// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package aes

import (
	"crypto/aes";
	"os";
	"strconv";
)

// The AES block size in bytes.
const BlockSize = 16;

// A Cipher is an instance of AES encryption using a particular key.
type Cipher struct {
	enc []uint32;
	dec []uint32;
}

type KeySizeError int
func (k KeySizeError) String() string {
	return "crypto/aes: invalid key size " + strconv.Itoa(int(k));
}

// NewCipher creates and returns a new Cipher.
// The key argument should be the AES key,
// either 16, 24, or 32 bytes to select
// AES-128, AES-192, or AES-256.
func NewCipher(key []byte) (*Cipher, os.Error) {
	k := len(key);
	switch k {
	default:
		return nil, KeySizeError(k);
	case 16, 24, 32:
		break;
	}

	n := k + 28;
	c := &Cipher{make([]uint32, n), make([]uint32, n)};
	expandKey(key, c.enc, c.dec);
	return c, nil;
}

// BlockSize returns the AES block size, 16 bytes.
// It is necessary to satisfy the Key interface in the
// package "crypto/modes".
func (c *Cipher) BlockSize() int {
	return BlockSize;
}

// Encrypt encrypts the 16-byte buffer src using the key k
// and stores the result in dst.
// Note that for amounts of data larger than a block,
// it is not safe to just call Encrypt on successive blocks;
// instead, use an encryption mode like AESCBC (see modes.go).
func (c *Cipher) Encrypt(src, dst []byte) {
	encryptBlock(c.enc, src, dst);
}

// Decrypt decrypts the 16-byte buffer src using the key k
// and stores the result in dst.
func (c *Cipher) Decrypt(src, dst []byte) {
	decryptBlock(c.dec, src, dst);
}

// Reset zeros the key data, so that it will no longer
// appear in the process's memory.
func (c *Cipher) Reset() {
	for i := 0; i < len(c.enc); i++ {
		c.enc[i] = 0;
	}
	for i := 0; i < len(c.dec); i++ {
		c.dec[i] = 0;
	}
}