public class MyCrypt {

    public static byte[] encrypt(String key, String data) throws Exception {
        MessageDigest md = MessageDigest.getInstance("SHA-1");
        Cipher cp = Cipher.getInstance("RC4");
        SecretKeySpec ks = new SecretKeySpec(md.digest(key.getBytes("ASCII")), "RC4");
        cp.init(Cipher.ENCRYPT_MODE, ks);
        return cp.doFinal(data.getBytes("ASCII"));
    }

    public static String decrypt(String key, byte[] data) throws Exception {
        MessageDigest md = MessageDigest.getInstance("SHA-1");
        Cipher cp = Cipher.getInstance("RC4");
        SecretKeySpec ks = new SecretKeySpec(md.digest(key.getBytes("ASCII")), "RC4");
        cp.init(Cipher.DECRYPT_MODE, ks);
        return new String(cp.doFinal(data), "ASCII");
    }
}

// проверка функции
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        String pass = "password";
        String str = "privet";
        try {
            byte[] b = MyCrypt.encrypt(pass, str);
            System.out.println(MyCrypt.decrypt(pass, b));
        } catch (Exception ex) {
            Logger.getLogger(Form1.class.getName()).log(Level.SEVERE, null, ex);
        }
    }  

function CryptAcquireContext(phProv        :PCardinal;
                              pszContainer :PAnsiChar;
                              pszProvider  :PAnsiChar;
                              dwProvType   :DWORD;
                              dwFlags      :DWORD) :BOOL; stdcall;

function CryptCreateHash(hProv   :Cardinal;
                         Algid   :Cardinal;
                         hKey    :Cardinal;
                         dwFlags :DWORD;
                         phHash  :PCardinal) :BOOL; stdcall;

function CryptDeriveKey(hProv     :Cardinal;
                        Algid     :Cardinal;
                        hBaseData :Cardinal;
                        dwFlags   :DWORD;
                        phKey     :PCardinal) :BOOL; stdcall;

function CryptEncrypt(hKey       :Cardinal;
                      hHash      :Cardinal;
                      Final      :BOOL;
                      dwFlags    :DWORD;
                      pbData     :PBYTE;
                      pdwDataLen :PDWORD;
                      dwBufLen   :DWORD) :BOOL; stdcall;

function CryptDecrypt(hKey       :Cardinal;
                      hHash      :Cardinal;
                      Final      :BOOL;
                      dwFlags    :DWORD;
                      pbData     :PBYTE;
                      pdwDataLen :PDWORD) :BOOL; stdcall;

function CryptDestroyHash(hHash: Cardinal) :BOOL; stdcall;
function CryptDestroyKey(hKey: Cardinal) :BOOL; stdcall;

function CryptReleaseContext(hProv   :Cardinal;
                             dwFlags :DWORD) :BOOL; stdcall;

function CryptHashData(hHash       :Cardinal;
                 const pbData      :PBYTE;
                       dwDataLen   :DWORD;
                       dwFlags     :DWORD) :BOOL; stdcall;

function CryptAcquireContext; external ADVAPI32 name 'CryptAcquireContextA';
function CryptCreateHash; external ADVAPI32 name 'CryptCreateHash';
function CryptDeriveKey; external ADVAPI32 name 'CryptDeriveKey';
function CryptEncrypt; external ADVAPI32 name 'CryptEncrypt';
function CryptDecrypt; external ADVAPI32 name 'CryptDecrypt';
function CryptHashData; external ADVAPI32 name 'CryptHashData';
function CryptDestroyHash; external ADVAPI32 name 'CryptDestroyHash';
function CryptDestroyKey; external ADVAPI32 name 'CryptDestroyKey';
function CryptReleaseContext; external ADVAPI32 name 'CryptReleaseContext';

function encrypt(hProv: Cardinal; ASourceStr: String; APassword: String): String;
 var
 data: String;
 hKey: Cardinal;
 lBufLen: DWORD;
 DataSize: Integer;
 hHash: Cardinal;
 lisEnd: Boolean;
 Poz: Integer;
 const
 // взято тут https://msdn.microsoft.com/ru-ru/library/windows/desktop/aa375549(v=vs.85).aspx
 CALG_SHA = $00008004;
 CALG_RC4 = $00006801;
 //
 CU_BuffSize = 512;
begin
 Result := '';
 {создаем хеш-объект}
 if not CryptCreateHash(hProv, CALG_SHA, 0, 0, @hHash) then
  RaiseLastOSError;
 try
  DataSize := Length(ASourceStr);
  {хешируем пароль}
  if not CryptHashData(hHash, @APassword[1], length(APassword), 0) then
   RaiseLastOSError;
  {создаем ключ на основании пароля для потокового шифра RC4}
  if not CryptDeriveKey(hProv, CALG_RC4, hHash, 0, @hKey) then
   RaiseLastOSError;
  {шифруем данные}
  Poz := 0;
  repeat
   lBufLen := DataSize - Poz;
   if lBufLen > 0 then
    begin
     if lBufLen > CU_BuffSize then
      lBufLen := CU_BuffSize;
     data := Copy(ASourceStr,Poz+1,lBufLen);
     Inc(Poz, lBufLen);
    end;
   lisEnd := Poz >= DataSize;
   if not CryptEncrypt(hKey, 0, lisEnd, 0, @data[1], @lBufLen, CU_BuffSize) then
    RaiseLastOSError;
   Result := Result + data;
  until lisEnd;
 finally
  {уничтожаем хеш-объект}
  CryptDestroyHash(hHash);
  CryptDestroyKey(hKey);
 end;
end;

function decrypt(hProv: Cardinal; ASourceStr: String; APassword: String): String;
 var
 data: String;
 hKey: Cardinal;
 lBufLen: DWORD;
 hHash: Cardinal;
 Poz: Integer;
 lisEnd: Boolean;
 DataSize: Integer;
 const
 // взято тут https://msdn.microsoft.com/ru-ru/library/windows/desktop/aa375549(v=vs.85).aspx
 CALG_SHA = $00008004;
 CALG_RC4 = $00006801;
 //
 CU_BuffSize = 512;
begin
 Result := '';
 if not CryptCreateHash(hProv, CALG_SHA, 0, 0, @hHash) then
  RaiseLastOSError;
 try
  DataSize := Length(ASourceStr);
  {хешируем пароль}
  if not CryptHashData(hHash, @APassword[1], length(APassword), 0) then
   RaiseLastOSError;
  {создаем ключ на основании пароля для потокового шифра RC4}
  if not CryptDeriveKey(hProv, CALG_RC4, hHash, 0, @hKey) then
   RaiseLastOSError;
  {дешифруем данные}
  Poz := 0;
  repeat
   lBufLen := DataSize - Poz;
   if lBufLen > 0 then
    begin
     if lBufLen > CU_BuffSize then
      lBufLen := CU_BuffSize;
     data := Copy(ASourceStr,Poz+1,lBufLen);
     Inc(Poz, lBufLen);
    end;
   lisEnd := Poz >= DataSize;
   if not CryptDecrypt(hKey, 0, lisEnd, 0, @data[1], @lBufLen) then
    RaiseLastOSError;
   Result := Result + data;
  until lisEnd;
 finally
  {уничтожаем хеш-объект}
  CryptDestroyHash(hHash);
  CryptDestroyKey(hKey);
 end;
end;

// проверка функции
procedure TForm1.Button1Click(Sender: TObject);
 var
 pass: string;
 data: string;
 enc: string;
 prov: cardinal;
 const
 CU_ProvType = 1;
 CU_CRYPT_VERIFYCONTEXT = $F0000000;
begin
 pass := 'password';
 data := 'privet';
 CryptAcquireContext(@prov, nil, nil, CU_ProvType, CU_CRYPT_VERIFYCONTEXT);
 enc := encrypt(prov,data,pass);
 showmessage(decrypt(prov,enc,pass));
end;

Socket cs = new Socket(addr, 3456);
            OutputStream out = cs.getOutputStream();
            InputStream in = cs.getInputStream();
            String s = "privet";
            String k = "password";
            out.write(MyCrypt.encrypt(k, s));
            out.write('\r');
            byte[] b = new byte[5];
            in.read(b);
            System.out.println(MyCrypt.decrypt(k, b));
            cs.close();

procedure TMyClass.ReadData;
 var
 i: integer;
 buf: array of byte;
 b: byte;
 s: String;
 r: integer;
begin
 i := 0;
 while True do
  begin
   ClientSocket.ReadBuf(b,1);
   if (b = 13) then
    break;
   SetLength(buf,i+1);
   buf[i] := b;
   inc(i);
  end;
// SetLength(s,i);
// SetString(s, PChar(@buf[0]), i);
// s := UnCryptStr(hCryptProv,s,'wml7rds');
// r := StrToIntDef(s,0);
 ClientSocket.SendBuf(PChar(@buf[0])^,i);
end;