Concepts: Value Commitments

This page gives the formal definitions used by ZAIR value commitments.

Native scheme

When the configured value-commitment scheme is native, each pool exposes its native Zcash value commitment, see the references and Zcash specification for details:

• Sapling: ${\mathsf{cv}}_{\mathsf{Sapling}}:={\mathsf{ValueCommit}}_{\mathsf{rcv}}^{\mathsf{Sapling}}(value).$
• Orchard: ${\mathsf{cv}}_{\mathsf{Orchard}}:={\mathsf{ValueCommit}}_{\mathsf{rcv}}^{\mathsf{Orchard}}(value).$

Here rcv is the randomness used by the pool-native commitment scheme.

SHA-256 scheme

When the configured value-commitment scheme is sha256, both Sapling and Orchard use:

$$cv\_sha256:=SHA256(\text{"Zair"}\Vert LE64(v)\Vert rcv\_sha256).$$

Here rcv_sha256 is the randomness used by the SHA-256 commitment scheme, and $LE64(v)$ is the value as 8 little endian bytes, and the prefix "Zair" is a fixed 4-byte ASCII domain-separation tag.

Plain scheme

When the configured value-commitment scheme is plain, the note value is exposed directly as a single public field element with no commitment or randomness:

$$\mathsf{value}:=v$$

This provides no privacy for the note value. It is useful when value hiding is not required and a simpler, more compact public input is preferred. No rcv or rcv_sha256 randomness is needed.