def makeKeyLen(key, length):
    mulLen, restLen = divmod(length, len(key))
    return key * mulLen + key[:restLen]

def encryptChar(m, k):
    return chr((ord(m) + ord(k)) % 127);

def decryptChar(c, k):
    return chr((ord(c) - ord(k) + 127) % 127);

def encryptECB(msg, key):
    key = makeKeyLen(key, len(msg))
    return "".join(encryptChar(m, k) for m, k in zip(msg, key))

def decryptECB(msg, key):
    key = makeKeyLen(key, len(msg))
    return "".join(decryptChar(m, k) for m, k in zip(msg, key))

def OFB(msg, key, c):
    key = makeKeyLen(key, len(msg))
    encKey = c;
    res = ""
    for m, k in zip(msg, key):
        encKey = encryptChar(k, encKey)
        res += chr(ord(encKey) ^ ord(m))
    return res;