smallprp.py

# https://eprint.iacr.org/2012/254

def random(K):
    ctr = 0
    while True:
        yield AES(K, ctr)
        ctr += 1

def PRP(K, x):
    return (x, 0, N, 0, random(K))

def Permute(x, alpha, l, d, R)
    if l == 1:
        return alpha
    if beta_d(alpha+x) == 0:
        xdash = C0(beta_d, alpha, x)
        return Permute(xdash, alpha, C0(beta_d, alpha, l), d+1, R)
    else:
        xdash = C1(beta_d, alpha, x)
        return Permute(xdash, alpha + C0(beta_d, alpha, l), C1(beta_d, alpha, l), d+1, R)

def Unpermute(y, alpha, l, d, R)
    if l == 1:
        return 0
    if y < C0(alpha, l, d):
        ydash = y
        xdash = Unpermute(ydash, alpha, C0(beta_d, alpha, l), d+1, R)
        return C0inv(beta_d, alpha, xdash+1)
    else:
        ydash = y - C0(beta_d, alpha, l)
        xdash = Unpermute(ydash, alpha + C0(beta_d, alpha, l), C1(beta_d, alpha, l), d+1, R)
        return C1inv(beta_d, alpha, xdash+1)

def C0(...):
    ...

def C0inv(...):
    ...

def C1(...):
    ...

def C1inv(...):
    ...