This paper is the first known proposal for a blockchain protocol.

Chaum describes the design of a distributed computer system that can be established, maintained, and trusted by mutually suspicious groups.

It is a public record-keeping system with group membership consistency and private transaction computations that protects individual privacy through physical security.

The building blocks of this system include physically-secure “vaults”, existing cryptographic primitives (symmetric and asymmetric encryption, cryptographic hash functions, digital signatures), and a new primitive introduced by Chaum—threshold secret sharing, i.e. “where some threshold of sub-partial keys are sufficient to reconstruct the original partial key from which the sub-partials were originally formed”.

For more on the history of blockchain technologies, consider On the Origins and Variations of Blockchain Technologies.