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abumq · Aug 28, 2017 · 1560004 · 1560004
1 parent e70f76f
commit 1560004
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Showing 3 changed files with 50 additions and 13 deletions.
diff --git a/package/mine.cc b/package/mine.cc
@@ -407,6 +407,27 @@ void AES::invShiftRows(State *state)
     std::swap(state->at(0)[3], state->at(1)[3]);
 }
 
+///
+/// Finds the product of {02} and the argument to
+/// xtime modulo {1b}
+///
+byte AES::xtime(byte x)
+{
+    return ((x << 1) ^ (((x >> 7) & 1) * 0x11b));
+}
+
+///
+/// Multiplies numbers in the GF(2^8) field
+///
+byte AES::multiply(byte x, byte y)
+{
+    return (((y & 0x01) * x) ^
+            ((y >> 1 & 0x01) * xtime(x)) ^
+            ((y >> 2 & 0x01) * xtime(xtime(x))) ^
+            ((y >> 3 & 0x01) * xtime(xtime(xtime(x)))) ^
+            ((y >> 4 & 0x01) * xtime(xtime(xtime(xtime(x))))));
+}
+
 ///
 /// multiplies in GF(2^8) field selected column from state
 /// with constant matrix defined by publication
@@ -418,16 +439,7 @@ void AES::invShiftRows(State *state)
 ///
 void AES::mixColumns(State* state)
 {
-    // Finds the product of {02} and the argument to xtime modulo {1b}
-    // mentioned in Sec. 4.2.1 of FIPS.197
-    // taken from http://gauss.ececs.uc.edu/Courses/c653/extra/AES/xtime.cpp
-    auto xtime = [](byte x) {
-        return ((x << 1) ^ (((x >> 7) & 1) * 0x11b));
-    };
-
     for (int col = 0; col < 4; ++col) {
-
-
         Word column = state->at(col);
         // let's take example from publication, col: [212, 191, 93, 48]
         // t == 6
@@ -440,9 +452,24 @@ void AES::mixColumns(State* state)
     }
 }
 
+///
+/// Inverse multiplication with inverse matrix defined on Sec. 5.3.3
+///
+/// [ 0e  0b  0d  09 ]
+/// | 09  0e  0b  0d |
+/// | 0d  09  0e  0b |
+/// [ 0b  0d  09  0e ]
+///
 void AES::invMixColumns(State* state)
 {
-    (void)state;
+    for (int col = 0; col < 4; ++col) {
+        Word column = state->at(col);
+        // see Sec. 4.2.1 and Sec. 5.3.3 for more details
+        state->at(col)[0] = multiply(column[0], 0x0e) ^ multiply(column[1], 0x0b) ^ multiply(column[2], 0x0d) ^ multiply(column[3], 0x09);
+        state->at(col)[1] = multiply(column[0], 0x09) ^ multiply(column[1], 0x0e) ^ multiply(column[2], 0x0b) ^ multiply(column[3], 0x0d);
+        state->at(col)[2] = multiply(column[0], 0x0d) ^ multiply(column[1], 0x09) ^ multiply(column[2], 0x0e) ^ multiply(column[3], 0x0b);
+        state->at(col)[3] = multiply(column[0], 0x0b) ^ multiply(column[1], 0x0d) ^ multiply(column[2], 0x09) ^ multiply(column[3], 0x0e);
+    }
 }
 
 ByteArray AES::cipher(const ByteArray& input, const Key* key)

diff --git a/package/mine.h b/package/mine.h
@@ -572,6 +572,16 @@ class AES {
     ///
     static void shiftRows(State* state);
 
+    ///
+    /// \ref Sec. 4.2.1
+    ///
+    static byte xtime(byte x);
+
+    ///
+    /// \ref Sec. 4.2.1
+    ///
+    static byte multiply(byte x, byte y);
+
     ///
     /// \brief Mixing columns for the state
     /// \ref Sec. 5.1.3

diff --git a/test/main.cc b/test/main.cc
@@ -1,9 +1,9 @@
 #include "test.h"
-//#include "base16-test.h"
-//#include "base64-test.h"
+#include "base16-test.h"
+#include "base64-test.h"
 #include "aes-test.h"
 #include "zlib-test.h"
-//#include "rsa-test.h"
+#include "rsa-test.h"
 
 INITIALIZE_EASYLOGGINGPP