Blockchain Privacy and Searchable Encryption

Flashcards covering Zero Knowledge Proofs (ZK-SNARKs, ZK-STARKs, Zcash) and Searchable Encryption (SSE, PEKS, and related security attacks).

Blockchain

A decentralized ledger spread over networks to allow transactions over different computers; it is immutable and allows transactions over multiple processes.

Zero Knowledge Proof (ZKP)

A protocol where a prover sends a proof to a verifier to verify information while hiding specific inputs and amounts from other sources.

Completeness

A property of ZKPs where if the prover has made a true statement, it will be accepted by both parties.

Soundness

A property of ZKPs where if a statement is false, no cheating prover can prove it correct to the verifier.

Zero Knowledge (Property)

The requirement that the verifier learns nothing except the fact that the statement is true, without gaining access to the prover's inputs.

ZK-SNARKs

An acronym for Zero Knowledge Succinct Non-Interactive Argument of Knowledge.

Succinct

A characteristic of ZK-SNARKs meaning they use very few computations and are very fast to verify.

Non-interactive Argument

The ability in ZK-SNARKs to send only one proof instead of multiple rounds of communication to reduce time and execution costs.

QAP (Quadratic Arithmetic Program)

A format that contains mathematical computations converted from an algorithm, used to generate proofs in the SNARKs process.

Common Reference String (CRS)

Public parameters generated during a one-time trusted setup used to verify if calculations match the prover's claims.

Groth 16

The version of SNARKs used in Zcash that requires a trusted setup ceremony to generate public parameters.

Trusted Setup Ceremony

A process using multiple coordinators and randomness to generate public parameters while preventing the creation of counterfeit proofs.

Toxic Waste

The secret trapdoor information used to create public parameters in a trusted setup that must be destroyed to ensure system security.

ZK-STARKs

A newer version of zero knowledge proofs that utilizes a transparent setup and is quantum resistant.

Halo

An advanced improvement for zero knowledge proofs used in the Zcash version to address limitations of previous SNARKs.

Searchable Encryption

The ability to perform searches on data held by an untrusted third party without decrypting the data first.

Sequential Scan

An indexing method where one computes down the encrypted document comparing values until a match is found.

Document-based Indexing

An indexing method where keywords are embedded directly into the encrypted file to make searches more efficient.

Keyword-based Index

A method that links keywords to a file's location, increasing search efficiency at the expense of complexity when updating the index.

SSE (Symmetric Searchable Encryption)

A method that uses a cryptographically secure pseudo-random number generator (PRNG) and XORs the output with plain text to produce ciphertext.

PEKS (Public Key Encryption with Keyword Search)

A model where a keyword is encrypted with a public key and the receiver computes a trapdoor with their private key to test against keywords on the server.

Trapdoor

In searchable encryption, an encrypted form of a keyword (similar to a hash) that is sent to a server to perform a search without revealing the plaintext keyword.

Keyword Guessing Attack

A query recovery attack on PEKS where an attacker tests individual encrypted keywords using a captured trapdoor and a public key.

File Injection Attack

A query recovery attack where a malicious server sends emails to itself so that when a client encrypts them, the server can identify which keywords correspond to the queries.