Patient provides a protected EMR attached to DID to HAC

P.1 Patient $\to$ HAC : $\underset{M}{\underbrace{DID,{\left\{EMR\right\}}_k}}$ , ${\left\{H\left(M\right)\right\}}_{k_p^{-1}}$ , ${\left\{k\right\}}_{k_c}$

HAC looks for k_b linked DID in Indy

P.2 HAC $\to$ Indy : DID

P.3 Indy $\to$ HAC : DID, k_b, ${\left\{H\left(DID,k_b\right)\right\}}_{k_p^{-1}}$

HAC challenges Patient to prove that he is the owner of k_b

P.4 HAC $\to$ Patient : DID, N_c

P.5 Patient $\to$ HAC : ${\left\{H\left(DID,N_c\right)\right\}}_{k_b^{-1}}$