Elliptic Curve Diffie-Hellman-Merkle (ECDHM) addresses are Bitcoin address schemes that increase privacy. ECDHM addresses can be shared publicly, and are used by senders and receivers to secretly derive traditional Bitcoin addresses that passive blockchain observers cannot predict. The result is that ECDHM addresses can be "reused" without the loss of privacy that usually occurs from traditional Bitcoin address reuse.

Description

ECDHM addresses are based on the elliptic curve form of the Diffie-Hellman-Merkle (also known as Diffie-Hellman) protocol. Through asymmetric cryptography, this protocol allows two parties to exchange information over a public channel and establish a shared secret that only those two parties can mathematically derive. On this basis, two Bitcoin clients can exchange information publicly and create a shared secret that serves as an address for the sender to send to and the receiver to receive at.

Motivation

When traditional Bitcoin addresses are reused — when they receive more than one UTXO/payment — privacy is weakened. In the Bitcoin whitepaper, Satoshi advises parties not to reuse addresses, as this serves to definitely establish common ownership between Bitcoin transactions, and enables trivial graph analysis of the blockchain. This privacy damage can impact not only the owner of a reused address, but also her trading partners.

ECDHM addresses allow two parties to derive a secret address only known by the two of them from information shared publicly by both parties. The public information can be shared through some combination of the Bitcoin blockchain and other channels of communication. Different ECDHM protocols formulate different approaches to deriving and transmitting information, and have different trade-offs.

Proposals

Stealth Address

TODO

BIP47 Reusable Payment Code

Proposed by Justus Ranvier, Reusable Payment Codes (RPCs)… TODO