def get_crypto_obj(algo, filename=None, key=None):
if filename is None and key is None:
raise ValueError('you need to specify either filename or key')
if key is not None:
bio = BIO.MemoryBuffer(str(key))
else:
bio = BIO.openfile(filename)
# we can know what's the algorithm used thanks to the filename
if algo.startswith('RS'):
obj = _RSA.load_pub_key_bio(bio)
elif algo.startswith('DS'):
obj = _DSA.load_pub_key_bio(bio)
else:
raise ValueError('unknown algorithm')
return obj
