Use the common helper function crypto_authenc_extractkeys() for key
parsing. Also ensure the keys do fit into the corresponding buffers.
Otherwise memory corruption might occur.
Cc: Christian Hohnstaedt <chohnstaedt@innominate.com> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Mathias Krause <mathias.krause@secunet.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>