Using Win32 functions in Visual FoxPro Image Gallery
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How to create MD-5 and SHA-1 hash values from a string

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Before you begin:
Test the presented class as follows:
obj = CREATEOBJECT("TheHash")

? obj.CreateSHA1("test string")

* returns 661295C9CBF9D6B2F6428414504A8DEED3020641

? obj.CreateMD5("test string")
* returns 6F8DB599DE986FAB7A21625B7916589C

See also:
  • Simple class that encrypts and decrypts files using Cryptography API Functions
  • CryptoAPI: Collection of Providers class
  • WinINet function CreateMD5SSOHash
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    3548 bytes  
    Created: 2005-03-07 15:21:11  
    Modified: 2013-09-20 13:30:28  
    Visits in 7 days: 133  
    Listed functions:
    CryptAcquireContext
    CryptCreateHash
    CryptDestroyHash
    CryptGetHashParam
    CryptHashData
    CryptReleaseContext
    GetLastError
    Printer friendly API declarations
    My comment:
    Transact-SQL HASHBYTES() function computes MD5 and SHA1 hashes identical to those produced by VFP and C# code samples above.



    * * *
    One-way hash functions can be used for creating a fingerprint for a block of data.

    Also hash functions can be used to evaluate passwords. In Users table of your FoxPro application you store not passwords but their hash values.

    It is extremely difficult, if ever possible, to find the original string for a given hash value -- depends on the hash algorithm as well as computer power and methodology you have.

    * * *
    Message Digest: The representation of text in the form of a single string of digits, created using a formula called a one-way hash function.

    One-Way Hash Function: An algorithm that turns messages or text into a fixed string of digits, usually for security or data management purposes. The "one way" means that it is nearly impossible to derive the original text from the string.

    Hash Collision: More than one input message producing identical hash output.

    * * *
    Secure Hash Algorithm, a hash function developed by the NSA for use with NIST Digital Signature Standard (DSS). NSA almost immediately developed a minor change known as SHA-1. Both SHA and SHA-1 produce a 160-bit digest. SHA-1 is used in SSL.

    * * *
    MD-5 is a one-way message-digest hash function. The algorithm processes input text and creates a 128-bit message digest which is unique to the message and can be used to verify data integrity.

    MD-5 was developed by Ron Rivest and is intended to be used in digital signatures applications. Earlier message digest algorithms include obsolete MD-2 and MD-4.

    See also:
  • RFC 1321 - The MD5 Message-Digest Algorithm
  • What are MD2, MD4, and MD5?
  • Example C Program: Creating an MD-5 Hash From File Content.
  • MD5 Online Cracking using Rainbow Tables
  • RFC 3174 - US Secure Hash Algorithm 1 (SHA1)
  • More on Newly Broken SHA1 on Alex Feldstein"s blog
  • Hash Collisions Q&A
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    User Contributed Notes:
    Malcolm Greene | 2005-04-06 00:16:27
    Are there any Windows version (or service pack) dependencies with this code (advapi32.dll)? I've been burned trying to get the FFC _Crypto class to work across different versions of Windows, re: different flavors of rsaenh.dll. (I noticed that rsaenh.dll is not referenced in above code, but I'm still concerned about the same problem version dependencies).

    Thoughts?
    Malcolm

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