I still see a lot of people crafting their own MD5 implementation.
A lot of the existing MD5 implementations do not work well in Delphi 2009 and later (because they need to be adapted to Unicode).
Many of those existing implementations behave differently if you pass the same ASCII characters as AnsiString or UnicodeString.
The MessageDigest_5 unit has been available in Delphi since Delphi 2007.
This is the location relative to your installation directory: source\Win32\soap\wsdlimporter\MessageDigest_5.pas
(Edit: 20091223: Since Delphi 7.01, Indy has provided the unit IdHashMessageDigest which also does md5, see the comments below)
So this unit used by the WSDL, and more importantly: works with Unicode (if you pass it a string with Unicode characters, it will convert them to UTF-8 first).
The unit is not in your default search path, and has not been very well promoted (the only link at the Embarcadero site was an article by Pawel Glowacki), so few people know about it.
Now you know too 
Note that MD5 is normally used to hash binary data.
It is not wise to send a non ASCII string through both the AnsiString and UnicodeString versions: because of the different encoding (and therefore a different binary representation), you will get different results depending on the Delphi version used.
A sample of the usage showing the above AnsiString/UnicodeString issue is not present for ASCII strings, nor for ANSI strings: this is because both get encoded using UTF-8 before hashing.
Delphi 2007 did not do the UTF-8 encoding, so you will see different results here.
You will also see that Writeln uses the Console for encoding, and those are different than the code editor.
Edit: 20091216 – added RawByteString example to show that the conversion does not matter.
program md5;
{$APPTYPE CONSOLE}
uses
SysUtils,
MessageDigest_5 in 'C:\Program Files\Embarcadero\RAD Studio\7.0\source\Win32\soap\wsdlimporter\MessageDigest_5.pas';
// Vista/Windows 7: MessageDigest_5 in 'C:\Program Files (x86)\Embarcadero\RAD Studio\7.0\source\Win32\soap\wsdlimporter\MessageDigest_5.pas';
function GetMd5(const Value: AnsiString): string; overload;
var
hash: MessageDigest_5.IMD5;
fingerprint: string;
begin
hash := MessageDigest_5.GetMD5();
hash.Update(Value);
fingerprint := hash.AsString();
Result := LowerCase(fingerprint);
end;
function GetMd5(const Value: UnicodeString): string; overload;
var
hash: MessageDigest_5.IMD5;
fingerprint: string;
begin
hash := MessageDigest_5.GetMD5();
hash.Update(Value);
fingerprint := hash.AsString();
Result := LowerCase(fingerprint);
end;
var
SourceAnsiString: AnsiString;
SourceUnicodeString: UnicodeString;
SourceRawByteString: RawByteString;
begin
try
SourceAnsiString := 'foobar';
SourceUnicodeString := 'foobar';
SourceRawByteString := 'foobar';
Writeln(GetMd5(SourceAnsiString));
Writeln(GetMd5(SourceUnicodeString));
Writeln(GetMd5(SourceRawByteString));
SourceAnsiString := 'föøbår';
SourceUnicodeString := 'föøbår';
SourceRawByteString := 'föøbår';
Writeln(SourceAnsiString, ' ', GetMd5(SourceAnsiString));
Writeln(SourceUnicodeString, ' ', GetMd5(SourceUnicodeString));
Writeln(SourceRawByteString, ' ', GetMd5(SourceRawByteString));
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
end.
–jeroen
