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Source file src/crypto/aes/cipher.go

Documentation: crypto/aes

     1  // Copyright 2009 The Go Authors. 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/cipher"
     9  	"crypto/internal/subtle"
    10  	"strconv"
    11  )
    12  
    13  // The AES block size in bytes.
    14  const BlockSize = 16
    15  
    16  // A cipher is an instance of AES encryption using a particular key.
    17  type aesCipher struct {
    18  	enc []uint32
    19  	dec []uint32
    20  }
    21  
    22  type KeySizeError int
    23  
    24  func (k KeySizeError) Error() string {
    25  	return "crypto/aes: invalid key size " + strconv.Itoa(int(k))
    26  }
    27  
    28  // NewCipher creates and returns a new cipher.Block.
    29  // The key argument should be the AES key,
    30  // either 16, 24, or 32 bytes to select
    31  // AES-128, AES-192, or AES-256.
    32  func NewCipher(key []byte) (cipher.Block, error) {
    33  	k := len(key)
    34  	switch k {
    35  	default:
    36  		return nil, KeySizeError(k)
    37  	case 16, 24, 32:
    38  		break
    39  	}
    40  	return newCipher(key)
    41  }
    42  
    43  // newCipherGeneric creates and returns a new cipher.Block
    44  // implemented in pure Go.
    45  func newCipherGeneric(key []byte) (cipher.Block, error) {
    46  	n := len(key) + 28
    47  	c := aesCipher{make([]uint32, n), make([]uint32, n)}
    48  	expandKeyGo(key, c.enc, c.dec)
    49  	return &c, nil
    50  }
    51  
    52  func (c *aesCipher) BlockSize() int { return BlockSize }
    53  
    54  func (c *aesCipher) Encrypt(dst, src []byte) {
    55  	if len(src) < BlockSize {
    56  		panic("crypto/aes: input not full block")
    57  	}
    58  	if len(dst) < BlockSize {
    59  		panic("crypto/aes: output not full block")
    60  	}
    61  	if subtle.InexactOverlap(dst[:BlockSize], src[:BlockSize]) {
    62  		panic("crypto/aes: invalid buffer overlap")
    63  	}
    64  	encryptBlockGo(c.enc, dst, src)
    65  }
    66  
    67  func (c *aesCipher) Decrypt(dst, src []byte) {
    68  	if len(src) < BlockSize {
    69  		panic("crypto/aes: input not full block")
    70  	}
    71  	if len(dst) < BlockSize {
    72  		panic("crypto/aes: output not full block")
    73  	}
    74  	if subtle.InexactOverlap(dst[:BlockSize], src[:BlockSize]) {
    75  		panic("crypto/aes: invalid buffer overlap")
    76  	}
    77  	decryptBlockGo(c.dec, dst, src)
    78  }
    79  

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