Adding description of M values

.github/workflows/pylint.yml

@@ -0,0 +1,23 @@
+name: Pylint
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.8", "3.9", "3.10"]
+    steps:
+    - uses: actions/checkout@v3
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v3
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install pylint
+    - name: Analysing the code with pylint
+      run: |
+        pylint $(git ls-files '*.py')

README.md

@@ -12,4 +12,5 @@ pip install -r requirements.txt
 ```
 
 ## References
-* [Specification of Secure Hardware Extensions, AUTOSAR FO R19-11](https://www.autosar.org/fileadmin/user_upload/standards/foundation/19-11/AUTOSAR_TR_SecureHardwareExtensions.pdf)
+* [AUTOSAR Specification of Secure Hardware Extensions - R22-11](https://www.autosar.org/fileadmin/standards/R22-11/FO/AUTOSAR_TR_SecureHardwareExtensions.pdf)
+* [Description of the M* values](./m_value_description.md)

m_value_description.md

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+# M1
+
+| UID' | ID | AuthID |
+| --- | --- | --- |
+| 120 bits | 4 bits | 4 bits | 
+
+M1 = UID' | ID | AuthID
+
+# M2
+
+> **Note** K1 is the derived encryption key used in M2
+
+K1 = KDF(K<sub>AuthID</sub>, KEY_UPDATE_ENC_C)
+
+C<sub>ID</sub> = 28 bit counter value for key
+
+F<sub>ID</sub> = 5 bit key flag value
+
+M2 = ENC<sub>CBC,K1,IV=0</sub>(C<sub>ID</sub> | F<sub>ID</sub> | "0...0"<sub>95</sub> | K<sub>ID</sub>)
+
+# M3
+
+> **Note** K2 is the derived CMAC authentication key used in M3.
+
+K2 = KDF(K<sub>AuthID</sub>, KEY_UPDATE_MAC_C)
+
+M3 = CMAC<sub>K2</sub>(M1|M2)
+
+# M4
+
+> **Note** K3 is the derived encryption key used in M4
+
+K3 = KDF(K<sub>ID</sub>, KEY_UPDATE_ENC_C)
+
+> **Note**
+> AES ECB mode is used in the spec. Since we are only encrypting 1 block, this is equivalent to CBC mode with an IV=0.
+
+M4 = UID | ID | AuthID | ENC<sub>ECB,K3</sub>(C<sub>ID</sub>)
+
+# M5
+
+K4 = KDF(K<sub>ID</sub>, KEY_UPDATE_MAC_C)
+
+M5 = CMAC<sub>K4</sub>(M4)
+
+# Key Derivation
+
+Keys are derived using the Miyaguchi-Preneel compression algorithm based on [NIST800_108]. Derived
+keys are calculated by compressing the correctly preprocessed concatenation of a secret K and
+a constant C.
+
+KDF(K,C) = AES-MP(K | C)