Merge pull request #6731 from tom-cosgrove-arm/issue-6293-mod_exp

Require input to mbedtls_mpi_core_exp_mod() to already be in Montgomery form

scripts/mbedtls_dev/bignum_common.py

@@ -251,6 +251,12 @@ class ModOperationCommon(OperationCommon):
         # provides earlier/more robust input validation.
         self.int_n = hex_to_int(val_n)
 
+    def to_montgomery(self, val: int) -> int:
+        return (val * self.r) % self.int_n
+
+    def from_montgomery(self, val: int) -> int:
+        return (val * self.r_inv) % self.int_n
+
     @property
     def boundary(self) -> int:
         return self.int_n

scripts/mbedtls_dev/bignum_core.py

@@ -759,12 +759,23 @@ class BignumCoreExpMod(BignumCoreTarget, bignum_common.ModOperationCommon):
     """Test cases for bignum core exponentiation."""
     symbol = "^"
     test_function = "mpi_core_exp_mod"
-    test_name = "Core modular exponentiation"
+    test_name = "Core modular exponentiation (Mongtomery form only)"
     input_style = "fixed"
 
+    def arguments(self) -> List[str]:
+        # Input 'a' has to be given in Montgomery form
+        mont_a = self.to_montgomery(self.int_a)
+        arg_mont_a = self.format_arg('{:x}'.format(mont_a))
+        return [bignum_common.quote_str(n) for n in [self.arg_n,
+                                                     arg_mont_a,
+                                                     self.arg_b]
+               ] + self.result()
+
     def result(self) -> List[str]:
+        # Result has to be given in Montgomery form too
         result = pow(self.int_a, self.int_b, self.int_n)
-        return [self.format_result(result)]
+        mont_result = self.to_montgomery(result)
+        return [self.format_result(mont_result)]
 
     @property
     def is_valid(self) -> bool:

scripts/mbedtls_dev/bignum_mod_raw.py

@@ -92,10 +92,9 @@ class BignumModRawConvertToMont(bignum_common.ModOperationCommon,
     arity = 1
 
     def result(self) -> List[str]:
-        result = (self.int_a * self.r) % self.int_n
+        result = self.to_montgomery(self.int_a)
         return [self.format_result(result)]
 
-
 class BignumModRawConvertFromMont(bignum_common.ModOperationCommon,
                                   BignumModRawTarget):
     """ Test cases for mpi_mod_raw_from_mont_rep(). """
@@ -106,7 +105,7 @@ class BignumModRawConvertFromMont(bignum_common.ModOperationCommon,
     arity = 1
 
     def result(self) -> List[str]:
-        result = (self.int_a * self.r_inv) % self.int_n
+        result = self.from_montgomery(self.int_a)
         return [self.format_result(result)]