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#173: How can I calculate the hash for string (CryptAPI)?

today I want to continue the serie of tips for Crypt API in Delphi.
I'll show the code to calculate the MD5 hash for any string. You may easy to modify the code to calculate the hash for file/any stream or use SHA-algorithm (or any other) instead MD5.

function MD5(const Value: string): string;
var
  hCryptProvider: HCRYPTPROV;
  hHash: HCRYPTHASH;
  bHash: array[0..$7F] of Byte;
  dwHashLen: dWord;
  i: Integer;
begin
  dwHashLen := 16;
  if (Value = '') then
  begin
    Result := 'd41d8cd98f00b204e9800998ecf8427e';
    exit;
  end
  else
    Result := '';

  {get context for crypt default provider}
  if CryptAcquireContext(@hCryptProvider, nil, nil, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT or CRYPT_MACHINE_KEYSET) then
  begin
    {create hash-object MD5}
    if CryptCreateHash(hCryptProvider, CALG_MD5, 0, 0, @hHash) then
    begin
      {get hash from password}
      if CryptHashData(hHash, @Value[1], Length(Value), 0) then
      begin
        if CryptGetHashParam(hHash, HP_HASHVAL, @bHash[0], @dwHashLen, 0) then
        begin
          for i := 0 to dwHashLen-1 do
            Result := Result + IntToHex(bHash[i], 2);
        end;
      end;
      {destroy hash-object}
      CryptDestroyHash(hHash);
    end;
    {release the context for crypt default provider}
    CryptReleaseContext(hCryptProvider, 0);
  end;

  Result := AnsiLowerCase(Result);
end;

For SHA algorithm use the CALG_SHA instead CALG_MD5.
For this code you need the Crypt API headers too (same as in my previous tip)

Published: April 3, 2007

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