diff options
| -rw-r--r-- | pySim/utils.py | 32 |
1 files changed, 26 insertions, 6 deletions
diff --git a/pySim/utils.py b/pySim/utils.py index 17dc693..ba94702 100644 --- a/pySim/utils.py +++ b/pySim/utils.py @@ -49,11 +49,29 @@ def rpad(s, l, c='f'): def lpad(s, l, c='f'): return c * (l - len(s)) + s +def half_round_up(n): + return (n + 1)//2 + +# IMSI encoded format: +# For IMSI 0123456789ABCDE: +# +# | byte 1 | 2 upper | 2 lower | 3 upper | 3 lower | ... | 9 upper | 9 lower | +# | length in bytes | 0 | odd/even | 2 | 1 | ... | E | D | +# +# If the IMSI is less than 15 characters, it should be padded with 'f' from the end. +# +# The length is the total number of bytes used to encoded the IMSI. This includes the odd/even +# parity bit. E.g. an IMSI of length 14 is 8 bytes long, not 7, as it uses bytes 2 to 9 to +# encode itself. +# +# Because of this, an odd length IMSI fits exactly into len(imsi) + 1 // 2 bytes, whereas an +# even length IMSI only uses half of the last byte. + def enc_imsi(imsi): """Converts a string imsi into the value of the EF""" - l = (len(imsi) + 1) // 2 # Required bytes + l = half_round_up(len(imsi) + 1) # Required bytes - include space for odd/even indicator oe = len(imsi) & 1 # Odd (1) / Even (0) - ei = '%02x' % l + swap_nibbles(lpad('%01x%s' % ((oe<<3)|1, imsi), 16)) + ei = '%02x' % l + swap_nibbles('%01x%s' % ((oe<<3)|1, rpad(imsi, 15))) return ei def dec_imsi(ef): @@ -61,13 +79,15 @@ def dec_imsi(ef): if len(ef) < 4: return None l = int(ef[0:2], 16) * 2 # Length of the IMSI string - swapped = swap_nibbles(ef[2:]) + l = l - 1 # Encoded length byte includes oe nibble + swapped = swap_nibbles(ef[2:]).rstrip('f') oe = (int(swapped[0])>>3) & 1 # Odd (1) / Even (0) - if oe: + if not oe: + # if even, only half of last byte was used l = l-1 - if l+1 > len(swapped): + if l != len(swapped) - 1: return None - imsi = swapped[1:l+2] + imsi = swapped[1:] return imsi def dec_iccid(ef): |