dexter has uploaded this change for review. ( https://gerrit.osmocom.org/c/pysim/+/37931?usp=email )

Change subject: scp: fix key length in dek_encrypt and dek_decrypt ......................................................................

scp: fix key length in dek_encrypt and dek_decrypt

When creating the DES cipher object with DES.new, we use the property card_keys.dek. This property may hold a 16 byte key, but DES uses an 8 byte key. Pycryptodome does not automatically ignore excess key bytes. Instead it throws an exception. This means we need to make sure to supply only the first 8 bytes of card_keys.dek

Related: OS#6531 Change-Id: I92e0dc6a6196b532bd8b53fca7b9e78070d6903f --- M pySim/global_platform/scp.py 1 file changed, 2 insertions(+), 2 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/pysim refs/changes/31/37931/1

diff --git a/pySim/global_platform/scp.py b/pySim/global_platform/scp.py index f68bcf9..17463ff 100644 --- a/pySim/global_platform/scp.py +++ b/pySim/global_platform/scp.py @@ -230,11 +230,11 @@ super().__init__(*args, **kwargs)

def dek_encrypt(self, plaintext:bytes) -> bytes: - cipher = DES.new(self.card_keys.dek, DES.MODE_ECB) + cipher = DES.new(self.card_keys.dek[:8], DES.MODE_ECB) return cipher.encrypt(plaintext)

def dek_decrypt(self, ciphertext:bytes) -> bytes: - cipher = DES.new(self.card_keys.dek, DES.MODE_ECB) + cipher = DES.new(self.card_keys.dek[:8], DES.MODE_ECB) return cipher.decrypt(ciphertext)

def _compute_cryptograms(self, card_challenge: bytes, host_challenge: bytes):