I came across HMAC ( Hash-based message authentication code ) functions when developing a RESTful client application in Delphi. The RESTful Web Service API required me to send HMAC_SHA256 signatures (Base64 encoded) with each HTTP request.
HMAC functions take two parameters: a key and a message. The purpose of the HMAC function is to authenticate the message and guarantee the data integrity of the message.
The cryptographic strength of the HMAC function lies on the underlying hashing function that it uses: MD5, SHA1, SHA256, etc.
So, these functions are usually are termed HMAC_SHA256, HMAC_SHA1, HMAC_MD5 to connote the core hashing function being used.
The outcome of a HMAC function is basically an array of bytes, but it is usually represented as a hexadecimal string or encoded as a Base64 string. (The RESTful Web Service API needed the Base64 encoded output).
I Googled around for a bit, but I didn’t get a clean implementation of HMAC_SHA256 in Delphi (encoded as Base64). I glued together the pieces from some questions on StackOverflow and coded an Indy based implementation that uses generics to specify the core hashing function.
Brief description: I created a helper class called THMACUtils. Note that this class uses generics to indicate the hashing algorithm (TIdHMACSHA256, TIdHMACSHA1). Three functions are provided: the main thing happens in the HMAC(...) function; HMAC_HexStr(...) and HMAC_Base64(...) are simply decorations of the output.

unit HMAC;

interface

uses
System.SysUtils,
EncdDecd,
IdHMAC,
IdSSLOpenSSL,
IdHash;

type
THMACUtils<T:TIdHMAC, constructor>= class
public
class function HMAC(aKey, aMessage: RawByteString): TBytes;
class function HMAC_HexStr(aKey, aMessage: RawByteString): RawByteString;
class function HMAC_Base64(aKey, aMessage: RawByteString): RawByteString;
end;

implementation

class function THMACUtils<T>.HMAC(aKey, aMessage: RawByteString): TBytes;
var
_HMAC: T;
begin
if not IdSSLOpenSSL.LoadOpenSSLLibrary then
Exit;

_HMAC:= T.Create;
try
_HMAC.Key := BytesOf(aKey);
Result:= _HMAC.HashValue(BytesOf(aMessage));
finally
_HMAC.Free;
end;
end;

class function THMACUtils<T>.HMAC_HexStr(aKey, aMessage: RawByteString): RawByteString;
var
I: Byte;
begin
Result:= '0x';
for I in HMAC(aKey, aMessage) do
Result:= Result + IntToHex(I, 2);
end;

class function THMACUtils<T>.HMAC_Base64(aKey, aMessage: RawByteString): RawByteString;
var
_HMAC: TBytes;
begin
_HMAC:= HMAC(aKey, aMessage);
Result:= EncodeBase64(_HMAC, Length(_HMAC));
end;

end.
原文地址： HMAC of Function

I came across HMAC (Hash-based message authentication code) functions when developing a RESTful client application in Delphi. The RESTful Web Service API required me to send HMAC_SHA256 signatures (Ba function Id HMAC SHA1 (BaseString,HashKey:String):TIdBytes; //OK begin with TId HMAC SHA1 .Create do Key := ToBytes(HashKey); Result := HashValu...