RLP

RLP, or Recursive Length Prefix encoding, is a simple serialisation method used to encode arbitrarily nested arrays of binary data. It is designed for compact representation and efficient decoding, and it is a core encoding scheme in Ethereum for encoding various protocol data structures such as transactions, blocks, receipts, and state data. RLP is characterized by its use of prefixes to indicate the length of encoded items, enabling straightforward parsing and streaming.

The encoding rules distinguish between strings (raw byte sequences) and lists (arrays of encoded items). For a string, several cases apply: the empty string is encoded as a single byte 0x80; a single byte with value in the range 0x00 to 0x7f is encoded as that byte itself (no prefix); a string with length L between 1 and 55 is prefixed with 0x80 + L followed by the data; a string longer than 55 bytes is prefixed with 0xb7 + the length of the length, followed by the length in big-endian form and then the data. Lists are encoded similarly but with different prefix ranges: a list with total payload length up to 55 bytes uses 0xc0 + length as the prefix, followed by the concatenation of the encoded items; longer lists use 0xf7 + length of the length, followed by the length and the payload. The empty list is encoded as 0xc0.

Examples help illustrate: encoding the string "cat" (three bytes) yields 0x83 63 61 74; encoding the list ["cat", "dog"] yields 0xc8 0x83 63 61 74 0x83 64 6f 67. RLP is not a cryptographic primitive; it is an encoding scheme used to enable compact, unambiguous data transmission and storage within Ethereum.