Decode Mac Open Firmware Password

decode_firmware_pwd.py

# I forgot the firmware password on my MacBook Air and didn't want to take it in:
#   http://support.apple.com/kb/TS2391
# info
#   http://paulmakowski.blogspot.com/2009/03/apple-efi-firmware-passwords.html

# run the following command to retrieve your obfuscated firmware password:
#   sudo nvram -p | grep security-password
security_password = "%..."

# take the complement of every second bit:
decode_byte = lambda byte: chr(int(byte, 16) ^ int('10101010',2))

# decode the security password, which contains %-prefixed hex values:
decode = lambda pwd: "".join([decode_byte(x) for x in pwd.split('%') if x != ''])

print(decode(security_password))