Running one-block SHA-256 in reverse

Assume 20 rounds, t = 0:19, with Kt known but Wt XOR'd with secret key bits Sj

a-h values are shown at the end of a round:


t = 14          a       b       c       d       e       f       g       h
                 \       \       \       \       \       \       \
                  \       \       \       \       \       \       \
                   \       \       \       \       \       \       \
          T1+T2     \       \       \      +T1      \       \       \
             \       \       \       \       \       \       \       \
              \       \       \       \       \       \       \       \
               \       \       \       \       \       \       \       \
t = 15          a       b       c       d       e       f       g       h
                 \       \       \       \       \       \       \
                  \       \       \       \       \       \       \
                   \       \       \       \       \       \       \
          T1+T2     \       \       \      +T1      \       \       \
             \       \       \       \       \       \       \       \
              \       \       \       \       \       \       \       \
               \       \       \       \       \       \       \       \
t = 16          a       b       c       d       e       f       g       h
                 \       \       \       \       \       \       \
                  \       \       \       \       \       \       \
                   \       \       \       \       \       \       \
          T1+T2     \       \       \      +T1      \       \       \
             \       \       \       \       \       \       \       \
              \       \       \       \       \       \       \       \
               \       \       \       \       \       \       \       \
t = 17          a       b       c       d       e       f       g       h
                 \       \       \       \       \       \       \
                  \       \       \       \       \       \       \
                   \       \       \       \       \       \       \
          T1+T2     \       \       \      +T1      \       \       \
             \       \       \       \       \       \       \       \
              \       \       \       \       \       \       \       \
               \       \       \       \       \       \       \       \
t = 18          a       b       c       d       e       f       g       h
                 \       \       \       \       \       \       \
                  \       \       \       \       \       \       \
                   \       \       \       \       \       \       \
          T1+T2     \       \       \      +T1      \       \       \
             \       \       \       \       \       \       \       \
              \       \       \       \       \       \       \       \
               \       \       \       \       \       \       \       \
t = 19          a       b       c       d       e       f       g       h


Wt = ROTR(Sj,k) XOR Mt,                       t = 0:7,   j = t,        k = 3*j+(t>>3)

     ROTR(Sj,k) XOR Mt,                       t = 8:12,  j = t-5

     ROTR(Sj,k) XOR Mt,                       t = 12:15, j = (t-12)%3

     ROTR(Sj,k) XOR func(t-2,t-7,t-15,t-16),  t = 16:19, j = (63-t)%8
     
T1 = h + func(e,f,g) + Kt + Wt
T2 = func(a,b,c)
h = g
g = f
f = e
e = d + T1
d = c
c = b
b = a
a = T1 + T2