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//------------------------------------------------------------------------------ // <copyright file="CryptoUtil.cs" company="Microsoft"> // Copyright (c) Microsoft Corporation. All rights reserved. // </copyright> //------------------------------------------------------------------------------ namespace System.Web.Security.Cryptography { using System; using System.Runtime.CompilerServices; using System.Security.Cryptography; using System.Text; using System.Web.Util; // Contains helper methods for dealing with cryptographic operations. internal static class CryptoUtil { /// <summary> /// Similar to Encoding.UTF8, but throws on invalid bytes. Useful for security routines where we need /// strong guarantees that we're always producing valid UTF8 streams. /// </summary> public static readonly UTF8Encoding SecureUTF8Encoding = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: true); /// <summary> /// Converts a byte array into its hexadecimal representation. /// </summary> /// <param name="data">The binary byte array.</param> /// <returns>The hexadecimal (uppercase) equivalent of the byte array.</returns> public static string BinaryToHex(byte[] data) { if (data == null) { return null; } char[] hex = new char[checked(data.Length * 2)]; for (int i = 0; i < data.Length; i++) { byte thisByte = data[i]; hex[2 * i] = NibbleToHex((byte)(thisByte >> 4)); // high nibble hex[2 * i + 1] = NibbleToHex((byte)(thisByte & 0xf)); // low nibble } return new string(hex); } // Determines if two buffer instances are equal, e.g. whether they contain the same payload. This method // is written in such a manner that it should take the same amount of time to execute regardless of // whether the result is success or failure. The modulus operation is intended to make the check take the // same amount of time, even if the buffers are of different lengths. // // !! DO NOT CHANGE THIS METHOD WITHOUT SECURITY [MethodImpl(MethodImplOptions.NoOptimization)] public static bool BuffersAreEqual(byte[] buffer1, int buffer1Offset, int buffer1Count, byte[] buffer2, int buffer2Offset, int buffer2Count) { Debug.ValidateArrayBounds(buffer1, buffer1Offset, buffer1Count); Debug.ValidateArrayBounds(buffer2, buffer2Offset, buffer2Count); bool success = (buffer1Count == buffer2Count); // can't possibly be successful if the buffers are of different lengths for (int i = 0; i < buffer1Count; i++) { success &= (buffer1[buffer1Offset + i] == buffer2[buffer2Offset + (i % buffer2Count)]); } return success; } /// <summary> /// Computes the SHA256 hash of a given input. /// </summary> /// <param name="input">The input over which to compute the hash.</param> /// <returns>The binary hash (32 bytes) of the input.</returns> public static byte[] ComputeSHA256Hash(byte[] input) { return ComputeSHA256Hash(input, 0, input.Length); } /// <summary> /// Computes the SHA256 hash of a given segment in a buffer. /// </summary> /// <param name="buffer">The buffer over which to compute the hash.</param> /// <param name="offset">The offset at which to begin computing the hash.</param> /// <param name="count">The number of bytes in the buffer to include in the hash.</param> /// <returns>The binary hash (32 bytes) of the buffer segment.</returns> public static byte[] ComputeSHA256Hash(byte[] buffer, int offset, int count) { Debug.ValidateArrayBounds(buffer, offset, count); using (SHA256 sha256 = CryptoAlgorithms.CreateSHA256()) { return sha256.ComputeHash(buffer, offset, count); } } /// <summary> /// Returns an IV that's based solely on the contents of a buffer; useful for generating /// predictable IVs for ciphertexts that need to be cached. The output value is only /// appropriate for use as an IV and must not be used for any other purpose. /// </summary> /// <remarks>This method uses an iterated unkeyed SHA256 to calculate the IV.</remarks> /// <param name="buffer">The input buffer over which to calculate the IV.</param> /// <param name="ivBitLength">The requested length (in bits) of the IV to generate.</param> /// <returns>The calculated IV.</returns> public static byte[] CreatePredictableIV(byte[] buffer, int ivBitLength) { // Algorithm: // T_0 = SHA256(buffer) // T_n = SHA256(T_{n-1}) // output = T_0 || T_1 || ... || T_n (as many blocks as necessary to reach ivBitLength) byte[] output = new byte[ivBitLength / 8]; int bytesCopied = 0; int bytesRemaining = output.Length; using (SHA256 sha256 = CryptoAlgorithms.CreateSHA256()) { while (bytesRemaining > 0) { byte[] hashed = sha256.ComputeHash(buffer); int bytesToCopy = Math.Min(bytesRemaining, hashed.Length); Buffer.BlockCopy(hashed, 0, output, bytesCopied, bytesToCopy); bytesCopied += bytesToCopy; bytesRemaining -= bytesToCopy; buffer = hashed; // next iteration (if it occurs) will operate over the block just hashed } } return output; } /// <summary> /// Converts a hexadecimal string into its binary representation. /// </summary> /// <param name="data">The hex string.</param> /// <returns>The byte array corresponding to the contents of the hex string, /// or null if the input string is not a valid hex string.</returns> public static byte[] HexToBinary(string data) { if (data == null || data.Length % 2 != 0) { // input string length is not evenly divisible by 2 return null; } byte[] binary = new byte[data.Length / 2]; for (int i = 0; i < binary.Length; i++) { int highNibble = HttpEncoderUtility.HexToInt(data[2 * i]); int lowNibble = HttpEncoderUtility.HexToInt(data[2 * i + 1]); if (highNibble == -1 || lowNibble == -1) { return null; // bad hex data } binary[i] = (byte)((highNibble << 4) | lowNibble); } return binary; } // converts a nibble (4 bits) to its uppercase hexadecimal character representation [0-9, A-F] private static char NibbleToHex(byte nibble) { return (char)((nibble < 10) ? (nibble + '0') : (nibble - 10 + 'A')); } } } |