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import sys
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import math
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import random
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import binascii as ba
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import os
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from struct import unpack as u
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from struct import pack
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is2 = sys.version_info[0] < 3
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def bt(b):
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    if is2:
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        return b
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    return ord(b)
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def b2i(b):
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    return int(ba.b2a_hex(b), 16)
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def i2b(i):
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    h = '%x' % i
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    if len(h) % 2 == 1:
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        h = '0' + h
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    if not is2:
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        h = h.encode('utf-8')
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    return ba.a2b_hex(h)
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def rs(a, o):
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    if a[o] == bt(pack('B', 0x81)):
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        return (u('B', a[o + 1])[0], 2 + o)
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    elif a[o] == bt(pack('B', 0x82)):
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        return (u('>H', a[o + 1:o + 3])[0], 3 + o)
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def ri(b, o):
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    i, o = rs(b, o)
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    return (b[o:o + i], o + i)
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def b2me(b):
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    if b[0] != bt(pack('B', 0x30)):
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        return (None, None)
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    _, o = rs(b, 1)
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    if b[o] != bt(pack('B', 2)):
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        return (None, None)
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    (m, o) = ri(b, o + 1)
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    if b[o] != bt(pack('B', 2)):
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        return (None, None)
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    e = b[o + 2:]
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    return (b2i(m), b2i(e))
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def der2me(d):
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    if d[0] != bt(pack('B', 0x30)):
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        return (None, None)
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    _, o = rs(d, 1)
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    while o < len(d):
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        if d[o] == bt(pack('B', 0x30)):
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            o += u('B', d[o + 1:o + 2])[0]
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        elif d[o] == bt(pack('B', 0x05)):
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            o += 2
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        elif d[o] == bt(pack('B', 0x03)):
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            _, o = rs(d, o + 1)
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            return b2me(d[o + 1:])
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        else:
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            return (None, None)
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def rsa_enc(der, msg):
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    m, e = der2me(der)
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    h = pack('BB', 0, 2)
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    d = pack('B', 0)
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    l = 256 - len(h) - len(msg) - len(d)
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    p = os.urandom(512).replace(pack('B', 0), pack(''))
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    return i2b(pow(b2i(h + p[:l] + d + msg), e, m))
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