Data Encoding

Also known as base16, this method represents binary data using the 16 symbols 0-9 and a-f. Each byte (8 bits) is represented by two hexadecimal characters.

• Key Use: The standard human-readable format for representing cryptographic hashes, public keys, transaction IDs, and raw bytecode on blockchains like Ethereum.
• Example: A common Ethereum address prefix is 0x followed by 40 hex characters (e.g., 0x742d35Cc6634C0532925a3b844Bc9e...).

A space-efficient serialization method created for Ethereum. It encodes arbitrarily nested arrays of binary data and is the primary method for serializing objects in Ethereum's execution layer.

• Key Use: Encoding transactions, block headers, and the nodes of the Merkle Patricia Trie (state tree). It is deterministic, ensuring the same input always produces the same encoded output for consistent hashing.

The serialization standard for Ethereum's consensus layer (the Beacon Chain). Designed for efficiency and Merkleization, it enables the easy construction of Merkle proofs for any part of the data structure.

• Key Use: Serializing BeaconBlock and BeaconState objects. Its deterministic and canonical nature is critical for consensus and light client support in proof-of-stake Ethereum.

Encoding efficiency directly impacts transaction costs. Compact formats like RLP (Recursive Length Prefix) and ABI encoding are designed to minimize on-chain storage and computation gas. Inefficient encoding can lead to:

• Excessive calldata costs on L2s where data availability is priced.
• High execution gas for decoding complex nested structures in smart contracts.
• Optimization techniques like using bytes32 for packed data and selective decoding are critical for cost-effective contracts.

Malformed or maliciously crafted encoded data is a primary attack vector. Contracts must rigorously validate inputs before decoding to prevent:

• Buffer overflows and out-of-bounds reads that can corrupt memory.
• Denial-of-service (DoS) via intentionally complex or deep nested structures that exhaust gas limits during decoding.
• Logic bypasses where unexpected data shapes trigger unintended code paths. Always use safe libraries (e.g., OpenZeppelin's BytesLib) and check encoded data length and structure preemptively.

For blockchain consensus, encoding and decoding must be strictly deterministic. Any non-determinism in a client's implementation can cause a network fork. This is crucial for:

• State root validation: All nodes must compute identical hashes from the same encoded data.
• Light client proofs: Merkle-Patricia Trie proofs rely on a single, agreed-upon encoding scheme (RLP for Ethereum).
• Cross-chain communication: Bridges and oracles must use identical, versioned encoding to interpret messages reliably.

Encoding schemas are part of a system's permanent API. Changes can break existing contracts and integrations. Key considerations include:

• Versioning: Explicit version bytes or function selectors to distinguish encoding formats.
• Schema evolution: Adding new optional fields vs. breaking changes to existing fields.
• Storage layout: In upgradeable proxies, changing the encoding of stored data can lead to permanent data corruption. Patterns like EIP-1967 use specific storage slots with fixed encoding to mitigate this.

Encoding defines what data is signed and hashed. Inconsistencies here are catastrophic. Critical practices involve:

• EIP-712 structured hashing: Standardizes encoding of typed data for signatures, preventing signature malleability and replay attacks across domains.
• Precise ABI encoding: For ecrecover, the signed message must be the keccak256 hash of the tightly packed, ABI-encoded parameters. Any deviation in padding or order invalidates the signature.
• Commit-Reveal schemes: The encoded form of the committed data must be immutable between commit and reveal phases.

Reliance on external libraries for encoding/decoding introduces dependency risks. Assess:

• Audit status: Use widely-audited libraries like Solidity's abi global, @ethersproject/abi, or ethereumjs/rlp.
• Edge case handling: How does the library handle malformed data? Does it revert, return garbage, or panic?
• Gas efficiency: Different libraries may have varying overhead. Inline assembly can be used for critical, gas-sensitive decoding but increases complexity and risk.

The process of translating a data structure or object state into a format that can be stored or transmitted and reconstructed later. In blockchain, this is essential for creating deterministic transaction hashes and for peer-to-peer communication.

• Examples: RLP (Ethereum), Protocol Buffers (Libp2p), Borsh (Solana).
• Purpose: Ensures all nodes compute identical hashes from the same data, guaranteeing consensus.

A space-efficient serialization format used extensively in Ethereum. It encodes arbitrarily nested arrays of binary data and is the primary method for encoding objects like transactions and blocks before hashing.

• Key Property: It lacks explicit type definitions, focusing solely on structure and length.
• Function: Forms the input for the Keccak-256 hash that produces transaction and state root identifiers.

The standard way for external systems, like front-end applications or other contracts, to interact with an Ethereum smart contract. It defines how to encode function calls and data into low-level EVM bytecode and how to decode the returned data.

• Contains: Function signatures, argument types, and event logs.
• Encoding: Uses a tightly packed, hexadecimal representation prefixed with a function selector.

A binary-to-text encoding scheme that represents binary data in an ASCII string format. It is commonly used to encode smart contract bytecode, cryptographic keys, or data payloads in JSON-RPC APIs and blockchain explorers.

• Character Set: Uses 64 printable characters (A-Z, a-z, 0-9, +, /).
• Use Case: Makes binary data safe to transmit over protocols designed for text, like HTTP.

The serialization and Merkleization standard for Ethereum 2.0. It is designed to be deterministic, efficient, and optimized for Merkle tree generation, which is central to the beacon chain's consensus.

• Features: Provides consistent hash tree roots and efficient proofs.
• Contrast to RLP: SSZ has a rigid, schema-based structure, enabling faster serialization and verification.

In the EVM, calldata is a read-only byte array containing the arguments of an external function call. Its encoding follows the ABI specification. Understanding this encoding is crucial for low-level contract interactions, gas optimization, and writing assembly code.

• Gas Cost: Using calldata for function arguments is cheaper than memory for external calls.
• Structure: Includes a 4-byte function selector followed by the ABI-encoded arguments.