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global_platform/scp: fix dek_encrypt/dek_decrypt for SCP02

The methods dek_encrypt/dek_decrypt use the wrong algorithm and the
wrong key material. The algorithm should be 3DES rather then single
DES and the key must be the DEK session key instead of the static
DEK key from which the DEK session key is derived.

Related: SYS#7902
Change-Id: I3d0cc7378680b346fa39152c8b7074446d2c869d
---
M pySim/global_platform/scp.py
1 file changed, 4 insertions(+), 2 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/pysim refs/changes/87/42287/1

diff --git a/pySim/global_platform/scp.py b/pySim/global_platform/scp.py
index e674766..124b4c5 100644
--- a/pySim/global_platform/scp.py
+++ b/pySim/global_platform/scp.py
@@ -266,11 +266,13 @@
         super().__init__(*args, **kwargs)
 
     def dek_encrypt(self, plaintext:bytes) -> bytes:
-        cipher = DES.new(self.card_keys.dek[:8], DES.MODE_ECB)
+        # See also GPC section B.1.1.2, E.4.7, and E.4.1
+        cipher = DES3.new(self.sk.data_enc, DES.MODE_ECB)
         return cipher.encrypt(plaintext)
 
     def dek_decrypt(self, ciphertext:bytes) -> bytes:
-        cipher = DES.new(self.card_keys.dek[:8], DES.MODE_ECB)
+        # See also GPC section B.1.1.2, E.4.7, and E.4.1
+        cipher = DES3.new(self.sk.data_enc, DES.MODE_ECB)
         return cipher.decrypt(ciphertext)
 
     def _compute_cryptograms(self, card_challenge: bytes, host_challenge: bytes):

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