Security Improvements: Introduction of SecureBigInteger

Resolves: No entry
shinji-san · Jun 2, 2024 · 2a6d8b1 · 2a6d8b1
1 parent b4dbd2d
commit 2a6d8b1
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Showing 8 changed files with 612 additions and 17 deletions.
diff --git a/src/Cryptography/ShamirsSecretSharing.cs b/src/Cryptography/ShamirsSecretSharing.cs
@@ -5,6 +5,11 @@ namespace SecretSharingDotNet.Cryptography;
 /// </summary>
 public abstract class ShamirsSecretSharing
 {
+    /// <summary>
+    /// The minimum number of shares required to reconstruct the secret
+    /// </summary>
+    protected const int MinimumShareLimit = 2;
+
     /// <summary>
     /// Saves the known security levels (Mersenne prime exponents)
     /// </summary>

diff --git a/src/Cryptography/ShamirsSecretSharing`3.cs b/src/Cryptography/ShamirsSecretSharing`3.cs
@@ -70,7 +70,7 @@ public class ShamirsSecretSharing<TNumber, TExtendedGcdAlgorithm, TExtendedGcdRe
     public ShamirsSecretSharing(TExtendedGcdAlgorithm extendedGcd)
     {
         this.extendedGcd = extendedGcd ?? throw new ArgumentNullException(nameof(extendedGcd));
-        this.SecurityLevel = 13;
+        this.SecurityLevel = SecurityLevels[0];
     }
 
     /// <summary>
@@ -84,7 +84,7 @@ public int SecurityLevel
 
         set
         {
-            if (value < 13)
+            if (value < SecurityLevels[0])
             {
                 throw new ArgumentOutOfRangeException(nameof(value), value, ErrorMessages.MinimumSecurityLevelExceeded);
             }
@@ -128,7 +128,7 @@ public Shares<TNumber> MakeShares(TNumber numberOfMinimumShares, TNumber numberO
 
         int min = ((Calculator<TNumber>)numberOfMinimumShares).ToInt32();
         int max = ((Calculator<TNumber>)numberOfShares).ToInt32();
-        if (min < 2)
+        if (min < MinimumShareLimit)
         {
             throw new ArgumentOutOfRangeException(nameof(numberOfMinimumShares), numberOfMinimumShares, ErrorMessages.MinNumberOfSharesLowerThanTwo);
         }
@@ -187,7 +187,7 @@ public Shares<TNumber> MakeShares(TNumber numberOfMinimumShares, TNumber numberO
     {
         int min = ((Calculator<TNumber>)numberOfMinimumShares).ToInt32();
         int max = ((Calculator<TNumber>)numberOfShares).ToInt32();
-        if (min < 2)
+        if (min < MinimumShareLimit)
         {
             throw new ArgumentOutOfRangeException(nameof(numberOfMinimumShares), numberOfMinimumShares, ErrorMessages.MinNumberOfSharesLowerThanTwo);
         }
@@ -215,20 +215,40 @@ public Shares<TNumber> MakeShares(TNumber numberOfMinimumShares, TNumber numberO
     /// </summary>
     /// <param name="numberOfMinimumShares">Minimum number of shared secrets for reconstruction</param>
     /// <returns></returns>
+#if NET6_0_OR_GREATER
+    private unsafe Calculator<TNumber>[] CreatePolynomial(int numberOfMinimumShares)
+#else
     private Calculator<TNumber>[] CreatePolynomial(int numberOfMinimumShares)
+#endif
     {
         var polynomial = new Calculator<TNumber>[numberOfMinimumShares];
         polynomial[0] = Calculator<TNumber>.Zero;
         byte[] randomNumber = new byte[this.mersennePrime.ByteCount];
-        using (var rng = RandomNumberGenerator.Create())
+#if NET6_0_OR_GREATER
+        fixed (byte* pointer = randomNumber)
         {
+            var span = new Span<byte>(pointer, this.mersennePrime.ByteCount);
+            using var rng = RandomNumberGenerator.Create();
             for (int i = 1; i < numberOfMinimumShares; i++)
             {
-                rng.GetBytes(randomNumber);
-                polynomial[i] = (Calculator.Create(randomNumber, typeof(TNumber)) as Calculator<TNumber>)?.Abs() % this.mersennePrime;
+                rng.GetBytes(span);
+                polynomial[i] = (Calculator.Create(randomNumber, typeof(TNumber)) as Calculator<TNumber>)?.Abs() %
+                                this.mersennePrime;
             }
-        }
 
+            span.Clear();
+        }
+#else
+         using var rng = RandomNumberGenerator.Create();
+         for (int i = 1; i < numberOfMinimumShares; i++)
+         {
+             rng.GetBytes(randomNumber);
+             polynomial[i] = (Calculator.Create(randomNumber, typeof(TNumber)) as Calculator<TNumber>)?.Abs() %
+                             this.mersennePrime;
+         }
+
+         Array.Clear(randomNumber, 0, randomNumber.Length);
+#endif
         return polynomial;
     }
 

diff --git a/src/Cryptography/SharedSeparator.cs b/src/Cryptography/SharedSeparator.cs
@@ -41,5 +41,5 @@ internal static class SharedSeparator
     /// <summary>
     /// Separator array for <see cref="string.Split(char[])"/> method usage to avoid allocation of a new array.
     /// </summary>
-    internal static readonly char[] CoordinateSeparatorArray = { CoordinateSeparator };
-}
+    internal static readonly char[] CoordinateSeparatorArray = [CoordinateSeparator];
+}
diff --git a/src/Cryptography/Shares.cs b/src/Cryptography/Shares.cs
@@ -118,7 +118,7 @@ internal Shares(Secret<TNumber> secret, IList<FinitePoint<TNumber>> shares)
     public static implicit operator Shares<TNumber>(string s)
     {
         var points = s
-            .Split(new[] {Environment.NewLine}, StringSplitOptions.RemoveEmptyEntries)
+            .Split([Environment.NewLine], StringSplitOptions.RemoveEmptyEntries)
             .Select(line => new FinitePoint<TNumber>(line))
             .ToArray();
         return new Shares<TNumber>(points);

diff --git a/src/Math/Calculator.cs b/src/Math/Calculator.cs
@@ -117,7 +117,7 @@ protected static Dictionary<Type, Func<TParameter, TCalculator>> GetDerivedCtors
         var parameterExpression = Expression.Parameter(paramType);
         foreach (var childType in ChildTypes)
         {
-            var ctorInfo = childType.Value.GetConstructor(new[] {paramType});
+            var ctorInfo = childType.Value.GetConstructor([paramType]);
             if (ctorInfo == null)
             {
                 continue;

diff --git a/src/Math/ExtendedEuclideanAlgorithm.cs b/src/Math/ExtendedEuclideanAlgorithm.cs
@@ -60,7 +60,11 @@ public ExtendedGcdResult<TNumber> Compute(Calculator<TNumber> a, Calculator<TNum
             checked
             {
                 var quotient = lastR / r;
-
+#if NET6_0_OR_GREATER
+                (lastR, r) = (r, lastR - quotient * r);
+                (lastX, x) = (x, lastX - quotient * x);
+                (lastY, y) = (y, lastY - quotient * y);
+#else
                 var tmpR = r;
                 r = lastR - quotient * r;
                 lastR = tmpR;
@@ -72,11 +76,10 @@ public ExtendedGcdResult<TNumber> Compute(Calculator<TNumber> a, Calculator<TNum
                 var tmpY = y;
                 y = lastY - quotient * y;
                 lastY = tmpY;
+#endif
             }
         }
 
-        var coefficients = new[] {lastX, lastY};
-        var quotients = new[] {x, y};
-        return new ExtendedGcdResult<TNumber>(lastR, coefficients, quotients);
+        return new ExtendedGcdResult<TNumber>(lastR, [lastX, lastY], [x, y]);
     }
-}
+}