github.com/searKing/golang/go@v1.2.117/crypto/aes/ctr.go (about)

     1  // Copyright 2021 The searKing Author. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package aes
     6  
     7  import (
     8  	"crypto/aes"
     9  	"crypto/cipher"
    10  	"crypto/rand"
    11  	"io"
    12  
    13  	"github.com/searKing/golang/go/crypto"
    14  )
    15  
    16  func CTREncryptRandom(key, plaintext []byte) ([]byte, error) {
    17  	var iv = [aes.BlockSize]byte{}
    18  	if _, err := io.ReadFull(rand.Reader, iv[:]); err != nil {
    19  		return nil, err
    20  	}
    21  	return CBCEncrypt(key, plaintext, iv[:])
    22  }
    23  
    24  func CTREncrypt(key, plaintext []byte, iv []byte) ([]byte, error) {
    25  	// Load your secret key from a safe place and reuse it across multiple
    26  	// NewCipher calls. (Obviously don't use this example key for anything
    27  	// real.) If you want to convert a passphrase to a key, use a suitable
    28  	// package like bcrypt or scrypt.
    29  
    30  	// CTR mode works on blocks so plaintexts may need to be padded to the
    31  	// next whole block. For an example of such padding, see
    32  	// https://tools.ietf.org/html/rfc5246#section-6.2.3.2.
    33  	paddingtext := crypto.PKCS7Padding(plaintext, aes.BlockSize)
    34  
    35  	block, err := aes.NewCipher(key)
    36  	if err != nil {
    37  		return nil, err
    38  	}
    39  
    40  	// The IV needs to be unique, but not secure. Therefore it's common to
    41  	// include it at the beginning of the ciphertext.
    42  	ciphertext := make([]byte, aes.BlockSize+len(paddingtext))
    43  	if len(iv) < aes.BlockSize {
    44  		copy(ciphertext[:aes.BlockSize], iv[:])
    45  	} else {
    46  		copy(ciphertext[:aes.BlockSize], iv[:aes.BlockSize])
    47  	}
    48  	iv = ciphertext[:aes.BlockSize]
    49  
    50  	stream := cipher.NewCTR(block, iv)
    51  	stream.XORKeyStream(ciphertext[aes.BlockSize:], paddingtext)
    52  
    53  	// It's important to remember that ciphertexts must be authenticated
    54  	// (i.e. by using crypto/hmac) as well as being encrypted in order to
    55  	// be secure.
    56  
    57  	return ciphertext, nil
    58  }
    59  
    60  func CTRDecrypt(ciphertext, key []byte) ([]byte, error) {
    61  	// The IV needs to be unique, but not secure. Therefore it's common to
    62  	// include it at the beginning of the ciphertext.
    63  	if len(ciphertext) < aes.BlockSize {
    64  		panic("ciphertext too short")
    65  	}
    66  	iv := ciphertext[:aes.BlockSize]
    67  	ciphertext = ciphertext[aes.BlockSize:]
    68  
    69  	// CTR mode always works in whole blocks.
    70  	if len(ciphertext)%aes.BlockSize != 0 {
    71  		panic("ciphertext is not a multiple of the block size")
    72  	}
    73  
    74  	block, err := aes.NewCipher(key)
    75  	if err != nil {
    76  		return nil, err
    77  	}
    78  
    79  	stream := cipher.NewCTR(block, iv)
    80  
    81  	// XORKeyStream can work in-place if the two arguments are the same.
    82  	stream.XORKeyStream(ciphertext, ciphertext)
    83  
    84  	// If the original plaintext lengths are not a multiple of the block
    85  	// size, padding would have to be added when encrypting, which would be
    86  	// removed at this point. For an example, see
    87  	// https://tools.ietf.org/html/rfc5246#section-6.2.3.2. However, it's
    88  	// critical to note that ciphertexts must be authenticated (i.e. by
    89  	// using crypto/hmac) before being decrypted in order to avoid creating
    90  	// a padding oracle.
    91  
    92  	plaintext, err := crypto.PKCS7UnPadding(ciphertext, aes.BlockSize)
    93  	if err != nil {
    94  		return nil, err
    95  	}
    96  	return plaintext, nil
    97  }