TAtlasHash

Create constructor

constructor Create(Kind: TAtlasHashKind = hkSHA256); overload;

Starts a plain hash of the given kind.

Hash := TAtlasHash.Create(hkSHA512);

Create constructor

constructor Create(Kind: TAtlasHashKind; const HmacKey: TBytes); overload;

Starts an HMAC with HmacKey. Any key length is accepted, including an empty key.

Hash := TAtlasHash.Create(hkSHA256, Key);

Destroy destructor

destructor Destroy; override;

Releases the CNG hash and algorithm handles. Call Free as usual, whether or not Finish was called.

Update method

procedure Update(const Data: TBytes); overload;

Adds Data to the hash. An empty array is allowed and changes nothing. Raises EAtlasCryptoError after Finish.

Hash.Update(TAtlasBytes.OfString(Text));

Update method

procedure Update(const Buffer; Count: Integer); overload;

Adds Count bytes starting at Buffer, for data held in a static array or a memory block. A negative Count raises EAtlasCryptoError.

Hash.Update(Buffer, SizeOf(Buffer));

UpdateFromStream method

procedure UpdateFromStream(Stream: TStream);

Adds everything from the stream's current position to its end, reading 256 KB at a time. A nil stream raises EAtlasCryptoError. It is a separate name, not an Update overload, so that Update(nil) always means an empty byte array.

Hash.UpdateFromStream(Stream);

Finish method

function Finish: TBytes;

Returns the digest (DigestSize bytes). Afterwards Update and Finish raise EAtlasCryptoError (The hash has been finished; create a new one).

Digest := Hash.Finish;

DigestSize method

class function DigestSize(Kind: TAtlasHashKind): Integer; static;

Returns the digest length in bytes: 32, 48, 64, 20 or 16 for SHA-256, SHA-384, SHA-512, SHA-1 and MD5.

Size := TAtlasHash.DigestSize(hkSHA384);  // 48

Compute method

class function Compute(Kind: TAtlasHashKind; const Data: TBytes): TBytes; static;

Returns the digest of Data in one call. nil is the empty message.

Digest := TAtlasHash.Compute(hkSHA256, Data);

OfString method

class function OfString(Kind: TAtlasHashKind; const Text: string): TBytes; static;

Returns the digest of the UTF-8 encoding of Text.

Digest := TAtlasHash.OfString(hkSHA256, 'abc');

OfFile method

class function OfFile(Kind: TAtlasHashKind; const FileName: string): TBytes; static;

Returns the digest of a whole file, read in 256 KB pieces. The file is opened for reading with writes by others denied; a missing or locked file raises the RTL's EFOpenError.

Digest := TAtlasHash.OfFile(hkSHA256, FileName);

Hmac method

class function Hmac(Kind: TAtlasHashKind; const Key, Data: TBytes): TBytes; static;

Returns the HMAC of Data under Key in one call.

Tag := TAtlasHash.Hmac(hkSHA256, Key, Data);

Hash in pieces and authenticate with HMAC

The incremental digest equals the one-call digest, and the HMAC matches RFC 4231 test case 2. Prints TRUE and TRUE.

uses System.SysUtils, Atlas.Crypto;

procedure HashAndHmac;
var
  Hash: TAtlasHash;
  Pieces: TBytes;
begin
  Hash := TAtlasHash.Create(hkSHA256);
  try
    Hash.Update(TAtlasBytes.OfString('ab'));
    Hash.Update(nil);
    Hash.Update(TAtlasBytes.OfString('c'));
    Pieces := Hash.Finish;
  finally
    Hash.Free;
  end;
  WriteLn(TAtlasBytes.ConstantTimeEquals(Pieces, TAtlasHash.OfString(hkSHA256, 'abc')));
  WriteLn(TAtlasBytes.ToHex(TAtlasHash.Hmac(hkSHA256, TAtlasBytes.OfString('Jefe'),
    TAtlasBytes.OfString('what do ya want for nothing?'))) =
    '5bdcc146bf60754e6a042426089575c75a003f089d2739839dec58b964ec3843');
end;