CHash 1.5 - An MFC hashing class

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Introduction

A few times I've seen implementations of individual hashing algorithms, and thought it may be a good idea to group them together in an easy to use class. Well, here it is.

What are hashes anyway?

Hashes are a string of letters/numbers. They are used as a representation of an amount of data, but they are one way, you cannot go from a hash back to the original data; as hashes are fixed length, you also cannot determine the length or amount of the data represented. This lends hashes to practical security uses, as well as integrity uses.

Why use hashes?

There are multiple uses for hashes, the main one being data integrity. For example, a P2P client would use hashes to validate a file on completion, to check it's not corrupt or "fake". In this way, by generating a hash of a file, you can compare it against another hash, and check whether the files are the same.

Using the code

Putting CHash into use is relatively simple.

The main functions that will be used are:

• DoHash
• SetHashAlgorithm
• SetHashFile
• SetHashOperation
• SetHashString

An example of hashing a string with MD5:

// Define a CHash object

CHash hashObj;

// Set the algorithm

hashObj.SetHashAlgorithm(MD5);

// Set the operation

hashObj.SetHashOperation(STRING_HASH);

// Set the string

hashObj.SetHashString("String to hash");

// Hash the string

CString outHash = hashObj.DoHash();

An example of hashing a file with SHA-1:

// Define a CHash object

CHash hashObj;

// Set the algorithm

hashObj.SetHashAlgorithm(SHA1);

// Set the operation

hashObj.SetHashOperation(FILE_HASH);

// Set the file

hashObj.SetHashFile("C:\\Windows\\Explorer.exe");

// Hash the file

CString outHash = hashObj.DoHash();

The code is the same throughout, except for SHA-2, which has an extra function, SetSHA2Strength, which takes one parameter, the strength of the hash, which can be 256, 384 or 512.

An example usage of this is:

// Define a CHash object

CHash hashObj;

// Set the operation

hashObj.SetHashOperation(FILE_HASH);

// Set the algorithm

hashObj.SetHashAlgorithm(SHA2);

// Set the SHA-2 strength

hashObj.SetSHA2Strength(256);

// Set the file

hashObj.SetHashFile("C:\\Windows\\Explorer.exe");

// Hash the file

CString outHash = hashObj.DoHash();

Choosing which algorithms to include

In version 1.5, I made the class modular, so you can exclude/include specific algorithms (cutting down on unnecessary code if you don't want certain ones). To choose which you want to use, go to CHash.h, and find:

// Choose which algorithms you want

// Put 1s to support algorithms, else 0 to not support

Under here you will find defines such as:

#define        SUPPORT_CRC32          1

Change the 1s to 0s if you wish to exclude an algorithm.

Hashing styles

In version 1.2, I added hashing styles. This allows the programmer to customize the output hashes. There are four styles:

• Lowercase, no spaces:

  b4df98798c02b7c7a500d18632bf5b7d

• Lowercase, spaces:

  b4 df 98 79 8c 02 b7 c7 a5 00 d1 86 32 bf 5b 7d

• Uppercase, no spaces:

  B4DF98798C02B7C7A500D18632BF5B7Dd

• Uppercase, spaces:

  B4 DF 98 79 8C 02 B7 C7 A5 00 D1 86 32 BF 5B 7D

These can be set with SetHashFormat().

Acknowledgements

• Thanks to Dominik Reichl for his excellent ReHash program.
• Thanks to Markku-Juhani O. Saarinen for his GOST-Hash implementation.
• Thanks to Dr. Brian Gladman for the SHA-1/SHA-2 implementations.

History

• 1.0
  • 1^st May, 2005: First public release.
• 1.1
  • 2^nd May, 2005: Added SetHashAlgorithm() and DoHash() as recommended.
• 1.2
  • 3^rd May, 2005:
    • Added hashing styles.
    • Added the GOSTHash algorithm.
    • Added GetHashAlgorithm().
    • Rewrote the hashing functions to be more efficient.
• 1.3
  • 4^th May, 2005: Updated the demo project.
• 1.5
  • 8^th May, 2005:
    • Added CRC32.
    • Made the class "modular" so that you can exclude algorithms from compile.
    • Added GetHashFormat().
    • Updated the code as suggested.