tea.py

def tea_decipher(v, key):
    vc = v.copy()
    btea(vc, -len(vc), key)
    return vc


def tea_encipher(v, key):
    vc = v.copy()
    btea(vc, len(vc), key)
    return vc


def btea(v, n, k):
    MX = lambda: ((z >> 5) ^ (y << 2)) + ((y >> 3) ^ (z << 4)) ^ \
            (sum ^ y) + (k[(p & 3) ^ e] ^ z)
    U32 = lambda x: x & 0xFFFFFFFF
    DELTA = 0x9e3779b9
    sum = 0
    y = v[0]
    if n > 1:
        z = v[n-1]
        for _ in range(0, 6 + 52//n):
            sum = U32(sum + DELTA)
            e = U32(sum >> 2) & 3
            p = 0
            while p < n - 1:
                y = v[p+1]
                z = v[p] = U32(v[p] + MX())
                p += 1
            y = v[0]
            z = v[n-1] = U32(v[n-1] + MX())
        return True
    elif n < -1:
        n = -n
        sum = U32((6 + 52//n) * DELTA)
        while sum != 0:
            e = U32(sum >> 2) & 3
            p = n - 1
            while p > 0:
                z = v[p-1]
                y = v[p] = U32(v[p] - MX())
                p -= 1
            z = v[n-1]
            y = v[0] = U32(v[0] - MX())
            sum = U32(sum - DELTA)


if __name__ == "__main__":
    v = [1, 2, 3, 4]
    k = [5, 6, 7, 8]
    r = tea_encipher(v, k)
    r2 = tea_decipher(r, k)

    assert(id(r2) != id(v))
    assert(v == r2)