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// 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 "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) Error() 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, 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 Block interface in the

// package "crypto/cipher".

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 CBC (see crypto/cipher/cbc.go).

func (c *Cipher) Encrypt(dst, src []byte) { encryptBlock(c.enc, dst, src) }

// Decrypt decrypts the 16-byte buffer src using the key k

// and stores the result in dst.

func (c *Cipher) Decrypt(dst, src []byte) { decryptBlock(c.dec, dst, src) }

// 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

        }

}