From c595221bc3b92b995f14f2ab0ef742e8a85bcf0d Mon Sep 17 00:00:00 2001 From: Philipp Maier Date: Mon, 26 Aug 2024 13:56:58 +0200 Subject: [PATCH] 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 (56 bit + 8 bit integrity). 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 See also: https://pycryptodome.readthedocs.io/en/latest/src/cipher/des.html Related: OS#6531 Change-Id: I92e0dc6a6196b532bd8b53fca7b9e78070d6903f --- pySim/global_platform/scp.py | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/pySim/global_platform/scp.py b/pySim/global_platform/scp.py index f68bcf91..17463ff8 100644 --- a/pySim/global_platform/scp.py +++ b/pySim/global_platform/scp.py @@ -230,11 +230,11 @@ class SCP02(SCP): 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):