Как реализовать aes-256-gcm в delphi?

Не могу написать функцию для расшифровки строки, используя алгоритм aes-256-gcm. Использую SynCrypto Вот перечень функций из модуля SynCrypto.pas :

type
  /// low-level AES-GCM processing
  // - implements standard AEAD (authenticated-encryption with associated-data)
  // algorithm, as defined by NIST and
  TAESGCMEngine = object
  private
    /// standard AES encryption context
    // - will use AES-NI if available
    actx: TAES;
    /// ghash value of the Authentication Data
    aad_ghv: TAESBlock;
    /// ghash value of the Ciphertext
    txt_ghv: TAESBlock;
    /// ghash H current value
    ghash_h: TAESBlock;
    /// number of Authentication Data bytes processed
    aad_cnt: TQWordRec;
    /// number of bytes of the Ciphertext
    atx_cnt: TQWordRec;
    /// initial 32-bit ctr val - to be reused in Final()
    y0_val: integer;
    /// current 0..15 position in encryption block
    blen: byte;
    /// the state of this context
    flags: set of (flagInitialized, flagFinalComputed, flagFlushed);
    /// lookup table for fast Galois Finite Field multiplication
    // - is defined as last field of the object for better code generation
    gf_t4k: array[byte] of TAESBlock;
    /// build the gf_t4k[] internal table - assuming set to zero by caller
    procedure Make4K_Table;
    /// compute a * ghash_h in Galois Finite Field 2^128
    procedure gf_mul_h(var a: TAESBlock); {$ifdef FPC} inline; {$endif}
    /// low-level AES-CTR encryption
    procedure internal_crypt(ptp, ctp: PByte; ILen: PtrUInt);
    /// low-level GCM authentication
    procedure internal_auth(ctp: PByte; ILen: PtrUInt;
      var ghv: TAESBlock; var gcnt: TQWordRec);
  public
    /// initialize the AES-GCM structure for the supplied Key
    function Init(const Key; KeyBits: PtrInt): boolean;
    /// start AES-GCM encryption with a given Initialization Vector
    // - IV_len is in bytes use 12 for exact IV setting, otherwise the
    // supplied buffer will be hashed using gf_mul_h()
    function Reset(pIV: pointer; IV_len: PtrInt): boolean;
    /// encrypt a buffer with AES-GCM, updating the associated authentication data
    function Encrypt(ptp, ctp: Pointer; ILen: PtrInt): boolean;
    /// decrypt a buffer with AES-GCM, updating the associated authentication data
    // - also validate the GMAC with the supplied ptag/tlen if ptag<>nil,
    // and skip the AES-CTR phase if the authentication doesn't match
    function Decrypt(ctp, ptp: Pointer; ILen: PtrInt;
      ptag: pointer=nil; tlen: PtrInt=0): boolean;
    /// append some data to be authenticated, but not encrypted
    function Add_AAD(pAAD: pointer; aLen: PtrInt): boolean;
    /// finalize the AES-GCM encryption, returning the authentication tag
    // - will also flush the AES context to avoid forensic issues, unless
    // andDone is forced to false
    function Final(out tag: TAESBlock; andDone: boolean=true): boolean;
    /// flush the AES context to avoid forensic issues
    // - do nothing if Final() has been already called
    procedure Done;
    /// single call AES-GCM encryption and authentication process
    function FullEncryptAndAuthenticate(const Key; KeyBits: PtrInt;
      pIV: pointer; IV_len: PtrInt; pAAD: pointer; aLen: PtrInt;
      ptp, ctp: Pointer; pLen: PtrInt; out tag: TAESBlock): boolean;
    /// single call AES-GCM decryption and verification process
    function FullDecryptAndVerify(const Key; KeyBits: PtrInt;
      pIV: pointer; IV_len: PtrInt; pAAD: pointer; aLen: PtrInt;
      ctp, ptp: Pointer; pLen: PtrInt; ptag: pointer; tLen: PtrInt): boolean;
  end;

Только в виду своей малообразованности в программировании и отсутствии примеров, не пойму как их заюзать. Помогите составить каркас действий.