Algorithm 7 The Challenge–Response Step 2.4 [SN]

Inputs:  $RE{S}^{*}$       SN compute $HRE{S}^{*}\leftarrow LEFT(128,H_{SHA-256}(RAND\parallel RE{S}^{*}))$       Check if $HRE{S}^{*}=HXRE{S}^{*}$, Abort in the negative case. Otherwise, continue    Outputs. SN sends $RE{S}^{*}$ to HN.