators observes an event on a source chain (e.g., a token lock) and produces a multi-signature or threshold signature as proof. This signature bundle is a detached attestation that is relayed to the destination chain, where a smart contract verifies it before minting equivalent assets or executing a command, enabling trust-minimized cross-chain state transitions.

Privacy protocols like Zcash or Aztec use detached signatures (specifically, zero-knowledge proofs) to authorize transactions without revealing sender, recipient, or amount. A user generates a zk-SNARK proof—a form of detached signature—that proves they know a valid spending key for an input note and have correctly computed the output notes, all without linking the two. The network verifies only the proof, ensuring transaction validity while maintaining privacy.

In blockchain client and smart contract development, detached signatures verify the integrity and authorship of released software. Developers sign the cryptographic hash (e.g., SHA-256) of a binary or source code release using a private key. Users can download the software from any mirror, then independently verify the hash and the attached PGP/GPG signature against the developer's public key. This ensures the code has not been tampered with, a critical practice for wallet software and node clients.

Verifiable Credentials (VCs) in decentralized identity systems are built on detached signatures. An issuer (like a university) creates a cryptographic signature over a claim (e.g., a degree) and issues it to a holder. The holder stores this signed credential (the detached signature) in their digital wallet. They can then present it to a verifier (like an employer), who checks the signature against the issuer's public Decentralized Identifier (DID) to confirm its authenticity without contacting the issuer directly.

A digital signature is a cryptographic scheme that verifies the authenticity and integrity of a digital message or document. It is generated using a private key and can be verified by anyone with the corresponding public key. Detached signatures are a specific implementation where the signature is stored separately from the data it signs.

• Core Components: Private/Public Key Pair, Signing Algorithm (e.g., ECDSA, EdDSA).
• Purpose: Provides authentication, non-repudiation, and data integrity.
• Contrast: An attached signature is embedded within the signed data structure (e.g., a Bitcoin transaction), whereas a detached signature exists as a separate file.

Public key cryptography (or asymmetric cryptography) is the foundational system that enables digital signatures. It uses a pair of mathematically linked keys: a public key, which is shared openly, and a private key, which is kept secret.

• How it works for signing: The private key generates a signature; the public key verifies it without revealing the secret.
• Common Algorithms: RSA, Elliptic Curve Cryptography (ECC/ECDSA), Ed25519.
• Blockchain Application: This is the basis for blockchain addresses and transaction authorization. A detached signature is the output of applying this cryptography to a hash of the data.

A cryptographic hash function (e.g., SHA-256, Keccak-256) is an algorithm that takes an input of any size and produces a fixed-size, unique output called a hash or digest. Detached signatures typically sign the hash of the data, not the data itself.

• Properties: Deterministic, pre-image resistant, collision resistant.
• Role in Signing: Signing a compact, fixed-length hash is more efficient than signing large datasets. The signature validates that the hash—and thus the original data—has not been altered.
• Example: Git commits use detached signatures (via GPG) on the commit hash to verify authorship.

Commit signing in Git uses detached signatures to cryptographically verify the author of a code commit. The signature is attached to the commit object as a separate payload, proving it was created by someone with the corresponding private key.

• Mechanism: Git signs the SHA-1 hash of the commit object using GPG or SSH keys, generating a detached signature block.
• Platform Enforcement: GitHub and GitLab display a "Verified" badge for signed commits.
• Security Benefit: Protects against repository compromises where an attacker could forge commit metadata (author/email).

EIP-712 is an Ethereum standard for signing typed structured data with a detached signature. It moves beyond signing raw transaction hashes to signing human-readable representations of complex data, improving security and user experience for dApps.

• Key Innovation: Presents users with a clear, structured representation of what they are signing.
• Detached Nature: The signature is generated off-chain and then submitted in a transaction (e.g., for permit functions in DeFi).
• Use Case: MetaTransactions, gasless token approvals (permit), and decentralized exchange orders.