ProSapien LLC A SAID (Self-Addressing IDentifier) is a special type of content- addressable identifier based on encoded cryptographic digest that is self-referential. The SAID derivation protocol defined herein enables verification that a given SAID is uniquely cryptographically bound to a serialization that includes the SAID as a field in that serialization. Embedding a SAID as a field in the associated serialization indicates a preferred content-addressable identifier for that serialization that facilitates greater interoperability, reduced ambiguity, and enhanced security when reasoning about the serialization. Moreover, given sufficient cryptographic strength, a cryptographic commitment such as a signature, digest, or another SAID, to a given SAID is essentially equivalent to a commitment to its associated serialization. Any change to the serialization invalidates its SAID thereby ensuring secure immutability evident reasoning with SAIDs about serializations or equivalently their SAIDs. Thus SAIDs better facilitate immutably referenced data serializations for applications such as Verifiable Credentials or Ricardian Contracts. SAIDs are encoded with CESR (Composable Event Streaming Representation) [CESR] which includes a pre-pended derivation code that encodes the cryptographic suite or algorithm used to generate the digest. A CESR primitive's primary expression (alone or in combination ) is textual using Base64 URL-safe characters. CESR primitives may be round-tripped (alone or in combination) to a compact binary representation without loss. The CESR derivation code enables cryptographic digest algorithm agility in systems that use SAIDs as content addresses. Each serialization may use a different cryptographic digest algorithm as indicated by its derivation code. This provides interoperable future proofing. CESR was developed for the [KERI] protocol.